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THESIS

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This is to certify that the
thesis entitled

Windrow Management Methods for Composting
Straw Amended Dairy Manure

presented by

Michael C. Kenny

has been accepted towards fulfillment
of the requirements for

Jesters—degree in Agicultml Technology
& Systems Management

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0-7639 MS U is an Affirmative Action/Equal Opportunity Institution

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1]” COMM“

WINDROW MANAGEMENT METHODS FOR COMPOSTING STRAW AMENDED

DAIRY MANURE

BY

Michael C. Kenny

A THESIS

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

AGRICULTURAL TECHNOLOGY AND SYSTEMS MANAGEMENT

Department of Agricultural Engineering

1999

ABSTRACT

WINDROW MANAGEMENT METHODS OF COMPOSTING STRAW AMENDED

DAIRY MANURE

BY

Michael C. Kenny

On—Farm windrow composting methods of dairy manure needed
to be studied to determine an optimal method of management.
Temperature, carbon dioxide and time were used to determine
an optimum method of windrow management during the
composting of five straw amended dairy manure windrows. It
was concluded using carbon dioxide as an indicator to time
windrow turnings while having a minimum number of turns in

a given time period is optimal.

ACKNOWLEGMENTS

I would like to thank my major professor Dr. Ted London for
taking a chance on me and for his guidance and patience
during my research and writing of this thesis. I would also
like to thank Dr. Cynthia Fridgen and Dr. Howard Person for
serving on my committee. Dr. Cynthia Fridgen helped me
understand the large scope of waste management issues and
brought a non-engineer flavor to my committee. Dr. Howard

Person provided his insight to compost engineering.

I would like to thank the many individuals associated with
the Manure Management Demonstration Project for their time
and effort in helping me understand the value composting
brings to agriculture. Christopher Lufkin, who managed the
project, deserves credit for giving me direction and
guidance in my composting studies. Jim Scott and Keith
Meyers helped with equipment needs and provided their

valuable time to the project.

Finally, I would like to thank my parents and my future
wife Liz. My parents have guided me positively through life
and patiently helped teach me to never give up. Liz helped

keep my spirits up and pushed me towards my goals.

iii

TABLE OF CONTENTS

List of Tables ........................................ viii
List of Figures ....................................... ix
Chapter 1: Introduction ............................... 1
Chapter 2: Objectives ................................. 3
Chapter 3: Literature Review .......................... 4
3.1 Compost Definition ................................ 4
3.2 Compost Systems ................................... 5
3.2.1 Reactor ..................................... 6

3.2.1.1 Horizontal Flow and Inclined Flow

Processes .......................... 6

3.2.1.2 Agitated Bins ...................... 6
3.2.1.3 Static Bins ........................ 7

3.2.2 Nonreactor .................................. 7
3.2.2.1 Static Solid Beds .................. 8
3.2.2.2 Agitated Solids Bed ................ 8

3.3 Biological Fundamentals of Compost ................ 10
3.3.1 Microbe Types ............................... 10
3.3.1.1 Bacteria ........................... 10
3.3.1.2 Actinomycetes ...................... 11
3.3.1.3 Fungi .............................. 12

3.3.2 Microbial Growth ............................ 12

w

3.3.3 Microbial Destruction ....................... 14

3.3.3.1 Heat Inactivation .................. l4

3.3.3.1.1 Exponential Decay of

Microbes ................. l4
3.3.3.1.2 Nonexponential Decay of
Microbes ................. 16

3.3.3.2 Microbe Destruction Limitations.... 16

3.4 Empirical Studies of the Compost Process .......... 18
3.4 1 Temperature ................................. 18
3.4.2 Oxygen and Carbon Dioxide ................... 19
3.4 3 Aeration .................................... 21

3.4.3.1 Aeration types ..................... 21
3. 4. 3. 1. 1 Forced Aeration .......... 21
3. 4. 3. 1. 2 Natural Aeration ......... 21
3.4.3.2 Aeration Mechanisms ................ 22
3. 4. 3. 2. 1 Convection ............... 22
3. 4. 3. 2. 2 Diffusion ................ 23
3. 3. 3 Heat Transfer ...................... 24
3. .3 4 Moisture Vapor ..................... 26

3.5 Physical Properties ............................... 27
3.5.1 Windrow Size ................................ 27
3. 5.2 Particle Size ............................... 29
3. 5.3 Free Air Space .............................. 31

3.5.3.1 Bulk Density ....................... 32
3. 5.3.2 Moisture ........................... 33
3.5.4 Volume Reduction ............................ 33

3.6 Chemical Properties ............................... 34

3.6.1 C/N Ratio ................................... 34
3.6.1.1 Carbon ............................. 35

3.6.1.2 Nitrogen ........................... 36

3.6.1.3 Substrate Biodegradability ......... 37

3.6.2 pH .......................................... 37

3.7 Properties of Finished Compost .................... 38
3.7.1 Curing Phase ................................ 38
3.7.2 Humus Development ........................... 39
3.7.3 Disease Suppression Characteristics ......... 40
Chapter 4: Methods .................................... 42
4.1 Composting Site ................................... 42
4.2 Manure Origin ..................................... 42
4.3 Windrow Management ................................ 43
4.4 Windrow Turning Mechanism ......................... 45
4.5 Windrow Design .................................... 45
4.6 Temperature Measurement ........................... 47
4.7 Carbon Dioxide Measurement ........................ 47
4.8 Moisture Content .................................. 48
4.9 Cross Sectional Area Measurement .................. 49
4.10 Bulk Density ..................................... 50
4.11 Windrow Sampling Technique ....................... 51
4.12 Germination Test ................................. 52
4.13 Sieve Analysis ................................... 53
Chapter 5: Results and Discussion ..................... 55
5.1 Windrow Turning ................................... 55
5.2 Windrow Temperature ............................... 56
5.3 Windrow Carbon Dioxide ............................ 60
5.4 Windrow Moisture Content .......................... 63
5.5 Windrow Cross Sectional Area ...................... 65
5.6 Bulk Density ...................................... 68
5.7 Windrow Total Mass Change ......................... 70
5.8 Chemical Tests .................................... 71
5.8.1 Windrow Carbon Content ...................... 72
5.8.2 Windrow Nitrogen Content (TKN) .............. 75
5.8.3 C/N Ratio ................................... 78
5.8.4 pH .......................................... 81

5.9 Germination Tests ................................. 83
5.10 Sieve Analysis ................................... 84
5.11 Data Summary ..................................... 86

vi

Chapter 6: Conclusions ................................ 88
Chapter 7: Further Research ........................... 90

Literature Cited ...................................... 91

vii

ITJ'L'.““.H

twirl-5‘s. -.‘ I.“ u”i~q;n

LIST OF TABLES

Table 3.1: Effect of windrow size on temperature and

oxygen content ............................. 28
Table 4.1: Windrow treatments ......................... 44
Table 4.2: Sieve size and shake times. ................ 54

Table 5.1: Comparison of windrow turns and % TKN
nitrogen loss on a dry mass basis .......... 78

Table 5.2: Cress Seed Germination as a % of Control... 83

Table 5.3: Data Summary ............................... 87

vm

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

.10:

.11:

.12:

LIST OF FIGURES

Specific humidity as a function of air

temperature ...............................

Sieve analysis of composted yard

trimmings .................................

Mean temperature values for all
the windrows ..............................

Changes in windrow carbon dioxide levels
during composting .........................

Changes in windrow carbon dioxide levels
for the weekly turned windrows ............

Changes in windrow moisture content
during composting .........................

Changes in windrow cross sectional area
during composting .........................

Windrow bulk density (dry) measurements
at the beginning and end of the compost
process ...................................

Total dry mass change during composting...

Changes in windrow carbon percentage
during composting .........................

Changes in percent of Total Keldajl
Nitrogen (TKN) in the compost windrows....

Windrow dry mass nitrogen totals based
on % TKN .................................

Changes in windrow C/N ratios during
Composting ...............................

Changes to windrow pH during composting ..

m

27

30

58

61

61

64

66

68

71

73

76

77

79

81

Figure 5.13: Percent rejects from sieving cured
Compost. Values are means of two samples
per windrow .............................. 85

Chapter 1
Introduction

Waste management in agriculture is an increasing problem
for the farmer has populations expand into agricultural
areas. Some of the problems encountered by the animal
farmer are the availability of land for manure application,
odors, flies and negative perceptions by the general public

of manure waste management.

Composting of the manure is one option that the farmer has
for waste management on the farm. Composting of manure
reduces flies, odors and volume of the manure when properly
performed. Prior composting research has focused on the
many aspects of waste management from industrial sludge to
garbage and animal agriculture. Many experiments have been
facilitated by bench scale methods and do not generally
take into account larger scale manure management operations

such as a farm.

Rynk et al (1992) gives a good overview of the composting
process and how to manage composting farm operations,

however, more in depth research for on—farm practices is

needed to help bring the use of composting into common
practice. Recently, Lopez-Real and Baptista (1996) have
compared three different composting systems of windrow,
minimal intervention and forced aeration methods of
composting dairy manure. Based on common on-farm manure
handling practices, it was decided that the windrow system
of composting is more suitable with the manure handling
capabilities and machinery on a farm, so it was chosen for

study.

The research presented here focuses on the effect different
management techniques have on the process parameters during
the windrow composting of dairy manure. There was not an
attempt to conduct a replicated research analysis. The
research was part of a demonstration project to demonstrate
and compare different windrow management schemes. The
methods used to evaluate the compost were based on the
composting process being used as a manure management tool

for on-farm applications.

Chapter 2

Objectives

The objectives of this research are; (1) to study the
effect that turning windrows based on different process
parameters has on the composting of dairy manure; (2) to
develop better understanding of the windrow composting
process and how it can be utilized in animal waste
management; (3) to develop dairy manure windrow composting
techniques based on experimental results and observations

of the process parameters during composting.

Chapter 3

Literature Review

3.1. Compost Definition

Composting is defined in many ways. Bell (1973) wrote that
composting is a self-heating, thermophilic, aerobic
decomposition process, which occurs naturally in
accumulations of biodegradable solid organic matter. Haug
(1980) states it is the biological decomposition and
stabilization of organic substrates under conditions that
allow development of thermophilic temperatures as a result
of biologically produced heat, with a final product
sufficiently stable for storage and application to land
without adverse environmental effects. Haug (1993) then
added to the above statement that the resulting compost
must be free of pathogens and weed seeds. Mathur (1991)
describes composting as a biological conversion of organic
wastes, under controlled conditions, into hygienic, humus
rich, relatively biostable product that improves land and

fertilizes plants.

Hoitink et al (1991) divides the composting process into
three phases. In the first phase the temperatures rise to
40-50 C and the easily degradable substances are destroyed.
In the second phase the temperatures range from 45-65 C and
less degradable substrates of cellulose are destroyed while
lignins are slowly broken down. In the third phase, known
as the curing phase, humic substances accumulate and

mesophilic organisms recolonize the compost.

3.2. Compost Systems

Reactor and nonreactor are the two main classifications of
compost systems (Haug 1980). Reactor systems are also
referred to as in—vessel or mechanically operated. Reactor
systems include vertical flow, horizontal, inclined flow
and nonflow processes. Within these systems are the
rotating drum, agitated bin and static bed bins. Nonreactor
systems are referred to as open systems or those in which
the compost materials are not placed into a reactor (Haug

1980).

3.2.1. Reactor

The vertical flow systems are divided into classifications
by agitation. If the solids are agitated while they move
down the reactor then it is considered a moving agitated
bed reactor. If the substrates are mixed before placement
into the reactor and are not agitated through the process
then it is considered a moving packed bed system (Haug

1993).

3.2.1”1.Horizontal Flow and Inclined Flow Processes

Rotating drum reactors operate by rotating the composting
material inside of a drum mechanism. The drum is usually
inclined so that the materials will move down the incline
as the drum is rotated. The process can be a continuous
movement down the incline or the drum can have cells and
the composting material is moved from one cell to the next

as the process proceeds down the drum.

3.2.1.2. Agitated Bins

Agitated bins are another form of the Horizontal flow

composting process. Bins of varying shapes and sizes are

used in this process. The material is placed into the bins
and during the composting process the material can be
agitated using shaking, augers, or other agitation devices
depending on the design of the system. Air maybe forced
through the bins during the process to satisfy the aeration

requirements of the active organisms.

3.2.1.3. Static Bins

Static bed bins are similar to the agitated bins except
that the composting material is not agitated within the
bins. Air is forced through the bins and the material is
moved from one stage to the next by conveyor, hydraulic

pushing or through the use of a walking floor.

3.2.2. Nonreactor

Nonreactor systems include static, agitated solids bed, and
pile or windrow processes. The majority of on-farm
composting operations use the nonreactor compost systems

(Rynk 1994).

3.2.2.1. Static Solids Bed

In the static pile process there is no mechanical or other
type of agitation after the pile formation. The aeration
requirement is maintained through forced or natural
ventilation. Mathur (1991) used perforated pipe placed
across the bottom of the windrow to facilitate air movement
by convection through the windrow due to the temperature
stratification within the windrow. This became known as the

passively aerated windrow system.

3 . 2 . 2 . 2 Agitated Solids Bed

Windrow composting is considered the main form of the
agitated solids bed process (Haug 1993). In the windrow
process the substrates are formed into the shape of a
windrow and turned or agitated periodically. Various forms
of equipment can do the turning or agitation. Forced or

natural ventilation processes are used in the process.

Typically on-farm manures are composted using the windrow
process. Voghtmann and Besson (1978) stated windrow
processes were used in Europe to compost manures. Fabian et

al. (1992) describes the use of agitated windrows for farms

from small to large in size. LaCross and Graves (1992)
indicate that windrow composting for farmers is the most

common system used.

Windrow processes are used on the farm because it is a
relatively low technology method that can utilize existing
machinery found on most farms. Bell (1973) describes the
use of a front-end loader to turn windrows as a method of
composting. Rynk (1992) includes farm machinery, such as a
manure spreader and front-end loader to agitate the windrow

for compost windrow management.

The disadvantage of using existing farm machinery is the
time it takes to turn the windrows (Rynk 1992 and Fabian et
al 1992). Specialized equipment has been developed to
accelerate the windrow agitation. There are self-propelled
and power-assisted windrow turners available. Included in
the power—assisted compost turners are those which are
pulled and mechanically driven with a tractor. This type of
compost turner is often used on farms where composting is
done. Rynk (1992) gives a good overview of the specialized
composting equipment that can be used on the farm. Fabian

et a1 (1992) indicate the advantages a windrow compost

turner can provide in particle size reduction, mixing and

reduction in time it takes to turn the windrows.

3.3 Biological Fundamentals of Compost

3.3.1 Microbe Types

There are many different types of organisms that can be
found in the composting environment. Factors that will
influence the types and quantities of microbes found are
temperature, moisture, pH, aeration, and feed sources for
the microbes. Bacteria, actiomycetes and fungi are the
primary organisms in compost systems, however, there are
groups such as algae, protozoas and viruses which are less
significant. There has been confusion in classifying
actiomycetes because they have characteristic of both
bacteria and fungi. Haug (1980) includes actiomycetes in

the bacteria group for ease.

3.3.1”].Bacteria

Bacteria are the smallest living organisms known to man.

They can be unicellular or multicellular. Reproduction of

bacteria mainly occurs by binary fission. During the

10

composting process bacteria are generally divided into
thermophilic and mesophilic categories. Bacillus
stearothermophilus, thermomonospora, and clostridium
thermocellum are prominent bacteria during the thermophilic

composting process (Atlas and Bartha 1981).

Cysts, microcysts and endospores are capable of producing
dormant forms of cells, which are more resistant to heat,
radiation and chemical disinfection. Endospores are
considered the most stable of the three under adverse
conditions and become significant when heat inactivation is

considered (Haug 1980).

3 . 3 . 1 . 2 Actinomycetes

Actinomycetes comprise a group of branching unicellular
microorganisms. They form a mycelium which may be of a
single kind, designated as substrate or vegetative, or of
two kinds, substrate and aerial. They reproduce by fission
or by means of special spores or conidia. Actinomycetes are
found in virtually every natural substrate and live and
multiply most abundantly in various depths of soil. Waksman
et al (1934) shows that actinomycetes are abundant in high

temperature composts of manure and plant residues.

11

Thermoactinomyces and other thermophilic genera grow
abundantly in stable manure and in high temperature

composts (Waksman 1967).

3.3.153Fungi

Fungi are eukaryotic heterotrophic spore-bearing organisms,
which lack chlorophyll. Fungi can be split into two groups:
Slime molds and true fungi (Atlas and Bartha 1981). The
molds are aerobic while the true fungi can be both aerobic
and anaerobic. The fungi molds have an advantage over
bacteria in low moisture and nitrogen environments (Haug

1980).

Geotrichum candidum, aspergillus fumigatus, mucor pusillus,
chaetomium thermophile, thermoascus auranticus and torula
thermophila are prominent fungi during the thermophilic

phase of the composting process (Atlas and Bartha 1981).

3.3.2 Microbial Growth

The rate of microbial growth depends on the concentration

of substrates if no other factors are limiting. Equation

3.1 developed by Monad in 1942 and given in Haug (1980)

12

describes the effect of substrate concentration on the rate
of substrate use by a microbe. Equation 3.2 describes the
growth rate of microbes with regard to the utilization of

substrate.

‘15 "SX (3.1)

m

dt K +S

 

Where

dS / dt = rate of substrate utilization, mass/volume - time
X = concentration of microbes, mass/volume
km = maximum utilization coefficient, maximum rate of substrate utilization at
high substrate concentration, mass substrate/mass microbes - day
K 3 = half — velocity coefficient, also reffered to as the Michaelis — Menton coefficient, mass/volume
S = concentration of the rate limiting substrate, mass/volume

ELY," kmSX —keX (3.2)
dt K +5

5

 

Where

dX / dt = net growth rate of microbes, mass / volume - time
Ym = groth yield coefficient, mass of microbes / mass of substrate

k e = endogenous respiration coefficient, tirne'l or mass of
microbes respired / mass of microbes - time

Values for Ym,km,K,andkemust be known for the particular

substrate and microbe under consideration. The coefficient

13

values have been determined for various substrates under

both aerobic and anaerobic conditions.

3.3.3 Microbial Destruction

3.3.3.] Heat Inactivation

One of the goals of composting is to produce a sanitized
product that is beneficial to plant growth (Zucconi and
Bertoldi 1987). Strauch (1987), after an extensive
literature review, states the requirements needed to
disinfect sludge for the windrow process as the composting

must be operated for at least three to four weeks with the
temperature of the windrow exceeding 65° C for at least one

of the weeks. Haug (1980) states that heat inactivation of

microbes are a function of time and temperature.

3.3.3.1.1 Exponential Decay of Microbes

Heat inactivation of certain microbes can result in

straight-line first order decay as described by Equation

3.3.

14

Where

n = viable cell population
k d = thermal inactivation coefficient

The thermal inactivation coefficient is a function of

temperature and can be described by Equation 3.4.

_Ce—Ed/RTk (3,4)

kd—

Where

T k = Temperature, °K

E d =inactivation energy, kcal/mole

C = Constant
R = universal gas constant =1.99 cal/deg - mol

The constant C and inactivation energy Ed is determined by

plotting the logarithm of kd'versus l/Tk.

During composting there are phases of heating, holding and
cooling, therefore, kg will not be constant. Haug (1980) in

Equation 3.5 describes this effect.

" “[Ed’RTk(’)ld. (3.5)

I
mi: IfCe
f 0

3

15

.,

" I

II:

7V.
.5»

C .
T2
”be

nah

 

Y

9‘
c..QL

a
V
‘1

V.

X

I
a

I"
v

Where

n = no att = O, to final conditions, n = n att =t

f f '

3.3.3.1.2 Nonexponential Decay of Microbes

In certain situations during composting there may be a lag
then an exponential decay or an exponential decay followed
by a retardant die away of microbes. Wei and Chang (1975)
propose that clumping of organisms is a major factor for
nonexponential decay of microbes. Lag decay results from a
large percentage of the microbe population existing in
clumps while the asymptotic decay results from a large
percentage of microbes existing as discrete particles along
with a number of clumps of unusual size. Large particles
that have formed during composting may not receive adequate
oxygen and would significantly reduce heat buildup within

the particle itself.
3.3.3.2NUcrobe Destruction Limitations
Particle size can limit microbe destruction as described

earlier. Haug (1980) analyzed the effect of particle size

on heating and concluded clumps larger than 20 cm in radius

16

could effect heating potential and may limit the

destruction of microbes.

Temperatures in the outer zones of the composting mass may
cause no microbial destruction. Turning of the compost
redistributes the compost mass, submitting more of the mass
into the higher temperature zones. Haug (1980) describes
the effect of turning on the inactivation of microbes in

Equation 3.6.

(3.6)

Where

n, = number of organisms surviving

r10 = intial number of organisms present

f1 = fraction of composting material in the sublethal temp. zone
f, = fraction of composting material in the lethal temp. zone

At = time interval between turnings

kd = thermal death coefficient

N = number of turnings

l7

Bacterial growth after the compost temperatures have
reduced to sub—lethal temperatures is another factor that

limits thermal inactivation. Satriana (1974) presented data
compiled by Dr. William Gaby that shows temperatures of 49°

to 55° C reduce coliform levels to numbers under the minimum
level of detection. However, coliforms reestablished
themselves in the latter stages of the compost process of
refuse and sewage sludge. Also in the study, Fecal

streptococci maintained populations even when temperatures

reached 55° C to 60° C.

3.4 Empirical Studies of the Compost Process

3.4.1 Temperature

Schulze (1962b) studied the effect of controlling
temperature by restricting the air supply to an enclosed
mass of decomposing material. It was found that at the
beginning of the thermophilic phase long periods of airflow
were needed to increase the temperature to the preset
maximum. Snell (1960) states there were three objectives of
high temperature composting, (1) destroy pathogenic

organisms, (2) destroy weed seeds and (3) destroy fly eggs

18

and larvae. Lynch and Cherry (1996) studied the effect of
cold ambient temperatures in Ontario Canada on the
composting process and concluded it was possible to compost

through the winter months.

Wiley (1957) indicates the optimal temperature for maximum
decomposition is in the 54° to 63° C range. Snell (1960)
observed that in the initial phase of composting garbage
the optimal temperature for oxygen uptake was 35° C, but
later in the thermophilic range, the optimal temperature
was 45° C. Finstein (1980) concluded that 55° C was the

optimum temperature for thermophilic microbial activity.

3.4.2 Oxygen and Carbon Dioxide

Lambert and Davis (1934) indicates the sum of the carbon

dioxide and oxygen content percentages in mushroom compost

heaps approximately equals twenty-one. Schulze (1960) along

with Lambert and Davis (1934) concluded the respiratory

quotient (RQ) of compost could be figured by Equation 3.7.
_ V01umeofC02 produced :

R ' 1 .7
Q Volumeof02 consumed (3 )

 

l9

Oxygen consumption rates varied directly with temperature.
Equation 8 defines the relation between temperature and the
oxidation reaction rate and is usually expressed as the

temperature coefficient (Schulze, 1960).

K!

Q10 = K -10

 

(3.8)

Vflwfir

Q10 = temperature Coefficient
Kt = the oxidation reaction rate at temperature t
K :40 = the oxidation reaction rate at temperature t - 10 ( 10° C. lower)

Lambert and Davis (1934) found oxygen content within
compost heaps was greater towards the outside of the heaps
while the carbon dioxide content increased as sampling
moved toward the lower center of the heap. Miller et al
(1996) found oxygen content decreased while carbon dioxide
content increased as measurements approached the lower
center in Phase 1 composting stacks. Miller et al (1996)

and Michel et al (1996) reported that turning frequency had

no significant affect on windrow oxygen concentrations.

20

3.4.3 Aeration

3.4.3.1 Aeration Types

3.4.3.1.1 Forced Aeration

Forced aeration uses mechanical devices to supply the
aeration requirement of the composting substrates. Aeration
can be continuous or intermittent depending on the
parameter used. Schulze (1962), Hansen et al (1989),
Fernandes and Sartaj (1997) and Emerton et a1 (1988) used
temperature as an indictor for aeration. Schultze (1960)
used the oxygen content of compost exhaust air as an
indicator for aeration. Bell (1970) used continuous
aeration while comparing two different aeration rates to
determine optimum aeration requirements in the composting

of poultry manure and ground corncobs.

3.4.3.1.2 Natural Aeration

Naturally aerated composting does not include mechanical
means for air delivery, rather it relies on diffusion and
convection has the means of aeration. Emerton et al (1988)

compared natural versus forced aeration methods on dairy

21

manure solids and concluded that under natural aeration the
static compost piles achieved temperatures high enough for
optimum composting. Fernandes and Sartaj (1997) found that
naturally aerated composting is slower than forced or
passive, however, it was still feasible for composting

poultry manure slurry amended with sphagnum peat.

3 . 4 . 3 . 2 Aeration Mechanisms

Michel et al (1996) indicates primarily turning the windrow
does not do oxygenation of windrow composting but rather
convection and diffusion appear to be the primary aeration

mechanism.

3.4.3.2.1 Convection

The density difference between the warm moist air within
the interior of the windrow and the colder, less moist
ambient air outside the windrow produces an upward buoyant
force that induces natural ventilation of the windrow (Haug
1993). Natural convection is not easily measured due to the
non-homogeneity, spatial variability and the difficulty

measuring small air velocities (Miller et al 1989).

22

Lambert and Davis (1934) concludes the convex shaped
temperature contours from a cross sectional area of a
compost heap are the result of convection currents. Tietjen
(1961) indicated that the structure of the compost piles
have an effect on the movement of gases within the air

pores.

Mathur et a1 (1986) and Lynch and Cherry (1996) used
perforated pipes at the bottom of the compost piles to aid
the convection currents in increasing the oxygen

concentration near the bottom of the piles.

3.4.3.2.2 Diffusion

Another aeration mechanism for composting is molecular
diffusion. Molecular diffusion results from constant and
random collisions between molecules of a fluid. The
molecules have a tendency to move from a zone of high
concentration to low concentration (Haug 1993). Oxygen
diffusion through smaller pores and into the aqueous film
surrounding compost particles is essential to maintaining
aerobic conditions for the active microorganisms (Richard
1996). Diffusion rates will vary with stack porosity, which

is affected by location within the stack, compaction,

23

mixing, moisture content and the extent of decomposition

(Miller et a1 1989).

3.4.3.3 IHeat Transfer

Conduction, convection and radiation are the three
mechanisms of heat transfer. Convection is the process in
which heat energy is carried from place to place by the
bulk movement of fluid (Cutnel and Johnson 1989). Movement
of air within a bed of composting particles such as the
evaporation of water from the composting particles is an

example of convective and latent heat transfer (Haug 1993).

Heat transfer from contact between particles is an example
of conduction. Fourier’s law (Equation 3.9) explains the

quantitative law of heat conduction.

d_Q_'WdT (3.9)
dt dx

 

Where

dQ = amount of heat
dA = plane of area
dt = amount of time

T .
2;- = temperature gradient

k = thermal conductivity

24

Air movement across the compost produces convective heat
loss resulting in a temperature difference. Heat is then
conducted from the interior of the compost to the outer

layers to compensate for the loss of heat. Equation 3.10

describes this heat transfer within the compost piles.

q=UA(Tl-T2) (3.10)

Where

q = rate of heat transfer

U = overall heat transfer coefiicient, which includes both conductive and convective

heat transfers, cal / h - cm2 -°C

A = area perpidecular to direction of heat transfer, cm2

Tl’ T 2 = temperatures at position land position 2, °C

When a warm compost surface is exposed to cooler ambient
air, such as after turning a windrow or pile, a rapid
surface temperature drop should result from radiative and
convective losses with the outside ambient air (Haug 1993).
Stefan—Boltzmann law given in Equation 3.11 describes

radiant heat transfer between two bodies.

_ 4_ 4 (3.11)
q _ aA(Ta Tb )Fa F,

25

Where

a = Stefan —Boltzmann consant, 4.87 x 10'8 kcal / (h - m2 -°K 4)

Fa = configurational factor to account for the relative position and geomeny of the bodies
Fe = emissivity factor to account for non — black body radiation

T a , 7}, = absolute temperature of bodies A and B, °K

3.4.3u4 Moisture Vapor

Haug and Haug (1978) describes the two major energy fluxes
of the composting processes are heats released as a result
of organic decomposition and energy required for latent
heat moisture evaporation. Finstein (1980) concludes that
microbial generated heat is removed by evaporative cooling

of the compost.

Haug and Haug (1978) estimates a value of ten grams of

water per gram of degradable organic can be used as a rule
of thumb to judge the thermodynamics of the composting

process. Below ten grams there should be sufficient energy
available for temperature elevation and water evaporation.
If the water ratio is above ten then other factors, such as
surface drying, will be needed to provide sufficient energy

for the composting process.

26

The amount of water that can be carried by air increases

exponentially with increases in air temperature, as shown

in Figure 3.1.

3.

Specific Humidity Hp]. Dry Air

0.5 a- ma 1.” _--1-...-- ----- -----.,-.._-- .-- - -

 

0.5 I
Assumed Conditions

760mm Total Pressure
100% relative Humidity
0.4 «~
Normal Composting
Temperature Range

 

 

0.3 a If

0.2 ~~

0.1 «»

 

 

0 .0 w l + .
0 10 20 30 40 50 60 70 80

Alr Temperature ° c.

Figure 3.1 : Specific Humidity as a Function of Air
Temperature (Haug 1993)

5 Physical Properties

3.5.1 Windrow Size

Windrow size is an important factor of the windrow

composting process. An oversized windrow retains too much

heat and could compress, thereby, reducing the aeration

rates. A windrow too small can cool too readily and inhibit

27

the heating process of composting, while a windrow too

large inhibits the oxygen content (Strom et al 1980).

Windrow sizing effects and their remedies are listed in

Table 3.1.

Table 3.1: Effect of windrow size on temperature and oxygen content.

(Stram et el 1980)

 

Windrow Size

 

 

 

 

 

Too Large Too Small Acceptable
Temperature (°C) >60 <20 20 to 50
Oxygen Content (5 )5 >5
(%V/VI
Remedy Both the Temperature
temperature and requirements

 

0; requirements
call for a

smaller windrow

 

call for a
larger windrow,
possibly
conflicting with
the O,

requirement

 

 

Strom et a1

(1980)

concluded that windrows of composting

leaves should have a height of four feet with a width of

seven feet.

favored in the early stages of the process.

28

With this windrow size oxygen diffusion is

Combining

 

windrows during the later stages of composting can insulate
the windrows from cooling too quickly. Diaz et al (1993)
states an ideal composting windrow is six to seven feet
high with a width of eight to thirteen feet, depending on

equipment used.

Loaf shaped windrows tending toward a flattened top are
appropriate in dry windy conditions due to the ratio of
exposed surface to overall volume. A conical shape with a
less flattened top would be conducive in wetter conditions
because it would be more likely to shed water. The overall
volume of the hot zone is greater in triangle or conical

shaped windrows, (Diaz et a1 1993).

3.5.2 Particle Size

The significance of particle size is in the amount of the
surface area of the composting process exposed to microbial
attack (Diaz et al 1993). Michel et al (1996) found
particle size decreases with increasing turning frequency
and piles handled by a tractor loader compared to windrows
of composted yard trimmings had higher levels of larger
particles. Figure 3.2 shows the effect of turning frequency

on particle size. Windrows lA-IE were turned seven times

29

every four weeks, windrows 2A-2E were turned once every

four weeks and piles 3A-3E were turned once every four

weeks.

Particle size distribution of compost defines the use of
the compost. Uniform distribution of particle size would be
used in the nursery industry, while less uniform compost
would be used as a soil amendment (Diaz et al 1993). ).
Particle size affects the moisture requirements of the

composting process (Jeris and Regan 1973).

0|
0
JJ

   
  
   
 

 

'0'an 1A-1 E
-0-\Mndrws 2A-2E
-°-Pile 3A-36

&
O

 

 

 

Percent rejects (96)
N on
O O

—L
O
L_J._JJ_.LL

 

0 ..e e: .: . :.44 .. . ——
0 1/8 1/4 3/8 112 5/8 3/4 7/8 1
Sleve Size (Inches)

Figure 3.2: Sieve Analysis of Composted Yard Trimmings

(Michel, et a1 1996)

30

3.5.3 Free Air Space

Free airspace is important in the composting mixture in
determining quantity of oxygen available and movement of
air through the mixture (Haug 1993). Free air space is
determined primarily by moisture content and bulk density
(Schulze 1962a). Schulze (1962a) concluded that a minimum
of thirty- percent free air space should be maintained
during the composting of garbage refuse. Jeris and Regan
(1973a) found that oxygen consumption rates were optimal
between twenty-eight and thirty-two percent free air space.
Free air space can be determined from Equation 3.12 if bulk
weight and specific gravity from Equation 3.13 are known

(Schultze 1962a).

 

Freeairspace,%=1—(wadmjxdm (3.12)
Sg

Where

bw = bulkweight, g / cm3

dm = dry matter in percent

sg = specific gravity, g/ cm3

31

s _ 1003va (3.13)

s _
lOOsv + pv(sf —sv)

 

Where

S S 2 specific gravity of raw material
5,, = specific gravity of volatile matter
sf = speczfic gravity of fixed solids or ash

p, = % volatile matter in raw material

3.5.3.1.Bulk Density

Bulk density, which is inversely related to compost volume
and particle size, was the characteristic most affected by
windrow turning frequency (Michel et al 1996). Bulk
densities primarily increase in the composting process as
shown by Singley et al (1973), Lopez-Real and Baptista
(1996), Michel et al (1996) and Jackson and Line (1997).
Lopez-Real and Baptista (1996) found there was no
significant difference in the percent of bulk density
change when comparing the windrow and the static pile

composting methods.

32

3.5.3.2 Moisture

Moisture levels during the composting process must be high
enough to sustain microbial activity but not so high as to
limit free air space and reduce the rate of oxygen
transfer. The optimum moisture content is a tradeoff
between the moisture and oxygen requirements of the

microbes within the composting process (Haug 1993).

Snell (1960) indicates moisture content should be
maintained from fifty to sixty- percent throughout the
composting process. Jeris and Regan (1973a) found sixty-
five to seventy percent moisture content of composting

garbage refuse maximized the oxygen consumption rate.

3.5.4 Volume Reduction

Jackson and Line (1997) concluded volume reduction was
closely related to the increase in bulk density and
reduction of gravimetric water content during the
composting of paper mill sludge while using a front-end

loader to perform the turning. Lopez-Real and Baptista

33

(1996) concluded the biggest volume reduction of cattle
manure compost occurred in the windrow system when compared

to the forced and passive aeration systems.

3.6 Chemical Properties

3.6.1 C/N Ratio

Organic carbon is oxidized.tc>CIb by dry or wet combustion
and measured as C02. Compost nitrogen is usually determined
by the Kjeldahl method. The C/N serves as an index of the
decomposability of the material (Keller 1961). Livshutz
(1962) when discussing improving windrow composting

methods, describes the optimum starting C/N ratio should be
around 30:1. Mathur (1991) concludes the optimum C/N ratio

for mature compost is about 10.
Schulze (1962b) used Equation 3.14 to figure the carbon
content of the C/N ratio. Total nitrogen was figured using

the Kjeldahl method.

%C=(_“£“l_‘:_°flh_) (3.14)

34

Lopez-Real and Baptista (1996) compared three different
manure composting systems and concluded the C/N ratio for
each fell from an initial value of approximately 30 to an
ending value of approximately 14. Michel et al (1996) used
different feedstock mixtures during the composting of yard
trimmings and concluded the C/N ratios decreased from
around 25 at the start to between 12 and 19 in the finished

compost.

3.6.111.Carbon

Carbon accounts for approximately 50% of the dry mass of
most organisms and is needed to synthesize the variety of
organic molecules used in the structure and machinery of
the cell. Two sources of carbon are available: carbon in
the form of organic molecules, used by heterotrophs, and
the carbon present in carbon dioxide, used by autotrophs
(Haug 1993). The carbon content for the C/N ratio should
be figured from the biodegradable fraction of the organic

substrate (Kayhanian and Tchobanogous 1992).

35

3.6.1.2 Nitrogen

Sufficient nitrogen is needed to supply the microorganisms
with a feed source while composting. During composting
the organisms use about 15-30 parts of carbon for each part
of nitrogen (Haug 1980). Part of the nitrogen in organic
compounds is released on breakdown as NHg. Depending on
circumstances, the greater part of NH3is either assimilated
by organisms to NOzcnrlKh or it escapes to outside air
(Keller 1961). A low C/N ratio and an alkaline pH in the
decomposing stage combined with a high temperature has lead
to nitrogen volatilization as ammonia (Zucconi and Bertoldi
1987). Hansen et al (1989) concluded that the C/N ratio,
stirring frequency and particle size had the biggest impact
on nitrogen retention. During the composting of poultry
manure Vanstaen et al (1980) found that the addition of
straw helped immobilized the nitrogen. Lopez-Real and
Baptisa (1996) found the percent nitrogen content of the
compost generally increased through the process due to the
loss of volatile solids during composting, regardless of

composting system.

36

3.6.1438ubstrate Biodegradability

The degradability of the substrates determines the quantity
of available heat, mass balance and the stoichiometeric
oxygen demand of the composting process. Substrate
biodegradability can be predicted from Equation 3.15

(Chandler et al 1980).

B = 0.830—(0.028)X (3 . 15)

Where:

B = biodegradable fraction of the volatile soilds
X = lignin content, % of VS

Jann, Howard and Salle (1960) found that the completion of

the composting process can be determined if the compost
stays alkaline while the organic matter is held at 55° C

four 24 hours. Jeris and Regan (1973) obtained maximum

thermophilic composting rates in a pH range of 7.5 to 8.5.

37

3.7 Properties of Finished Compost

3.7.1 Curing Phase

The curing phase of the composting process follows the
active composting stage. During the curing phase the rate
of oxygen consumption decreases and the composting slows to
a rate where the compost can be piled without further
aeration (Rynk 1992). Haug (1980) describes the curing
phase as compost stabilization. Haug states stabilization
of compost occurs when the rate of oxygen consumption is
reduced to the point where the compost can be stored

without odors or anaerobic conditions.

After mature compost has gone through the stabilization
period, maturity can be measured in a variety of ways.
Jann, Howard and Salle (1960) state pH stabilization can be
used to measure stability while Keller (1961) summarizes
that maturity can be measured by physical, chemical,
biological characteristics or temperature. Mathur (1993)
conducted a literature review on the numerous tests for
biomaturity of composts. The tests include:

1” C/N Ratio of Compost

22.0rganic C/N Ratio in Water Extract of Compost
I3.Nitrogen Ratio in Water Extracts

38

4” Circular Chromatography Test of Alkali Extracts
£5.Humification Indicators
6. Microbial Activity
'7.CEC
8.Weter Extracts of Compost

9.Reheating

10. Direct Phytotoxicity

Mathur concluded that there was no one best way for
measuring maturity and no one test is adequate by it’s

self. Which test is used and the degree of compost maturity

needs to be decided by the use of the compost.
3.7.2 Humus Development

Humification of the compost can be described as the ratio
between total humic like substances and the total organic
matter (Zuccini and Bertoldi 1987). The three main groups
of humic substances include Fulvic acids, Humic acids and
Humus carbons (Keller 1961). Humic acids have the highest
cation exchange capacity and aids in the availability of
nutrients for plant uptake when applied to soil (Steffen
1979). Lenhard (1963) describes humus as having an
indirect effect on crop production by stabilizing clays and

cations and increasing the soil water holding capacity.

39

3.7.3 Disease Suppression Characteristics

Hoitink et al (1976) investigated differences between
composted and non—composted hardwood bark and the survival
of certain plant pathogens that were buried in those piles.
Selected pathogens of Phytophthora cinnamomi, Pythium
irregulare, Rhizictonia solani, Botrytis cinerea, and
Erwinia carotovara var. chrysanthemi could not be found
recovered in the composted piles. However, P. cinnamoni, P.
irregulare and R. solani were found in the non-composted
piles. Hoitink et al (1977) concluded that hardwood bark
compost is suppressive of Phytopthora cinnamomi. In
another studied by Chef et al (1983) composted hardwood
bark was found to be suppressive of Fusarium wilt of flax

and Chrysanthemum.

Chen et a1 (1987) studied which factors affect the
suppression of Pythium ultimum damping-off in container
media amended with compost. Compost was taken from
different temperature zones of the compost piles and used
in a bioassay test to determine damping-off. It was
determined that compost samples taken from the low
temperature outer edges of the compost piles suppressed

while the samples taken from the high temperature (60 C)

40

zones were conductive of Pythium ultimum. It was concluded
those compost samples taken from the high temperature zones
had reduced microflora activity after incubation at low
temperatures which caused a biological vacuum where P.
ultimum could thrive. The low temperature compost samples
had the highest microflora activity after incubation,
therefore, it was concluded the microflora suppressed the
P. ultimum by actively taking up the nutrients the P.
ultimum needed to survive. The effects of other factors
such as the carbon sources and the level of organic matter
decomposition have been investigated (Chung et al 1988 and

Mandelbaum and Hadar 1990).

Vogtmann et a1 (1978) studied the effect composting has on
the concentration of the antibiotic Zn-Bacitracin in
poultry manure. The results of the study showed that the
concentration of Zn—Bacitracin was 150 ppm in the fresh
poultry manure while the composted manure had concentration

levels less than 30 ppm.

41

Chapter 4

Methods

4.1 Composting Site

The composting was conducted on a compost pad at a landfill
in Belding, Michigan. The compost pad was constructed based
on recommendations in Rynk (1992) with a three-percent
slope in the direction of the windrows and no cross slope.
The pad was approximately 122 meters in length with the
high point centered perpendicular to the length of the pad.
The base of the pad consisted of fine sand fill that
existed at the site and capped with approximately 20 cm. of

road gravel (Michigan Spec. 23A).

4.2 Manure Origin

The manure used to form the windrows came from the same
milking herd and from milking cows that were fed the same
rations. This was done to ensure the manure would be as
consistent as possible from one windrow to the next. The

dairyman used sawdust in the alleys of the barn to absorb

42

liquids; therefore, the manure used had a small percentage

of sawdust in it.

4.3 Windrow Management

Five windrows (CDA, CDL, TMP, WTL, WCT) were built and
managed for the experiment. The windrows were managed
according to time, carbon dioxide or temperature, depending
on the windrow (Table 4.1). All the windrows were built to
approximately the same specification except for windrow

CDA, which had a high clay content soil added.

Windrows CDA and CDL were managed according to the carbon
dioxide level of the windrow. If mean carbon dioxide level
exceeded 10% the windrow was turned with a compost turner.
Clay soil was added at approximately 10% by volume to
windrow CDA to determine if an addition of a clay soil
helps to retain nutrients through the process. Windrows CDA

and CDL were never turned more than once every two days.

Windrow TMP was managed according to the mean temperature

level of the windrow. The windrow was turned with the
compost turner when the windrow temperature exceeded 65° C.,

but never more than once every two days.

43

Windrow WCT and WTL were turned on a time schedule of once
every week. The compost turner was used for windrow WCT and

a tractor loader turned windrow WTL.

Table 4.1: Windrow treatments

 

 

 

 

 

 

Treatment Turning Turning Frequency
Mechanism Threshold
CDA Compost 10 % Carbon Never more than
Turner Dioxide Levels once every 2
days
WCT Compost Time Weekly
Turner
WTL Tractor Time Weekly
Loader
CDL Compost 10 % Carbon Never more than
Turner Dioxide Levels once every 2
days
TMP Compost 65° Celsius Never more than
Turner once every 2
days

 

 

 

 

 

 

44

4.4 Windrow Turning Mechanism

The windrows were mixed using either a farm scale compost
turner or a tractor loader depending on the windrow. The
compost turner used to mix and aerate the windrows was a
single-drum, tractor-drawn turner developed in Austria and
sold under the trade name Sandberger. Production of this
turner had been licensed to Midwest Bio-systems in Tampico,
IL. This unit has a capacity of up to 1150 cubic meters
per hour. The turner was advanced slowly (less than 0.8
km/h) along the windrow. This requires the use of a
hydrostatic-drive tractor. The tractor used was an
International Harvester Hydro 84. A loader attachment
having a capacity of 0.8 cubic meters was used on this

tractor to turn the loader turned windrow.

4.5 Windrow Design

The windrows were sized to the specifications of the

compost turner that was used. This required a maximum

height of 1.5 meters and a maximum width of 3.0 meters in a

parabolically shaped windrow.

45

The building of each windrow consisted of laying down 15
bales of straw end to end and then placing another 15 in
the same manner along side. This produced a windrow
approximately 15.2 meters in length. The compost turner was
then run through the bales to break them up leaving bedding
on which the manure was placed. A volume of 13.8w? of
manure, which was lightly bedded with sawdust, was placed
on top of the straw with a tractor loader. For the windrow
containing clay, 2.3 cubic meters of clay was evenly
distributed across the windrow on top of the manure. Each
windrow was mixed with two passes of the compost turner to

start the process on October 3 1994.

The windrows were covered with a geosynthetic fabric made
from polypropylene. The cover is sold under the trade name
Top Tex”. It is 4 meters wide and is adequate to cover a
windrow 3 meters at the base and 1.5 meters high. This
“fleece blanket” sheds water while still allowing for
gaseous exchange through the material. It was used to avoid
excessive moisture in the windrows from rainfall. Lynch and
Cherry (1996) used a similar cover to prevent material loss
due to wind and provide insulation against cold
temperatures and excessive moisture during winter

composting.

46

4.6 Temperature Measurement

The temperature of each windrow was measured using a
Reotemp FRK probe with a 7001K—thermocouple thermometer.
The probe was placed approximately 30 centimeters into the
windrow from top center. Lambert and Davis (1934) described
this area to have the highest temperatures in compost
heaps. A temperature measurement was recorded at 5 equally
spaced intervals along the length of each windrow. The
means of the five values are presented in the results
section. Each windrow was monitored Monday, Wednesday and

Friday for temperature.

4.7 Carbon Dioxide Measurement

Carbon dioxide measurements were taken in each windrow
using a Bachrach Inc. fyrite volume expansion gas analyzer.
This instrument uses potassium hydroxide to react with the
carbon dioxide. A known volume of potassium hydroxide is
sealed into a fixed volume container. The air sample is
pumped into the container and the potassium hydroxide

depletes the carbon dioxide in the air sample, which

47

creates a vacuum that allows the fluid level to rise up the

graduated column for measurement.

Previous research by Lambert and Davis (1934) showed the
highest carbon dioxide levels of composts occur near the
lower center of the pile. Carbon dioxide measurements were
taken approximately 30 centimeters from the bottom center
of the windrow. Previous cross sectional carbon dioxide
profiles of windrows showed this area usually had the
highest percent of carbon dioxide in the pore spaces of the

compost.

Windrows that were managed by carbon dioxide levels were
measured at five equally spaced locations along the
windrow. Windrows that were not turned based on carbon
dioxide concentrations were checked at four equally spaced
locations along the windrow to save the expense of
frequently replacing the fluid in the expansion gas

analyzer.

4.8 Moisture Content

Moisture was determined for each subsample by drying

approximately 100 grams of the material in an oven at 50° C

48

for 48 hours. Weight of the sample was recorded before and
after drying to obtain moisture content. The sampling

procedure used is described in section 4.11. As recommended
by Rynk (1992) a low drying temperature was used so that no

organic material was burned off during the process.

4.9 Cross Sectional Area Measurement

Cross sectional area was measured throughout the composting
process by recording the height at top center of the
windrow and the width across the base of the windrow.
Height was measured with a slender probe placed down into
the windrow from the top center until the tip of the probe

touched the hard surface of the ground.

Cross sectional area measurements for the windrows using
the compost turner were figured by a formula given by Rynk
(1992) for windrows which have a base (b) at least twice
the height (h) (Equation 4.1). Area was measured three

times in each windrow and then averaged.

Area = h * (b-h) (4.1)

49

Cross sectional area measurements for the windrows using
the tractor loader were figured by a formula given by Rynk
(1992) for windrows which are turned using a bucket loader
(Equation 4.2). Measurements were replicated three times

and averaged.

Area = 2/3 X b x h (4.2)

4.10 Bulk Density

Bulk density was measured as the windrow was being reformed
behind the turner. A pan 41.91cm in diameter and 8.89cm
deep was placed in the windrow behind the turner so that
the top of the pan was at the same height as the drum of
the compost turner. The compost turner drum was then
brought to 200 rpm and the turner moved forward into the
compost. This formed the windrow behind the turner and over
the pan. After the windrow was formed, the pan was
carefully removed and the compost was leveled off to the
top of the pan. It was weighed and corrected for moisture.
This was repeated three times in each windrow and the
values were then averaged. Bulk density measurements were

taken at the beginning and end of the process.

50

A different method had to be used for the windrow WTL,
which was turned with the tractor loader. Using a
pitchfork, the material from the windrow was dumped into
the pan. An up swing motion with the pitchfork and then a
quick release from under the material was used to mimic the
action of the loader, as it would dump the material into a
windrow. The material would dump into the pan and this
would be repeated until the material was at a height equal
to the windrow over the pan. After the windrow was formed
on top of the pan it was carefully removed and the compost
was leveled off to the top of the pan. It was weighed and
corrected for moisture. Lynch and Cherry (1996) used a
similar method to figure bulk density with loader turned

windrows.

4.11 Windrow Sampling Technique

Samples for laboratory analysis were taken from the
windrows at various times throughout the process. The
sampling technique consisted of taking samples by hand at
various depths from the surface of the windrow at ten
locations down each side of the windrow and ten from the
top middle. Hand sampling was used because the straw

particles could then be extracted along with the manure in

51

wi

Q»

-ru

La

06

a!

a consistent manner each time a sample was taken. When
applicable this was performed after a turning. These 30
samples were then mixed together and a subsample was taken.
This was repeated three times to get 3 subsamples from each
windrow. Lopez-Real and Baptista (1996) adopted similar

sampling methods of cattle manure mixed with straw.

Samples were sent to the Research-Extension Analytical
Laboratory at the Ohio Agricultural Research and
Development Center, Ohio State University. The samples were
analyzed for pH, Nitrate-N, TKN, Ammonia-N, C/N ratios and

total carbon.

4.12 Germination Test

Germination tests were performed using watercress seed
(Mathur et al. 1986) in finished compost. Germination in
distilled water and commercial topsoil was used for a
comparison. A 20ml compost, water or topsoil sample was
placed in a 60ml petri dish. A Whatman #42 filter disk was
then placed on top of the sample. Distilled water was added
until a film of water formed on top of the filter paper.
Twenty seeds were than added to the petri dish. The petri

dishes were covered and placed in a dark room at 20°C for

52

96 hours. The numbers of seeds germinated were counted and
a percent germination value was calculated. Five

replications for each windrow were completed.

4.13 Sieve Analysis

A sieve analysis was performed to determine particle size
distribution at the end of the process using an
approximately 100-gram sample of finished compost. The
compost sample was placed onto the sieve with a catch pan
underneath. The sieve was shaken with a back and fourth
action for a specific amount of time for each sieve size
starting with the largest sieve opening and successively
moving to a smaller sieve opening. The shake times were
determined from prior experience to eliminate excess
shaking and particle deterioration for each sieve size. To
keep the particles from breaking apart no vertical motion
was used. The sieves size and shake times used are listed

in Table 4.1.

53

Table 4.2 : Sieve size and shake times. A # indicates the standard U.S. Sieve number.

 

 

 

 

 

 

 

 

 

 

 

Sieve Size Shake Time Sieve Siée Shake Time
(0.952cm) 158. # 12 (0 170cm) 505
(0.792cm) 15s. # 14 (0.140cm) 60s

it 4 (0.475cm) 208. # l6 (0.118cm) 60s
# 6 (0.335cm) 30$. # 20 (0.085cm) 75$
#77 (0.280cm) 308. # 30 (0.060cm) 90s
$8 (0.236cm) 408. ii 50 (0.030cm) 1208

 

54

 

 

Chapter 5

Results and Discussion

5.1 Windrow Turning

Windrows managed by carbon dioxide were turned the most
often. Windrow CDA was turned 24 times while windrow CDL
was turned 20 times. Both the WTL and WCT windrows were
turned 12 times. The temperature—managed windrow was turned

the least with 11 turnings. The TMP windrow was turned
frequently early in the process but it cooled to below 65° C
after day 26 due to increased wind speeds at the composting

site and never reheated enough to reach the turning

temperature threshold.

As the windrows were turned repeatedly the substrates of
the windrows became homogenous as the composting process
progressed. Windrows CDL and CDA were turned more often
which relocated a higher percentage of the substrates into

the active composting areas of the windrows.

The TMP windrow was turned with sufficient frequency early

in the process. However, once the temperature of the

55

windrow declined below the preset turning level of 65° C
the windrow did not receive another turning. Since the
windrow was not turned after day 26 the TMP windrow had the
highest carbon and C/N ratio levels at the end of the

monitoring process.

Michel et a1 (1996) concluded turning frequency has little
effect on windrow temperatures, however, the lack of
turning after day 26 for windrow TMP shows that turning can
provide greater substrate utilization and sustain higher

temperature levels longer into the process.

5.2 Windrow Temperature

Figure 5.1 gives the mean of the temperatures taken along
the windrow through the sampling period for all the
windrows. Temperatures in all the windrows reached

thermophilic levels within three days. Each windrow
achieved a temperature of at least 65° C. Windrows WCT, CDL,

and TMP achieved 65° C on day four, windrow CDA on day eight
and windrow WTL day 12. Temperatures were similar in all

the windrows until day 38.

56

Temperatures within TMP started to decline at day 29 and by
day 38 had declined enough to separate itself from the

other windrow temperature measurements. Windrow WCT

temperatures abruptly declined from a value of 58° C on day

47 to 27° C on day 50 and steadily declined to ambient as

the days progressed.

Temperatures within windrows CDA and CDL, which were turned
according to carbon dioxide levels, closely resembled each
other until day 49 when windrow CDL temperatures started to

decline more rapidly.

Weekly turned windrows resulted in the most variable
temperatures with temperatures staying at higher levels
longer into the process. Temperatures would peak after
turning and would then decline through the week until the
next turning. Temperatures in Windrow WTL, which was
turned with a tractor loader, declined the slowest and had

not reached ambient by day 78.

57

 

 

L L—o— CDA +wcr +WTL +cof 33126

 

80a.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I IL . l ‘ ' l 1 "
IL LLI'L'IILLL
701 LLL LL LLLaLL11
W? ITILI'
so. A . iLLL1I+
*‘ LI ll 9’1) ,LILH.
504 L; L ‘ JLILL
L ‘ L I 1 I;
3 IL 1 L L LR u L LI
940 . -L
8 [TL LL [\A\ILLL
30 (ILLI LJ ‘ L‘LLLLL
'LLLLL 7. L ‘1\ \IL
zoLILLLaLM la 1 La all
LLLill 71L Lama‘s
|10L.LLLLLL_LI LILLL L. “
LLLLWLLJLIL L L,
LOLLLL.LLLLLLaLLLLLLL LL LLLLL
5

81012151719222426293138384043454750525759618471737578
L DaysintoProcess

Figure 5.1: Mean Temperature Values for all the Windrows.

Temperatures in all the windrows stayed above 60° C for the
first three weeks of the process providing enough time to
kill unwanted weed seeds and pathogens. From day 10 through
day 17 all the windrows had temperatures above 65° C

providing for a sanitized product as described by Strauch

(1987).

The weekly turned windrows WCT and WTL had more pronounced
peaks and valleys in their temperature profiles when
compared to windrows TMP, CDA and CDL. This may be

attributed to thermal inactivation of microbes, which

58

————.————___.A ! A M-gi .vi-Afi

ail

according to Haug (1980) can be reduced by more frequent
turnings of the windrow. The more consistent temperatures
in windrows TMP, CDL and CDA may be attributable to this
effect. Equation 3.6 describes the relationship between
turnings and thermal inactivation. No organism counts were
taken to determine whether organism populations in the

windrows followed the thermal inactivation curve.

The TMP windrow cooled earlier in the process due to a lack
of turning after day 26. It can be concluded that without
additional turnings after day 26 there was less substrate
utilization in the outer regions of the windrow as compared
to the other windrows. As a result the TMP windrow had the
lowest carbon reduction percentage. A windrow management
scheme that contributes to a minimum number of turns over a
period of time would have resulted in better substrate
utilization. The TMP temperature profile would have been
expected to more closely follow the other windrows in the
latter stages of the composting process if a minimum number

of turns was defined.

Figure 5.1 shows temperature differences in management

schemes became more apparent after temperatures declined to

less than 60° C. There were no apparent differences in the

59

temperature profiles between the windrow CDA and CDL. The
addition of a high clay soil did not seem to affect

temperature.

5.3 Windrow Carbon Dioxide

Figure 5.2 shows that each windrow had reached a twenty-

percent carbon dioxide level by day three. The measurements

were at or near twenty percent in all windrows until day 22

 

when they all decreased followed by a rebound on day 26 and -,
then a greater decrease on day 29. Measurements of carbon

dioxide on day 29 were significantly lower than on day 26

in all windrows. After day 29 there were significant

variations between windrows.

Figure 5.3 shows from day 22 until day 64 Windrows WCT and
WTL, which were turned weekly, had higher carbon dioxide
levels following a turning of the windrow and then declined
until the windrow was turned again. Windrow TMP had carbon
dioxide levels above fifteen percent until day 29 and

stayed at ten or below after day 31.

The carbon dioxide measurements for Windrows CDA and CDL

closely followed each other until day 52. After day 52

6O

until

day 59 windrow CDA stayed above ten percent while

windrow CDL stayed below five percent. After day 59 both

windrows CDA and CDL were below five percent.

25

20<

15

SEClflMuIDknflde

Figure 5.3: Changes in windrow carbon dioxide levels for the weekly turned windrows. Arrows

 

L—o—CDA +yvcr +wn “529}- +1.43:

 

 

id

1
-___
—_‘fi
1
-fi

 

 

YT'LT- L . T 1".L
. I‘LL .'

1 LL I ll ILL!
L LI LL IL LLlL
L.L. LILLL‘LLLLL'LIL
LIL_;'ELL_ ll;

‘1 LL"? l‘if

 

 

 

 

p_

 

 

 

 

 

 

A
/
:3:

 

 

Lie
\\ {\va

 

 

 

 

 

 

 

 

 

 

ll! 1L .
:L i. !~ ;
ILLLLLLLI. Up
I. TLQ A\ ;.L
'LL'LILIIL LL»
LLgLLL.L LL
1 L1 _._.._=.. -._i __ "L— L L . L L A L l L . -
l L L 1 L l L L
I. . L .i . LL L L a K; ’K \:
LI.I.L:L.LL..L>

 

 

1 3 4 5 8 10 12 16 17 19 22 24 26 29 31 36 38 40 43 46 47 60 62 67 68 61 64 71 73 76 78
Figure 5.2: Changes in windrow carbon dioxide levels during composting.

:91“! 5 L 7*- w_ LEI

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

LVLLLLL-LLL LLLL ' L L LL LL
.. LL LL LJLL 'LLL . '9
WW! II 1:
LI LLILL I. H W

 

 

 

 

 

 

  

 

 

 

 

1 3 4 5 I 10 12 15 I7 19 22 24 2C 2. 31 3| 3| 4O 43 45 47 5° 52 57 5. .1 I4 71 71 7S 7.

indicate a turning event.

61

 

"rt‘rru-aluxnip
h

 

Carbon dioxide levels quickly reached the 20% level in all
the windrows indicating rapid microbial growth and carbon
degradation resulting in high levels of carbon dioxide
evolution. After day 26 Figure 5.2 shows a sharp decrease
in carbon dioxide levels. This decrease is a result of high
winds at the composting site, which increased the
convection currents and caused more air movement through

the pile reducing carbon dioxide levels.

Figure 5.2 shows windrows WCT and WTL had more pronounced
variations in carbon dioxide content than the other
windrows. The carbon dioxide levels of the weekly turned
windrows increased after the windrows were turned and
slowly declined until the next turning (Figure 5.3). This
rise and fall trend can be seen in the other windrows but
not with as much amplitude. Michel et al (1996) reports
similar results of rising oxygen concentrations after

turning with a decline in the concentrations within hours.

Figure 5.3 also shows a difference in carbon dioxide levels
between turning weekly with a loader and weekly with a
compost turner. There was more carbon dioxide content

variation with the loader turned windrow. Carbon dioxide

62

1|

Q;

A!

levels in WCT declined to fewer than 5% approximately ten
days before those of WTL. Visually, the windrow WTL had
clumps of substrate and larger particle sizes when compared
to WCT. Therefore, later in the composting process the
tractor loader turned windrow was still degrading readily
available carbon sources that a compost turner would have
exposed to areas of increased microbial degradation earlier

in the process.

Figure 5.2 shows that the TMP windrow carbon dioxide levels
did not rise above 13% after the winds between days 26 and
29. This resulted from either better rates of aeration or
decreased microbial activity. Since other windrows showed
increased carbon dioxide levels after the winds subsided it
can be concluded there was a decrease in microbial

activity.

5.4 Windrow Moisture Content

Windrow moisture content data given as % wet basis are
presented in Figure 5.4. Samples taken at the beginning of
the composting process showed initial moisture contents
ranging from 64-70%. Windrow CDA had the lowest moisture

content at 64% and windrows CDL and TMP had the highest at

63

70%. Ending moisture contents ranged from 46% to 54%.
Windrow CDA had the lowest moisture content while the other

four windrows were between 50 and 54%.

Windrow CDA lost 39% of its initial water content during
the composting process. The other four windrows had
reductions of 29% for windrow WCT, 30% for CDL and 32% for

windrows WTL and TMP.

 

 

:9— CDA +WCT +WTL #x—CDL +LfiiPL

 

 

 

3 1O 22 29 38 45 57
Days Into Woo.“

Figure 5.4: Changes in windrow moisture content during composting.

Ending moisture content values were in the acceptable range
of 40% to 65% as given by Rynk (1993). The addition of a
high clay soil had a significant effect (P=0.025) on

windrow moisture level reduction. The lower moisture levels

for windrow CDA can be attributed to the addition of the
high clay soil that was dryer than the compost when added

to the windrow.

Using the Top Tex” cover controlled windrow moisture by
limiting evaporative moisture loss and also reduced the
amount of moisture soaking into the windrows during rain
and snow events. Generally, it would be expected that the
windrows would have had higher moisture losses during the
summer months due to higher ambient temperatures and less

likelihood of a rain event.

5.5 Windrow Cross Sectional Area

Windrow cross section change can be used as an indicator of
volumetric change as long as the windrow length remains
constant. The initial cross-sectional area measurements
ranged from 0.95n3 for windrow TMP to 1.05 n? for windrow
WTL (Figure 5.5). All windrow cross-sectional areas
decreased steadily during composting. Final measurements
indicated the values decreased to 0.62 n? for windrow CDA,
0.51 a? for windrow WCT, 0.76 n? for windrow WTL, 0.59 m2

for windrow CDL and 0.62 a? for windrow TMP.

65

 

Windrow WTL had the lowest reduction percentage at 27.62%
during the composting process. Windrow WCT had the highest
reduction value of 46.88%. Windrows CDA, CDL, and TMP,
which were turned has needed using the compost turner, had
reductions of 30.0%, 38.74% and 38.54% in cross-sectional

area .

L_+L LCEA—+—~W_C:r—b+_WTL :x: CDL +_ “7MP L
1.20 Y s L W

 

 

 

 

1.00 .c —— .__- . 7_____. ' _.__+_

 

0.80

 

 

"h 0.60 L

 

0.40 L

 

0.20 L

 

 

 

 

0.00

 

3 1 7 38 45 79
Days Into Process

Figure 5.5: Changes in windrow cross sectional area during composting.

Cross Sectional area measurements decreased as the
composting process progressed, as expected. Differences in
turning mechanisms became quite evident after investigating

the physical properties of windrow composting.

The compost turner produced smaller particles with better

uniformity. The loader turned windrow had much larger

66

clumps of substrate and did not condense in size has
readily as the other windrows. The WTL had the smallest
reduction in cross sectional area as a result of the
tractor loader’s inability to break down the clumps of
substrate into more readily degradable particles like those

produced by the compost turner.

Another factor that caused a smaller cross sectional area
reduction in WTL was that is was easier to keep the length
of the windrow from increasing using the loader. The
rotating drum action of the compost turner had a tendency
to increase the length of the windrow, thereby, reducing

the height.

The WCT windrow had the largest reduction in cross
sectional area. This may be explained by a combination of
compaction and mass degradation. The windrow was only
turned on a weekly basis and had more time to settle and
compact before a measurement was taken. This settling is
evident early in the process because the weekly turned
windrows WTL and WCT had steeper reduction lines than the
other windrows which were turned more often during the

initial two weeks of monitoring.

67

5.6 Bulk Density

The initial dry bulk density values were highest in windrow
CDA at 224 kg/m3. The other windrows had values ranging from
156 kg/m3 for windrow TMP to 170 kg/m3 for windrow WCT
(Figure 5.6). All windrows increased in dry bulk density

values from the initial to final measurements.

Windrows WCT and TMP had an 8% increase in bulk density.
Windrow CDL increased 11% while windrow CDA increased 15%.
Windrow WTL had the largest increase with a 75% increase in

bulk density.

.mmu .Flnal

 

 

 

 

 

Figure 5.6: Windrow bulk density (dry) measurements at the beginning and end of the compost
process.

There were no bulk density measurement techniques reported

in the literature that could be utilized and adapted to an

68

open windrow method of composting. Previously bulk density
measurements have been taken either by core sampling
(Tietjen and Banse 1961) or were taken by simulating
compaction by packing a graduated cylinder with compost and
dropping it from a known height with repeating action
(Jackson and Line (1997). Neither of these techniques are
sufficient in comparing the effects of using different

turning mechanisms.

As expected, the windrow with the addition of a high clay
soil initially had the highest level of bulk density. Bulk
density increased in all the windrows with WCT and TMP
increasing 8% while CDL and CDA increased 11% and 15%. The
WTL windrow had an increase of 75% in bulk density. This
large increase is not normal when compared to the other

windrows.

Measurement methods were different for a loader turned
windrow then a windrow using a compost turner and the
results may not be comparable. A factor to consider is that
the loader dropped larger particle sizes and increased

compaction into the catch container upon impact.

69

Th

CC

Mi

ir

The likely reason for the outlying value is some of the
composting pad made from gravel had been mixed into the
compost windrow during turning with the tractor loader.
Michel et a1 (1996) had similar problems with rocks

introduced into compost samples from the turning mechanism.

If the final density measurement of WTL was not skewed due
to debris in the density sample then it could be assumed
the free air space of the windrow was quite small and there
that would have caused a significant difference in moisture
reduction from the other windrows. This did not seem to be
the case. Therefore, it can be concluded the bulk density

value was skewed by debris.

5.7 Windrow Total Dry Mass Change

Figure 5.7 shows mass reductions for the windrows turned
with a compost turner ranged from 44.8% for CDA to 45.9%
for TMP. Windrows WCT and CDL had reductions of 45.7% and

45.8% respectively. WTL had an increase in mass of 23.4%.

The increase in mass by the WTL windrow was a result of the
increased final dry bulk density measurement of the

windrow. The total mass was figured by multiplying the

70

volume of the windrow by the bulk density. The skewed bulk
density value lead to a skewed total mass value.

LIInitlal .FlnalL

, \,

Total Windrow Dry m Kn

 

Figure 5.7: Total dry mass change during composting.

5.8 Chemical Tests

Sample variances in the chemical property results from
within the same windrows were relatively high. Three sub—
samples per windrow may not be enough to accurately
characterize the material. The sub-samples were acquired
from extensive sampling, however the amount of material

that is used for the chemical tests does not always

71

an:

meL

All

to

7T1

COI‘

represent actual results of the windrow. The composting
process is too dynamic for a full understanding from small

quantities of materials used for the testing.

5.8.1 Windrow Carbon Content

The initial carbon contents of the windrows varied from
22.7% for windrow CDA to 37.9% for windrow TMP. Windrows
WCT, WTL and CDL had starting carbon contents of 34.9%,
28.4% and 35.3% (Figure 5.8). Carbon contents for each
windrow declined at each measurement with the exception of
measurements taken on day 40 during which windrows CDA, WTL
and CDL had slightly increasing values over the prior

measurements.

All the windrows showed a reduction from the initial values
to the ending measurements. Weekly turned windrows WCT and
WTL had carbon content reductions of 46% and 48% during the
composting process. Windrow CDL had a 35% reduction while

windrow CDA and TMP had reduction values of 22% and 18%.

72

:CD'A :i—WCT :WfL Se CDL'TiTh/IlD—L

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.0 L

 

Figure 5.8: Changes in windrow carbon percentage during composting.

Carbon data showed considerable variations between
windrows. This may be explained by the difficulty in
getting a representative sample of the windrow in the early
stages off the process due to the nature of the manure and
straw mix. The sample size of 1 to 2 grams used by the lab

may not represent the kilogram sub-sample taken in the

 

field and an extra particle off sand or straw in the lab

sample could hinder the results.

73

Windrow carbon reductions were greater during the final 40
days when comparing the mean reduction values for all the
windrows. The mean carbon reductions during the initial 40
days were 10% while the final carbon reductions for the
last 40 days was 25%. This may be explained by the

temperature data presented in Figure 5.1.

During the initial 40 days the windrow temperatures were
almost exclusively above 60° C. Wiley (1958), Snell (1960)
and Finstein (1980) describe the optimal temperature range
for maximum decomposition to be from 45° C to 55° C,
depending on the author. After the windrow temperatures
decreased below the 55° C it would be expected that more

carbon is decomposed, which corresponds to the temperature

range after day 40 in the data presented here.

The C/N ratios decreased more rapidly during the initial
stages of the composting process while the carbon
percentages decreased more rapidly during the final 40 days
of the process. This indicates nitrogen retention occurred

more prevalently during the early stages.

74

 

5.8.2 Windrow Nitrogen Content (TKN)

Windrow nitrogen content is expressed on a % dry matter
basis, measured by the Total Kjehdal test. This test
includes nitrogen in the organic and ammonia forms but does
not include nitrate. The initial nitrogen content values
ranged from 0.84% for CDA to 1.34% for windrow WCT.
Windrows WTL, CDL and TMP had values of 0.93%, 1.15%, and
1.23% (Figure 5.9). The percent TKN increased through the
first three measurements for all the windrows as the dry
matter decreased. The last measurements, which were taken
on December 81, showed a decrease in percent TKN from the
previous values taken on day 40 for all the windrows with

the exception of, windrow CDA.

Windrows CDA and CDL, which were turned according to the
carbon dioxide level, increased in percent TKN by 48% and
52%. Windrows WTL and TMP increased by 31% and 33% while

windrow WCT had only an increase of 10%.

75

ZXP Jr

Q»

 

[+CDA +WCT +WTL _)(_CDL +TM‘PT

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0,8

 

4»— L——<>— — L «r— -

0.8

 

0.4

 

96 TKN
—<+———— 1L ._._ LL- i . 14

0,2

 

 

 

 

 

Figure 5.9: Changes in percent of Total Keldajl Nitrogen (TKN) in the compost windrows.

Figure 5.10 shows that except for windrow WTL, there was an
overall reduction in the mass of nitrogen per windrow based
on the TKN method from the start of the process to the end.
Since the bulk density for the WTL windrow was quite high,
the calculations for the mass of the windrow gave an
increased value of dry mass; therefore, the percent of TKN
nitrogen was skewed high. The nitrogen value for the WTL
windrow would have approached that of the WCT windrow if

the bulk density measurements were similar.

76

Initial I Final

 

 

 

Total Wlndrow Dry Mass (Kg)

 

 

 

Figure 5.10: Windrow Dry Mass Nitrogen Totals based on % TKN

Hansen et a1 (1989) used the Taguchi method of data
analysis on eight controllable composting factors and
concluded that stirring frequency impacts nitrogen
retention during the bench scale composting of poultry
manure. Comparing the windrows turned with a compost turner
Table 5.1 suggests that increased turning frequency in the
early stages of composting resulted in less nitrogen loss
based on dry mass calculation of % TKN. The CDL, CDA and
TMP windrows required a greater number of turns in the

early stages of the process when compared to WCT.

77

Table 5.1: Comparison of windrow turns and % TKN nitrogen loss on a dry mass basis.

 

 

 

 

 

 

Treatment # of’Turns Nitrogen Loss
CDL 20 17.5%
CDA 24 18.5%
TMP 11 27.9%
WCT 12 40.0%

 

 

 

Nitrate nitrogen could not be added to the dry mass
equations because the lab conducted the tests on a
saturated extract basis with no way to correlate the

results into a mass balance equation.

5.8.3 C/N Ratio

C/N ratio data is presented in Figure 5.11. At the start of
the composting process the C/N ratios ranged from a value
of 26.7 for windrow WCT to 31.0 for windrow TMP. The
initial C/N ratios for all the windrows are generally
within the range recommended for starting windrows

subjected to intensive management.

Windrows WCT, WTL, and CDL had a final C/N ratio value at

or near 13.0 and these windrows had similar C/N ratio

reduction from 52% for windrow WCT to 57% and 58% for

78

 

windrows WTL and CDL respectively. Windrow CDA had an
ending value of 15 with a C/N ratio reduction of 44%.
Windrow TMP had the highest ending value of 19.7, which
corresponded to the lowest reduction in the C/N ratio of

37%.

_:CDAL:'WTT +WTL *CDL :T—MF‘

 

 

 

30.0 .—

 

 

 

 

 

 

 

 

20.0 41—

15.0

 

CINRIflo

10.0 L»— ——~

 

5.0

 

 

 

0.0

 

 

Days Into Process

Figure 5.11: Changes in windrow C/N ratios during composting.

The initial C/N ratios for all the windrows were within the
Optimal range and were not significantly different (a=0.05)
which indicates the ratio of manure and straw were equal
between the windrows. The final C/N ratios also were not

significantly different between the windrows.

79

o varn— a". .._nmv-.'
i

l—K-x‘. -r‘ml.‘ 0‘

The C/N ratios are the result of dividing the TKN values

into the total carbon values. C/N ratio reductions were

highest during the first two weeks of the composting

process except for the WCT windrow. This rapid reduction

indicates there is rapid biodegradation of carbon

occurring, however, increasing nitrogen values were as

important as the reduction in carbon values. For example, L5
the WCT windrow had a C/N ratio reduction of 15% during the

first two weeks but the carbon reduction was only 2% during

the same time frame.

The TMP windrow had the highest ending C/N ratio and the
lowest overall C/N ratio reduction. The low reduction is a

result from the windrow not being mixed after the windrow
temperature decreased below 65° C. If the windrow would

have been turned after the temperature fell below 65° C the

C/N ratio would have more closely matched the other

windrows.

C/N ratio reductions ranged from 37% for TMP to 58% for
CDL. These values correspond to values Lopez—Real and
Baptisa (1996) found of 52% to 59% reduction during the

composting of dairy manure and straw.

8O

 

pH values for the windrows were initially measured at 8.4
for windrow CDA, 8.6 for windrow WCT, 8.7 for windrow WTL,
8.4 for windrow CDL and 8.7 for windrow TMP (Figure 5.12).
Fourteen days after the initial measurements were taken all
the windrows except windrow CDA showed a decrease in the pH
value. At the time of the third measurement on day 40
windrows WCT, WTL and CDL showed an increase in pH while
windrow TMP stayed the same. Windrow CDA had a decrease in

pH during this same time.

 

L+CDA +WCT +WTL +CDL +TM5J‘.

 

8.8

L L
8.6 . W_X.XL‘

; //,r;f¢!’L “\‘ . n
L
L
L
L
L

 

 

 

 

 

 

8.2

 

 

pH

.
L

L
7.8 L _

L

7.6 L L
3 17 40 81
Days Into Process

8.0 LV ‘ -1

 

 

 

 

 

Figure 5.12: Changes to windrow pH during composting.

Final pH values taken on day 81 showed that all the
windrows had decreased in pH from the initial value to the
final values. Windrow CDA had a final pH of 8.2 while
windrows WCT, WTL, CDL, and TMP had pH values of 8.1, 8.0,

8.4 and 8.5.

The pH mean values stayed close to the optimal range of 7.5
to 8.5 for maximum thermophilic composting as described by
Jeris and Regan (1973). Each windrow had a decrease in pH
by the end of the process with increased reduction

occurring in the final 40 days of the process.

A decreasing pH indicates a production of organic acids
(Miller et a1 1991). The production of organic acids
results from the humification of the compost. During the
last 40 days there was a decrease in the pH values
resulting from the build up of humus and indicates the

compost became more stable.

The CDA windrow was the only windrow to have an increasing
pH during the first two weeks of composting. A rise in pH
could indicate ammonification, however, the pH only
increased 0.1. Therefore, and it can not be said that the

increase in pH is a definite result of ammonification. The

82

 

addition of the clay soil may have caused the difference in
pH but there are too many other factors at work to make a

definite conclusion.

5.9 Germination Tests

Table 5.2 gives the results of the cress seed germination

test. Distilled water was used as the control. Windrow WTL

L‘. b. ‘L:“ 3- KM:

had the lowest germination at 56% of the control. Windrows

J a- V

CDL and TMP had germination values of 75% of control while

 

ig’..§!fo ‘.'.
1

windrows CDA and WCT had values of 89% and 84%

respectively.

Table 5.2: Cress Seed Germination as a '/o of Control

 

 

 

 

 

 

 

Sample % of Control
Windrow CDA 89
Windrow WCT 84
Windrow WTL 56
Windrow CDL 75
Windrow TMP 75
Bagged Top Soil 66

 

 

 

 

 

 

83

The germination test using sensitive watercress seeds is a
measure of the phytotoxicity of the composts. The WTL
windrow was the only windrow below the germination
percentage of the bagged topsoil. The low germination
percentage of the WTL windrow can not be explained from the
chemical tests. The WTL windrow had the nearest neutral pH
of all the windrows and the C/N ratio was not out of range
from the other windrows, which had greater germination

percentages.

The large clumps of substrate in the WTL windrow could
cause poor germination. The clumps of substrate were not
completely composted and could hinder germination of the
watercress seeds. Additional tests would need to be
performed to describe further the difference in

phytotoxictity levels between the windrows.

5.10 Sieve Analysis

Cured compost samples were passed through a series of
sieves with the percent rejections by weight of particles
given in Figure 5.13. The WTL windrow had 20% rejects by
weight at the 9.5mm sieve opening while the other windrows

were fewer than 2%. The WTL windrow had 50% rejection at

84

 

1.7mm while the other four windrows reached the 50%
rejection level between 0.85mm and 0.60mm. Using a compost
turner gave similar results of particle size rejection

regardless of the windrow management scheme.

 

E’CD‘A'1‘WCT 1...-WTL -.,..'CDL ,1ij

mo

 

 

 

 

L
L
L

 

 

  
  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

L
1
L

*1

9.5mm 8mm 4.75mm 3.35mm 2.8mm 2.36mm 1.7mm 1.4mm 1.18mm 0.85mm 0.6mm 0.3mm
Sleve Openhg

00

Figure 5.13: Percent Rejects from Sieving Cured Compost. Values are means of two
samples per windrow.

The sieve analysis shows a distinct difference between
managing a compost windrow with a compost turner and a
tractor loader. The compost turner produced similar
particle sizes regardless of whether the windrow was turned

weekly or by temperature and carbon dioxide levels.

85

 

Even though the WTL windrow had greater percentages of
larger particles, the compost would have been sufficient
for a farm application however it may not have been
suitable for use in a greenhouse or nursery container

media.

The compost turner produced compost with suitable particle
size for most applications. A compost turner is necessary

if a consistent compost product is desirable.

5.11 Data Summary

Table 5.3 presents a summary of the results taken from the
data presented. Values given have been rounded to the
nearest whole number for ease in presentation. The
asterisks in the WTL data indicate a different bulk density
measurement method was used for the windrow, which affected

the noted values.

86

 

 

Table 5.3: Data Summary

 

 

 

 

 

 

 

 

 

 

('1'

 

 

 

CDA WCT WTL CDL TMP
Number of turns based 24 12 12 20 11
on treatment indicator
Moisture Reduction 39% 29% 32% 30% 32%
Cross SectiOnal Area 30% 47% 27%' .39% 35%
Reduction
Bulk Density Change +15% +8% *+75% +41%' +8%
Total Dry Mass Change -45% -46% *+23% -46% -45%
% Carbon Reduction 22% 46% 48%' .35% 18%
Nitrogen change based -19% -40% *+62% -18% -28%
on % TKN of Dry Mass
C/N Ratio Reduction 44% 52% 58% 58% 37%
Watercress seed 89% 84% 56% 75% 75%
germination in finished
compost
(% of Distilled Water,
used as control)
50 % Rejection Level of 0.83 0.87 2.03 0.81 0.85

Particle Size in
millimeters

 

 

 

 

 

 

 

* May not be directly comparable because it is based on a

different bulk density measurement technique.

87

7..”

 

 

Chapter 6

Conclusions

Dairy manure amended with straw can be successfully
composted on a farm scale using various methods of

management.

The addition of a high clay content soil showed a
benefit in the germination study and also, based on
carbon dioxide evolution and temperature levels in the
latter stages of the process, kept the composting

process more active.

Using carbon dioxide levels of 10% compared to using 65°
C as the temperature threshold to initiate the turning
of dairy manure compost windrows maintained higher
temperature and carbon dioxide levels over a longer
period of time and produced a product with greater

nitrogen retention and lower phytotoxicity.

A compost turner produces smaller more uniform particle

size and greater mass reduction of the windrow.

88

 

 

Regular turning of the compost windrows produced the
best end product. Turning based on carbon dioxide

produced the greatest nitrogen retention.

Using carbon dioxide as an indicator to time windrow

turnings while having a minimum number of turns in a

given time period is optimal.

89

 

Chapter 7

Further Research

A standard method to measure bulk density in compost

windrows needs to be developed.

An optimal composting method needs to be developed to

maximize nitrogen retention in animal manure composting.

Further research is needed to quantify variations in
compost windrow sampling in relation to test lab methods

so that a representative sample can be achieved.

Additional research using a high clay content amendment
to dairy manure compost needs to be examined further to

validate the beneficial results shown in this research.

Finding an optimum number of turns based on substrate

utilization for a given time period during windrow

composting dairy manure is needed.

90

Literature Cited

91

 

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MICHIGAN S

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312