: s. a?! 7“” I .. .,|L... .1 ,. a .65 1.2-3 t a. i.-. n- {N “I; “a?" . i V . ”an... .HmLLn. ( ‘ THESIS ' .7 L. [I 4'36) 3 1293 01410 llllllllllllllllm This is to certify that the thesis entitled EVALUATION OF LIQUID/SOLID SEPARATION TECHNIQUES APPLIED T0 SAND-LADEN DAIRY MANURE presented by Andrew Walter Nedel has been accepted towards fulfillment of the requirements for M.S. Ag. Enq. degree in ZZZ/‘Jgg Major professor 0-7639 MS U i: an Affirmative Action/Equal Opportunity Institution LIBRARY Michigan State University PLACE ll RETURN BOX to move this checkout from your record. TO AVOID FINES rotum on or More dot. duo. DATE DUE DATE DUE DATE Dug MSU in An Affirmative Action/Equal Opporumity Instituion W EVALUATION OF LIQUID/SOLID SEPARATION TECHNIQUES APPLIED TO SAND-LADEN DAIRY MANURE By Andrew Walter Wedel A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Agricultural Engineering 1995 ABSTRACT EVALUATION OF LIQUID/SOLID SEPARATION TECHNIQUES APPLIED TO SAND—LADEN DAIRY MAN URE By Andrew Walter Wedel Sand is the bedding material of choice for dairy freestall barns. Although sand possesses many favorable characteristics from a cow health standpoint, it is incompatible with long-term manure storage systems. Separating sand bedding prior to long-term storage would allow the use of conventional manure handling and disposal systems such as irrigation, tanker spreading, and sub-surface injection. An assortment of liquid/solid separation techniques common to wastewater treatment operations as well as the dairy, mining, and petroleum refining industries were applied to sand-laden dairy manure. Separation techniques considered include: i) screening, ii) sedimentation, iii) the hydrocyclone, iv) dissolved air flotation, and v) the belt filter press with polymer conditioning. A sand separator, the batch aerated grit chamber (BAGC), was developed based on the separation techniques previously considered. The BAGC is capable of yielding a dilute manure fraction that can be pumped, stored, and land applied via conventional manure handling techniques, as well as a sand fraction clean enough that it may be reused as bedding. Cepyright by Andrew Walter Wedel 1 995 To my beloved family...Mother, Dad, Kandice, and Kenny. iv ACKNOWLEDGMENTS The date was 30 January 1991. I was studying for a Physics H final exam and faced with a decision; either spend the entire evening studying physics or attend the Cecil County Dairy Night at the Calvert Grange Hall, Calvert, MD, at which I was told the nation's leading expert on dairy facilities from the MSU Department of Agricultural Engineering would be addressing a group of dairy farmers. I opted to forgo studying and attend Dairy Night. Not even in my wildest dreams could I have imagined that such a seemingly inconsequential decision would have a profound impact upon my future, for the speaker that night was Dr. William G. Bickert, my future Major Professor. Thank you Dr. Bickert for granting me the opportunity to study under your guidance. It has been a challenging and truly rewarding experience. I would also like to thank the following individuals for serving on my guidance committee: Dr. Howard L. Person and Dr. James F. Steffe, MSU Department of Agricultural Engineering; and Dr. Blaine F. Severin, The Michigan Biotechnology Institute (MBI). I am very appreciative of Dr. Michael Allen, MSU Department of Animal Science, for allowing me access to his laboratory throughout this study as well as David Main and R. Dewey Longuski, for their technical laboratory assistance. Furthermore, assistance afforded to me by the following people proved invaluable: Dr. Dennis Welch and Richard Wolthuis, MSU Dept. of Agricultural Engineering Research Laboratory; George Atkeson, MSU Extension, Ionia County; Jean Steavens and Valerie Geyer, secretaries in the MSU Department of Agricultural Engineering. I would also like to thank my friends from the MSU Department of Agricultural Engineering and MBI. Their contributions, although oftentimes non-academic, have helped make graduate school an enjoyable experience. Last but certainly not least I would like to thank DeLynne Anne Vail for her incessant support throughout this study, especially during times when being completely absorbed in my research caused my research to become completely absorbed in me. Andrew Walter Wedel .TABLE OF CONTENTS LIST OF TABLES - - - - -- - - x LIST OF FIGURES - -- - -- ......... xii 1.1: Scope of the Industry ........................................................................... l 1.2: Statement of the Problem .................................................................... 1 1.2.1: Purpose of Bedding ............................................................... 1 1.2.2: Advantages of Using Sand Bedding ...................................... 1 1.2.3: Disadvantages of Using Sand Bedding .................................. 2 1.3: Approach to the Problem--Sand Separation ......................................... 2 1.4: Objectives ........................................................................................... 3 1.5: Organization of the Thesis .................................................................. 3 2. LITERATURE REVIEW -- -5 2.1: General Comments ............................................................................. 5 2.2: Screening ............................................................................................ 5 2.2.1: Stationary Screens ................................................................. 5 2.2.2: Vibrating Screens .................................................................. 7 2.3: Sedimentation ..................................................................................... 8 2.3.1: Continuous Flow Aerated Grit Chamber (CAGC) .................. 9 2.3.2: Sedimentation Basins and Aprons ....................................... 13 2.4: Hydrocyclones .................................................................................. 15 2.5: Dissolved Air Flotation (DAF) .......................................................... 16 2.6: Belt Filter Press (BFP) With Polymer Conditioning .......................... 18 2.7: Aeration ............................................................................................ 20 2.7.1: Aeration Applications ......................................................... 20 2.7.1.1: Mining Industry ..................................................... 20 2.7.1.2: Petroleum Refineries ............................................. 23 2.7.2: Aeration Modeling ............................................................... 24 2.7.2.1: Mixing intensity ..................................................... 24 2.7.2.2: Power Dissipation ................................................. 25 2.7.2.3: Agitation Time ...................................................... 25 2.7.2.4: Pick-Up Velocity and Gas Bubble Dynamics ........ 26 vii 2.7.2.5: Summary of Aeration Tank Design Considerations ...................................................... 27 3. EXPERIMENTAL METHODS ................................................................... 28 3.1: General Comments ...................................................................................... 28 3.2: Standard Techniques and Procedures ........................................................... 28 3.2.1: Hot Weighing Samples .................................................................. 28 3.2.1.1: Materials .......................................................................... 29 3.2.1.2: Methodology .................................................................... 30 3.2.2: Dry Matter Content (TS) ................................................................ 30 3.2.2.1: Materials .......................................................................... 30 3.2.2.2: Methodology .................................................................... 30 3.2.3: Fixed Solids (FS) and Volatile Solids (VS) Content ....................... 31 3.2.3.1: Materials .......................................................................... 31 3.2.3.2: Methodology .................................................................... 31 3.2.4: Sand Content (8) ............................................................................ 31 3.2.4.1: Materials .......................................................................... 32 3.2.4.2: Methodology .................................................................... 32 3.2.5: Sand Particle Size Analyses ........................................................... 33 3.2.5.1: Materials .......................................................................... 33 3.2.5.2: Methodology .................................................................... 34 3.2.6: Manure Sampling ........................................................................... 35 3.2.6.1: Materials .......................................................................... 35 3.2.6.2: Methodology .................................................................... 35 3.2.7: Criteria for Acceptable Cleanliness of Bedding Sand .................... 36 3.3: Analysis of Sand Separation Systems ......................................................... 36 3.3.1: Sedimentation ................................................................................ 37 3.3.1.1: Type-3 Settling Analysis .................................................. 37 3.3.1.1a: Materials .............................................................. 37 3.3.1.1b: Methodology ....................................................... 37 3.3.1.2: Batch Settling Analysis .................................................... 40 3.3.1.2a: Materials .............................................................. 4O 3.3.1.2b: Methodology ....................................................... 41 3.3.2: Screening ....................................................................................... 42 3.3.2.1: Materials ............................................................... 42 3.3.2.2: Methodology ......................................................... 43 3.3.3: Hydrocyclone ................................................................................ 43 3.3.3.1: Materials .......................................................................... 43 3.3.3.2: Methodology .................................................................... 43 3.3.4: Dissolved Air Floatation (DAF) ..................................................... 43 3.3.4.1: Materials .......................................................................... 43 3.3.4.2: Methodology .................................................................... 44 viii 3.3.5: Dewatering System-Belt Filter Press With Polymer Conditioning ........................................................... 45 3.3.5.1: Materials .......................................................................... 45 3.3.5.2: Methodology .................................................................... 45 3.3.6: Batch Aerated Grit Chamber (BAGC) ............................................ 46 3.3.6.1: Materials: ......................................................................... 46 3.3.6.2: Methodology .................................................................... 46 4. RESULTS AND DISCUSSION -- - .............. - ...... 51 4.1: General Comments ...................................................................................... 51 4.2: Bedding Sand Usage Rates and Physical Characteristics ............................. 51 4.3: Determination of Recovery Quality Criteria ................................................ 55 4.4: Physical Characteristics of SLDM ............................................................... 55 4.4.1: Settling Behavior ........................................................................... 56 4.4.1.1: Type-3 Settling Analysis .................................................. 56 4.4.1.2: Batch Settling Analysis .................................................... 57 4.5: Existing Liquid/Solid Separation Systems .................................................... 58 4.5.1: Screening ....................................................................................... 58 4.5.2: Hydrocyclone ................................................................................ 65 4.5.3: Dissolved Air Floatation ................................................................ 66 4.5.4: Belt Filter Press With Polymer Preconditioning (BFP) ................... 67 4.5.5: Batch Aerated Grit Chamber (BAGC) ............................................ 69 4.5.5.1: Mixing Intensity (G) ........................................................ 70 4.5.5.2: Recovery Efiiciency and Recovery Quality ...................... 7l 5. SUMMARY AND CONCLUSIONS - - - -- --..--75 5.1: Summary ............................................... p ...................................................... 75 5.2: Conclusions ................................................................................................. 76 LIST OF REFERENCES -- -- - - ....... - ....... 78 APPENDIX _ _ _ _ -_ - ____________ 82 ix Table 2.1: 2.2: 3.1: 3.2: 3.3: 3.4: 3.5: 3.6: 4.1: 4.2: 4.3: 4.4: 4.5: 4.6: 4.7: 4.8: A1: LIST OF TABLES Page Types of Settling Phenomena in Wastewater Treatment ...................................... 1 1 Typical Aerated Grit Chamber Specifications ...................................................... 12 US Standard Sieve Series ................................................................................. 34 SandzManure Ratios (SzM) ................................................................................. 38 Quantities of Manure, Sand, and Water Required for Type-3 and Batch Settling Analyses .............................................................................. 40 Measurement Times ........................................................................................... 40 Quantities of Manure, Sand, and Water Required for BAGC Testing .................. 49 Experimental Design for BAGC Testing ............................................................. 50 VS (db) of Commonly Used Bedding Sands ....................................................... 54 Acceptable and Unacceptable Recovery Quality Ranges ..................................... 55 Sand Recovery Using Screening ......................................................................... 65 Analysis of Recovered Fractions from a Hydrocyclone Separator ....................... 66 Volume of Polymer Required to Achieve Coagulation ........................................ 67 The Effect of the BFP on TS .............................................................................. 68 The Effect of the BFP on VS (db) ...................................................................... 69 BAGC Power Input and Mixing Intensity ........................................................... 71 Sand Bedding Acceptability Survey .................................................................... 82 X A2: Sieve Analysis Comparison--Raw Manure and 2N8 Sand ................................... 83 A3: Sieve Analysis Comparison--Raw Manure and 2M8 Sand ................................... 83 A4: Sieve Analysis Comparison--Raw Manure and 3FS Sand .................................... 84 A5: SLDM Slurry Temperature ................................................................................. 85 A6: BAGC Data for Q=0 Umin ................................................................................ 86 A7: BAGC Data for Q=5 L/min ................................................................................ 87 A8: BAGC Data for Q=10 L/min .............................................................................. 88 A9: BAGC Data for Q=20 L/min .............................................................................. 89 A10: BAGC Data for 0:30 Umin .............................................................................. 90 xi Figure 2.1: 2.2: 2.3: 2.4: 2.5: 2.6: 2.7: 2.8: 2.9: 2.10: 2.11 2.12: 3.1: 3.2: 3.3: 3.4: 3.5: 3.6: LIST OF FIGURES Page Stationary Screen Schematic ................................................................................ 6 Vibrating Screen Schematic .................................................................................. 7 Force balance about a particle settling in a quiescent fluid ..................................... 9 Cross-sectional view of a continuous-flow aerated grit chamber ......................... 12 Sedimentation Basin ........................................................................................... 14 Sedimentation Apron .......................................................................................... 14 Hydrocyclone Schematic .................................................................................... 16 Dissolved Air Flotation System--Entire Flow Pressurization ............................... l7 Dissolved Air Flotation System--Recycled Flow Pressurization ........................... 17 Belt Filter Press Schematic ................................................................................. 19 Pachuca Tank Configurations ............................................................................. 22 Airlift Pump Schematic ....................................................................................... 23 Plexiglas Settling column .................................................................................... 39 Plexiglas Batch Settling Column With False Bottom ........................................... 41 Batch Settling Analysis Sampling Procedure .......................... 42 Experimental Dissolved Air Flotation Unit .......................................................... 44 Experimental BAGC Unit ................................................................................... 47 BAGC System Schematic ................................................................................... 48 xii 4.1: 4.2: 4.3: 4.4: 4.5: 4.6: 4.7: 4.8: 4.9: 4.10: 4.11: 4.12: Frequency Distribution of Sand Usage ................................................................ 52 Bedding Sand Particle Size Distribution .............................................................. 53 A Comparison of SLDM Height Ratios at Various Dilutions After 24 hrs of Static Settling ................................................................................................ 59 Type-3 Settling Analysis, DR=0.5:1 ................................................................... 60 Type-3 Settling Analysis, DR=1:1 ...................................................................... 60 Type-3 Settling Analysis, DR=2:1 ...................................................................... 61 Type-3 Settling Analysis, DR=3:1 ...................................................................... 61 Type-3 Settling Analysis, DR=5:1 ...................................................................... 62 Recovered Sand Concentration vs. Dilution Rate ................................................ 63 Bedding Sand and Raw Manure Particle Size Distributions ................................. 64 Recovery Efficiency vs. Air Flow Rate for Various Dilutions .............................. 72 Recovery Quality vs. Air Flow Rate for Various Dilutions .................................. 73 CHAPTER 1 INTRODUCTION 1.1: Scope of the Industry As of 1992, there were approximately 338,000 dairy cows in Michigan, a 5.3% decrease since 1988. In 1992, Michigan farms produced 2.5 million kg (5.4 million 1b) of milk, a 3.2% increase since 1988. Furthermore, in 1992, milk from Michigan farms accounted for 4.2% of the total US. milk production (Michigan Department of Agriculture (MDA), 1993). A byproduct of milk production is manure. The average 1,400 lb dairy cow produces 52 kg (115 lb) of manure per day (MWPS, 1985) or 18,980 kg (41,980 lb) per year. In terms of the 1992 average milk production per cow of 7,228 kg (15,920 lb) (MDA, 1993), approximately 2.6 mass parts of manure were produced per mass part of milk. L2: StaLtement of the Problem 1.2.1: Mose of Bedding Providing an environment conducive to milk production is an essential aspect of dairy herd management. Freestall barns serve this need very well. One aspect of freestall barn management is the implementation and maintenance of an efi‘ective freestall bedding material. There is a variety of bedding materials for dairy farmers to choose from including sand, chopped straw, saw dust, or wood shavings. The purpose of bedding is to keep cows free from urine, feces, dripped milk, as well as to act as a comfortable cushion. Hurnick (1981) states that comfortable resting stimulates rumination and thus feed intake, feed conversion efficiency, and milk yield. 2 1.2.2: Advantages of Using Sand Bedding In Michigan, it is estimated that sand is used as bedding in more than 50% of the freestall barns (W edel and Bickert, 1994). Sand is often considered the bedding of choice for freestalls due to a variety of reasons. Sand is an inorganic material that offers little or no nutrients for pathogens since it is not a carbon or nitrogen source (Britten, 1994). Furthermore, Bramley and Neave (1975) report that maintenance of low levels of coliform contamination (less than 106/gram bedding) in bedding is the only effective method of mastitis control. Stalls bedded with sand tend to stay drier than those bedded with organic bedding since liquids such as urine and milk are able to infiltrate through the sand (W edel and Bickert, 1994). Sand improves cow traction in free stall alleys due its abrasiveness (McFarland and Gamroth, 1994). Veterinarians Cox and Marion (1992) used a sand box stall to rehabilitate a cow unable to rise due to a leg injury. They reported that the sand remained free from urine, thus keeping the cow clean, and also provided sure footing while the recuperating cow was attempting to rise. 1.2.3: Disadvantages of Using Sand Bedding Although sand bedding is very conducive to cow health, it poses significant problems when used in conjunction with long-term manure handling systems. The addition of sand to manure has a negative impact on the physical characteristics of manure. The primary difficulty in handling sand-laden dairy manure (SLDM) is the inability to obtain a homogeneous mixture even during extended agitation. When earthen manure pits are employed, extensive agitation has the potential to cause pit liner damage. prumping out occurs while the sand is not suspended, ' only some sand, manure solids, and liquid are removed. Ifthis process is repeated, the sand and manure solids that remain will eventually decrease the storage capacity. From a machinery standpoint, sand is detrimental to moving parts, thus 3 requiring repair and maintenance at shorter time intervals. Pump housings and impellers often require replacement or rebuilding on a yearly basis. 1.3: Approach to the Problem-Sand Separation One way to facilitate the use of bedding sand in conjunction with a long- term manure handling system is to separate the sand from the manure prior to long-term storage. A sand separator capable of yielding a sand-free manure fraction offers a number of manure handling options associated with long-term storage which are currently not recommended due to the presence of sand. Furthermore, a sand separator capable of yielding reusable sand could offset bedding costs and aid in offsetting the cost of a separator. Currently, in wastewater treatment operations as well as the dairy, mining, and petroleum refining industries, there exists an assortment of liquid/solid separation and agitation systems. The applicability of these systems to SLDM is investigated. Concepts employed in these systems may offer insight into developing a unique and effective sand separation system. 1.4: Obiectfies At the present time, a device specifically designed to separate bedding sand from dairy manure is not commercially available. Therefore, the objectives of this study are as follows: 1. Evaluate some of the physical characteristics of sand-laden dairy manure relevant to handling, treatment, and storage. 2. Evaluate the performance of existing liquid/solid separation techniques. 3. Develop a separator capable of yielding: i) a sand fraction, clean enough that it may be reused as bedding, and ii) a dilute manure fraction, free from sand, that can be pumped, stored, and land applied via conventional manure handling techniques. 1.5: Organization of the Thesis Chapter 2 describes liquid/solid separation and agitation systems employed in wastewater treatment operations, as well as the dairy, mining, and petroleum refining industries. Chapter 3 describes the laboratory methods used to test SLDM physical characteristics (as well as its individual components (sand and manure). The procedures used to test existing sand separation systems are also presented. Chapter 4 ofiers the results of the tests performed in Chapter 3 and a discussion of the results. Chapter 4 also presents the development and the results of testing a novel sand separation technique. Chapter 5 summarizes the study and offers conclusions. CHAPTER 2 LITERATURE REVIEW 2.1: General Comments In wastewater treatment operations as well as the dairy, mining, and petroleum refining industries there exists a host of liquid/solid separation and agitation techniques that may be directly applied to separating sand from dairy manure. Separation systems considered include: i) screening, ii) sedimentation, iii) the hydrocyclone, iv) dissolved air flotation, and v) the belt filter press with polymer preconditioning. Applications of aeration which may be directly applicable to separating sand from dairy manure, such as the pachuca tank and air- lift pumping, are also investigated. 2.2: Screening Screening is a technique that separates particles on the basis of size differences. Stationary and vibrating screens are commonly used in the dairy industry to separate organic solids from dilute manure slurries (Merkel, 1981 and Schutt et. al., 1972). In the mining industry, screening is used to classify aggregates (Taggart, 1945). In wastewater treatment, coarse screens are used to remove large debris such as pieces of wood, plastic materials, and rags from wastewater influent (Reynolds, 1982). 2.2.1: tation Screens Figure 2.1 is a schematic diagram of a stationary screen. Stationary screens operate by allowing manure to flow over an inclined sloping screen. Liquids pass through the screen and the manure solids are retained. As the solids collect on the screen, they slowly slide downward due to gravity and the suction 5 6 created behind the screen by the flowing liquid (Merkel, 1981). Some difficulties are experienced with clogging due to film formation on the screen. The problem is remedied by periodically cleaning the screen by brushing away the film. iNFLUENTl E 71:3 I [SCREE \‘fi EFFLUENT SOLIDS FIGURE 2.1: Stationary Screen Schematic (Shutt et al., 1972). II‘J 2.2.2: Vibrating Screens Vibrating screens (Merkel, 1981 and Schutt et al., 1972) operate similarly to stationary screens due to the fact they both separate solids from liquids on the basis of particle size. The primary difference between vibrating and stationary screens is that, as the name implies, vibrating screens are subjected to reciprocal shaking in order to encourage solids to move across the screen, thereby reducing clogging. Figure 2.2 is a schematic diagram of a vibrating screen. iNFLUENT SCREEN r ------------- / soups LIQUID FIGURE 2.2: Vibrating Screen Schematic 2.3.: Sedimentation A number of sand separation devices function on the basis of settling, such as aerated grit chambers and sedimentation basins. The principles of sedimentation also apply to the classification of the settling behavior, under quiescent conditions, of raw manure and SLDM. Therefore, a general discussion pertaining to sedimentation theory is pertinent to this thesis. Sedimentation theory is presented in most journal articles pertaining to removing grit (sand) from sewage (Camp, 1946, Kivell and Lund, 1940, Tark and Gilbert, 1940) as well practically all environmental engineering texts (Davis and Comwell, 1991, Metcalf and Eddy, Inc., 1979, and Reynolds, 1982). Sedimentation is the separation from water, by gravitational settling, of suspended particles that are heavier than water (Metcalf and Eddy, 1979). Reynolds (1982) states that sedimentation is used extensively in wastewater treatment for grit (sand) as well as silt removal. Consider the free-body diagram of a discrete particle settling in a quiescent fluid (Figure 2.3). When a particle is released in a still fluid, it will accelerate until the drag force (upward) plus the buoyant force (upward) equals the weight of the particle (downward) and the buoyant forces (downward). At which time, the particle has reached its terminal or settling velocity. Assuming spherical, discrete particles and a Reynolds number less than 0.3, Stokes' law, 2 = g“): 3:)“: .......................................... [2.1] Vs where: vS = terminal settling velocity of a discrete particle, m/s d5 = diameter of settling particle, m acceleration due to gravity, 9.81 m/s2 or: II density of settling particle, kg/m3 '0 m N 9 pm = density of medium, kg/m3 p. = dynamic viscosity of medium, Pa 3 is used to calculate terminal settling velocity. See Davis and Comwell (1991), Metcalf and Eddy (1979), or Reynolds (1982) for the derivation of Stokes' law. DRAG BUOYANT FORCE FORCE WEIGHT FIGURE'2.3: Force Balance About a Particle Settling in a Quiescent Fluid. There are four different classes of settling: i) discrete, ii) flocculant, iii) hindered, and iv) compression (types 1, 2, 3, and 4, respectively). To complicate matters, all types of settling phenomena may occur simultaneously. See Table 2.1 for a description of the four types of settling phenomena. 2.3.1: Continuous Flow Aerated Grit Chamber (CAGC ) CAGC's are used to remove grit, sand, cinders and other inorganic materials from municipal wastewater in order to prevent excessive wear on pumps, comminutors, and settling tank scrapers. Furthermore, if allowed to enter a 10 wastewater treatment plant, grit will settle in piping, clarifiers, and digesters, resulting in the need for frequent and expensive cleaning. A CAGC consists of either a circular or rectangular concrete tank with air diffusers positioned 0.45 to 0.6 m (1.5 to 2 ft) above the bottom of the tank (Metcalf and Eddy, 1979). Figure 2.4 is a schematic diagram of a CAGC. Typical design data are presented in Table 2.2. A CAGC operates as follows: i) influent wastewater containing water, organic matter, and grit enters the tank (into the cross-section depicted in Figure 2.4) and flows in a circular or rolling pattern, ii) grit settles out of the 'roll' as organic material is suspended and carried out of the tank, iii) grit accumulates in the grit hopper and is removed from the tank via air- lift, screw conveyors, or grab buckets, and iv) effluent containing water and suspended organic matter flows out of tank. Flow into and out of the chamber is in a direction perpendicular to the rolling motion. Influent and outfluent conduits are located on opposite ends of the tank. CAGCs are capable of removing sand particles as small as 0.2 mm (0.008 in). The velocity of the tank roll is crucial to effective grit removal. Data indicate that a velocity of 0.23 m/s (0.75 fps) is required to move a 0.2 mm sand particle along the tank bottom toward the grit trap (see Figure 2.4) (Kappe and Neighbor, 1950). In addition, a vertical fluid velocity of 1.8 m/s (6 fps) is necessary to elevate sand particles. Therefore, this should be considered the absolute maximum roll velocity since, if the roll velocity exceeds 1.8 m/s, sand particles are carried 11 TABLE 2.1: Types of Settling Phenomena in Wastewater Treatment (Metcalf and Eddy, 1979). Type of Settling Phenomenon Description Application Discrete particle Refers to the sedimentation of Removal of grit and sand (type 1) particles in a suspension of low solids concentration. Particles settle as individual entities, and there is no significant interaction between particles (Stokes' law). Flocculant Refers to dilute suspensions of Removal of chemical floc (type 2) particles that coalesce, or flocculate, during the sedimentation operation. By coalescing the particles increase in mass and settle at a faster rate than would an individual particle. Hindered, also Refers to suspensions of Occurs in secondary called zone intermediate concentration, in settling facilities used in (type 3) which interparticle forces are conjunction with sufficient to hinder the settling of biological treatment neighboring particles. The facilities (activated particles tend to remain in fixed sludge). positions with respect to each other. The mass of the particles settle as a unit. A solids-liquid interface develops at the top of the settling mass. Compression Refers to settling in which the Usually occurs in the (type 4) particles are of such concentration lowest layers of a deep that a structure is formed and sludge mass, such as in further settling can occur only by the bottom of secondary compression of the structure. settling facilities. Compression takes place from the weight of the particles, which are constantly being added to the structure by sedimentation from the supernatant liquid. TABLE 2.2: Typical Aerated Grit Chamber Specifications (Metcalf and Eddy, 1 979) Item Range Dimensions: Depth, in 2-5 length, m 7.5-20 Width, m 2.5-7.0 Width to depth ratio 121-521 Detention time at peak flow, min 2-5 Air supply, m /(min*m of 0.15-0.45 1225mm Air in. Q Water level Settling Air diffuser 't Grit trap FIGURE 2.4: Cross-sectional view of a continuous-flow aerated grit chamber. 13 out of the tank. Also, from data it has been determined that air supplied at a rate of 280 um per meter (3 cfm per foot) of tank length creates a flow velocity of 0.6 m/s (2 fps) (Kappe and Neighbor, 1950). 2.3.2: Sedimentation Basins and Ap_rons Sedimentation basins (Figure 2.5), when used in conjunction with a flush manure handling system, are commonly used to separate sand from manure. Sand settles in the basin as the scouring (horizontal) velocity along the floor slows to less than 0.3 m/s (1 fps) (Fairbank, et al., 1984). The liquid fraction passes through a vertical porous dam with 1.3 cm (0.5 inch) spacing and into an additional pit. A skimmer board may be placed before the vertical porous dam to retain any floating solids. The walls of the sedimentation basin are constructed of concrete and slope inward to enable front-end loaders to enter and remove the sand and manure solids. These basins have a hydraulic detention time of approximately four days. Sedimentation aprons (Figure 2.6) are similar structures except they are conceptually designed to settle out solids from lot runoff and milking center wash water. Sedimentation aprons are designed to retain the wash water from one milking for no less than one hour. Due to the short detention time, sedimentation aprons lack the capacity to handle the water and manure from flush systems. l4 FIGURE 2.5: Sedimentation Basin (Fairbank et al., 1984). FIGURE 2.6: Sedimentation Apron (Fairbank et al., 1984). 1 5 2.4: Hydrocyclones A hydrocyclone is a device which separates solid particles on the basis of differences in specific gravity between particles and a carrier fluid. Hydrocylones are used extensively in mining operations to separate organic slimes from fine aggregates (sand). Hydrocyclones are also used to degrit sludge in wastewater treatment plants where grit chambers are not used, or where grit removal capability is exceeded at peak flow (Metcalf and Eddy, 1979). Metcalf and Eddy (1979) note that cyclone separation is the most effective method of degritting sludge. Figure 2.7 is a schematic diagram of a hydrocyclone. A hydrocyclone functions as follows: i) a dilute suspension of solid particles is pumped tangentially into the top of the hydrocyclone cylinder, thus subjecting the solid particles to centrifugal force, ii) particles with relatively higher specific gravities such as grit are forced to the walls of the hydrocyclone and exit through the lower opening, or underflow, and iii) particles of relatively lower specific gravities such as organic solids remain in the center, or inner spiral of the hydrocyclone and, in addition to water, are forced out of the upper opening, or overflow. Currently, on a commercial dairy, a hydrocyclone separator is being used to separate sand from dairy manure. Theoretically, hydrocycloning lends itself well to separating sand from manure since the specific gravity of sand is approximately 2.5 times the specific gravity of manure. However, in order for a hydrocyclone to operate effectively, the solids feed concentration must remain constant or separation efficiency will fluctuate (Metcalf and Eddy, 1979). I” solid 86pm Opera! 53'5ch 350 k; 16 EEELUENT OUTER SPIRAL INNER SPIRAL SOLIDS FIGURE 2.7: Hydrocyclone Schematic (Schutt et al., 1972). 2.5: Di lved Air Flo tion AF Dissolved air floatation (DAF) systems are used to separate low density solid or liquid particles from liquid (Reynolds, 1982). This type of liquid/solid separation system is utilized extensively in water and wastewater treatment operations, primarily to thicken sludges and/or remove oil emulsions. In a DAF system (Figure 2.8), the entire waste stream is pressurized to, and held at 275 to 350 kPa (40 to 50 psig) for several minutes, causing air bubbles to become dis. red Fl 17 dissolved in the liquid. The air saturated mix is then released via a pressure reducing valve into a flotation tank at atmospheric pressure in which the air comes 3 § § Skimmer 3 030 0 r T Skimmer! Air I: ‘ ‘ - a Solid: 5 Tank ’ . EMS Feed _ MP Air Dissolution Tank FIGURE 2.8: Dissolved Air Flotation System--Entire Flow Pressurization (Reynolds, 1982). GE ISkImlo A 0% Flotation Tank :ui Feed M Pleasure Re- lease Valve a '3 3. Air 3' «4 Pump F & Air Dissoiu- I" tion Tank U Purim FIGURE 2.9: Dissolved Air Flotation (DAF)--Recycled Flow Pressurization (Reynolds, 1982). out an. sol p2 ch 01?. act 18 out of solution in the form of minute bubbles. As the bubbles rise they become attached to solid particles causing them to float to the top of the tank. The floating solid mat is removed from the top of the tank by a mechanical skimmer mechanism. The entire DAF process may be enhanced by polymer preconditioning the inflow A variation of this system (Figure 2.9) is the recycled flow pressurization method in which, instead of pressurizing the entire feed flow, part (5 to 10%) of the effluent is diverted to a pressurization tank prior to being released back into the flotation tank. The remainder of the system functions the same as the entire waste stream pressurization method. 2.6: Belt Filter Press (BFP) With Polmer Conditioning The purpose of a belt filter press (BFP) (Figure 2.10) is not to degrit sludge, but instead to dewater sludge. Prior to the actual dewatering operation it is necessary to condition the sludge. The object of sludge conditioning is to coagulate the solid particles into larger masses, or flocs. Detailed accounts of coagulation chemistry are presented by Davis (1991) and Metcalf and Eddy (1979). Coagulation is enhanced by the addition of coagulants such as polymers. Typically, solid particles in wastewater are repelled due to their surface charges. The object of coagulation is to reduce the surface charge to a point where the particles are no longer repelled from each other. Since the colloids are negatively charged, the addition of coagulant aids such as cationic polymers cause a reduction of surface charge. Polymers are long-chain anionic, cationic, or polyamphotype (no charge) organic compounds of high molecular weight that have many active sites. The active sites adhere to the flocs, thus joining them together. Polymer type and GIIVIIyDniup Coup! Dull low-Pressure “firm". W W I4 0‘ .4 I \ ll \ 1’ I g» ' I \ .o.o. . .o . . ,o. "” f . IIItIt HM "V“ W cm... ._ 322'; _.L m__. s“? s“? [ Step Sludge Nix-r G, 1 mm“ w' . C9 8 ' . «J 5 New ....'.... 3 \ L ' J SIutIp Wuhm Cake FIGURE 2.10: Belt Filter Press Schematic (Davis and Comwell, 1991). 20 dosage vary based on the individual wastewater, as well as on a seasonal basis (Davis and Comwell, 1991). The belt filter press consists of two continuous and converging belts. In addition to preconditioning, a BFP operation consists of two zones: i) draining and ii) compression (Davis and Comwell, 1991). In the first zone, the sludge is allowed to drain by gravity. The sludge then enters the compression zone where pressure is applied to the sludge due to the converging belts. The belts continue to converge, resulting in increased pressure being applied to the sludge. A wash spray is also applied to the lower belt in order to remove solids and, therefore, prevent belt clogging. As the sludge cake exits the converging belts, it is removed by a scraper. Reynolds (1981) notes, when applied to raw primary sludge, a belt filter press in conjunction with polymer conditioning is capable of yielding sludge cakes of 28 to 44 percent dry solids. 2.7: Aeration Aeration has long been used in industry for the purpose of agitation and mixing. It is most commonly used with slurries which posses high solids concentrations and are either abrasive or corrosive in nature. Besides for industrial applications, aeration has also been used to agitate harbors and channels in the winter to prevent freezing (Railsback, 1992). In addition to agitation and mixing, aeration is capable of promoting aerobic biological decomposition of organic matter and removal of odors and toxic gasses (S zabo, 1971). 2.7.1: Aeration Applications 2.7.1.1: Mining Indusg The Brown or pachuca tank is an example of aeration applied to the mining industry. In the mining industry pachuca tanks are used to: i) suspend solids, ii) scrub films from solid particles, and iii) aerate pulp. In South Africa, pachuca 21 tanks are used for leaching (purifying) gold ores, a process which takes advantage of each application mentioned above (i-iii). In Canada, pachuca tanks are used for acid leaching of Uranium ores. In the acid leach process, aeration is used to suspend solids. Pachuca tanks are very desirable for this Operation since there are no moving parts exposed to the acid pulp (Lamont, 1958). Pachuca tanks are circular vessels with conical bottoms. The mineral processing literature lacks typical design values (diameter, depth, and air flow rate) for pachuca tanks. However, Lamont (1958) refers to a tank 13.7 m (45 ft) deep and 6.9 m (22.5 ft) in diameter, operated at 8,500 L/min (300 cfm) of air. The tank was being used to agitate a suspension with a specific gravity equal to 1.6. Typically, the included angle of the conical bottom is 60 degrees. Air is introduced at the apex of the conical bottom. The purpose of the conical bottom is to redirect settled solids into the upward flowing fluid so that they may be returned to the top of the tank (resuspended) (Lamont, 195 8). Figure 2.11 shows four different pachuca tank configurations: i) full-center column, ii) full-center column, with shallow air introduction, iii) stub-column tank, and iv) free-airlift tank. The BAGC proposed in this thesis is an example of a free-airlift pachuca tank (iv). Based on an analysis of energy transfer in pachuca tanks, Lamont (195 8) states that the full-center column (i) and the stub-column (iii) configurations are superior to the free-airlift tank (iv) since they are both capable of developing higher pulp flow rates at tank bottoms. An additional application of the airlift principle is the airlift pump. They are commonly used in the petroleum industry to clean materials such as boring debris from around oil well heads. Some characteristics of airlift pumps which render them desirable for this type of operation are: i) good reliability (minimal equipment needed-only a dependable air compressor), ii) low maintenance 22 requirements (few or no moving parts), and iii) the ability to handle hazardous materials safely (Vargas, 1992). Air in I (i) (ii) (iii) (iV) full—center full-center stub-column free-air column column with lift shallow air introduction FIGURE 2.11: Pachuca Tank Configurations (Lamont, 1958). Figure 2.12 is a schematic diagram of an airlift pump, which consists of a vertical tube partially submerged in liquid and an air pipe connected near the bottom of the vertical tube. An airlift pump works as follows: i) air is pumped via compressor and air pipe into the bottom of the vertical tube, ii) air mixes with the slurry, decreasing its bulk density, and iii) the air-liquid-solid mixture moves upward in slug flow and is discharged above the liquid surface. For this application, the lift and air supply pipes were 15 cm (6 in) and 4 cm (1.5 in), respectively. In order to raise the slurry to the required height (HS + H1) of 60 m (200 ft) a 256 kW (343 hp) air compressor was required. 23 Compressed air for agitation plays an important role in the refinement of petroleum products (Kaufman, 1930). In the refining process, air is used for blending of light oils, kerosene, and gasoline. Kaufman (1930) concludes that increased agitation is achieved with deep rather than shallow tanks using the same air flow rate for each case. This is due to the fact that agitation is caused by the expansion of rising air and the speed at which the air rises. Both of these factors are greater in deep rather than shallow tanks. In a specific example, the author notes that in order to achieve the same degree of agitation in both a 0.91 m (3 ft) and a 2.7 m (9 ft) deep tank, the shallow tank would require twice the air flow compared to the deep tank. For this study, the author neglects to indicate tank geometry other than height. . . Discharge Arr inlet, Q T 0” 0 ° .._......_ Hl VWaterlevel Slug of water Slug of air Air bubbles T Fluid inlet FIGURE 2.12: Airlift Pump Schematic (Vargas, 1992). 24 2.7.2: Aeration Modeling 2.7.2.1: Mixing intensig Mixing is an essential aspect of water and wastewater treatment operations. Some operations require a certain regulated degree of agitation. A measure of mixing intensity, or velocity gradient (G), was developed by Camp and Stein (1943). Velocity gradient or G, depends upon: i) the amount of power dissipated by the fluid, ii) the volume being agitated, and iii) the fluid viscosity. The equation for the velocity gradient in mechanically or pneumatically agitated G = Liv ................................................. [2.2] where: G = Velocity gradient or mixing intensity, s-l vessels is P = Input power, W p. = Dynamic viscosity, Pa 3 V = Active volume, m3 The velocity gradient is related to the shear forces in a fluid. Therefore, large velocity gradients produce high shear forces which, in turn, result in a high degree of agitation. For instance, to preserve water softening floc, relatively low velocity gradients are required in order to minimize the shearing effect between the fluid and the floc, as well the rate of particulate collisions. The operation of air agitated tanks is most economical when velocity gradients range between 30 and 300s-1 Szabo (1971). Mixing may also be characterized by Gt (dimensionless), the product of the velocity gradient and detention time. The values G and Gt may be related to the number of particle collisions per unit time and the total number of particle 25 collisions in a vessel, respectively (Reynolds, 1981). Typical G an Gt values for a variety of water and wastewater treatment operations are reported by Davis and Comwell (1991). 2.7.2.2: Power Disflpgio_n Knowing the amount of power dissipated in air induced mixing and agitating is useful in appropriately sizing air supply units. The following equation is used to calculate the power dissipated by rising bubbles in pneumatic mixing and stirring Reynolds (1982); the derivation of which can be found in (Fair et al., 1971) H+10.33 ’5 0.3.) P =1.689an( ) ...................................... [2.3] Power dissipated by air bubbles, W where: P H = Height of fluid over air discharge point, m Q = Air flow rate, L/min From this equation, it is evident that power dissipated, P is directly proportional to the natural logarithim of the height of fluid over the air discharge point, H and air flow rate, Q_ 2.7.2.3: Agitation Time Machina and Bewtra (1987) conducted an extensive study of bulk mixing using diffused air in circular and rectangular vessels. The circular vessels were 1.5 m (5.0 ft) in diameter and fluid depth was varied from 0.45 to 1.1 m (1.5 to 3.5 ft). Dimensional analysis was used to obtain the following equation for agitation time required to achieve m-percent uniformity of dye and salt solutions in circular vessels. 26 /7} zm=117+14’900—210—}1 .................................. ///f/; G D / where: tm = Mixing time required to achieve m-percent uniformity, s Mixing intensity, 5‘1 Vessel diameter, cm LEGO II = Depth of air inlet, cm The authors note that the most cost effective air agitation sysrem is one which minimizes mixing time, tm and G. Therefore, the dimensionless parameter Gtm should be minimized. As expected, percent uniformity increased with mixing time. 2.L2.4: Pick-Ur) Velocity and Gas BuLbble Dvniamics Recognizing that dimensional analysis is the most common approach used to determine the suspension characteristics of solid-liquid mixtures in mechanically agitated vessels, Narayanan et a1. ( 1969a) derived an analytical expression for pick-up velocity, or the minimum fluid velocity required to elevate a particle. The author states that an equation for pick-up velocity based on fluid dynamics and vertical transport phenomena would be more rigorous than one derived empirically from dimensional analysis. Once again, considering a force balance analysis about a solid particle, this time in a vertically flowing medium, the minimum fluid velocity required to initiate the suspension of a solid particle is flagipp‘l’u)[2dp + HSHH ““2 ....................... [25] II = " VP 1 3PM pP+HSpL I 2’] ,/ where: do = Particle diameter, cm 27 g = Acceleration due to gravity, 981 crn/s2 HH = Fluid depth, cm HS = Mass basis solids concentration, unitless pM = Density of fluid medium, g/ml p5 = Density of suspended particle, g/ml Vp = Fluid pick-up velocity, cm/s This equation assumes no slip between the particle and the fluid. But when dealing with solids of high density, the slip between the two phases is inevitable (Narayanan, et al., 1969b). Even dilute SLDM slunies possess high concentrations of particles of high density (sand), flowing in a medium composed of concentrated low-density solids (manure). Therefore, the analytical equation for pick-up velocity is not applicable to SLDM slurries. 2.7.2.5: Summag of Aeration Tank Desigp Considerations 1. Pneumatic agitation and separation systems are ideal for slurries which posses high solids concentrations and are either abrasive or corrosive in nature. 2. Deep, instead of shallow tanks are preferred since, as bubbles rise, they also expand. The result is a higher degree of agitation. 3. For the most economical operation of aeration tanks, design G-values should range from 30 to 300 8'1. CHAPTER 3 EXPERIMENTAL METHODS 3.1: General Comments This chapter is dedicated to describing the experimental methodology used to test an assortment of sand separation systems as well as the physical properties of sand and manure samples. Initially, the standard analytical techniques used to determine physical properties such as total solids (TS), organic or volatile solids (VS), and sand content (S) are discussed. These analytical techniques were then used throughout the study to evaluate the efficacy of the separation systems considered. 3.2: Standard Techniques and Procedures The experimental procedures used to determine total solids TS, VS, and S were adopted from Van Soest and Robertson's (1985) guide to analyzing the physical and chemical properties of forages. These methods are described as a "hot basis" analyses since all mass measurements are performed on hot samples, as opposed to a cool basis method in which samples are cooled in a desiccator prior to weighing. 3.2.1: Hot Weighing Samples The "hot basis" technique is preferred over the "cool basis" technique in which a desiccator is used to cool samples prior to weighing, since it decreases the possibility of samples gaining additional moisture from the atmosphere and/or faulty desiccant. 28 29 3.2.1.1: Materials The following equipment is required for hot weighing samples: American Scientific Products Constant Temperature Oven (:1 0C) Mettler AB 200 Balance 10.0001 g Lotus Measure data acquisition program IBM PS2/Mode1 20 computer 50 m1 beakers 3.2.1.2: Methodology The procedure for hot weighing samples includes the following steps: i) empty 50 ml beakers, stored in the drying oven, are weighed on a the Mettler AB 200 Balance, ii) the balance is tared in order to take into account any moisture the beaker may have absorbed from the atmosphere, iii) samples are placed in the 50 m1 beakers and the mass (mm-,1) each is recorded. All data is recorded using the Lotus Measure data acquisition program. After placing a sample on the balance pan, the Lotus Measure program records the sample weight twenty times and then stores the minimum value. The beaker is then removed from the pan and Lotus Mleasure records the average of twenty tares. The minimum sample weight is then corrected using the average tare. 3.2.2: m Matter Content ([8) Total solids content (TS) is a measure of the dry matter remaining after drying a sample to equilibrium at 106 0C. TS is directly related to moisture content in that the sum of the TS and moisture content equal 100% (Sobel, 1966). 3.2.2.1: Materials The equipment required for TS analyses is identical to that which is required for hot weighing. 3.2.2.2: Methodology The procedure for determining TS is as follows, i) samples are weighed out into 50 m1 beakers using the hot weigh method, ii) samples are allowed to dry at 30 106 0C for 12 hours, and iii) the masses of the dried samples are then recorded using the hot weigh method. The TS of a sample is a ratio of the mass of the solid material remaining after drying, over the initial mass of the sample (wet), or rs = E— *100 ......................................... [3.1] minitial where: TS = Total solids content, % mdry = sample mass after drying at 106°C, g minim = initial (wet) mass of sample, g 3.2. : Fixed Solids S and Volatile Solids S ontent Total solids are composed of both fixed (FS) and volatile solids (VS). The FS, or inorganic matter content, is a measure of the material remaining after ' igniting a sample at 500 oC. Similarly, the VS, or organic matter content, is a measure of sample weight loss after ignition. 3.2.3.1: Materials The equipment required for this analysis is the same as that which is required for hot weighing, and TS determination with the exception of a muffle furnace capable of attaining a temperature of 500 0C. For this study the following muffle frnnace was used: Thermolyne Type 30400 Furnace (:1 0C) 3.2.3.2: Methodology The experimental procedure for determining FS or VS (Van Soest and Robertson, 1985) is the following: i) hot weigh and dry samples as previously outlined, ii) ignite samples in Thermolyne muffle furnace at 500 0C for six hours (complete ignition), iii) record sample mass after ignition using the hot weigh method. The ashes that remain after ignition are the fixed solids. The F8 of a sample can be expressed as: 31 FS=-—m‘“—"*100 ....................................... [3.2] merino! where: FS = Fixed (inorganic) solids, % mash = sample mass after ignition at 500°C, g minitial = initial (wet) sample mass, g Conversely, the VS of a sample is the weight loss after ignition over the original mass of the sample prior to drying (wet), vs =1-fl’i‘inoo ..................................... [3.3] militia! where: VS = Organic or volatile solids, % mash = sample mass after ignition at 500°C, g minim = initial (wet) sample mass, g Recognizing the relationship between TS, FS, and VS, TS = FS+VS ........................................ [3.4] VS can also be expressed as VS = TS - FS ....................................... [3.5] Note that in this instance, FS, and VS are calculated on a wet basis. To convert VS to dry basis simply divide VS by TS, VS VS db =—*100 .............................. 3.6 ( ) TS [ l where: VS(db) = Dry basis volatile or organic solids content, % 3.2.4: Sand Content (S l: * Sand content (S) is a mass basis measure of the amount of sand contained in a sample. In the previous analysis, the total amount of fixed solids in a sample Was determined. However, in the case of SLDM, both sand and manure 32 contribute to the fixed solids. For SLDM the FS mass balance can be expressed as: FS, = FSMM + FSmd ................................ [3.7] where: FST = Sum total of fixed solids, % FSmmm = Fixed solids of manure component, % FSmd = Fixed solids of sand component, % Therefore, in order to determine S, a test capable of distinguishing between Fsmanure and Fssand is required. The analyses used in this study assume that the sand is free from organic matter. Therefore, Fssand is equal to S. An acid digestion procedure outlined by Van Soest and Robertson (1985) was used to distinguish between FSmanure and Fssand. The goal of the acid digestion is to eliminate the Fsmanure so that FSsand, or S remains. This test assumes the following: - FSmd are non-digestible. o FSmm are completely digestible. 3.2.4.1: Materials To perform the acid digestion analysis, the following items are required: 50 ml, 40-60 micron filter crucibles Vacuum pump 1 L of 0.1 M HCl Distilled water at 100 0C 3.2.4.2: Methodology The steps for determining S are as follows: i) hot weigh filter crucibles, ii) place previously ignited samples into filter crucibles (stored in oven) and hot weigh, iii) using an eye dropper, soak the contents of the filter crucibles with 0.1 M HCl, and let stand for fifteen rrrinutes, iv) vacuum filter each sample while 33 liberally rinsing the walls of the beaker and the undigested beaker contents using 100 0C distilled water, and iv) oven dry for twelve hours, then hot weigh. The material remaining after digestion and drying is sand, mm. The sand content of a sample is then expressed as: s = M * 100 ......................................... [3.8] mutual where: S = Sand content, % mm = Sand mass, g minim = Initial (wet) sample mass, g Again, note that in this instance S is calculated on a wet basis. To convert to dry basis simply divide S by TS. 3.2.5: Sand Particle Size Analyses (m Sieving, Wet Sieving, and Hydrometer Test Particle size analyses generate particle size distribution curves for different bedding sands. For the purpose of this study, three particle size determination techniques are utilized: i) dry sieving, ii) wet sieving, and iii) hydrometer (sedimentation) test. Sieve analyses (dry and wet) are used for samples composed of particles greater than 0.053 mm. For particles smaller than 0.053 mm (a clay particle), the hydrometer test is used. 3.2.5 1: Materials These analyses were conducted in accordance to the American Standards for Testing and Materials (ASTM, 1991) standard Dry Sieving Fine Aggregates (C136) and Particle Size Analysis of Solids (D422). The following is required in order to perform these analyses: US Sieve Series (6, 10, 12, 14, 16, 20, 30, 50, 100, 140, and 270) Sieve shaker ASTM Standard Hydrometer (ASTM 152H) 34 1000 ml graduated cylinder Plastiseal, 10 cm x 10 cm Ohaus TS4KS Balance (:01 g) 500g sample, dry Distilled water TABLE 3.1: US. Standard Sieve Series U.S. Sieve Opening Number Size (mm) 6 3.66 10 2.00 12 1.68 14 1.41 16 1.19 20 0.84 30 0.59 50 0.30 100 0.15 140 0.11 270 0.053 3.2.5.2: Methodology The experimental procedure to determine the particle size distribution of sand and silt particles is as follows: i) oven dry 3 500 g sand sample at 106 9C, ii) weigh empty sieves, iii) assemble the sieve series in the order of decreasing size, top to bottom, iii) place sample in top sieve and cover, v) activate sieve shaker for ten minutes, and vi) weigh sieves and maintain the fraction which passed through the last sieve (US 270). The hydrometer test predicts particle concentrations based on the buoyancy of the liquid phase in a settling column. The procedure for the hydrometer test used to determine clay content is as follows: i) place the material which passed through the last sieve (U S#270) into a 1000 ml beaker and fill to the 1000 ml mark with distilled water, ii) seal the end of the column with Plastiseal, iii) mix by inverting the column several times, iv) allow the sample to settle for 8 hours then place the hydrometer into the suspension and record its depth, and v) refer to 35 ASTM D422 and determine the particle concentration (clay content) that corresponds to the previously recorded hydrometer depth, and vi) plot a cumulative particle size distribution for each sand tested. The wet sieve analysis is used to determine the particle size distributions of paste-like substances like raw manure. The test proceeds as follows: i) weigh empty sieves, ii) assemble the sieve series in the order of decreasing size, top to bottom, iii) place a 200 g wet manure sample in the top sieve, iv) using tap water, wash the solids through the sieve series until the sieve effluent is clean, v) dry the sieves and record the mass of each sieve, and vi) plot a cumulative particle size distribution. The US 20, 50, and 140 screens were not used in the wet sieve analysis of manure due to difficulties experienced with screen clogging 3.2.6: Manme Sampling In section 3.3 a variety of sand separation systems are analyzed. With the exception of the hydrocyclone, which is a working on-farm unit, the separators are laboratory scale. Therefore, for each laboratory trial, manure and sand are collected and then mixed in the appropriate proportions in order to achieve the desired rate of dilution. 3.2.6.1: Materials The following equipment is required for the collection of raw manure : 20 L bucket Hand operated alley scraper Scooping device 3.2.6.2: Methodology Manure samples were collected from the milking parlor holding pen and return alley at the Michigan State University Dairy Research Unit, East Lansing, MI. This location was selected for sampling since the manure there is free from any bedding (the MSU Dairy uses wood shavings and newspaper bedding). 36 Sampling proceeded as follows: i) following the AM. milking (0600 to 0730), the entire holding pen and return area was scraped into a common pile and thoroughly mixed, and ii) the appropriate volume of manure was sampled from the pile by the method of quartering (Van Soest and Robertson, 1985), then transported to the laboratory for immediate use. A type of sand referred to as 2N S (MDOT, 1990) was used for each trial, and is described in detail in Chapter 4.. This type of sand was selected for two reasons: i) 2NS is a commonly used bedding sand, and ii) it possesses a negligible amount of organic matter, therefore, simplifying laboratory analyses. All sand was donated by Gale Briggs and Son, Charlotte, MI. 3.2.7: Criteria for Acceptable Cleanliness of Bedding Sand Bishop et a1. (1980) reported that coliform counts greater than 106 per gram of bedding pose a significant threat to udder health due to mastitis. Currently, there is no literature relating sand bedding VS (db) to coliform bacteria count. Such a relationship would prove useful in establishing a reasonable goal for the acceptable amount of VS (db), or recovery quality, of sand recovered from a separator. To establish a reasonable goal for recovery quality, samples of sand bedding were removed from the rear (adjacent to drive alley) 61.0 cm of 3 freestalls (11 farms). Mr. George Atkeson, MSU Cooperative Extension, Ionia County, judged each stall either "acceptable" or "unacceptable" from the standpoint of contamination from manure solids. Samples were tested for TS and VS (db). As a result an "acceptable" as well as an "unacceptable" range of VS (db) in bedding sand was established. 3.3: Analysis of Sand Separation Systems The following section outlines the experimental methodology used to analyze a variety of liquid/solid separation systems. Systems examined include: 37 i) sedimentation, ii) screening, iii) the hydrocyclone, iv) dissolved air floatation (DAF), and v) the belt filter press. 3.3.1: Sedimentation The objectives of the settling tests were twofold: i) to analyze the settling characteristics of dilute SLDM and thereby gain an understanding of the interactions between the manure, sand, and water, and ii) based upon the results of the settling analyses, to determine whether or not sedimentation is a feasible method for separating sand from dairy manure. 3.3.1.1: Typg-3 Settling Analysis Type-3 settling analyses are used to monitor type-3 or hindered settling (described in Chapter 2). This is accomplished by measuring the height of the liquid/solid interface as well as the height of sand particles in the solid fraction during twenty four hours of quiescent settling. Twenty four hours was selected as the settling time since this would be the maximum detention time for a batch sedimentation chamber capable of handling one day's worth of SLDM. 3.3.1.1a: Materials The materials required for the type-3 settling analysis are as follows: Tap water Ohaus TS4KS Balance (:0.1 g) Inversion mixer (5) Plexiglas settling columns (D=12.7 cm and H=56.8 cm) (Figure 3.1) Ruler 3.3.1 .1b: Methodology The methodology for the type-3 settling analysis can be broken down into two distinct categories: i) sample preparation, and ii) the actual settling analysis. Sample preparation includes the mixing of sand and manure. The ratio of sand to manure (SzM) used in samples was determined by taking the average mass of sand 38 used per cow-day over the average mass of manure produced per 636 kg (1400 lb) dairy cow-day. The value used for average manure mass produced was 52.3 kg/cow-day (115 kg/cow-day) (MWPS, 1985). The average amount of sand used was altered during the study due to the fact, as the sand usage survey expanded, the calculated average amount of sand used changed. TABLE 3.2: Sand:Manure Ratios (S:M). Manure Sand Produced Usage Date (kg/cow- (kg/cow- (S:M) day)* day) August 1993 52.3 31 0.59 January 1994 52.3 25 0.48 *(MWPS, 1985) All tests were performed at S:M equal to 0.59 unless otherwise noted. Throughout this study SLDM slmries are classified by mass basis dilution ratio (DR). For instance, a 2:1 dilution indicates that the mixture is composed of 2 mass parts of water to 1 mass part SLDM. The relative quantities of sand, manure, and water required were calculated in a manner such that, for different dilution ratios, fluid height in each column would be equal. Table 3.3 summarizes the relative amounts of sand, manure, and water required to attain the specified dilution while maintaining a constant volume. Sample preparation includes the following steps: i) in Plexiglas columns (Figure 3.1), prepare 0, 0.5, 1, 2, 3, and 5:1 SLDM mixtures using the quantities of sand, manure, and tap water outlined in Table 3.3 and, ii) mix using inversion mixer for 10 minutes. The inversion mixer is capable of simultaneously mixing three settling columns by rotating them about their centroids at a rate of 15 RPM. This mixing technique was chosen over a rotary (propeller) mixer since it reduces turbulence and encourages settling primarily along the y-axis of each column. 39 fiflfliyfiflfl BRASS I SAMPUNG PORT a I JIHLMEN! 100cm 100cm 568cm 1,... Amie _.L FIGURE 3.1: Plexiglas Settling Column. The actual settling analysis includes the following steps: i) allow samples to settle under quiescent conditions for twenty four hours, and ii) measure the height of the liquid/solid interface (hl) and the height of the sand (hs) in the solid layer at the intervals outlined in Table 3.4. A sand height ratio (hsr) and solid/liquid interface height ratio (hlr) are calculated to obtain a relative measure of the sand height and the liquid/solid interface height in the settling column. The sand height ratio is a ratio of the highest point at which sand is found (PS) and the column height (hi)- Similarly, the liquid/solid (hlr) interface ratio is a ratio of the height of the liquid/solid interface (hl) with respect to column height (hi). Note that this analysis only pertains to SLDM that is agitated and allowed to settle. 40 TABLE 3.3: Quantities of Manure, Sand, and Water Required for Type-3 and Batch Settling Angyses. Manure Sand Water Dilution Mass Mass Volume Rate (a) (g) (ml) 0:1 5074.4 2465.6 0.0 0.521 3075.4 1494.3 2284.8 2206.3 1072.0 3278.3 1409.6 684.9 4188.9 : 1035.6 503.2 4616.3 5:] 676.6 328.7 5026.7 TABLE 3.4: Measurement Times. Reading Elapsed Reading Elapsed Number Time Number Time 1 30 sec 7 60 nrin 2 l min 8 2 hrs 3 3 min 9 4 hrs 4 5 min 10 8 hrs 5 10 min 11 16 hrs 6 30 min 12 24 hrs 3.3.1.2: Batch Settling Analysis A batch settling analysis is used measure the amount of solids settled over after a specified amount of time. It is also capable of confirming the results found using the type-3 analysis. 3.3%: MM The following equipment are required for the batch settling analysis: Tap water Ohaus TS4KS Balance (3:0.1 g) Inversion mixer 41 (5) Plexiglas settling columns (D=12.7 cm and H=56.8 cm) equipped with sampling ports and false bottoms (Figure 3.2) To facilitate sampling of the liquid fractions each Plexiglas column is equipped with brass sampling ports spaced every 10.0 cm. In addition, each column is equipped with a false bottom which enables sampling of the settled solids following the removal of the liquid fraction. T I IQEMIEW re 0 10.0 cm _x_ M 3 12.7 cm 10.0 cm 55.3 cm I I QQMEQNENLLLSI 10.0 cm 1. Brass sampling ports ¥ (>