€03? AMI ENERGY REQUIREMEMS 0F
SLUDGE HANDLING AND ULTIMATE

LAND DISPGSAL METHODS

Tkests for II“ Degree of M. S.
MICHIGAN STATE UNIVERSITY

Charles R. BristoI
W75

 

‘ 25:53“.

 

V“)

x
0<
I
x 7‘0

V\ ABSTRACT
CA COST AND ENERGY REQUIREMENTS OF
SLUDGE HANDLING AND ULTIMATE
LAND DISPOSAL METHODS
by

Charles R. Bristol

A sequential decision model known as dynamic programming
was used to analyze cost and energy consumption for 15 processes
involved in sewage sludge treatment. Three conditions were con—
sidered: (l) the economic Optimum using capital costs, operating
power, and labor; (2) the optimum for an energy poor future using
capital costs and operating power and; (3) the energy optimum using

capital and operating energy.

For the first case dissolved-air flotation, aerobic digestion
and lagooning was found to be the best treatment scheme at a flow of
1 million gallons per day (MGD). For 10 MGD and 100 MGD the best
treatment scheme was found to be gravity thickening, anaerobic
digestion and lagooning. No change was found in these treatment
schemes for case 2. For case 3, the best treatment scheme was found
to be gravity thickening, anaerobic digestion and lagooning for all

3 design flows.

COST AND ENERGY REQUIREMENTS OF
SLUDGE HANDLING AND ULTIMATE

LAND DISPOSAL METHODS

by

Charles R. Bristol

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Civil and Sanitary Engineering

1975

ACKNOWLEDGEMENT

This work was sponsored through a research assistantship
from the Institute of Water Research as part of a grant from the
Rockefeller Foundation. This assistance is greatly acknowledged.
In addition, the author extends his appreciation to Dr. Mackenzie
L. Davis of the Department of Civil Engineering, Dr. George Coulman
of the Department of Chemical Engineering and Dr. Frank Hatfield,
Director, Cooperative Education -- Engineering, for their kind

advise and guidance.

INTRODUCTION .
LITERATURE REVIEW
Thickening .
Stabilization.
Conditioning.
Dewatering .
Reduction
Final Disposal .
METHODS . . . . .
RESULTS
Thickening .
Stabilization
Conditioning . .
Dewatering
Reduction .' . .
Final Disposal .
CONCLUSION. . .
APPENDICES »
Appendix A . .
Appendix B .
Appendix C .
Appendix D .
Appendix E .
Appendix F .
Appendix G .
REFERENCES CITED.

TABLE OF CON TENTS

iii

Page

24
35
40
47
56
57
58
58
59

. 61
80
81
82
84

. 9O
. 97
. 102

. 111
.115
.122

Table

16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.

L15 T OF TABLES

Gravity Thickener Power Consumption . . .
Dissolved Air Flotation Thickening Costs . .

Dissolved Air Flotation Thickening Power
Consumption. . . . . . . . . . .

Digester Tank Sizes . . . . . . . . . .
Sludge Heating Units . . . . . . . . . .
Installed Hp and Electrical Power . . . . .
Chemical Costs . . . . . . . . . . . .
Thermal Sludge Conditioning . . . . . . .
Uses of Dewatered Sludge . . . . . .
Vacuum Filter Costs . . . . . . . . . .
Centrifuge Costs . . . . . . . . . .
Centrifuge Performance and Operating Costs .
Centrifuge Power Requirements . . . . .
Pressure Filter Costs . . . . . . . . .
Capital Incinerator Costs . . . . . . . .
Land Spreading of Sludges . . . . . . .
Sludge Quantity Assumptions . . . . . . .
Design Parameters . . . . . . . . .
Sewerage Construction Cost Index . . . . .
Sludge Quantities . . . . . . . . .
Thickening . . . . . . . . . . . . .
Stabilization . . . . . . . . . . . '. .
Conditioning . . . ' . . . . . . . . .

Dewatering Power and Labor. . . . . . .

Dewatering Costs and Energy. . . . . . .

Reduction..............

FinalDisposal. . . . . . . . . . .

iv

28.
29.
30.

Proccs 5 Limitations .

Step 6 Combinations .

Final Treatment Schemes .

62
65
78

15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.

LIST OF FIGURES

Gravity Thickening Capital Costs .

Costs of Gravity Thickening .

Gravity Thickening Labor Requirements .

Dissolved-Air Flotation Capital Costs .

Dissolved -Air Flotation Labor Requirements .
Aerobic Digestion Capital Costs .

Aeration Basin Structure Construction Costs .

Aerobic Digestion Labor, Requirements .

Unit Anaerobic Digestion Costs .

Anaerobic Digestion Labor Requirements .

Sludge Lagoon Construction Costs .

Sludge Lagoon Labor Requirements . .

Sludge Lagoon Material and Supply Costs .

Vacuum Filter Construction Costs .

Vacuum Filter Labor Requirements .

Centrifugation Construction Costs .

Centrifugation Labor Requirements .

Drying Beds Construction Costs .
Drying Bed Labor Requirements .

Multiple Hearth Incineration Costs .

Incineration Labor Requirements .

Incineration Material and Supply Costs .

High Pressure Oxidation Costs .

Low Pressure Oxidation Costs .

Transportation Costs for Liquid Sludge .

Sanitary Landfill Costs . . .

Sludge Handling Process Flowsheet .

Example Process Flowsheet .
Flow - 1.0 MGD for Case 1 .

vi

10
12
13
15
16
18
19
20
21
26
27
29
32
33
34.
37
38
39
41
42
44
45
54
64
68

30.

31.

32.
33.
34.
35.
36.
37.

Flow
Flow
Flow
Flow
Flow
Flow
Flow
Flow

1.0 MGD for Case 2 .
1.0 MGD for Case 3 .
10.0 MGD for Case I .
10.0 MGD for Case 2 .
10.0 MGD for Case 3 .
100.0 MGD for Case 1 .
100.0 MGD for Case 2 .
100.0 MGD for Case 3 .

vii

69
TO
72
73
74
75
76
77

IN TRODUC TION

Most methods of municipal wastewater treatment have an end pro -
duct of large quantities of sewage sludge. This amounts to some 4.2
million tons per year in the United States alone. 1 It comprises about
50% of the total treatment cost and 90% of the operators headaches. The
characteristics of the sludge vary both with source (i.e.: industrial or
municipal), and with the sewage treatment process employed (i. e.:
physical, chemical, or biological). These variations dictate the choice
of sludge treatment. 2

The choice of sludge treatment must be made with regards to
costs and energy requirements. The ultimate goal of any well managed
community is to use the treatment scheme that will have the best cost-
performance ratio and also the lowest energy consumption. Energy con-
sumption not only includes the operating energy, but also the amount of
energy needed for materials fabrication used in treatment facilities
(herein termed "capital energy" because of the analogy to capital costs).
Energy is considered separately in order to investigate design decisions
that would be made if the price of energy increases dramatically to
become the dominant cost.

It is the purpose of this paper to present a comparative cost
analysis of specific processes involved in sewage sludge treatment,
and also to present a comparative energy consumption analysis of these
same processes. The analysis is done under three conditions which are
(l) the economical optimum for now and in the future, (2) the optimum
for an energy affluent present with an energy poor future and (3) the
energy optimum for now and the future.

The processes considered in this research are gravity thicken-
ing and dissolved -air flotation in the thickening step of sludge handling;
anaerobic digestion, aerobic digestion and sludge lagooning in the sta-

bilization stage of treatment; chemical conditioning, heat treatment

2

and freezing in the conditioning process; vacuum filtration, centrifu-
gation, filter pressing and sand bed drying in the dewatering stage;
incineration and wet -air oxidation in the reduction of sludges; and
landfilling, land application for soil conditioning, and lagooning in the
final disposal step.

The sludge used in the above processes is a mixture of primary
sludge (settled sewage from the primary sedimentation tanks) and

activated sludge (wasted, biologically active solids from the secondary

settling tanks).

LITERATURE RE VIEW

THICKENING

Thickening or concentration is defined as removing water from

 

sludge after its initial separation from wastewater. 3 The objective is
to reduce the volume of liquid sludge to be handled in subsequent pro-
cesses. Common types of thickening are gravity thickening, dissolved -.
air flotation, and centrifugation. Centrifugation is covered later under
dewatering.

Gravity thickeners use natural gravity and gentle raking mech-
anisms to settle the sludge to the bottom of the tanks and thicken it.
Costs, power, and labor requirements depend on the size of the
thickening tanks, which in turn are dependent on the flow into the plant.
The cost of the installed thickener, which includes price of thickener,
erection, site preparation, pumps, piping, steel, instrumentation,
electrical, paint and indirect costs has been depicted as a function of
tank diameter. 4 The cost of an installed thickener increases as the
tank size increases as seen in Figure l.

The operating and maintenance (O and M) costs decrease with
the increase in dry solids or flow. Generally, O and M costs for gra-
vity thickeners at large plants are about $ 2. 00 per ton of dry solids.3
The construction costs, however, increase as the dry solids increase
as shown in Figure 2.

The raking mechanisms are the only part of the thickener that
requires power. Table 1 shows the electrical power requirements for
a one million gallon per day (MGD), 10 MGD and 100 MGD plant

thickening primary and activated sludge. 6

)

INSTALLED BASE COST (1972 DOLLARS

.9

 

 

   

 

 

OOO’OOO l 1 l l lllll | l lllllj
100,000.. A

I :

L- ..

- -I

" a
10,000 I l I llllll l 1 J l Ill

10 100 1,000

DIAMETER (FEET)

Figure 1. Gravity thickening capital cost [4]

COSTS (.$/DRY TON)

 

   
 

 

 

 

 

l lfillllll II IIITIIH I I TIIII
K.
10 9009 :1.
.0 -I
090 j
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E ’ 0a 2:
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: a. 1
'5 A
l IIIIIIII LI 1111111! 11 11111 .01
1 10 100 1,000
DRY SOLIDS (TON/DAY)
Notes:

1.

mph-DON

Index of 1827.

Figure 2.

Amortization at 7% for 20 years.
Labor rate of $6.25 per hour.
No chemicals.

Influent sludge with a solids content of 0.5%.

Costs of gravity thickening [5]

Minneapolis. Mar. 1972. ENR Construction Cost

CONSTRUCTION COST
(MILLIONS OF DOLLARS)

 

TABLE 1

POWER CONSUMPTION

 

PLANT SIZE PRIMARY=1= AC T1VATED>:<>:=
(MGD) (KWH/day) (KWHLday)
1 10. 2 10. 2
10 20.4 20.4
100 30. 6 . 40.8

 

*10ading rate = 16 poundséday/square foot (lb/d/ftz)
**loading rate = 8 lb/d/ft

The labor requirement of a gravity thickener increases as the
flow increases as shown in Figure 3.7 Operational hours increase
faster than the required maintenance hours.

In comparison to gravity thickeners, dissolved -air flotation
(DAF) is cheaper initially but requires large amounts of power and
chemicals. Dissolved -air flotation uses small air bubbles to raise all
the sludge to the surface and collects it there and usually works best
with waste activated sludge. 8

The installed cost of a D.A. F. unit is based on the size of the
pressure tank, which is dependent on the solids loading and sludge
characteristics. 5 Figure 4 shows the comparison between the installed
base cost and the tank capacity.4 The machine has a lower capital
cost than the gravity thickener but the expected lifetime is only half
that of a gravity thickener.4

The process costs fOr the D.A.F. machine are given in Table 2

for various plant sizes.

 

TABLE 2

D.A. F. THICKENING COST

 

PLANT SIZE COST (DOLLARS/TON DRY SOLIDS)*
(MGD) o and M AMORTIZATION TOTAL
1 9.00 ' 17. 00 26. 00
10 1.20 2. 80 4. 00
100 0.50 1.50 2.00

 

*Costs are based on: 1972 dollars, amortization at 7 % for 20 years,
labor rate of $ 6. ZS/hr, power cost of $ 0. Ol/KWH, no chemicals and
a surface loading rate of 14.4 lb/day/ftz.

ANNUAL HOURS

 

 

 

  

     
  
 
 

 

 

I I I I I l I I l I I I

1000 r— Operation
500 - ..

Maintenance
/
/
/
100.. // .1
/

50— L

10 I 1 L J l l 4 1 L 1 1

0.5 l 1.5 2 3 4 5 6 810 15 2025 100

PLANT DESIGN FLOW
(MGD)

Figure 3. Gravity thickening labor requirements [7]

INSTALLED BASE COST (1972 DOLLARS)

1,000,000

 

IIII

100,000

Tj IIIIII

I

10,000

 

1,000 II

I

IIIIIIII rlIIIIII

 
     
 

Illllll

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llllll

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11111111 11111111

 

10

Figure 4.

100 1,000
CAPACITY (CUBIC FEET)

Dis solved-air flotation capital costs [4]

The O and M and total costs decrease rapidly as the plant size
increases. Chemicals would add another $ 2. 00 to $7. 00 per ton to the
total cost. 5 Even though the operating costs are high, the rate at
which the sludge can be thickened is greater than the rate of a gravity
thickener. 3

The installed horsepower (Hp) of a D.A. F. unit is a function
of thickener surface area. The electrical power consumption varies
with the use of chemical thickening aids. Table 3 shows the electrical

power used for various size plants with and without chemical aids.

 

TABLE 3

D.A. F. POWER CONSUMPTION

 

 

Plant Size Work Required Power (KWH/day)
(MGD) Week Hp W/Chemicals* w/o Chemicals**
1 4o 14. 5 70 242
10 100' 50.0 608 1800
100 168 230. o 4692 18800

 

*loading rate = 2 lb/hr/ft2 2 '
**loading rate = 0. 5 lb/hr/ft

The number of manhours required for using the D.A.F. is
approximately twice that needed for the gravity thickener. Figure 5 4
shows that the operational hours increase faster than the maintenance

hours as the design flow increases.

STA BILIZA TION

The principle purposes of stabilization are to make the treated

 

sludge less odorous and less putrescible, and to reduce the pathogenic
organism population. The selection of a stabilization method depends
primarily on the final disposal procedure planned for the sludge.

If the sludge is to be dewatered and incinerated, frequently no
stabilization procedure is employed. 5 However, common types of
stabilization used are aerobic digestion, anaerobic digestion, and
lagooning. All three methods result in substantial decreases in the
amount of suspended sludge solids in the system. .

Aerobic digestion is the separate aeration of sludges. Cost

depends primarily on the size of the tanks which is a function of waste

ANNUAL HOURS

10

 

 

    
    
 

 

 

I I l l I T I I I I I I
5000 -
Operation
/
1000*- ..
Maintenance
500 .I
100.. ..
50" -
10 1 l l l I I I 4 I I 14
0.5 1 1.5 2 3 4 5 6 8 10 15 20 25 100
PLANT DESIGN FLOW
(MGD)
Figure 5. Dissolved-air flotation labor requirements [7]

11

sludge volume. Aerobic digestion tanks are normally uncovered and
unheated, and are much cheaper to construct than covered, insulated,
and heated anaerobic digestion tanks. 3

Figure 6 shows the capital costs of aerobic digestion as a func-
tion of tons of dry solids per day. 5 In terms of liquid volume the con-
struction costs of the basins for the digestion tanks are shown in
Figure 7.9 The construction cost of the basins increases at the same
rate as the construction costs Of the entire system as shown in
Figure ,6. The choice of aeration system, whether mechanical or
diffused air, will change the amount of the initial cost.

Dorr-Oliver, in 1968, developed cost equations for the acti-
vated sludge process from available equipment information. These
costs are similar to the capital cost of an aerobic digester with blowers.
The equations are:10

Tank Capital Cost: LOG(COST) = (0.806)LOG(V) + 0.306

where COST = thousands of dollars and V = volume, 1000 ft3.

Blower Capital Cost: COST = 3. 58(CAP) + 2. 53
where COST = thousands of dollars and CAP 2 capacity
in 1000 standard cubic feet per minute (SCFM).

Blower Operating Cost: COST = 0. 68 (CAP) + 0.14
where COST = dollars per hour and CAP 2 capacity in
1000 SCFM.

Mechanical Aerator Operating Cost: COST 2 l.42(V/100, 000)

where COST = dollars per hour and V = volume in ft3.

The operating costs for the aerobic digesters are quite similar
to the operating costs of the activated sludge tank. The major factor
in the high operating costs of the aerobic digestion process is the power
used in the blowers. About ten brake horsepower (BHp) per 10, 000
population is required for aeration.

The labor required for the operation and maintenance of aerobic
digestion is shown in Figure 8. The operational hours are about five
times the maintenance hours needed due to the air equipment.

Anaerobic digestion has a higher capital cost than aerobic diges -
tion due to the heaters required and tank coverings. Digestion tank

volume requirements, to which construction costs are related, depend

AMORTIZED COST (SB/DRY TON)

100

10

12

 

 

 

 

    
  

 

   
  
   
   

 

 

 

I III IIIIIII Fl llllllll llIl [Hi-10
: 112%.; : 1
: ed :

Z 21
= 1
E :
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)- .-

IIIIIIIIIII IIIIIIIIIII Illlllllll.01

1 10 100 1000
DRY SOLIDS (TON/DAY)
Notes:

1.

Minneapolis. Mar. 1972. ENR Construction
Cost Index of 1827.

2. Amortization at 7% for 20 years.
3.

Influent sludge of 38% primary and 62% waste
activated sludge with a solids content of 3.5%.
20 day volumetric displacement time.

Figure 6. Aerobic digestion capital cost [5]

1 CONSTRUCTION COST (MILLIONS OF DOLLARS)

:3 mumoo sofiosuumsoo ensuedfim Emma. coflmneau.

Emma OHmOO coo; .mEOqO> OBOE

.n 0.3th

 

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T .1.
I I
H. H
3 LI I
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I L
m H
I H

 

_

    
       
     

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14

on temperature, sludge characteristics, storage requirements, quan-
tity of sludge and the degree of digestion.

Dorr -Oliver developed a capital cost equation for anaerobic -
digestion which includes all heating, mixing and gas requirements,
sludge pumps, concrete tank requirements and a digester cover.

. . 10
The equation is:
LOG(COST) = 1/(o.31 LOG(V) + 0.37)

where COST 2 tenths of dollars per cubic foot and
v = volume in 1000 R3.

The volume of the tank depends on the type of sludge to be
digested. Table 4 shows the comparison of tank volumes as a func -

tion of flow and sludge type. 6

 

 

 

TABLE 4
DIGESTER TANK SIZES
PLANT SIZE VOLUME (FT3)
(MGD) PRIMARY ACTIVATED
1 8125 15,400
10 81,250 154,000
100 812,500 1,540,000

 

Activated sludge required about twice the tank volume of primary
sludge.

Operating costs for anaerobic digestion vary between $ 2. 00
and $4. 00 per ton of sludge treated.3 Figure 9 shows the O and M
costs as they decrease when the digester volume increases, but over
about 100, 000 ft3 the Operating costs remain constant. 5

Energy is consumed in anaerobic digestion by (l) heating the
incoming sludge and holding the temperature at 95 degrees and (2)
mixing the contents (gas recirculation). Table 5 shows the power

needed for the sludge heating units in terms of plant size.

ANNUAL HOURS

1000

500

15

 

 

Operation

Maintenance

    
  
 

/

 

 

/
/
100 / _
/
/
/
/
‘50 /
/
/
/
/
/
/
/
/
/
10/ IILIIIIIIIII
0.5 1 1.52 3 456810152025 100

PLANT DESIGN FLOW
(MGD)

Figure 8. Aerobic digestion labor requirements [7]

COSTS (5/1,000 CUBIC FEET/DAY)

10

0.01

1.0

16

 

T IIII'

FTII III]

IIIIII I

I I

 

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: 10

:
Nmortized _

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—

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——1

 

I IJIIIIII I I I I I IIIlIIII I IIIIIIIO.

 

10

DH

100 1,000 10,000 100,00
DIGESTER VOLUME (1,000 CUBIC FEET)

Notes:

I .

42.90?»

Minneapolis. Mar. 1972. ENR Construction (final Intlvx ol I837.
Amortization (II 7% for 20 years.

Labor I'ilI‘I‘ oI $6.25 ])(‘I' hour.

Sludge healing, circulating and control equipment. and rontrol

building inc I ll(I(‘(I.

Figure ‘1. Unit anaerobic digestion costs [5]

CONSTRUCTION COST (MILLIONS OF DOLLARS)

17

 

 

 

TABLE 5
SLUDGE HEATING UNITS
PLANT SIZE POWER NEEDED(BTU/HR)
(MGD) PRIMARY ACTIVATED
1 1 unit at 129,000 1 unit at 223,920
10 2 " 645,000 2 .. 1,119, 600
100 3 .. 4,300,000 3 .. 4,47§,_4oo

 

Table 6 shows the installed horsepower required and the electri-
cal power consumption for the anaerobic digesters operating 75% of

the time . 6

 

 

 

TABLE 6
INSTALLED Hp AND ELECTRICAL POWER
PLANT SIZE No. of UNITS AND POWER (KWH/day)
(MGD) PRIMARY ACTIVATED
1 1 unit at 6.0 Hp-100.8 1 unit at 6.4 Hp- 123.6
10 2 .. 8.3 " 307.0 2 .. 12.2 .. 456.4
100 3 H 21.3" 1146 5 .. 21.3" 1910

 

Tables 5 and 6 shows that activated sludge requires more energy
than primary sludge, but the detention time or time required for diges -
tion of the activated sludge is less than that of the primary sludge. This
means the activated sludge can be processed faster than primary
sludge.

The manpower required to operate and maintain the equipment
involved in anaerobic digestion is approximately double that needed for
aerobic digestion. Figure 10 shows higher operational hours than
maintenance hours in relation to plant flow.7

Sludge lagoons can be used for either digestion, drying or both
processes consequently. Construction costs of sludge lagoons are
directly related to volume and the initial capital cost is dependent on
local land rates. Figure 11 shows these construction costs and how
they increase as the volume increases with no apparent economy of
scale.

The principle factor affecting the O and M costs of the lagoons

is the quantity of material handled each year. Figures 12 and 13

ANNUAL HOURS

5000

I I I I I I I I I j I I
1000 Operation
/
500 / .—
/
/
100)- / _
/
50— / —
/
/
10 I I I I I II I I I I I
0.5 l 1.5 2 3 4 5 6 810 15 2025

18

 

 

     

 

 

PLANT DESIGN F LOW
(MG D)

Figure 10. Anaerobic digestion labor requirements [7]

100

19

:: mLmOO cofiosfimcoO coomfl empgm .: Ousmfih

HMMM OHQDO coo; .MEDJO.» HOQOJW

80.2 coo; OS 2
_:Z:_ I _:_____ _ IZJLN _ L

 

T

I

1

I

IIIIII I
IIIIII

 
   

OH

I

umOU HQHOH.

I

I
I

I
I

IIIII
IlIIl

OOH

I
I

I

I
I

IIIII

 

 

IIIII

 

_:_____ _ :LPPP__ r _::__.L _ coo;

I)II}I.I.SNOI)

' .I.SOI) NO] .I.

000‘ I?»

ANNUAL PAYROLL MAN- HOURS

20

 

I

1,000

I IIIII

I

 

7 IIIIIII I I IIIIIII I II

    
 
  

Maintenanc e labor \

 

LI IIIII

 

 

100 :
__ \Operation labor _
(based on but not including
_ sludge removal by contract) d
10 l IIIIIIII I I IIIIIII I II
100 1,000 10,000

Figure 12.

DRY SOLIDS APPLIED, TONS PER YEAR

Sludge lagoon labor requirements [11]

$1,000

ANNUAL COST,

1,000

100

10

21

 

I fl

I II—IIII

I

IIIWI

IIIIIII

l

 

I l

IIIIIII I IIIIIIII I II

IIIII

IIIIIL

I

I

      
 

Includes cost of
sludge removal
by contract __

IIIIII

 

IIIIIII L IIIJILIJ I ll

 

1,000 10,000

DRY SOLIDS APPLIED, TONS PER YEAR

Figure 13.

Sludge lagoons material and supply costs [11]

22

show the labor requirements and supply requirements and how they
increase steadily as the volume of solids handled per year increases.
The energy requirements of the sludge lagoon are very small
as it uses power only for pumping; no heating, aeration, or coverings
are required. Costs and power are kept at a minimum with the only
major disadvantage being the time required to hold the sludge. It
ranges anywhere from 3 to 5 years. 11
CONDITIONING

Conditioning is the pretreatment of sludge to facilitate de-

 

watering. Two basic types of conditioning are chemical and physical.
Chemical conditioning can use both organic and inorganic chemicals
and physical conditioning can be accomplished using freezing or

heat treatment.

Chemical conditioning is a coagulation and flocculation process.
Inorganic chemicals such as ferric chloride, lime and aluminum sul-
fate, as well as organic polyelectrolytes, primarily the cationic and
anionic polymers, have been effective in reducing the resistance to
dewatering of the sludges. Z The polyelectrolytes increase the
dewatering rate more than inorganic chemicals, but the cost of the
polyelectrolytes is very high. Table 7 presents the daily cost Of

chemicals for conditioning.

 

 

 

TABLE 7
CHEMICAL COSTS
Avg. Dose Flow Cost Usage Daily

Chemical (mgll) (MGD) ($ /day) (1b [day) Cost
Ferric

Chloride 110.0 4 0.066 918.0 242.36
Cationic

Polymer 1.35 4 1.45 11.3 65.56
Anionic

Polymer 0.75 4 1.35 6.25 33.76

 

If chemical conditioning is used, the capital, operating and
maintenance costs will be the same regardless of type of chemical.
The only choice affecting costs is in the type of chemicals used. There

are many conditioning chemicals from which to choose.

23

Freezing is a very unusual process to be used in sewage
treatment but it is a very effective sludge conditioner. 3 Costs of
this process are very high and include power, flocculants (if needed),
and expensive refrigerating fluids. It takes about 170 BTU's to freeze
one pound of sludge. 3

Capital costs of the freezing process include tanks, stirrers,
buildings, automatic controls and the freezing plant. 13 Capital costs
vary about a mean of $17, 000 per 1000 gallons of sludge processed. 14
Operating costs are in the range of $4.75 to $49. 50 per 1000 gallons

depending on the type of sludge. 3'14_15 The power required for this

process is very high ranging from 180 to 230 KWH per 1000 gallons. 1‘4

Very high operating costs and energy requirements have been
the major factors in keeping freezing from becoming a widely used
process. This process would be very effective in a cold climate.

On the opposite end of the scale, heat treatment uses tempera-
tures between 300 and 500 degrees F and pressures of 150 to 400 psig5
to condition sludge. Heat treatment improves the dewaterability of
sludges ten times better than chemical conditioning. It also has the
advantages of having no Odors, not requiring chemicals and reducing
the pathogens to zero.

The wet oxidation process Operated at low pressures can be
used for heat treatment. The operating costs would be less than wet
oxidation due to lower pressures and temperatures. Power require-
ments are high because of the higher than normal temperatures and

pressures. Table 8 shows the operating costs for thermal conditioning

 

 

 

in Kalamazoo, Michigan. 16
TABLE 8
THERMAL SLUDGE CONDITIONING
ITEMS ACTUAL COSTS PREDIC TED COSTS
Maintenance 8 3. 12 /MG 8 2. OO/MG
Power* $1.4l/MG $1. oo/MG
Fue1=:<=:< $ 1. 27/MG $ 2. ZOA/MG

 

*electrical rate : $ 0.01/KWH
=:=>I= fuel costs = $ 1. O/million BTU

24

DEWATERING

Sludge conditioning by either a chemical or physical condi-

 

tioner is used primarily with the dewatering step of sludge treatment.
The primary Objective of dewatering is to reduce the sludge moisture
content to a degree allowing ultimate disposal. The main methods of
dewatering consist of vacuum filteration, centrifugation, pressure fil-
tration and sand bed drying. Table 9 shows the relationship of

dewatering to other sludge treatment processes for typical municipal

 

 

 

 

sludges. 5
TABLE 9
Normal Use of Sludge Cake
Pretreatment Land Land Heat In cine r _

Method Thick en Condition Fill Spread D rving an‘ on
Vac. Filter yes yes yes yes yes yes
Centrifuge yes yes yes yes yes yes

' Filt. Press yes yes yes. variable ' no yes
Drying Bed variable no yes yes no no

 

Capital and construction costs of vacuum vilters, associated
equipment and structures are related to the filter surface area. The
filters themselves cost $ 95. 00 to $ 275. 00 per square foot.3 The
buildings usually double the cost. An equation developed by Dorr-Oliver
shows the relation between costs and filter area. The equationis:l

LOG(COST) = 0. 65-0. 66(LOG(A))

where COST = hundred dollars per ft2 and A 2 area in
100 square feet.

Equipment used in vacuum filters includes the filter, vacuum
receiver, vacuum pump, filtrate pump, chemical feed tanks, sludge
pump and sludge flocculator. Table 10 shows capital costs of vacuum

filters with their respective building areas.

25

 

 

 

TABLE 10
VACUUM FILTER COSTS (1972)
Filter Bldg* Const** Total
Type Size Cost Cost Cost Cost
Rotary lO'dia -l7 'face 58100 6000 20700 85, 800
Convent. 6' " - 6' " 30000 3000 10500 43, 500
Rotary 10' " -l4' " 53500 5000 18600 76,600

 

*assumed to be $ 10. 00 per sq. ft. of building
** assumed to be 35% Of the equipment cost

Figure 14‘ shows the steady rise in construction costs as the
size of filter increases. 11 Operation and maintenance costs depend on
chemicals (49 %), direct labor (20 %), supervisory and maintenance
labor (20%), power (9%) and supplies (2 %). 17 Power costs are
directly proportional to the filter area. This is shown in the following
equation:10

COST = 0. 15 (A) where A = area in sq. ft. and COST = cents
per hour (includes power cost of 1. 551’ per KWH)

The labor required for operation and maintenance of the vacuum
filter are shown in Figure 15. The operational labor for hauling the
sludge to a landfill is higher than that of conveying the sludge to an
incinerator. 1

Centrifugation has some advantages over vacuum filtration.

It is simple, compact, totally enclosed, flexible, and costs are moder-
ate. 3 Centrifugation uses less power and requires less maintenance
than vacuum filters.

Capital costs of centrifuges vary with the size of centrifuge
purchased, which is dependent on the flow. Table 11 shows the capital
costs of the Sharples SP-6500 centrifuges together with the building

0 O 15
requlrements and construction costs.

 

#mentioned product does not imply endorsement

26

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TABLE 11
CENTRIFUGE COSTS (1972)
No. of Unit B1dg='-< Const** Total
Units Cost(§) Cost($) Cost($) Cost
5 55,000 10,000 96,300 381,300
10 55, 000 20,000 192,500 762,500
2 55,000 4,000 38,500 152,500

 

>I‘assumed to be $ 10.00 per sq. ft.
** assumed to be 35% of the equipment cost

The capital cost of $ 55, 000 per unit remains constant, and the
construction costs and building size required are directly proportional
to the number of centrifuges employed. The equation developed by
Dorr -Oliver for the capital cost of centrifuges is: '

LOG(COST) = 2. 5 - 0.193LOG(I.F.)

where COST = dollars per pound and I.F. = influent flow
in lb dry solids/hour.

This equation involves only the cost of the centrifuges and does not
include any accessories or construction costs. Figure 16 shows

how the construction costs of centrifugation increases as the capacity

. 11
increases.

0 and M costs depend on the power used, the chemicals used,
and the amount of labor required. Table 12 shows the operating
cost in terms of maintenance, operating labor, energy, amortization

and chemicals .

29

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TABLE 12
CENTRIFUGE PERFORMANCE AND OPERATING COST

Plant No. Mach. Op. Maint. Labor Energy Amort* Total**

1 Flow of Size Hrs ($) ($) ($) ($) ($)

(M GD) Units (IN) ka ton ton ton ton ten
18 1 24-38 168 2.53 2.71 0.70 1.30 16.54
1 24-38 9 1. 75 0.94 0.39 13.20 16.28
3.8 1 24-60 21 2.63 7.17 0.49 7.65 30.74
8 2 24-38 35 1.74 1.00 0.35 3.23 6.32
45 2 24-60 60 1.90 2.50 1.39 7.65 13.44
6 2 18-42 48 2.73 1.53 0.59 4.32 14.89
1.5 1 18-42 7.5 0.97 7.40 1.33 71.70 92.60
1.7 1 18-42 30 1.36 9.00 1.58 20.30 44.55
1.2 1 24-38 3 0.24 12. 70 0.83 100.00 113. 77
20 3 24-60 40 2.16 1.05 0.31 3.10 14.62
7 1 24-60 40 3.66 3.20 0. 70 5.50 17.62
7. 5 2 24-60 168 4.32 3.26 1.65 3.65 26.818

 

*amortization based on 6% interest over 25 years
** includes chemicals at various costs and various dosages

As shown in Table 12, the components of the operating costs vary with
flow and hours of Operation per'week. Small plants running for just
a few hours a week spend more money on the process than do the
larger plants.

The power requirements of a centrifuge depend on the bowl size
and the Speed at which the machine is run. Table 13 shows the power

used in centrifugation in relation to plant flow.

 

TABLE 13
CENTRIFUGE POWER REQUIREMENTS

 

Plant Size Power Needed (KWH/day)
(MGD) Primary Activated
1 28. 0 90. 0
10 256. 0 435. 0
100 1400. 0 4348. 0

 

Centrifuges use approximately the same amount of power that vacuum

filters use.

31

The labor requirements of centrifugation depend on the ser-
vice required to operate and maintain the high solids removal charac-
teristics. Figure 17 shows the annual payroll hours needed for main-
tenance and operating labor. 11 The operational labor is more than
maintenance and is about the same as the labor requirements of
vacuum filtration.

Over six thousand wastewater treatment plants in the United
States use the method Of sand drying beds for dewatering sludges. 3
These plants, however, are older plants and the drying beds are
becoming obsolete as plants become larger and new dewatering tech—
niques are developed.

Construction costs are related to surface area requirements
which depend on the quantity and quality of sludge, local climate, and
whether or not the beds will be covered. 11 Figure 18 presents the
construction costs of twenty -two actual uncovered drying bed installa-
tions. 11 The cost rises with increasing surface area. The capital
cost of the beds can double if mechanical lifting and conveying equip-
ment is employed.

The O and M costs of drying beds are primarily due to the
loading and hauling of the dried sludge, and keeping the beds in proper
operating condition. Operating costs have been determined to range
between $ 1. 00 and $ 10. 00 per ton of dry solids. 3 The wide range is
due to the different techniques of loading and unloading the sludge from
the bed.

The labor required to keep the drying beds operational is shown
in Figure 19. 11 The required operational labor is more than the main-
tenance labor due to the loading and unloading technique used.

The last method of dewatering in use today is pressure filtration
or filter presses. Pressure filtration is a batch process and requires
a great deal of labor, but it produces higher solids concentration and
reduced chemical consumption.

Capital costs of pressure filters vary with size of filter used.
Cost of the filters includes the cost of presses, plate shifters, feed
pumps, precoat equipment, buildings, and installation. Table 14
presepgs the cost breakdown of four pressure filters in Virginia,

1972.

ANNUAL PAYROLL MAN-HOURS

32

 

    
   
    
      
  
 

 

 

 

100:000- I I IIIIFIT I I TIIIIII I I I ITII
r- ..
r- _
I— —
Haul sludge
tolandfill
10 000— Sludge con- __
, : veyed to :
_ incinerator a
T" "I
— Operation
labor -(
1,000 :
Maintenance labor
100 I I IIIIIII I I lllllll I IIIIIIL
100 1,000 10,000 100,000

DRY SOLIDS APPLIED, TONS PER YEAR

Figure 17. Centrifugation labor requirements [11]

$1,000

COXST RUCTION COST ,

33

 

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IIFII

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1111

 

10 100 1,000

SURFACE AREA, 1, 000 SQUARE FEET

Figure 18. Drying beds construction cost [11]

10,000

34

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TABLE 14
PRESSURE FILTER COSTS
No. of Size Bldg Cost (X1000 $)
Units (In.) Area Press Shift Prect Bldg=I< Inst** Total***
4 48 3200 80 9. 6 20 32 38.7 181.2
3 48 2100 69 6.9 15 21 32.1 144.9
1 48 1200 21 2.7 5 12 10.4 52.0
3 48 18000 67.5 6.6 18 18 31.5 139.5

 

*based on $10. 00/sq. ft.
>:<>I< based on 35 % of total equipment
::=>'.<>:< includes a $900- 00 feed pump

The initial cost of the filters ranges between $ 20, 000 and $ 22, 500
each and the total costs vary accordingly. 15

Operating cost of pressure filters depends on the labor
required (about 2 men per filter), the chemicals required, and the
power used (about 270 KWH/day for a 48" filter). Operating costs
without chemicals have been determined to be about $4. 69/ton, and
the chemicals add another $7. 29/ton. 5 Using chemicals with filter
presses increases the solids recovery, with a consequent increase in
the solids concentration.
REDUCTION

Sludge reduction processes are thermal processes. They pro-

 

vide a major reduction in the sludge solids. Common established pro-
cesses of reduction are incineration and the wet -air oxidation, or
Zimpro*, process.

Sludge incineration is generally more expensive than other sludge
disposal methods. The capital cost of incineration systems depends on
the type of incinerator, and whether or not pollution control equipment
is required. If the deoderizer is installed with the incinerator, the
capital cost increases about 3 %, and the operating cost increases
about 50%. Table 15 shows the capital costs of incinerators according

19

to manufacturer's 1968 prices.

 

*mentioned product does not imply endorsement

36

 

 

 

TABLE 15
CAPITAL INCINERATOR COSTS
Type Size (lb/hr) - Cost ($)

Fluid Solid 200 180, 000
400 300, 000
1000 550, 000
2000 825, 000
Multiple Hearth 500 300, 000
' 2000 550,000
4000 700, 000
6000 850, 000
Cyclo -burner 130 70, 000

 

The multiple hearth furnace is the most commonly used incinerator
in the United States today, and the prices and sizes show why. The
reported operating costs of multiple hearth furnaces vary substan—
tially due to moisture content of the sludge, labor, power and
auximilary fuel. Rochester, New York, reports operating costs of
$ 24. 55/ton for incineration while South Lake Tahoe reports an
operating cost of $ 12.71 per ten. 5 Figure 20 shows the decreasing
costs for Operating a multiple hearth furnace as the solids per day
increases.

The labor associated with incinerators is included in the opera-
tion and maintenance of conveyors, ash handling equipment, control
centers and the building enclosing the furnace. Figure 21 shows the
annual payroll hours required for incineration as a function of dry
solids burned per year.

The power requirements are due to the electrical power and
auxiliary fuel needed to maintain adequate temperatures within the
furnace. Raw primary sludge with 70 % volatile solids has a fuel
value of about 7800 BTU/lb of dry solids and will burn without fuel
once combustion has started. 20 The auxiliary fuel unit cost decreases
as the cake solids concentration from the dewatering process increases.
A solids concentration of over 30 to 35% will support combustion with-
out auxiliary fuel. Figure 22 shows the annual cost of electrical power

and fuel cost for an incinerator.

COSTS ($/DRY TON)

1000

100

10

1.0

37

 

 

 

 

 

 

L. I I I IIIIII I I IITIIII l I IIIII':-_~10O
L'. I
-- -I
Z : 10
I x, '—
I— =
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-o
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— mOrtized _.
l LIIIIJJI I IIIILIII l I 111111 0.1‘
1 10 100 ~ 1000
DRY SOLIDS (TON/DAY)
Notes:
1. Minneapolis. Mar. 1972. ENR Construction Cost
Index of 1827.
2. Amortization at 7% for 20 years.
3. Labor rate of $6.25 per hour.
4. Exhaust gas scrubber and enclosing structure
included.
5. Costs do not include deodorization of gases: where

required, add $4 to $10/dry ton.

Figure 20. Multiple hearth incineration costs [5]

CONSTRUCTION COST (MILLIONS OF DOLLARS)

ANNUAL PAYROLL MAN- HOURS

100,000

38

 

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10,000

IIIIII

I

1 ,000

 

100

I I ITIIIII I I ITIIIII l

 
      

Operation labor

   
 

Maintenance labor

I IIILLIII I IIIIIIII 1

LI [Iii

I

IIIIIL

441

ILIIIIJI

 

 

100

1,000 10,000
DRY SOLIDS INCINERATED, TONS PER YEAR

Figure 21. Incineration labor requirements [11]

ANNUAL COST , DOLLARS

100,000

39

 

III

I I

10,000

1,000

-
b
—
)—
_
p—
h—

100

 

I I

Electric power
and fuel costs

I J

IIIIITI. I I INIIIII I [j

      

Other material and
supply costs

IIIIIII I IIIllIII I II

I I

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1

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I

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100

1,000 10,000

DRY SOLIDS INCINERATED, TONS PER YEAR

Figure 22.

Incineration material and supply costs [11]

40

Operating costs for fluidized bed incinerators have been esti-
mated by the East Cliff Sanitary District, California. The costs were
reported to‘be $ 25. 32 per ton which includes $ 2. 50 per ton for fuel,
$4.47 per ton for power and $18.35 per ton for labor.3

Wet -air oxidation refers to the oxidation of sludge solids in
water by applying heat and pressure. Basic equipment is a reactor,
air compressor, heat exchanger, and a high pressure sludge pump.
The process can be run at both high and low pressures, with the high
pressure costing more. The economy of both processes depends on
recovery of heat.

Figure 23 shows the installed cost and the Operating cost of
the high pressure oxidation (HPO) system as a function of the capa-
city. 21 Figure 24 shows the same costs for a low pressure oxidation
(LPO) process. 21 The installed cost for the HPO system is 4 to 5
times the installed cost of the LPO system. The operating cost of
HPO is double the Operating costs of LPO. HPO costs more, but it
reduces twice the volume of insoluble volatiles than the LPO system.

At Wheeling, West Virginia, in 1965 a 5. 6 ton/day Zimpro
process was installed for $ 284,000. The operating costs were found
to be about $ 19.90 per ton processed. This includes power at
$ 6.11/ton (31%), chemicals at $4. 13/ton (21%), fuel at $ 1. 65/ton
(8 %), maintenance at $1.17/ton (6%) and labor at $ 6.91/ton (34%).

Power and labor are quite high in this process and make it uninviting

3-5

to an energy minded community.
FINAL DISPOSAL

No matter what thickening, stabilization, conditioning, de-
watering, or combustion process is employed, provision must be
made to dispose of the inevitable end product. Common methods of
final disposal include land spreading for fertilizer or soil conditioning,
lagooning and landfilling.

Using dewatered, digested sludge as a fertilizer and soil condi-
tioner is becoming a popular alternative to combustion and landfill.
The best sludge to be used for fertilizer is waste activated sludge that
has been vacuum filtered and heat dried. The high nitrogen content

of the sludge has not been destroyed by digestion. [Prices for nitrogen,

41

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43

phosphorus, and potash in 1968 were 20 .7, 10 9’. and 5 g! per lb,
respectively. This makes the activated sludge worth $ 20. 00/ton,

and digested primary sludge worth $ 11. OO/ton. 3 The only cost
involved in using sludge as a fertilizer is hauling to the farmland.

‘ Various locations around the country are using the land for
final disposal of sludge. Table 16 shows various cities that spread
sludge on the soil for many reasons and the costs that they incur during

the process.

 

 

 

TABLE 16
LAND SPREADING OF SLUDGES

‘ Plant Size Cost
Location (MGD) . ($ /Ton)
New York City --— ll. 89
Chicago 1300 26. 02
San Diego 90 10. 57
St. Marys, Pa. . 1.3 19.92
Little Miami, Ohio 1. 3 22. 00
Piqua, Ohio 3. 8 l7. 5 to 30. 00
Franklin, Ohio 4. 5 5. 00

 

f

If there is not a market for sludge then it can be sent to
lagoons. The area required for lagoons requires from 1.0 sq. ft.
per capita with primary digested sludge in an arid climate, to as high
as 4 sq. ft. per capita for activated sludge plants in rainy areas.

The Operating and capital cost Of the lagoons depends on the method
of transportation used. Figure 25 shows the transportation cost for
liquid organic sludges as a function of distance to the disposal site. 5
A pipeline has lower costs from 40 to 200 miles away. Beyond 200
miles, rail shipping becomes cheaper.

If combustion is used then provisions must be made to dispose
of the ash that results. Sometimes pressure filters are used in con-
junction with incineration so the ash from the furnaces can be used as
a precoat for the filter, Ash, and even dewatered sludge, is sometimes
dumped into a landfill area mixed with municipal refuse. Figure 26

shows the capital and O and M costs for sanitary landfills excluding

44

 

600

400 I-

200 -

100

IW'I T

0‘
0
II

I
II

TRANSPORTATION COST
(DOLLARS/TON DRY SOLIDS BASIS)

 

20

Tank truck \

Railroad tank car 4

III]

Pipeline

I

 

IIIIIIII I I

 

20

Figure 25.

4o 60 100 200 400
DISTANCE To DISPOSAL POINT (MILES)

Transportation costs for liquid sludges [5]

COSTS (SE/WET TON)

45

 

 

 

 

 

: I I IIIIIIF I I IIIIIII I I IIIIII:
6 E I:
4 " 5\ ..
_. x99 _
2 — 539%
\9 1
+0
\8
10 : e°° :
.. 00 ..
6 : 9“" :
L. Ota CO _
St
2 _ (6x01 _
1.0 : Z
_ J
4 I" _.
2 " .a
0.1 I I LIlIlIl I IIIJIIII I I IIJJI
10 2 4 6 100 2 4 6 1,000 2 4 6 10,
QUANTITY (WET TON/DAY)
Notes:
1. Minneapolis. Mar. 1972. ENR Construction Cost
Index of 1872.
2. Amortization of 7% for 20 years.
3. Labor rate of $6.25 per hour.
4. Quantity assumes 6-day work week.
5. Wet Sludge must be considered for cost per ton.

Figure 26.

Sanitary landfills costs [5]

1.0

0.1

CONSTRUCTION COST (MILLIONS OF DOLLARS)

46

the. cost of the land. The costs are soon to be relatively low and the
problems of the landfill are minimal in cmnparison with other
methods.

Ocean di3posa1 of the final sludge product is used by some
seacost cities at a very low cost, but environmental legislation has
stopped the granting of new ocean disposal facilities until further

studies are done .

Capital energy, as defined earlier, has not been found in any
of the literature reviewed.

47

METHODS

The first step in this analysis was the estimation of the amount
of mixed primary and activated sludge produced per million gallons
of wastewater treated. Each unit process was designed to handle the
estimated amount of sludge. Then the amount of materials (steel
and concrete) involved in the production or construction of each unit
process was determined to calculate the capital energy involved. The
capital and operating costs were obtained from values reported in
the available literature and together with the capital and operating
energy were compared to determine the optimum treatment scheme
with regard to energy and costs.

Three sizes of treatment plants were chosen to include most
treatment plants in the United States. These sizes are 1. 0 MGD,

10. O MGD, and 100. 0 MGD. The wastewater in these plants was
assumed to be of typical values for influent biological demand (BOD)
and influent suspended solids (SS) are 200 milligrams per liter (mg/1)
and 200 mg/l, respectively. Assumptions used in calculating the

quantity of sludge are shown in Table 17. 24

 

TABLE I7
SLUDGE QUANTITY ASSUMPTIONS
Raw Primary Sludge
removal efficiency of clarifier --------- 60% SS; 30% BOD

solids concentration ---------- 5 %

 

Waste Activated Sludge
effluent BOD ------ 10% ; solids yield ------ 50 %

solids concentration ------ 0. 7 5 %

 

 

Each process was designed according to Federal regulations
utilizing the estimated sludge generation rates. Table 18 lists the

basic criteria followed for each process designed.

48

 

TABLE 18
DESIGN PARAMETERS
PROCESS PARAME TER

Gravity thickenerZS-26 ----- Limiting solids flux rate = 6 lb per sq.

ft. /day

Influent solids concentration 2
1. 3 %

Underflow solids concentration =

6 %
Depth = 15. 0 feet
Wall width = l. 0 feet
Dissolved -air flotation5 ----- Solids loading = 2' lb/ftz/hr
Solids recovery = 50 to 80%

Maximum hydraulic loading = 0.80
gpm/sq. ft.

Volume of sludge = 56 ft3/mi11ion gallons
Detention time = 30 minutes

Anaerobic digestion2 ------ Solids loading = 30 to 100 1b volatiles/1000
cu. ft.

Detention time = 30 days

Temperature = 85 to 95 deg. F

Tank diameter = 20 to 115 feet

Water depth : 25 feet

Freeboard = 2. 0 feet

Well insulated covers

Waste efficiency = 0.75

Net growth rate = 526 lb/day
Aerobic digestion26 5 ------ Detention time = 20 days

Solids loading 2 0.1 to 0. 2 lb volatile
solids/cu. ft./day

49

 

TABLE 18 (continueQ
DESIGN PARAMETERS

PROCESS
26 —5

Aerobic digestion ------

Chemical conditioning26 - - - -

Heat treatment 5‘24 -26 _---

Drying bed326--. ..........

Vacuum filtration5 — ——————

19-26

Centrifugation ........

PARAMETER
Hydraulic detention time = 20 days
Air requirements = 25 SCFM/1000 ft3
Blower efficiency = 70 %
Contact time = 30 minutes
FeCl2 dosage = 2% (raw); 3% (dig.)
Motor efficiency = 80%
Pressure = 180 to 210 psig
Residence time = 30 minutes
Temperature = 350 to 390 deg. F
Solids loading = 15 lb/ftZ/yr
Open beds in northern climate
Bed slope = 5%
Application = 6 to 12 inch layers

Partitioned into 20 foot wide by 20 to 100
foot long sections

Loader efficiency = 80%

Yield = 4 lb/ftz/hr

Feed solids = 5%

Effluent solids = 20 to 30%
Feed solids : 2%

Effluent solids = 15 to 40%
Length/Diameter ratio = 3
Solids recovery = 80 to 95%
Bowl speeds = 3000 to 7000 rpm

Force = 2500 to 6000 G's

5O

 

TABLE 18 (continued)
PROCESS PARAMETER
. . 26-28 .
Pressure Filtration -—--Pressure = 60 to 225 p31
Detention time = 2 hours
Sludge cake thickness = l. 5"
Effluent solids = 30 to 50%

Cake volume = 3. 0 ft3/chamber

Cake density 105 lb/cu. ft.

Incinerationé’26 ........... solids loading = 2 lb/ftz/hr
Temperature = 1400 to 1700 deg. F
Capacity = 200 to 8000 lb/hr
Combustibles = 60% of sewage
Efficiency = 100% of combustibles
Wet oxidation5 ------------- Pressure = 1000 to 1750 psi
Temperature = 250 to 700 deg. F
Detention time = 30 minutes
Combustibles = 60% of sewage
Fertilizer and Soil5 -------- Solids loading = 15 tons dry solids per
Conditioner acre/year
Liquid application rate = 5000 gal/acre/day
(MAX)
Truck working efficiency = 80%
Hp operating efficiency = 60%
Lagoons5 ------------------ Depth = 5 feet

Bottom must be 18 inches above water
table

Solids loading : 2. 2 lb/ft3/yr

51

 

TABLE 18 (continued)

 

PROCESS PARAMETER

 

Landfills ------------------ Waste layers = 2. 0 feet
Compacted layers = 2. 0 feet

Spreading on soil5 ---------- Same as fertilizer

 

52

Once the size of the individual process was determined for all
three design flows, the capital costs, operating costs, operating
energy and capital energy we re determined. Capital costs were taken
from data gathered from professional literature and from manufac-
turers' data. Operating costs were considered to be entirely composed
of annual manhours needed for maintenance and operation based on a
labor rate of $ 7. 10 per hour for skilled labor. 2'7 Operating power was
calculated as a separate item.

The Sewerage Construction Cost Index (SCCI) determined by
the Environmental Protection Agency was used to adjust all capital
cost data to a base data of January, 197 5. Table 19 shows the Detroit
cost index which was used in this study. The base index of 100 is for
the period 1957-59.

 

 

 

TABLE 19
S.C.C. INDEX
Year Detroit
1969‘ 138.7
1970 ‘ 153.2
1971 163.4
1972 180.7
1973 188.9
1974 200.4
1975 . 239.6

 

1 Power, like money, can be expressed in both operating and
capital terms. Capital energy, like capital cost, is the initial amount
of energy used to produce a piece of treatment equipment .or construct
a unit process. In this study capital energy was taken to be the
energy required to produce the steel and concrete involved in the
equipment or process. This is, of course, only a first approximation
as transportation energy and construction energy also contributes to
the capital energy.

The total weight of steel and volume of concrete used in the
production or construction of a sludge process were used to compute

the capital energy for each unit process.

53

Both operating and capital energy can be expressed in dollars.
Once converted to dollars, capital energy can be amortized in the same
manner as capital cost at 8% interest over a standard design life of
20 years. In order to make energy costs comparable, it was assumed

that all the energy used in the production of the steel and concrete was

electrical power. This results in an average dollar value for the capi-

tal energy. A local energy cost of $ 0. 03 per KWH was used.

Knowing the operating and capital costs and the operating and
capital energy a decision as to the best treatment scheme can be made
by applying a sequential decision model known as dynamic programming.
Dynamic programming is applicable to the optimization of system-s
posesgsing a serial structure with no recycle. Figure 27 shows the
framework of sludge handling processes. This flow chart is a typical
serial structure with no recycle. For example, whatever happens in
the stabilization step influences the events of the dewatering step but
has no effect upon the thickening step.

Dynamic programming compares the independent variable of
each process with special regard to the limitations and determine
the optimum selection for sludge handling. In this work the optimum
selection was made for three different assumptions regarding energy
and cost for all three design flows mentioned earlier. The conditions
used were as follows:

1. Economic optimum - 1975 and future

2. Energy affluent present with energy poor future

3. Energy optimum - 1975 and future
Case one, the economical optimum, was calculated using only
operating and capital costs without separation of the energy component.
This case assumes that the energy costs will inflate at the same rate
as the equipment costs. Case two, the energy poor future, was cal-
culated using 1975 capital costs and considering operating energy in
the future. Case three, the energy optimum, was evaluated utilizing
only the capital energy and operating energy without consideration of
other costs. This leads to a limiting case involving only energy and

will be applicable if the energy costs escalate at a faster rate than

normal inflation.

 

54

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55

The three specific cases give an overall view at the sludge
handling scheme with regard to the major factors that could affect

a choice of treatment, energy and money.

 

56

RESULTS

Using the medium value for B. O.D. and 5.5. , the amount of
raw primary sludge was estimated to be 1000 lb per million gallons of
wastewater treated. Assuming a 5. 0% solids concentration, the
volume of primary sludge that must be treated was found to be 2330
gallons per day (gpd). The amount of waste activated sludge produced
per million gallons of wastewater treated was calculated to be 1068 lb.
Assuming a solids concentration of O. 75 %, the volume of sludge was
found to be 16, 578 gpd. Thus, the total volume of sludge produced
per million gallons of wastewater is about 18,908 gallons. Using a
specific gravity of 1. 03 and a solids concentration of the mixed primary
and activated sludge of 1.27%, the amount of sludge solids generated
is about 2530 ft3 per day. (See Appendix A for Calculations). 24 Table
20 shows the amount of raw primary, waste activated and total mixed

sludge that has to be handled for the three design flows.

 

 

 

TABLE 20
SLUDGE QUANTITIES
Plant Size Primary Waste Act. Total Sludge
(MGD) (GPD) (GPD) (MGD) (tons /day)
1 2,330 16,578 0.019 1.034
10 . 23,300 165,780 0.189 10.340
100 233,000 1,657,800 1.891 103.400

 

The volume of sludge determines the size of the unit process and
the size determines the capital cost, capital energy, labor requirements
and power needs. These four variables were determined for each stage
in the sludge treatment process.

Capital energy is the energy required for materials fabrication.
From manufacturing data it was found that the average value of energy
used in the production of one ton of finished steel is about 36 million (106)

B. T.U. 30 It was also determined that one 94 pound bag of cement

57

requires about 175, 000 B. T.U. 's to produce.31 Using a water cement
ratio of 0. 54 by volume and a concrete composition of 74 % aggregate,
3. 7% air, 9. 3% cement and 13 % water, yields an estimated require-
ment of 2. 5 sacks of cement for each cubic yard of concrete. A cubic
yard of concrete, therefore, requires about 437, 500 B. T.U. 's for
production (See Appendix A).

The first step of treatment is thickening using gravity thickeners
(GT) and dissolved -air flotation thickeners (DAF). Table 21 shows the
power, labor, capital cost and capital energy for both types of thickening.

The calculations are shown in Appendix B.

 

 

 

 

 

 

 

TABLE 21
THICKENING
Plant Power Labor Cost Energy 6
Size (kwhAday)_ (hrZyr) (1000$) (BTUx 10 )
(MGD) GT DAF GT DAF GT DAF GT DAF
1 10.2 140 220 340 74 23 66 340*N/A**
10 20.4 1216 780 1100 194 257 230 1196*49**
100 40.8 9384 3600 5000 841 2567 1600 5868* 269**

 

‘1‘ if steel tanks are used; ** if concrete tanks are used
N/A signifies that concrete tanks are not applicable here

Table 21 shows that even though gravity thickening uses less
energy during operations than the dissolved -air flotation machine, the
capital energy required to construct the GT is about five times that of
the DAF.

The next step in the sludge handling process is stabilization.
Anaerobic digestion (AND) and aerobic digestion (AD) stabilize the
sludge to make it less offensive and reduce its volume. Table 22
shows the power, labor, capital cost, and capital energy for the two

types of digestion. The calculations are shown in Appendix C.

58

 

 

 

 

 

TABLE 22
STABILIZATION
Plant Power Labor Cost Energy 6
Size (kWh/day) (hr/yr) (10003) (BTU x 10 )
(MGDL AND AD AND AD AND AD AND AD
1 124 233 225 96 222 89 742 57
10 456 2685 1125 480 555 398 5418 390
100 1910 31930 5700 2420 4990 3315 45111 3014

 

Anaerobic digestion uses less operating power than aerobic digestion but
costs more and requires more capital energy.

After digestion the sludge can be conditioned before dewatering.
Conditioning usually consists of chemical conditioning (CC) or heat
treatment (HT) if there is a market for fertilizer. Table 23 presents
the power, labor, capital costs, and capital energy for chemical condi-
tioning and heat treatment. Chemical conditioning is cheaper, uses less
operating energy and labor, and requires less capital energy than heat
treatment but heat treatment allows for easier dewatering and provides
a very useful end product for fertilizer, whereas chemical conditioning

does not. See Appendix D for calculations.

 

 

 

 

 

 

 

TABLE 23
CONDITIONING

Plant Power Labor Cost Energy 6
Size (kwhfiay) (hr/yr) (x 1000$) BTU x 10
(MGD) CC HT CC HT CC HT CC HT

1 3 305 1040 520 46 203 29 45
10 80 3050 2600 1300 129 422 324 765
100 917 30500 4368 2190 256 2581 2394 4339

 

After conditioning the next step is dewatering. Dewatering
reduces the volume of the sludge by reducing the water content. The

major types of dewatering are drying beds (DB), vacuum filtration (VF),

59

centrifugation (CT) and pressure filtration (PF). Table 24 shows
the comparison of the four types of dewatering with respect to the

power and labor used in the Operation of equipment.

 

TABLE 24

 

DEWATERING POWER AND LABOR

 

 

 

Plant

Size Power (kwyday) Labor (hr /yr)

(MGD) DB VF CT PF DB VF CT PF

1 90 52 90 62 1750 1640 1370 2080
10 477 531 435 620 17500 5650 4200 5200
100 1551 5208 4400 6204 175000 35500 30000 26208

 

The power used for dewatering increases greatly as the flow
increases except for drying beds which is lower due to the equipment
used for removing the dried sludge. The labor requirements for
drying beds at the 100. 0 MGD plant seem to be quite large. This is
due to the use of one man per loader manhour. These values are based
on operational data given for the specific equipment.

Another comparison of the four dewatering techniques is shown
in Table 25. Capital cost and capital energy are presented with respect

to the design flows.

 

 

 

 

 

TABLE 25
DEWATERING COSTS AND ENERGY
Plant Costs (x 1000 $_) EnerguBTU x 10:
(MGD) DB VF CT PF DB VF CT PF
1 91 211 422 183 307 180 86 79
10 829 475 844 366 350 510 288 137
100 11302 2638 2536 1468 2526 2727 1134 502

 

Pressure filters recently have become comparable in price with
other dewatering techniques due to vast improvements in filter operations
and size in the last few years. See Appendix E for calculations.

The high capital costs for the drying beds is due to the large number

of machines needed to unload the dried Sludge.

60

Dewatered sludge can be sent directly to disposal or it can be
reduced in volume and weight by incineration (INC) or wet oxidation (WO).
These two methods are the most common types of reduction used in
sludge handling. Incineration produces a dry ash which can be sent
to lagoons or to a landfill. Wet oxidation produces a wet ash slurry
which usually goes to lagoons but can be used as a soil conditioner or
fertilizer. Table 26 Shows the power, labor, capital cost and capital
energy needed for the use of the reduction step. See Appendix F for

the calculations .

 

 

 

 

 

 

 

TABLE 26
REDUCTION

Plant Power Labor Cost Energy
Size (kWh/day) (hr[yr) (x 1000 $) (BTU x 106)_
(MGD) INC WO INC wo INC WO INC wo

1 603 610 1900 520 530 469 601 45
10 1242 6101 5400 1300 928 1408 2558 765
100 4932 61006 39000 2190 2880 6568 14350 4339

 

The labor requirements are unusually high for incineration because the
dry ash cannot be pumped.

Once the sludge is in the smallest volume feasible the sludge is
deemed ready for "final disposal". The sludge can be used as a fer-
tilizer and soil conditioner in a digested form (FERT), or sent to a
sanitary landfill (LNF) as a dried cake or ash, or sent to permanent
lagoons (LAG) in a Slurry or as a dried cake. All of these methods
require capital costs and labor. Permanent lagoons do not use
operating power or capital energy as defined in this report. Table 27
shows the power, labor, capital costs and capital energy requirements
of the three basic methods of final disposal. The power involved in
using the fertilizer and landfill method is due to the use of heavy equip-
ment. Each process needs many machines to spread the sludge or to
bury it. See Appendix G for calculations.

The high labor requirements or final disposal are due to the
large volume of sludge that has to be spread. The trucks with larger

tanks can not be used because they bog down in the fields so more

61

 

 

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62

smaller tanks must be used and this requires more trucks and labor.

The lagoons and landfills were designed with the idea of using
a 25% solids cake for disposal. If the reduction step is used then the
costs and power requirements will decrease substantially. This is
shown in Appendix G calculations.

All six steps of sludge handling are shown in Figure 27. After
converting labor and power to dollars per year and amortizing the
capital costs and capital energy, a comparison can be made. Each
step has one or more choices and dynamic programming is used to
make the comparison.

Dynamic programming is a useful technique for making a
sequence of interrelated decisions. In an N stage process such as
shown in Figure 27, the best choice if sound in the Nth stage corre-
sponding to all possible decisions that could be made in the (N-l)th
stage. Now the two final stages are reduced into a single stage which
all the possibilities and costs are known. Now proceed to examine
the (N-l)th stage regarding the possible decisions in the (N-2)th stage.
Following the same procedure all the stages down to the first stage
can be examined. The restrictions or limitations for the six steps

Of sludgehandling are given in Table 28.

 

 

 

TABLE 28

PROCESS LIMITATIONS
ITEM _ RULE
FERT must be preceeded by Heat Treatment
LAG must be preceeded by Stabilization
LNF must be preceeded by Dewatering
INC must be preceeded by Dewatering
WO must be preceeded by Thickening
DB must be preceeded by Stabilization
VF, CT, PF must be preceeded by . Conditioning
CC, HT, AND, AD must be preceeded by Thickening ,

 

The following example shows how this decision process works

in the sludge handling flow scheme. The annual dollar values are

63

used for comparison and are not exact costs for each process but
are relative to one another.

For a flow of l. 0 MGD under Case 1 the annual cost of each
process is given in Figure 28. Starting with the final disposal step
or Step 6 the lowest dollar value is chosen with respect to the processes
in Step 5. There are six choices available in Step 6.

The six choices in Step 6 have twenty-two possible combinations
with Step 5. The three processes in Step 5 each have a cost in conjunc -
tion with Step 6. Table 29 shows the processes of Step 5 with the
combinations of Step 6. The best combinations with regard'to the
three processes in Step 5 are incineration with landfill at an amlual cost
of $ 74, 073 or $ 70,405, wet oxidation with lagooning at $ 60, 241 per
year and null with lagooning at $ 4, 555 per year. This shows that
landfill is best with incineration, lagooning is best with wet oxidation
or null and fertilizer is never best. Now Steps 5 and 6 are combined
as one solution step.‘ I

Following the same procedure Step 4 is examined in conjunction
with the costs and limitations of the combinations of Steps 5 and 6.
There are five possible processes of Step 4 and fifteen possible com-
binations with Steps 5 and 6. The best combinations with each dewatering
process are drying beds with null and lagooning at $ 27, 155, vacuum
filter with null and lagooning at $ 28, 224, centrifugation with null and
lagooning at $ 58, 241, pressure filtration with null and lagooning at
$ 38, 634 and null with null and lagooning at $4, 555 per year. This
shows that null of Step 5 and lagooning of Step 6 are best when used with
drying beds, vacuum filters, centrifuges, pressiIre filters and null
in the dewatering step. Incineration with landfill and wet oxidation
with lagooning are never best when used with dewatering. The sludge

handling has now been reduced to four steps as Steps 4, 5 and 6 are

incorporated into one step.
The three processes of Step 3 can be examined with regard to

the five choices made in Step 4. This makes fifteen possible process
combinations. The best processes to be used with chemical condi-

tioning are drying beds, null and lagooning at $39, 989 per year. Heat

64

 

CC
HT

NULL

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

GT DAF ,
$9,191 1 $6,249* J STEPI
_ AND 1 AD NULL
GT[ $25,567 1 $12,299 $0 El
STEP 2
DAFI $25,567 1 $12,299* I $0 I
CC HT NULL
AND $12, 834 NZA $0
AD $12, 834 N/A 5130* STEP 3
NULL $12,834 $27,738 $0
DB VF CT PF NULL
$22,600 $33,669 $53,686 $34,079 N/A
$22, 600 $33,669 $53, 686 $34,079 $0 STEP
N/A N/A N/A N/A $0*
INC WO NULJII._‘
DB N/A N/A $0
VF $74,073 N/A $0
CT $74,073 N/A $0 STEP 5
PF $74,405 N/A $0
NULL N/A $58,140 $0*
FERT LAG LNF
INC NjA $2,101 $0
WO N/A $2,101 N/A STEP 6
NULL $46, 923 $4, 555* $25, 724

 

 

 

 

 

EXAMPLE PROCESS F LOWSHEE T

 

FIGURE 28

 

65

 

TABLE 29

STEP 6 COM BINATIONS

 

 

 

 

 

 

Choice Cost ($) Combination Total Annual Cost
LNF INC W/ VF at $ 74073 74, 073
LNF INC w/ CT at $ 74073 74, 073
LNF INC W/ PF at $ 70405 70,405
LAG 2,101 INC w/ VF at $ 74073 76,174
LAG 2,101 INC w/ CT at $ 74073 76,174
LAG 2,101 INC W/ PF at $ 70405 72, 506
LAG 2,101 W0 W1 NULL at $ 58140 60, 241
LAG 4, 555 NULL w/ DB at $0 4, 555
LAG 4, 555 NULL w/ VF at $ 0 4, 555
LAG 4,555 NULL w/ CT at $0 4,555
LAG 4, 555 NULL w/ PF at $ 0 4, 555
LAG 4_, 555 NULL w/ NULL atfl 4, 555
FERT 46, 923 NULL W/ DB at $ 0 46,923
FERT 46,923 NULL w/ VF at $ 0 46, 923
FERT 46,923 NULL w/ CT at $ 0 46, 923
FERT 46,923 NULL w/ PF at $ 0 46,923
FERT 46, 923 NULLw/ NULL at $ 0 46, 923
LNF 25,724 NULL w/ DB at $0 25,724
LNF 25, 724 NULL w/ VF at $ 0 25, 724
LNF 25, 724 NULL w/ CT at $ 0 25,724
LNF 25, 724 NULL w/ PF at $ 0 25, 724
LNF 25,724 NULL W/ NULL at $ 0 25, 724

 

66

treatment has no best combinations due to process limitations given
in Table 28. The null of this Step is best with null, null and lagooning
at an annual cost Of $4, 555. Now the sludge handling scheme consists
of three steps since Steps 3, 4, 5 and 6 comprise one step.

Now Step 2 can be examined with regard to the combinations
already determined. With the three processes of Step 2 there are
six combinations available. Following the rules given the best combin—
ation to be used with anaerobic digestion is null, null, null and lagooning
at a cost of $ 30, 122 per year. Aerobic digestion works best with
null, null, null and lagooning at an annual cost of $ 16, 854.

The final choice to make is in Step I examined with the two
schemes given from the combination of Steps 2, 3, 4, 5 and 6. There
are two processes in Step 2 so there are four available combinations
to choose from. The six steps have reduced down to one choice 9
between four possible treatment schemes. They are gravity thickening,
anaerobic digestion, null, null, null and lagooning at $ 39, 313 per year;
gravity thickening, aerobic digestion, null, null, null and lagooning
at $ 26, 045 per year; dissolved -air flotation, anaerobic digestion,
null, null, null and lagooning at $ 36, 371 per year; and dissolved -air
flotation, aerobic digestion, null, null, null and lagooning at $ 23, 103
per year.

The final sludge treatment choice is made with regard to the
lowest dollar value and consists of gravity thickeners for thickening,
aerobic digestion for stabilization, no conditioning, no dewatering,
no reduction and lagooning for final disposal. It can be seen that even
though the final disposal stop is not the cheapest the overall treatment
scheme has the lowest cost.

The total treatment cost is about $ 23, 103 per year. This is
shown in Figure 28 where the chosen values are marked with an
asterisk. The choice made for a flow at l. 0 MGD given above is the

best Choice possible when considering capital costs, and operating

power and labor.
Following the procedure used in the example, the three design

flows were analyzed according to three cases:

67

1. Economic optimum - 1975 and future

2. Energy affluent present with energy poor future

3. Energy optimum - 19 75 and future
Figures 29 through 37 show the flow sheets and the costs of each indi-
vidual process. The values are the ones used for the comparison.

For a plant flow of l. O MGD the sludge treatment scheme that
would be best according to capital costs, operating power and operating
labor consists of dissolved -air flotation, aerobic digestion and lagooning.
The annual costs of this treatment scheme is about $ 23', 103 (see
Figure 29). This is a commonly used treatment scheme. This treat-
ment scheme is the best choice when costs and energy inflate at the
same rate and can be used for future planning.

If, at some time in the future, energy becomes scarce and the
costs of power increase faster than inflation, then the treatment scheme
that costs less and also uses the least amount of energy would be the
best. Under Case 2 the annual costs are based only on the operating
energy and capital costs. The treatment scheme with the lowest dollar
value wouldbe the best choice.

For the same plant flow of l. 0 MGD the best choice under Case 2
is lagooning, with its low power requirements, aerobic digestion and
dissolved -air flotation (see Figure 30). This treatment scheme pro-
vides the best treatment and keeps the power consumption down. It
is the same scheme chosen for the economic optimum (Case 1). The
total cost is lower than Case 1 due to neglecting operating labor. Since
the same treatment scheme is obtained for both Case 1 and Case 2, this
shows that the processes are not labor sensitive.

The cost of capital energy is usually included in the capital cost
of a product. If energy prices increase faster than inflation then pro-
ducts with a high capital energy component will have to increase in
price accordingly. Under Case 3 the best treatment scheme chosen
would be the one with the lowest capital and operating energy.

At a plant flow of l. 0 MGD the best treatment scheme was found
to be lagooning with anaerobic digestion and gravity thickeners (see
figure 31). This scheme is different from those chosen in Case 1 and

Case 2. This shows that under expensive energy conditions anaerobic

68

 

CC
HT

NULL

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

GT DAl"
$9,191 $6,249 STEP 1
, AND AD NULL
GT1 $25,567 $12,299 $0
STEP 2
DAFl $25,567 $12,299 I $0
CC HT NULL
AND $12,834 N/A $0
AD $12,834 N/A $0 STEP 3
NULL $12,834 $27,738 $0
DB VF CT PF NULL
$22,600 $22,600 $53,686 $34,079 N/A
$22,600 $33,669 $53,686 $34,079 $0
N/A N/A N/A N/A $0
INC WO NULL
DB N/A N/A $0
VF $74,073 N/A $0
CT $74,073 N/A $0 STEP 5
PF $70,405 N/A $0
NULL N/A $58,140 $0
FERT LAG LNF
INC N/A $2,101 $0
WO NjA $2, 101 N/A STEP 6
NULL $46,923 $4,555 $25,724
FLOW 1.0 MGD-- CASE 1

 

FIGURE 29

STEP

 

69

 

CC
HT

NUL

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

GT , DAF
$7,629 [ $3,835 STEP 1
_ AND , AD NULL
GTI $23, 969 I $11,617 $0 1 STEP 2
DAFl $23,969 1 $11,617 l $0 1
CC HT NULL
AND $5,450 N/A $0
AD $5,450 N/A $0 STEP 3
NULL $5,450 $24,046 $0
DB VF CT PF NULL
$10, 200 $22, 069 $43, 986 $19, 279 NZA
$10,200 $22,069 $43, 986 $19, 279 $0
N/A N/A N/A N/A $0
INC WO NULL
DB N/A N/A $0
VF $60,583 N/A $0
CT $60, 583 N/A $0 STEP 5
PF $56,915 N/A $0
NULL N/A $0
FERT LAG LNF
INC N/A $1,426 $0
WO N/A $1, 426 N/A STEP 6
NULL $26,191 $3, 738 $10, 956

 

 

 

 

 

FLOW 1.0 MGD-- CASE 2

 

FIGURE 30

STEP

 

70

 

CC
HT

NUL

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

GT DAF
$171 $1,837 STEP 1
AND AD NULL
GT $2,021 $2,603 $0
STEP 2
DAE $2,021 $2,603 $0
CC HT NULL
AND $56 N/A $0
AD $56 N/A $0 STEP 3
NULL $56 $3,380 $0
DB VF CT PF NULL
$1,255 $730 $1,063 $750 N/A
$1,255 $730 $1,063 $750 $0
N/A N/A N/A N/A $0
INC WO NULL
DB N/A N/A $0
VF $7,141 N/A $0
CT $7, 141 N/A $0 STEP 5
PF $3,473 N/A $0
NULL N/A $6, 720 $0
FERT LAG LNF
INC N/A $0 $0
WO N/A $0 N/A STEP 6
NULL $24,111 $0 $6,526
FLOW 1.0 MGD-- CASE 3

 

FIGURE 31

STEP

 

71

digestion is better than aerobic digestion and gravity thickening is
better than dissolved -air flotation thickening.

As the flow increases the treatment schemes obtained under
the three cases change. Going from a flow of 1.0 MGD to 10. 0 MGD
at Case 1, the economic optimum, the scheme changes from lagooning,
aerobic digestion and dissolved -air flotation to lagooning, anaerobic
digestion and gravity thickening. The annual cost of this treatment is
about $ 110, 896. The treatment scheme changes because the aerobic
digestion and dissolved -air flotation processes use too much energy
at this size plant (see Figure 32).

Increasing the flow to 10. 0 MGD under Case 2 causes the same
changes it did under Case 1. The treatment scheme consists of
lagooning, anaerobic digestion and gravity thickening (see Figure 33).
This is the same scheme chosen as the economic optimum (Case 1).
Labor is still not a dominant factor in the decision.

At 10. 0 MGD for Case 3 the treatment does not change from the
choices made for Case 1 and Case 2 (see Figure 34). The lagoons with
anaerobic digestion and gravity thickeners are still the best choice.
This treatment is the same chosen for the l. 0 MGD plant.

Increasing the plant flow to 100. 0 MGD does not alter any
choices made at the 10. 0 MGD flow for all three cases. Lagooning,
anaerobic digestion and gravity thickening is the best choice when con-
sidering costs, labor and energy (Case 1); costs and energy (Case 2);
and energy (Case 3) (see figures 35, 36, and 37). The estimated annual
cost for treatment at this scheme under Case 1 is $ 758,472.

At Case 2, however, lagooning with incineration, pressure
filtration, chemical conditioning and gravity thickening was only about
$ 100, 000 per year more than the treatment chosen. If maximum main-
tenance and operational care was exercised the two treatment schemes
might be comparable. Since incineration reduces the lagoon area by
60 %, the choice of treatment could be altered in this case if the price
and availability of land were more significant factors.

As a final disposal step lagooning is the best choice to keep
costs and energy requirements low for all three design flows. Table

30 Shows the treatment choices of all three cases for all three design

 

72

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

_ GT DAF
[ $25,521 I $47,280 STEP 1
, AND AD , NULL f
GT $69, 508 73, 344 0
l f $ 1 $ 1 STEP 2
DAFl $69,508 $73,344 I $0 I
CC HT NULL
AND $27, 243 N/A $0
AD $27,243 N/A $0 STEP 3
NULL $27, 243 N/A $0
DB VF CT PF NULL
CC $213, 926 $94, 315 $120, 563 $80, 989 N/A
STEP
HT $213,926 $60,169 $120,563 $80,989 $0 4
NUL N/A N/A N/A N/A $0
INC WO NULL
DB N/A N/A $0
VF $146, 457 N/A $0
CT $146,457 N/A $0 STEP 5
PF $140,161 N/A $0
NULL N/A $219, 441 $0
FERT LAG LNF
INC N/A $6,229 $25, 724
WO N/A $6,229 N/A STEP 6
NULL $469,247 $15, 867 $94,133

 

 

 

 

 

FLOW 10.0 MGD-- CASE 1

 

FIGURE 32

 

73

 

GT , DAF
$19,983 I $39,470 STEPl

 

 

 

 

_ AND AD f NULL 7
GT1 $61,520 $69,936 1 $0 1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

STEP 2
DAFI $61, 520 $69, 936 l $0 I
CC HT NULL
AND $8, 963 N/A $0
AD $8, 963 N/A $0 , STEP 3
NULL $8, 963 $76, 409 $0
DB VF CT PF NULL
CC $89, 626 $54, 215 $90, 763 $44, 089 N/A STEP
HT $89,626 $20,069 $90,763 $44,089 $0 4
NUL N/A N/A N/A N/A $0
INC WO NULL
DB N/A N/A $0
VF $108,117 N/A $0
CT $108,117 N/A $0 STEP 5
PF $101L821 NjA $0
NULL N/A $210, 211 $0
FERT LAG LNF
INC N/A $5,093 $10,956
WO N/A $5, 093 N/A STEP 6
NULL $261, 927 $14,198 $57, 213

 

 

 

 

 

FLOW 10.0 MGD-- CASE 2

 

 

 

FIGURE 33

74

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FLOW 10.0 MGD-- CASE 3

 

GT DAF
$429 1 $13,359 STEPl
f AND AD NULL
GT 9, 827 29, 749 0
l $ $ $ STEP 2
DAFl $9.827 $29,749 $0 ~
CC HT NULL
AND $1,166 N/A $0
AD $1,166 N/A $0 STEP 3
NULL $1,166 $34, 083 $0
DB VF CT PF NULL
CC $5,539 $6,272 $5,021 $6,912 N/A
STEP
HT $5,539 $730 $5,021 $6, 912 $0
NULL N/A N/A N/A N/A $0
INC WO NULL
DB N/A NjA $0
VF $15, 711 N/A $0
CT $15,711 N/A $0 STEP 5 ,
PF $9, 415 N/A $0
NULL N/A $67, 491 $0
FERT LAG LNF
INC N/A $0 $6, 526
WO N/A $0 N/A STEP 6
NULL $241, 132 $0 $37, 976

 

FIGURE 34

 

75

 

CC
HT

NULL

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

GT DAF
$111,663] $399,755 STEP 1
f AND , AD , NULL
GT1 $569,617 I $704, 44fl $0
STEP 2
DAF [$569,617 1 $704, 4491 $0
CC HT NULI;
AND $142, 369 N/A $0
AD $142,369 N/A $0 STEP 3
NULL $142,369 $612, 399 $0
' DB VF CT PF NULL
$2,410,484 $577,828 $519,480 $403,534 N/A
$2,410,484 $310,415 $519,480 $403, 534 $0
N[A N/A N/A N/A $0
INC WQ NULL
DB N/A N/A $0
VF $624,233 N/A $0
CT $624,233 N/A $0 STEP 5
PF $588,230 N/A $0
NULL N/A $1,352,516 $0
FERT LAG LNF
INC N[A $26, 332 $75, 661
W0 N/A $26, 332 N/A STEP 6
NULL 4,692,473 $77,192 $306, 592

 

 

 

 

 

FLOW 100.0 MGD-- CASE 1

 

FIGURE 35

STEP

 

76

 

CC
HT
NULL

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

GT f DAF ,
$86,103 I $364,255 J STEP 1
, AND AD , NULL
GTl $529,147 1 $687,267[ $0 1
STEP 2
DAFl $529,147 L$687,267l $0 1
CC HT NULL
AND $111,356 N/A $0
AD $111, 356 N/A $0 STEP 3
NULL $111,356 $596,850 $0
DB VF CT PF NULL
$1,167,984 $325,728 $306,480 $217,434 N/A
1,167,984 $58,315 $306,480 $217,434 $0 STEP
N/A N/A N/A N/A $0
INC WO NULL
DB N/A N[A $0
VF $347,333 N/A $0
CT $347, 333 N/A $0 STEP 5
PF $311,330 N/A $0
NULL N/A $1,336,967 $0
FERT LAG LNF
INC N/A $22,427 $38,741
wo N/A $22,427 N/A STEP6
NULL $2,619,273 $67,252 $244,566

 

 

 

 

 

FLOW 100.0 MGD-- CASE 2

 

FIGURE 36

 

77

 

CC
HT

NUL

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

o'r l)/\l"
$1,879 $102, 996 STEP 1
_ AND , AD NULL
GT $61, 202 $352, 320 $0
I. T l 1 STEP 2
DAF r$61,202 I $352, 320 I $0 I
CC HT NULL
AND 311. 889 N/A $0
AD $11, 889 N/A $0 STEP 3
NULL $11, 889 $337, 680 $0
DB VF CT PF NULL
$19, 240 $59, 469 $49,195 $68, 383 N/A
$19, 240 $6, 272 $49,195 $68, 383 $0 '
N/A N/A N/A N/A $0 ,
INC WO NULL
DB N/A N/A $0
VF $66, 852 N/A $0
CT $66,852 N/A $0 STEP 5
PF $30, 849 N/A $0
NULL N/A $671, 901 $0
FERT LAG LNF
INC N/A $0 $18, 989
WO N/A $0 N/A STEP 6
NULL $2,411,318 $0 $158, 193

 

 

 

 

 

FLOW 100.0 MGD-- CASE 3

 

FIGURE 37

STEP

 

78

 

 

 

 

 

Sam: some; ~22” momma: Samoa 20;; N33; 632:; 8222 380
360.
044 044 044 044 044 044 044 044 044 6
III III III II... III III III III III m
III III III III III III III III III w
III III III III III III III III III m
024 024 024 024 024 04 024 024 04 N
H0 P0 P0 H0 P0 040 P0 P0 040 4
6.2: 6.2 6.4 6.84 6.3 0.4 6.2: 6.3 o4 38%
m 0.400 N 0600 H «0de

mMEHEOmBZHEF<HMH133fih

 

ommdm<H

 

79

flows with their respective total costs. As seen in Table 30 treatment
steps three, four and five can be omitted thus reducing cost and energy

consumption .

80

CONCLUSIONS

The best treatment for sludge varies with flow and energy
requirements. Considering treatment costs only the best treatment
scheme consists of lagooning, aerobic digestion and dissolved -air
flotation for the 1.0 MGD plant but switches to lagooning, anaerobic
digestion and gravity thickening for the 10. 0 MGD and the 100. 0 MGD
plants. The choice of treatment here is the economic optimum for
1975 and also for any time in the future assuming inflation affects all
processes equally.

Removing the labor costs and comparing the processes only
capital costs and operating power does not change any of the treat-
ment choices. Lagooning with digestion and thickening stages pre-
sents the best treatment if operating power consumption becomes a
major factor. This choice of treatment will use the least power when
power prices increase dramatically.

Looking at the processes with regard to only the capital and
operating energy, the best treatment scheme is lagooning with anaero-
bic digestion and gravity thickening for all three design flows. This
choice of treatment results in the lowest energy consumption and could
be used for future planning. Since the treatment scheme has the
lowest energy consumption, when the price of energy increases faster
than inflation this specific scheme will have the smallest net increase
in cost, compared to other possible choices.

' In all nine treatment schemes examined there are no reduction,
dewatering or conditioning steps involved. Sludge can be treated
effectively without these steps. Since there is an end product to be
disposed of with any type of treatment, then stabilization and thickening
are all that is needed with the final disposal. No excess treatment
should be used in order to keep the costs and energy requirements to

a minimum .

 

81

APPENDICES

82

APPENDIX A
SLUDGE AND ENERGY CALCULATIONS

SLUDGE CALCULATIONS
As sumptions:
Influent B.O.D. = 200 mg/l = so
(200 mg/l) (8.34) = 1668 llo/day/lo6 gallons
Influent Suspended Solids = 200 mg/l = X
(200 mg/l) (8.34) = 1668 llo/day/lo6 gallons
Raw Primary Sludge:
Efficiency of primary clarifier = 60 % X0; 30 % S0
(1668 lb/day) (60 %) = 1000.8 llo/day/lo6 gallons
At 5% solids and specific gravity of 1. 03 the volume
of sludge per 106 gallons is:
(1000.8 lb[day)
(1.03) (0.05) (8.34)

Waste Activated Sludge:
B.O.D. removed = (A S) = influent BOD - effluent BOD

AS = 70% (200 mg/l) - 10%(70%) (200 mg/l)
= 126 mg/l =1052 115/day/106 gallons
Net solids production (A X) = AS (yield)
AX = 1052 lb/day (0. 5) = 526 1b/day
Total waste activated sludge = (1 -K) Xo - Xf + (X)

K = fraction of solids removed in primary

= 2, 330 gallons /day

tanks
Xf = effluent suspended solids
(1-0.6) (16681b/day) -(15 mg/l) (8.34) +
. 526 lb/day

1068 lb/day = waste activated sludge

83

At 0.75% solids and a Specific gravity of l. 03 the

volume of sludge per 10 gallons is:

(1068lb/day)
(1.03)(0.0075)(8.34)

Total Mixed Sludge:

(1000.8 lblday + 1068 lb/day)
(1.03) (62.4) lb/cu. ft.) (1.27 %)

where 1. 03 is the specific gravity and 1.27 % is

 

= 16, 578 gallons /day

 

2533. 5 It3/day

the solids concentrations of the mixed sludge from
the following mass balance:

(5 m (2330 gal) + (0.75%)_(16, 578 gal)

(18,908 gal) : 1°Z7%

CAPITAL ENERGY DATA
3O

 

From manufacturer's information the energy used for
one ton of finished steel is about 36 million
B. T.U. 's. The breakdown is about 71% coal,
18 % natural gas, 7 % fuel oil and 4 % electricity.

Concrete:31-32

Using a maximum size aggregate of l. 5 inches the

make up of concrete is:

Aggregate = 20 ft3/yd3

Air = 1 ft3/yd3

Cement = 2. 5 ft3/yd3

Water = 3. 5 ft3/yd3 with a water cement

ratio of 0. 54 by volume. For every cubic yard of
concrete there is about 2. 5 sacks of cement.

At an energy value of 175,000 BTU's per sack,

a cubic yard of concrete takes about 437, 500
BTU's to produce.

84

APPENDIX B

THICKENING CALCULATIONS

 

 

 

GRAVITY THICKENER25
Assumgions:
At = Qw (Mtw) (8.34)
C'L
where G = 6 lb/ftZ/day for a thickened sludge

L
of 6%; Q = sludge flow, MGD; M = sludge con-
w tw 2

centration, mg/l; and A = area of tank, ft .

3

Tanks are to be 15 feet deep.

 

 

Size:
Plant Size QW Area Diameter
(MGD) __ (fit. _(_f_£2__
1 0.019 336.3 20.7
10 0.189 3362.7 65.4
100 1.891 33627.9 206.9
Cost:
Diameter Cost* Cost Adj. Cost**
(ft) (1972§) (1975§) (1975$)
20.7 57, 000 68,733 73,800
65.4 150,000 180,877 194,000
206.9. 650,000 783,800 841,000

*from Figure l

** based on E.P.A. number of 1. 073 for Region V
Costs include purchased cost of thickener, erection,
site preparation, pumps, piping, concrete, steel,

instrumentation, electrical, paint and indirect costs.4

85

Capital Energy Requirements:

Weight of raking mechanisms (steel):

 

 

Dia. Wei ght>=< Energy=1<>l<
g3)_ (lb) (tons) (BTU x 106)
20.7 2605 1.30 46.8
65.4 8500 4.25 153.0
206.9 56100 28.05 1010.0

>I=fr om reference 3 6

6

 

 

based on 36 x 10 BTU's/ton
Wall volumes (concrete)
Dia. Depth Vol me of Wall* Energy'r’i‘ 6
(ft) (ft) (ft L (yd3) (BTleO )
20.7 15 500 18.5 8.2
65.4 15 1553 57.5 25.2
206.9 15 4887 181.0 79.2

>:<based on 12 inch thick walls
:zoic based on 437, 500 BTU's/Yd3

Floor volumes (concrete):

 

 

Arfa Vofllgrne of Floo3r* Energy**
(ft I (yd3 ) (BTleO )
336.3 336.3 12.5 5.6
3362.7 3362.7 124. 5 54.5
33627.9 33627.9 1245. 5 544.9

*based on 12 in. floor slabs
based on 437, 500 BTU's/yd3

Total capital energy:
the total capital energy is the sum of the steel

and concrete in B.T.U. 's.

 

 

Plant size Capital energy
(MGD) (million BTU'S)
1 66
10 230

100 1600

86

Operating Power and Labor:

 

DISSOLVED -AIR. FLOTATION

 

 

Plant size Power’k Laborrkrzz
(MGD) (kwhldayL (hr 3 (yr)
1 10.2 220
10 20.4 780
100 40.8 3600

*from Table l

** from Figure 3

5

 

Assumptions:

 

Size:

Cost:

Solids loading = 2 lb/hr/ftz

Solids recovery = 50 to 80%

Design solids = 4%

Maximum hydraulic loading = 0. 8 gpm/ft2
Best clarification time = 30 minutes

Area, ftz = (2068 lljdayLl06gaQ (7 day/week)
(2 lb/hr/ftz) (hours worked/week)

 

 

 

 

Plant Size Operation Tank area
(MGD) (hrs /wee15)_ (ftZL
l 40 181
10 100 724
100 168 43 08

sizes would be half those stated if only waste activated

sludge was thickened.

 

Area Capacity=i= Cost** Adj. Cost 2):

(£3 (ft3) (19728) (1975 $)
181 56 15,000 22, 600
724 560 170, 000 256,750

4308 5600 1,700, 000 2, 567,500

*based on 56 ft3 of sludge/30 minutes
** from Figure 4
#based on EPA number 1.139 for Region V

87

Costs include installed flotation machine, motor and
drive, piping, concrete, steel, instrumentation
and indirect costs.

Capital Energy Requirements:

- if steel tanks are used:

Area Steel>-'< Weight>1= Energyxok
(ftz) Tanks (lb -ea) (ton) (B TU' s)

 

181 lat 2001162 18850 9.43 339.5x106

724 3 at 250 ftz 22150 33.23 1196.3 x 106

4308 10 at 450 ft2 32600 163. 0 5868.0 x 106
*from reference 36

** based on 36 2:106 BTU's/ton

- if concrete tanks are used;

Tank Tank Tank No .
Length Width Ar a of

(ft) (ft) (ft ) Tanks

 

10 40 400 2
10 45 450 10
Volume of Concrete

Walls* Floors“< Total Energyi 6
(£13) (ft3) ($13) (BTU's x 10 )

N/A

2364 676 112.6 49.3
12870 3750 615.6 269.3

*based on 12 in. support walls and 9 in.
non-support walls and a depth of 10. 5 feet;
five foot wet wall added

** based on a 9 in. slab thickness; five foot

wet well add ed.

#based on 437, 500 BTU's/yd3

88

Operating Power and Labor

 

 

 

Plant size Powerrk Laborrzvz:
(MGD) (kwhgday) (hrs/yr)
1 140. 0 340
10 1216. 0 1100
100 9384. 0 5000

>:<from Table 3 - doubled due to twice the volume
of sludge

** from Figure 5

 

ANNUAL COSTS - STEP 1

 

 

 

 

 

 

 

 

 

Power:
Plant Size Power (kWh/day) Cost ($/yr)*
(MGD) g__'_I‘_ DAF _(}__’I_‘_ D_A_1:
1 10. 2 140 112 1533
10 20.4 1216 223 13315
100 40.8 9384 447 102755
*based on 35 0. 03/kwh
Labor:
Plant Size Labor (hrs/yr) Cost ($ /yr)*
(MGD)_ _(_}_'I_‘_ DAF g_'_I‘_ DAF
1 220 340 1562 2414
10 780 1100 5368 7810
100 3600 5000 25560 35500

*based on $7.10 per hour.

Capital Costs:

 

 

 

 

Plant Size Cost ($) Cost (35 /yr)*
(MGD) G_T_ ' """"1_9__'M~“ g_'r_ DAF
1 73800 22600 7517 2302
10 194000 256800 19760 26155
100 841000 2567500 85656 261500

*amortization at 8 % over 20 years.

89

Cafltal Energy:

 

 

 

 

Plant Capital Eneggy Cost*
Size (BTU x 10 ) ($ /year)
(MGD) GT DAF GT DAF
conc. steel conc. conc. steel conc.
1 66 340 N/A 59 304 N/A
10 230 1196 49 206 1071 44
100 1600 5868 269 1432 5253 241

*based on $0.03/kwh and 3413 BTU/KWH

and then amortized at 8 % over 20 years.

ANNUAL COST OF CASES - STEP 1

Case 1 (Power, labor and capital costs)

 

 

 

 

 

Plant Size GT DAF
(MGD) ($1211 ($1xr)
l 9191 6249
10 25521 47280
100 111663 399755
Case 2 (Capital costs and power)
Plant Size GT DAF
(MGD) (§ (yr) (§ (yr)
1 7629 3835
10 19983 39470
100 86103 364255
Case 3 (Capital energy and power)
Plant Size GT DAF-steel DAF -conc.
(MGD) ($11r) ($1y11L ($ /Yr)
1 171 1837 N/A
10 429 14386 13359

100 1879 108008 102996

90

APPENDIX C

STABILIZATION CALCULA TIONS

ANAEROBIC DIGESTION

As 8 umptions:
Loading = 30 to 100 1b volatile solids/1000 ft3/day

Detention time = 30 days

Temperature = 85 to 950F

 

Mean All Residence Time = 10 days 3
Sludge flow rate = 2068 Eli/dag; : 644 BEE—a
(62.4 —-3) (1.03) (0.05) V
ft
where 1.03 = specific gravity

percent solids of influent

= Sludge flow rate x detention time

= (644 £t3/day) (30 days)

= 19,320 11:3

0.05

Volume of digester

Size:
Tank Vol. No . of Tank Wate r Tota1=1=

 

 

Plant Size
(MGD) (11:3) Tanks Dia (ft) Depth(ft) Depth(ft)
1 19,320 1 35 20.0 22.0
10 193,200 3 55 27.1 29.6
100 1,932,000 6 110 33.9 36.4

*2. 0 feet freeboard for tanks less than 50 feet in diameter
and 2. 5 feet for tanks with diameters greater than 50 feet.
Tanks are circular and are seldom less than 20' or more

than 115 feet in diameter; water depth of not less than

25 feet at the center is recommended.

91

Cost:
Plant Size Dig Capita1>i= Capital
(MGD) Vol Cost Cost

(ft3) (19 72) (19 75)
1 19,320 160,000 222,000
10 193,200 400,000 555,000
100 1,932,000 3,600,000 4,990,000

*from Fig. 9

Costs will double if a thickening digester is installed.

Capital Energy Requirements

 

Covers (steel)34

 

 

 

Plant Size Gov? Area Wt of* Capital Ener y**
(MGD) (ft ) Covers (tons) (BTU's x 10 j
1 962 ea 16.8 ea =16.8 605
10 - 2376 ea 41.6 ea = 124.8 4493
100 9503 ea 166.3 ea = 997.8 35921

=:=based on 35 lb/ft2 of cover
** based on 36 x 106 BTU/ Ton
Heaters (Steel)34

1. to raise temperature of incoming sludge
BTU/hr =<2068 lb/day) (100) (95° - 68°)
. Q4 hrs/day) (5 %)

= 46, 530 per 106 gallons
2. to offset heating losses
(assuming a well insulated covers and well insulated side
walls no gas recirculation)
2600 BTU/HR/IOOO ft3 x 0.9 : 2340

where 0. 9 is the Michigan geographic correction factor.

 

 

 

Plant Dig Heat for Heat for Total
Size Vol Temp Losses Heat
(MGD) (ft3) (BTU/111:) (BTU r (BTU/_hr)
1 19,320 46,530 45,208 91,738
10 193,200 465,300 452,088 917,388
100 1,932,000 4,653,000 4,520,880 9,173,880
Heater=i= Heater>¥=
Size (BTU/hr) Weight(lbs)
140, 000 5, 600
1,000, 000 20,400
3 at 3,500,000 104,000

*from reference 34

92

Tanks (Concrete):

 

 

 

 

 

Tank No. Tank Wall* Floor Total
Dia of Depth Vol ea. Vol ea. V03
(ft) Tanks (ft) (£13) (ft3) (yd )
35 1 22 1227 990 82
55 3 29. 6 2580 2445 558
110 6 36.4 6318 9764. 3574
*based on 12 inch thickness
** based on 12 inch thickness and l to 6 floor slope.
Total Capital Energy: '
Plant Heaters>k Covers>i< 6 Tanks** 6 Total 6
Size (BTU x106) (BTU x 10 ) (BTU x 10 ) (BTU x10 )
(MGD
1 100.8 605 35.9 741.7
10 367.2 4493 558 5418.2
100 5616 35921 3574 54111.0

*based on 36 x 106 BTU/Ton of steel
** based on 43 7, 500 BTU's/yd3 of concrete

QperatinLPower and Labor:

 

 

 

Plant Size Power Labor
(MGDL (KWH/da1)* (hr 55:24.4

1 ' 123.6 225

10 - 4 56. 4 11 25

100 1910. 0 5700

*from Table 6, methane gas will provide extra heater fuel.

Methane Production:
1 ft3 of methane (at 70°F and 1 atm) has a net heating value of

960 BTU. Digester gas, 65% methane, has a heating

value of 600 BTu/fl:3 63 '

Quantity of methane gas can be calculated"3 from

C = 5.62 (ef - 1.42 %E )where C = ft3 of CH4/day

e = efficiency of waste
utilization

F = BODL added, lb/day

(See Appendix A)
F = 2068 lb/day

$3: 526 lb/day
dx = net growth rate

e = 0. 75 (average)63 d-f_
5.62 [(0. 75) (2068 lb/day) — 1.42 (526 1b/day)]

4519 ft3 / 106 gallons treated.

o
H

93

 

 

Plant C 4 Heat Heat
Size (ft /dzly) Value? Needed
(MGD) (BTU/day) (BTU/c1211)
1 4519 4.4x 10" 2.2x106
10 45189 4.4x 107 2.2):107
100 451892 4.4x 108 2.2x 108

*based on 960 BTU/ft3 of CH4
*3“ due to heat losses and heat requirements
Since gas produced is more than gas needed there will
be no extra fuel needed.
AEROBIC DIGESTION:

As sumption:

 

Current practice is to provide 15 days of detention time
for waste activated sludge. More time required

if primary sludge is involved. Use 20 days. 30

Hydraulic detention time = 18 to 22 days at 200C.

Solids loading = 0.1 to 0.2 lb vss/ft3/day

02 requirements = 1. 6 to 1.9 lb BODS/lb destroyed

Energy requirements for mixing:
mechanical = 0. 5 to l. 0 hp/1000 ft
air mixing = 20 to 30 SCFM/lOOO ft3

Solids = 644 ft3/day (See Anaerobic digestion)

Volume of Digesters = (644 ft3/day) (20 days) = 12880 ft3

Air req'd = (25 SCFM/lOOO ft3) (12880 ft3) = 322 SCFM
at 6. 5 psi estimated BHP = 12. 0

3

 

 

 

 

 

Size:
Plant Dig. No. Tank Dimensions
Size Vol of Depth Length Width Vol
(MGD) (ft3) Tanks (ft) (ft) (ft) fig)
1 12880 1 10.7 60 20' ' 12960
10 128800 4 12.5 130 20' 130000
100 1288000 20 15.0 172 25' 1290000
No. Est*
Plant Air (SCFM) Blowers (BHp) Wt. (lbs)
1 322 1 13 400
10 3220 1 150 2580
100 32200 4 1784 25200

*based on 1. 0 foot loss in diffusers, 30% loss in piping
and an efficiency of 70 ‘70. 26

94

 

Cost:
Plant Size Cost‘F Cost
(MGD) (1972 35) (1975 $)
1 67,000 89,000
10 300,000 ' 398,000
100 2, 500,000 3,315,000

Capital Energy Requirements:

 

Tanks (Concrete):

Plant Dig. Walls* Fl or*>1< Total
Size v61 (ft3) (ft ) (yd3)
(MGD) (ft3)
1 12960 1830 1200 113
10 130000» 10780 10400 785
100 1290000 71973 86000 5851

*based on support walls 12 inches thick, non support

walls 9 in. thick and 1. 5 feet freeboard
** based on 12 in. thick slab.
Capital Energy:

 

 

Plant Blower Tank Capital Energy
Size Wt. Vol Steel* 6 Concrete** Totalé
(MGD) (tons) (yd3) (BTU x 104 (BTU x 106) (BTU x 10 )
1 0.20 113 7.2 49.4 56.6
10 1. 29 785 46.4 343.4 389. 8
100 ' 12.60 5851 453.6 2560.0 3013.6

=:=based on 36 x 106 BTU/ton of steel
** based on 43 7, 500 BTU/yd3 of concrete

Operating Power and Labor:

 

 

Plant Size Power=1< Labopzok
(MGD) (kwhjdayL (hrs r
1 232. 7 96
10 2685. 0 480
100 31928. 0 2420

*based on estimated BHp of blowers and an Operating

efficiency of 70%
** from Figure 8

95

ANNUAL COSTS - STEP 2

 

 

 

 

 

 

Power:
Power (kWh/day) Costs ($ /Yr)*
Size (MGD) .3111; AD AND .3._D_
1 124 233 1358 2552
10 456 2685 4993 29400
100 1910 31930 20915 349634
*based on $ 0. 03/kwh
Labor:
Labor (hrs/yr) Costs ($/yr)*
Size (MGD) AND AD AND ALP.
l 225 96 1598 682
10 I 1125 ‘ 480 ' - 7988 3408
100 i 5700 2420 40470 17182

*based on $ 7.10/hr
Capital Cost:

 

 

 

Costs ($) Costs ($/yr)*

Size (MGD) AND AD AND AD
1 222000 89000 22600 9065
10 555000 398000 56527 40536
100 4990000 3315000 508232 337633

*based on 8% over 20 years

Capital Ene r gy;

 

 

 

Capital Energy (BTU) Cost* ($ /Yr)

Size (MGD) £1113 AD AND AD
1 7.4312108 5.7x 107 663 51
10 5.4 x109 3.9 x108 4834 349
100 4. 5 x 1010 3.0 x 109 40287 2686

*based on 35 0. 03/kwh and 3413 BTU/kwh and amortized

at 8% over 20 years.

ANNUAL COST OF CASES - STEP 2
Case 1 (Power Labor, Capital Cost):

 

 

 

Size (M691 AND ($/yr1 AD (8 1n)
1 25567 12299
10 69508 73344

100 569617 704449

96

Case 2 (Capital Costs and Power):

 

 

 

 

Size (MGD) AND (31/er
1 23969
10 61520
100 529147
Case 3 (Capital Energy and Power):
Size (MGD) AND (gs/H)
1 2021
10 9827
100 , 61202

AI)($/Tr)
11617
69936

687267

AI>($/Tr)
2603
29749
352320

97

APPENDIX D

C ONDITIONING CALCULATIONS

CHEMICAL CONDITIONING

As sumptions:

 

Size:

Plant
Size

1
10
100

FeCl dosage

3 1. 5 to 2. 5 % for fresh solids

l. 5 to 4. 0 % for digested
Use 2. 0 % for design. Equipment will be bigger if

digested sludge is used.

Dewatering is the main step that uses chemical condi-
tioning.

Solids = 5 % influent

Tanks must be lined with rubber.

Contact time = 30 minutes

If polyelectrolytes are used - feeders will be smaller
(2068 1b/day) (2.0%) = 41.361b/day/106 gallons

 

 

Feeders:
Plant Sludge Chemicals=i< Chemicals
Size ‘ (1b /day) (1b /day) (1b /min)
(MGD)
1 2068 41. 4 0. 03
10 20680 413.6 0.29
100 206800 4136.0 2.87

*based on 2% feed.
Mixing Tanks:

 

 

Vol of Vol of Total Tank* Hp**
Slud e Chemicals Vol Vol Required
(MGD) (gal day) (gal/day) (gal/day) (gal) per hr
18908 378 19286 401.8 0.5
189080 3782 192862 4017.9 6. 0
1890800 37816 1928616 40179.2 40.0

*based on 30 min detention time.
** from reference 35 -- 0.25 hp for 250 gal tank.
0. 50 hp for 500 gal tank.

98

 

 

Cost:
Plant Feed Feed Mixing* Cost (19 72$ )**
Size Rate Volume Tank Vol Feeder Mixing
(MGD) (lb/minL (gal) (gal) Cost Tank
1 ‘ 0.03 378 401.8 4500 30000
10 0.29 3782 4017.9 10000 52000
100 2.87 37816 40179.2 23000 170000

*based on 30 min detention time

** from references 4 and 35.

Cost include purchased cost of equipment, motors,
handling and setting, concrete, steel, electrical,

instrumentation, insulation, paint and indirect

 

costs.
Cost Chemical Cost>i<
(1975$) (1975 $Zyr)
45800 755. 6
79400 7548. 2
256000 75482.0

*based on 5¢/1b dry basis (East Lansing Sewage T. P.)

Capital Energy Requirements:

 

 

Plant Mixing Tanks* No. Capital**

Size Vol Wt. of energy 6
(MGD) (gal) (lbs) Tanks (BTU x 10 )
1 402 1600 1 at 500 28.8
10 4018 18000 12 at 350 324.0
100 40180 129600 81 at 500 2332.8

*from reference 35; stainless steel and includes feeder
weight

** based on 36 x 10(3

BTU/ton of steel

Operating Power and Labor:

 

 

 

 

Plant Size Power* Labor==<>l=
(MGD) (kWh/day) (hr 5 [yr)

1 2.7 1040

10 80.0 2600
100 895.0 4368

*based on Hp required for mixing in thr: 1 thr = 0. 7457
kwhr) and a 80% efficiency

>:<>:< based on 0. 5 operators per shift (MAX)4

99

HEAT TREATMENT

Assumptions:

 

Pressure = 180 to 210 psig

Residence time = 0. 5 hours

Temperature = 3500 to 3900F

Heat treatment is a wet oxidation process at lower pressures
and temperatures. Therefore Size, construction
requirements and operating labor are the same.
(See Appendix F).

Size: (Envirotech-Eimco):

 

 

 

 

 

Plant Reactor:< No. of Vol. of
Size Vol. Reactors Reactors
(MGD) (gal) .
1 394 2 250 gal each
10 3939 1 4300 gal
100 39392' 5 8000 galeach
*based on 30 minute detention time
Cost: .
Plant Loading Cost* Cost
Size (lb/hr) (19 70 $) (1975 $)
(MGD)
1 86. 2 130000 203300
10 861. 7 270000 422300
100 8616. 7 3 at 550000 2581000

*from Figure 24

Capital Energy Requirements:

 

(due to reactor and its respective heat exchanger)

Plant Reactor Reactor* Heater Ex. * Total Energy**

 

 

 

Size Vol. Wt. Wt. Wt. 6
(MGD) (gal) (lbs) (lbs) (tons) (BTU x 10 )
1 500 2500 N/A 1.3 45
10 4300 16700 25800 21.3 765
100 40000 141400 99700 120.6 4339.8

*from manufacturing data
>:=>1< based on 36 x 106 BTU/ton of steel

100

Operating Power and Labor:

 

 

Plant Size Power>i< Labor>1<>i<
(MGD (kWh/day) (hrs (fir)
l 305 520
10 3050 1300
100 30500 2190

*from reference 30; power includes electricity and fuel.
Assumed to be half the power needed for wet oxidation.

** based on 0. 25 men per hour of operation.

ANNUAL COSTS - STEP 3

 

 

 

 

 

 

 

Power:
Size Power (kWh/day) Cost ($ /yr)*
(MGD) CC HT CC HT
1 2. 7 305 30 3340
10 80 3050 876 33398
100 895 30500 9800 333975
*based on $ 0. 03/kwh
Labor:
Size Labor (hr/yr) Cost ($/hr)*
(MGD) CC HT CC HT
1 1040 520 7384 3692
10 2600 1300 18460 9230
100 4368 2190 31013 15549

*based on $ 7.10/hr
Capital Cost:

 

 

 

Size Cost ($) Cost ($ /yr)*
(MGD) CC HT CC ** HT
1 45800 203300 5420 20706
10 79400 422300 8087 43011
100 256000 2581000 101556 262876

*based on 8% over 20 years.

** includes chemical cost.

101

Capital Energy:
Capital Energy

 

Size (BTU x 106)

(MGD) __c__c__ HT _C_§__
1 29 45 . 26
10 324 765 290

100 2333 ' 4339 2089

*based on $0. 03/kwh and 2. 93 x 10-

Annual Cost‘l<

amortized at 8% over 20 years.

ANNUAL COST OF CASES -STEP 3

Case 1 (Capital Cost, Power, Labor)

 

 

 

 

 

 

Size (MGD) cc ($/er
1 12834
10 27423
100 142369
Case 2 (Capital Cost and Power)
Size (MGD) cc (yyr)
1 5450
10 8963
100 111356
Case 3 (Capital Energy and Power)
Size (MGD) cc ($/Yr)
1 56
10 1166

100 11889

_H_T_
40
685
3885

4 kwh/BTU and

HT ($114)
27738

85639
612399

Hfl?($j9r)
24046

76409
596850

EKF($19T)
3380
34083
337860

102

APPENDIX E

DEWA TERING

DRYING BEDS

 

Assumptions:

 

For mixed primary and waste activated digested sludge
assume a loading of 15 lb/ftZ/year (Open Beds-
Northern Climate)

30% solids concentration assumed

2068 lb sludge, for each 106 gallons treated

(2068 lb/day) (365 days/year) = 754,820 1b/year

(754, 8203/year)

_ 2 _
(151b/ft—‘7year) " 50,321 ft _ 1.16 acres

 

 

 

 

 

 

Plant Size Solids Be Area Acres
(MGD) (1b (yr) (ft L
1 754820 50321 p 1.16
10 7548200 503210 11. 55
100 75482000 5032100 115. 52
Area can be reduced by using chemical conditioning or
by using covered beds. _
Costs:
Plant Size Area 2 Costs* Costs
(MGD) (1000 ft ) (1971$) (1975$)
1 50.3 60000 90500
10 503. 2 550000 7 828800
100 5032.1 7500000 11302000

*from Figure 18
Costs include costs of normal excavation, piping
for sludge distribution, sand and gravel

drainage beds and underdrain collection

piping. 9

103

Capital Energy Reguirements:

— Beds

The drying area is partitioned into individual beds, about
20 ft. wide by 20 to 100 feet long, of a convenient size
so that one or two beds will be filled by a normal
withdrawl of sludge from the digesters. The interior
portions are usually two or three creosoted planks one
on top of the other, to a height of 15 to 18 inches stretch-
ing between slots in precast concrete posts. The outer
boundaries may be of similar construction on earthern

embankment for open beds, but concrete walls are required

 

 

if the beds are to be covered.26
Plant Are? Length‘a" Total ' Concrete Vol. **
Size (ft ) - (ft) Length (ft3) (yd3)
(MGD)
1 50321 224. 3 897 897 33. 2
10 503210 709.4 2837.5 2838 105.0
100 5032100 2243.2 8972.9 89 73 332.0

*beds assumed to be square for easy calculations
** volume of concrete was determined using a single wall
0. 5 feet thick and 2. 0 feet deep. 26

- Removal Requipment

Dried sludge will be removed using front-end loaders.

 

 

Plant Sludge* Loaders Req'd** Wt. of Loaders
Size Vol. No. and Vol. (lbs) (tons)
(M GD) (ft3 /d ayL
1 64.4 1 at 1.0 yd3 16200 8.1
10 644 1 at 1.5 yd3 16900 8.45
100 6440 3 at 5.0 yd3 132000 66.00
Operation
(hrs/day)
l. 5
8. 0
8. 0

*assuming 50% solids
>:=>:< based on a 30 minute cycle or 16 loads per 8 hr day

operating at 80 % efficiency (from Caterpillar handbook)

104

 

 

- Energy
Plant Conc ete Steel Capital Energy (BTU x 106)
Size (yd ) (tons) (Concrete)* Steel)** (Total)
(MGD)
. 1 33.2 8.10 15 292 307
10 105.0 8.45 46 - 304 350
100 332.0 66. 00 145 2376 2521

*based on 43 7, 500 BTU/yd3 of concrete
** based on 36 x 106 BTU/ton of steel.

QperatingPower and Labor:

 

 

 

 

Plant Size Power Labor 2)
' (MGD) (Hp -Hr/day)* (kwh/day)** (hrs (yr)
1 120 89. 5 1750
10 640 477. 3 17500
100 2080 1551.1 175000

*based on engine horsepower of the loaders operating
at 16 loads/day and at 80 % efficiency. (from Cater-

pillar Handbook).
** based on 1 hp-hr = 0. 7457 kwhr

#based on 8 hours per machine used.

VACUUM FIL TRATION

As sumptions:

Surface areas range from 50 to 300 ftz
Yield = 4. 0 1b/ft2/hr for mixed primary and waste
activated sludge.

2068 1b/day/106 gallons treated = 86.2 lb/hr

(2068 1ll/day) (7 days/weekL _ . 2
(4 lb/ft‘fhrfl x hours7week) — filter area, ft

 

 

Size:
Plant Operation Solids Filter Ar ea*
Size (hrs /wk) (lb/hr) (itZ)
(MGD) ,
1 40 362 90.5 (N/A)>:<
10 100 1447.6 361.9 (72.4)*
100 168 8617.7 2154.2 (430.8)*

*if heat treatment is used for conditioning the filter yield
may be about 20 lb/ftz/hr thus decrease the required

filter area by 80 %.
N/A - not good for flow g 3. O MGD

105

 

 

Costs:
Plant Filter Area Cost? Cost
Size 018) (1971$) (1975$)
‘ (MGD)
1 90.5 140000 211000 ---
10 362 315000 475000 (191000)
100 2154 1750000 2638000 (515000)

*from Figure 14
Costs include the normal cost of the vacuum filters,
auxiliary equipment, piping and structures.

Capital EnergLEquir ements:

 

 

 

Plant Filter Filteri'< Weight of Equipment *
Size Area Drums Filter Accessories’ki‘EI‘otal
(14(3)) (itZ) 190..and.Size (lbs) (lbs) (tong)
1 90.5 1 at 6' 7400 2500 4.95
10 362 1 at 12' 24300 4100 14.20
100 2154 5 at 14' 131000 20500 75. 75

*from reference 36

* =1< accessories include vacuum pump and filtrate pump.

 

Capitalt 6

Energy (BTU x lQ_)
1.80 (---)

(510 (180)

2727 (510)

‘ I #based on 36 x 106 BTU/ton of steel

Operating Power and Labor:

 

 

 

Plant Size Power* Labor=§<=l<
(MGD) (kwlrjdayL (hrs(yr)
1 52 1640
10 531 (52) ‘ 5650
100 5208 (531) 35500

*from reference 20
** from Figure 15 (will be more if sludge is hauled to
landfill).

106

CENTRIFUGATION
Assumptions:
Feed solids = 2%
Effluent solids = 15 to 40 %
Length/Diameter ratio = 2.8 to 3. 2
Solids recovery = 80 to 95%

 

 

Design was based on centrifuge performance presented

by manufacturing data.

 

 

 

Size:
Plant Sludge Operation Feed Rate
Size (gal/day) (hrs/week) (GPM)
(MGD)
1 18908 40 55. 2
10 189080 ' 100 220.6
100 p890800 168 1313.‘
Cost:
Plant Feed Rate Cost* Cost
Size (GPM) (1972$) (1975$)
(MGD)
1 55 280000 422000
10 221 560000 844000
100 1313 2000000 2536800

*from Figure 16

Costs include centrifuge equipment, sludge pumps and
piping, sludge cake conveyors, equipment hoists,
electrical facilities and enclosing structure.

Capital Energy Requirements:

 

 

 

 

Plant Feed No. Centrifuge Weight* Capita1=1<
Size Rate of Each Total Energy6
(MGD) (GPM) Cent at GPM (lbs) (tonsL (Btu x 10 )
1 55 lat 66 4800 2.4 86.4
10 221 lat 220 16000 8. 0 288
100 1313 9 at 150 7000 31. 5 1134

>i=from manufacturing shipping weights37
*2: based on 36 x 106 BTU/ton of steel

107

Operating Power and Labor:

 

 

Plant Size Power’k
(MGD) (kWh/day)
1 90
10 43 5
100 4400

*from Table 13

** from Figure 17

PRESSURE FIL TER

A s surnyations:

 

105 lb/it3

3. 0 ft3/chamber
Cake Thickness = 1.5 inches
Cake Length = 2. 0 hours

Cake Solids = 50% results

Cake Density 2

Cake Volume

Labor**
(hrs/yr)

1370
4200
30000

Loading 2 1.034 tons/day/lO6 gallons

 

 

 

 

 

 

 

Ash Admixture Ratio = 1. 5 to 1. 0
Size:
Plant Sludge Ash Total Moisturei‘
Size Load Load Solids Wt.
(MGD) (lb/day) (lbzday) (lb/day) (lb/day)
1 2068 3102 5170 5170
10 20680 31020 51700 51700
100 206800 310200 517000 517000
*based on 50 % moisture
Total Cake Cake**
Wt. Vol.
ab/aar) (831
10340 98. 5
103400 984. 8
1034000 9847.7
=kaased<n11051b/fl3 28
Plant Cake Operation No. *** No. of
Size Vol. Time of Filter
(MGD) (ft3) (hrs/day) Cycles Chambers
1 98.5 5.7 z/day 33/day
10 984.8 14.3 6/day 82/day
100 9847.7 24 11/day 657/day

*** based on cycle length of 2 hrs

with 2 hrs standby.

108

 

 

 

 

 

 

 

C ake * * * * Chambe r 5
Capacity Required
(ft (chamber) (No.)
3 16. 5
12 13. 7
15 59. 7
**** from manufacturing data38
Plant Size No. of Filters Filter Area
and Chambers (ft?)
1 2 at 9 46
10 1 at 15 92
100 3 at 20 369
Cost:
Plant Size Filter Area Cost* Cost
(MGD) (it?) (197235) (1975$)
1 46 138000 183000
10 92 276000 366000
100 369 1107000 1468000

*from Table 14; based on a total construction cost of
$ 3, 000 /£tz of filter
costs include filters, feed pumps, building and
installation.

C apital Ene r SLR equir ements:

 

Plant No. Weight of Filters’v’ Capital**
Size of Each Total Energy 6
(MGD) Filters (lbs) (tons) (btu x 10 )

1 2 2200 2. 2 79. 2

10 1 7600 3 . 8 136. 8

100 3 9300 13.95 502.2

*from manufacturing data
>:<>'.< based on 36 x 106 btu/ton of steel
Operating Power and Labor:

 

 

 

Plant Size Power* Labo r>1= >:<
(MGD) (kWh/day) (hr s /y£)
1 62. 0 2080
10 620. 4 5200
100 6204.0 26208

*based on 60 kwh/ton of sludge28

** based on one man per hours of operation per filter28

ANNUAL COSTS - STEP 4

 

 

 

 

109

 

 

 

 

 

 

 

 

 

 

Size Power (kWh/day)
(MGD) DB VF CT PF
1 89. 5 52 (-) 90 62
10 477.3 531(52) 435 620
100 1551 5208 (531) 4400 6204
Size Annual Cost*
(MGD) DB VF CT PF
1 980 569 (-') 986 679
10 5226 5815 (569) 4763 6789
100 16984 57208 (5815) 48180 67934
*based on $ 0. 04/kwh
Size Labor (hrs/year)
(MGD) DB VF CT PF
1 1750 1640 13 70 2080
10 17500 5650 4200 5200
100 175000 35500 30000 26208
Size Annual Costs’l< (x 1000)
(MGD) DB VF CT PF
1 12.4 11.6 9.7 14.8
'10 124.3 40.1 29.8 36.9
100 1242.5 252.1 213 186.1
*based on $ 7.10/hour
Size Capital Cost (x 1000 $)
(MGD) DB VF CT PF
1 90.5 211(-) 422 183
10 829 475 (191) 844 366
100 11302 2638 (515) 25361 1468
Size Annual Cost * (x 1000)
(MGD) DB VF CT PF
1 9.22 21.5 43 18.6
10 84.4 48.4(19.5) 86 37.3
100 1151 268.7 (52.5) 258.3 149.5 '

*based on 8% over 20 years

110

 

 

 

 

Size Capital Energy (btu x 106)
(MGD) DB VF CT PF
1 ” 307 180 (-) 86 79
10 350 510 (180) 288 137
100 2526 2727 (510) 1134 502
Size Annual Cost * ($ /year)
(MGD) DB VF CT PF
1 274.9 161(-) 77 71
10 313 456.6(161) 258 122.7
100 2256 2441 (457) 1015 449

*based on $ 0. 03/kwh, 2.93 x 10'4 kwh/btu and amortized

at 8% over 20 years.

ANNUAL COSTS OF CASES - STEP 4 *
Case 1 (Capital Cost, Power, Labor)

 

 

 

Size Annual Cost ($/year)
(MGD) DB VF CT PF
1 22600 33669 (-) 53686 34079
10 213926 94315 (60169) 120563 80989
100 2410484 577828 (310415) 519480 403534

*for calculations see Appendix C

The cost figures in parenthesis are for vacuum filtration if

used with heat treatment.

Case 2 (Capital Cost, Power)

 

 

Size Annual Cost ($ /year)
(MGD) DB VF CT PF
1 10200 22069(-) '43986 19279
10 89626 54215(20069) 90763 44089
100 1167984 325728(58315) 306480 217434
Case 3 (Capital Energy, Power)
Size Annual Cost ($ /year)
(MGD) DB VF CT PF
1 1255 730 (-) 1063 750
10 5539 6272 (730) 5021 6912
100 19240 59269 (6272) 49195 68383

111

APPENDIX F

REDUC TION

INCINERATION

Assumptions:

 

 

Solids loading = 2 lb/ftZ/hr for mixed primary and activated

Temperature 2 1400 to 1700 OF

Heat Requirements 2 1800 to 2000 btu/lb of water

Capacity 2 200 to 8000 1b/hr.

 

 

 

 

 

 

 

Size:
Plant Op. Solids Area* No. *
Size (hrs /week) Load Req'd of
(MGD) (lb/hr) (ftz) Hearths
1 40 362 181 9
10 100 1447. 6 724 8
100 168 8616. 7 43085 2 at 12
*based on 2 1b/hr/ft2
Costs:
Plant Area Solids Co st* Cost
Size (ftZ) (tons/day) (197235) (19 75$ )
(MGD
l 181 1.03 400000 530000
10 724 10.34 700000 928000
100 4309 103.40 2500000 3315000
*from Figure 20
Capital Energy Requirements:
Plant Area Weight of Incin. * Capital Energy=3==i=
Size (ftz) (lbs) (tons) (btu's x 10 )
(MGD)
1 181 33485 16.7 601.2
10 724 131044 ' 65.5 2358.8
100 4309 797165 398.6 13450.0

*based on manufacturing data; about 185 lb per ft2 of hearth

area (ENVIRO TECH)

‘112

Qpe ratinJgPowe r and Labo r:

 

 

 

 

Plant Size Power>l= Labor* :1:
(MGD) (kWh/day) (hrs/yr)
1 603 (268) 1900 .
10 1242 (667) 5400
100 4932 (1644) 39000

*from Figure 22 and) a power cost of $ 0. 015/kwh

** from Figure 21

values in parenthesis are for pressure filtration used with inc.
Assuming 60% combustibles in medium quality

sludge26 then the weight of ash is 48 % of the Sludge weight

generated; assuming 100% combustion of all combustibles

ash volume = .40 (2068 lb/day) : 8271b/day per million

gallons treated.

WET ~OXIDATION

 

A s sumptions:

 

Pressure 2 1000 to p750 psi
Temperature = 2500 to 7000 F

Residence Time = 20 to 60 minutes, 30 minutes average

 

 

 

 

 

Plant Size Sludge Reactor* No.
(MGD) Vol. Vol. of
(gal/dayL (gal) Reactors
1 18908 394 2 at 250 gal
10 . 189080 3939 1 at 4300 gal
100 1890800 39392 5 at 8000 gal
* based on 30 minute detention time
Cost:
Plant Size Optn. Loading Cost* Cost
(MGD) (hrs/wk) (lb/111;) (197035) (1975$)
l 40 362 300000 469000
10 100 1447. 6 900000 1408000
100 168 8616. 7 3 at 1400000 6568000

*from Figure 23

113

Capital Energy Reggirements:

 

(due to reactor and heat exchanger)

 

Plant Size Reactor Reactor* Heat Ex. * Total Energy**
(MGDL (gals) wt (lbs) wt (lbs) wt (tons) (btu x 106)
1 500 2500 - N/A 1.3 45
10 4300 16700 25800 21. 3 765
100 40000 141400 99700 120. 6 4339. 8

*from manufacturing data (ENVIROTECH-EIMCO)
** based on 36 x 106 btu/ton of steel
Operatingfower and Labor:

 

 

 

 

Plant Size Power>1< Labo ring:
(MGD) (kWh/daY) (hrs/yr)
1 610 520
10 6101 1300
100 61006 2190

*from Reference 30
** based on 0. 25 manhours/shift of operation4

Wet oxidation combustion is about 80 to 90% complete.26
The amount of combustibles in medium sewage is about 60 %.
Therefore, the weight of ash generated from each pound of sludge

burned is (40 %)(2068 lb/day) This amounts to 973.2 1b/day
85% per million gallons treated.

 

ANNUAL COSTS — STEP 5

 

 

 

 

 

 

 

Power:
Power (kWh/day) Costs ($ /Year)*
Size (MGD) INC WO INC WO
1 603 (268) 610 6603 (2935) 6680
10 1242 (667) 6101 13600 (7304) 66806
100 4932 (1644) 61006 54005 (18002) 668016
*based on $ 0. 03/kwh
Labor:
Labor (hrs/yr) Costs ($ /yr)*
Size (MGD) INC WO INC WO
1 1900 520 13490 3692
10 5400 1300 38340 9230
100 39000 2190 276900 15549

*based on 3,5 7.10/hour

114

Capital Cost:

 

 

 

 

 

 

Cost ($) ‘ Cost ($ /year)
Size (MC-D) INC WO INC WO
1 530000 469000 53980 47768
10 928000 1408000 94517 143405
100 2880000 6568000 293328 668951

*based on 8% over 20 years.

Capital Energy:

 

 

 

Energy (btu x 106) Cost ($ /Year)
Size (MGD) INC WO INC WO
1 601 45 538 40
10 2358 765 2111 685
100 14350 4339 12847 2885

*based on $0.03/kwh and 2. 93 x 10‘4 kwh/btu and amortized

at 8% over 20 years.

ANNUAL COSTS OF CASES - STEP 5
Case 1 (Power, Labor, Capital Costs)

 

 

 

 

 

 

 

 

Size (MGD) ' Annual Cost ($ /yr)
INC WO
1 74073 (70405) 58140
10 146457 (140161) 219441
100 624233 (588230) 1352516
Case 2 (Capital Costs and Power)
Size (MGD) Annual Cost ($/Yr)
INC WO
1 60583 (56915) 54448
10 108117(101821) 210211
100 347333 (311330) 1336967
Case 3 (Capital Energy and Power)
Size (MGD) Annual Costs ($/Yr)
INC WO
1 7141 (3473) 6720
10 15711 (9415) 67491

100 66852 (30849) 671901

115

APPENDIX G

FINAL DISPOSAL

FERTILIZER AND SOIL CONDITIONER:

Assumgcions:
Application 2 10 to 20 tons dry solids/acre/year

Can be applied in cake or slurry.

Must be digested or heat treated.

 

 

Plant Size Solids Area=3= Vol. to be**
(MGD) (tons/yr) (Acres) Spread(ga1@ay)
1 377.4 25. 2 4960
10 3774.1 251.6 49600
100 37741.0 2516.1 496000
*based on 15 tons/acre/year
** based on 5% solids concentration
Costs:

Costs will include costs of trucks to apply the sludge to

the land. Cost of land is assumed to be free.

 

Plant Size Vol. No. * of Tripsi< Capital**
(MGD) (gal/day) Trucks per day Cost (8 1975)
1 4960 1 2. 5 22000
10 49 600 10 2. 5 220000
100 496000 100 2. 5 2200000

*based on 2100 gal capacity/truck and 2. 5 trips/day
during one 8 hour working day at 80% efficiency. .
** based on $ 18, 000/truck and $4000/tank (from manu-
facturer's data (Rhynard Truck Sales, Lansing, Mich.)

116

Capital Energy Requirements:

(Due to weight of trucks)

 

 

 

Plant Size No. of Wt. of* Capital Energy=i==f=
(MGD) Trucks Trucks (tons) (btu's x 106)
1 1 5 . 180
10 10 50 1800
100 100 500 18000

*based on truck weight of 10, 000 lbs (from Rhynard
Truck Sales, Lansing, Michigan).
>:<* based on 36 x 106 btu/ton of steel.

Operating Power and Labor:

 

 

 

 

 

Plant Size Power Labori
(MGD) (Hp -Hr)=:< (kwh/day)** (hrs /75L

1 2933 2187 2920

10 29333 21874 29200

100 293333 218740 292000

*based on 220 Hp per truck operating 8 hrs a day at an
average efficiency of 60%.

** based on 1 Hp -Hr = 0. 7457 kwhr.

#based on 8 hours per day.

This size of truck was chosen because bigger trucks tend

to bog down. (Rhynard Truck Sales)

 

 

 

LAGOONING
As 8 umptions:
Depth = 5 feet
At least two lagoons must be provided
Solids loading = (MAX) 2.2 to 2.4 lb/yr/ft3 use 2.2
lb/year/cu. ft.
Lagoons will be permanent lagoons (assumed)
Size:
Plant Vol. of Lagoon’k Lagoon**
Size Sludge Vol. Area Area
(MGD) (lb/yr) (131:3) (ftz) (Acres)
1 754820 343100 68620 1.58(0.63)t
10 7548200 3431000 686200 15. 75 (6.3)
100 75482000 34310000 6862000 157. 53 (63. 0)

*based on solids loading of 2. 2 lb/year/ft3
** based on 5. 0 foot depth

#if a reduction method is used.

 

Costs:
Plant Lagoon 3 Cost* Cost )
(MGD) Vol. (1000 ft ) (1971$) (1975$)
l ' 343.1 25000 36700 (14000)**
10 3431.0 95000 139400 (50000)
100 34310.0 450000 660300 (220200)

*from Figure 11.

Costs include normal excavation, dike construction
and piping.
** if reduction step is used.

Capital Energy Requirements:

 

The building of the permanent lagoons require no cement
or steel and also requires no equipment to remove any sludge.

Even though there is no steel, concrete or brickused in
the construction of the landfills there is still a considerable
amount of energy used to construct the landfill. This energy was
ignored to satisfy the definition of capital energy used here.

Operating Power and Labor:

 

Power is almost non-existant except for lighting and pumps.

The lagoon itself doesn't use any power.

 

 

 

Plant Size Power Labor=i=
(MGD) Req'mts. Req'd.
(kWh/day) (hrs/yr)
1 N/A 115 (95)
10 N/A 235 (160)
100 N/A 1400 (550) :10:

*from Figure 12

** if a reduction step is used.

SA NI TARY LAND FILL

 

Assumptions:

 

Dried sludge or ash can be applied
2. 0 foot layers daily

6. 0 inches daily cover

Working face 2 20 to 300

Operation time is usually an 8 hour day.

118

 

 

 

 

Landfill Equipment
Plant Size Sludge Wt. * Shift Sludge Equipment>3<>3<
(MGD) (tons/day) (hrs/wk) (tong/8 hr) Needed
1 4.14 (0.42)# 40 5.8 (0.6) 1 crawler dozer
10 41.36 (4.14) 100 23.2 (2.3) 2 crawler dozer
100 413.60 (41.35) 168 137.9 (13.8) 3 rubber tire 1dr
*based on dewater sludge at 25% solids
** from Reference 69 ( ) values are if a reduction step
is used
Plant Equipment Flywheel>i< Machine=¥<
Size Descrip. Hp Wt. (lbs)
(MGD)
1 1x crawler dozer 80 (-) 19, 000 (~)
10 2 x crawler dozer 95 (80) 32, 000 (19000)
100 3 x rubber tired loader 160 (95) 29,400 (32000)
*from Reference 69.
( -) means it is two small to use
Plant Sludge Capital* Cost
Size Wt. Cost (19 75$)
(MGD) (tondeay) (19 72$)
1 4.14 (.42) 35000 46500 (-)
10 41.36 (4.14) 150000 199000 (46500)
100 413.60 (41.4) 650000 862000 (199000)

*includes cost of equipment from Figure 26, if incineration

is used their costs will decrease

Capital Energy Requirements:

 

No capital energy is used to construct the landfill since

it is often made of earthen walls or just a hole in the ground.

 

 

 

Plant Size Equipment Weight Capital Energy*
(MGD) (lbs) (tons) (btu x 106)
1 19000 9. 5 342 (-)
10 64000 32 1152 (342)
100 88200 44.1 1587.6 (576)

*based on 36 x 106 btu/ton of steel

( ) values are if a reduction step is used.

119

Operating Power and Labor:

 

 

 

Plant Size Power Labor**
(MGD) (hpheray)>3= (kWh/day) (hrs /year)
1 762 568(-) 2080(-)
10 4524 3374 (568) 5200 (2080)
100 19200 14317 (1687) 8760 (5200)
*based on engine horsepower and an average efficiency
of 60 %

** based on 1 man per machine for 8 hours.

ANNUAL COSTS - STEP 6

 

 

 

 

 

Power:

Size Power (kWh/day)

(hKHn FERT LAka LNF

1 2187 lfl/A. 568(568)
10 21874 hoax 3374(568)
100 218740 lv/A. 14317(1687)
Annual Cost*

FERT - LAG LNF
23950 ——— 6220(-)

239520 -—- 36945(6220)

2395203 --- 156771(18473)

*based on $0. 03/kwh

>703 due to permanent lagoons

 

 

 

 

 

 

Labor:
Size Labor (hrs/year)
(MGD) FERT LAG LNF
1 2920 115 (95) 2080 (2080)
10 29200 235 (160) 5200 (2080)
100 292000 1400 (550) 8760 (5200)
Annual Cost*
FERT LAG LNF
20732 817 (675) 14768 (-)
207320 1669 (1136) 36920 (14768)
2073200 9940 (3905) 62196 (36920)

*based on 35 7.10/hour.

( ) if a reduction step is used.

120

Capital Cost:

 

 

 

 

 

 

 

Size Cost (x 1000 $)
(IMGD) FERT LAG LNF
l 22 36. 7 46. 5 (—)

10 220 139.4 199.0 (46.5)

100 2200 660.3 362. 0 (199.0)
Annual Cost*
FERT LAG LNF
2241 3738 (1426) 4736 (-)
22407 14198 (5093) 20268 (4736)
224070 67252 (22427) 87795 (20268)

*amortized at 8% over 20 years.

(
C apital Ene r gy:

) values are if a reduction step is

 

used.

 

 

 

 

 

 

Size Energy (btu x 106)
(MGD) FERT LAG LNF
1 180 --- 342 (342)
10 1800 --- 1152 (342)
100 18000 --- 1588 (576)
Annual Cost *
FERT LAG LNF
161 --- 306(-)
1612 --- 1031 (306)
16115 —-— 1422(516)

*based on 2.93 x 10‘4 kwh/btu, $ 0.
at 8% over 20 years.
ANNUAL COST OF CASES - STEP 6
Case 1 (Capital Costs, Power, Labor)

 

03/kwh and amortized

 

 

Size Annual Costs
(MGD) FERT LAG LNF
1 46923 4555 (2101) 25724 (-)
10 469247 15867 (6229) 94133 (2572-1)
100 4692473 77192 (26332) 306592 (75661)

121

Case 2 (Capital Costs and Power)

 

Size Annual Costs
(MGD) FERT LAG LNF
1 26191 3738 (1426) 10956 (-)
10 261927 14198 (5093) ' 57213 (10956)
100 2619273 67252 (22427) 244566 (38741)

Case 3 (Capital Energy, Power)

 

 

Size Annual Costs
(MGD) FERT LAG LNF
1 24111 --- 6526
10 241132 --— 37976 (6526)
100 2411318 --— 158193 (18989)

Values in parenthesis are for use with a reduction step.

122

REFERENCES CITED

10.

ll.

12.

13.

14.

15.

123

REFERENCES CITED

Sludge Incineration and Fuel Conservation, N. E.R. C. ,
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Barnard, J. and Eckenfelder, W.W., Jr., "Inter—relationships
in Sludge Separations", in Water Qualitylmprovements by
Physical and Chemical Processes III, Gloynda and Ecken-
felder, P. 109, University of Texas Press, 1970.

Burd, R.A. , A Study of Sludge Handling and Disposal, U.S.
Department of the Interior Publication WP-20-4, May, 1968.

Blecker, H.G. , and Nichols, T.M. , Capital and Operating Costs
of Pollution Control Equipment Modules - Volume II - Data
Manualz EPA-R5-73 -0236, 1972.

Process Design Manual for Sludge Treatment and Disposal,
E.P.A. Technology Transfer, EPA625/1-74-006, 1974.

 

 

 

 

 

 

Electrical Power Consumption for Municipal Wastewater
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Estimating Staffing for Municipal Wastewater Treatment Facilities,
U.S. E.P.A., EPA68-01-0328, March, 1973.

Process Des_ign Manual for Upgrading_Existing Wastewater
Treatment Plants, E.P.A. Technology Transfer,
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Ritter, E. L. , "Design and Operating Experiences Using Diffused
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Dorr-Oliver, Inc. , Cost of Wastewater Treatment Processes,
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Patterson, W.L. and Banker, R.F. , EstimatingCosts and Man-
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Nickerson, G.L. , et. a1. , "Chemical Addition to Trickling Filter
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Doe, P.W., et. al., "Sludge Concentration by Freezing", Water
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"Review of Sludge Disposal Practices", Journal of the American
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Akers, D.J., and Moss, E.A. , Dewateringof Mine Drainage
51.11ng, U.S. E.P.A., EPA R2-73‘169, 19730

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Sherwood, R.J. , and Dahlstrom, D.A. , "Economic Costs of
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White, William F. , "Fifteen Years of Experience Dewatering
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Dorr-Oliver, Manufacturing Data, 1968.

 

 

 

 

 

 

Clark, John; Veissman, Warren; and Hammer, Mark, Water
Supply and Pollution Control, 2d. ed. , International Textbook
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State of the Art Review of Sludge Incinceration Practice, Depart-

 

 

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Dotson, G.K.; Dean, R. B.; and Stern, G. , "Cost of Dewatering
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"Sludge Dewatering", Manual of Practice No. 20, Water Pollution
Control Federation, 1969.

 

 

Vesilind, P. Aarne, Treatment and Disposal of Wastewater
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Goodman, Brian L. , Design Handbook of Wastewater Systems:
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"Current Labor Statistics", Monthly Labor Preview, V. 98, March,
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Forster, Hans W. "Sludge Dewatering by Pressure Filtration",
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Aguilar, Rodolpho, Systems Analysis and Design, Prentice -Hall,
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Personal communiques with Inland Steel Co. , Republic Steel Co. ,
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Personal communiques with Huron Cement Co. , Peerless Cement
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Trovell, G. E.; Davis, H. E.; and Kelly, J. W. , Composition and
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Operation, U.S. E.P.A., 1972.

 

11'...

 

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