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984101

ANAEROBIC PROCESSING OF PIGGERY WASTES: A REVIEW

By

D. P. Chynoweth*, A. C. Wilkie**, and J. M. Owens**Dept. of Agricultural and Biological Engineering

**Soil and Water Science DepartmentUniversity of Florida, Gainesville, Florida

Written for Presentation at the1998 ASAE Annual International Meeting

Sponsored by ASAE

Orlando, FloridaJuly 11-16, 1998

The swine industry is growing rapidly along with the world human population. The trend is toward moreconcentrated piggeries with numbers in herds in the thousands. Associated with these increased herdsare large quantities of wastes, including organic matter, inorganic nutrients, and gaseous emissions. The

trend in swine waste management is toward treatment of these wastes to minimize negative impact onthe health and comfort of workers and animals and on the atmosphere, water, and soil environments.This review discusses the present and future role of anaerobic processes in piggery waste treatment withemphasis on reactor design, operating and performance parameters, and effluent processing.

Piggery wastes, swine wastes, anaerobic treatment, anaerobic digestion, biogas

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ANAEROBIC TREATMENT OF PIGGERY SLURRY

D. P. Chynoweth*, A. C. Wilkie**, and J. M. Owens**Dept. of Agricultural and Biological Engineering

**Soil and Water Science DepartmentUniversity of Florida, Gainesville, Florida

A paper presented at the pre-conference session:

Management of Feed Resources and Animal Waste for Sustainable AnimalProduction in Asia-Pacific Region Beyond 2000Eighth World Conference on Animal Production

June 28 - July 4, 1998

Seoul, Korea

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ABSTRACT

The swine industry is growing rapidly along with the world human population. The trend is toward moreconcentrated piggeries with numbers of herds in the thousands. Associated with these increased herdsare large quantities of wastes, including organic matter, inorganic nutrients, and gaseous emissions. Thetrend in swine waste management is toward treatment of these wastes to minimize negative impact onthe health and comfort of workers and animals and on the atmosphere, water, and soil environments.Treatment of these wastes has traditionally involved land application, lagoons, oxidation ditches, andconventional batch and continuously stirred reactor designs. More sophisticated treatment systems arebeing implemented, involving advanced anaerobic digester designs, integrated with solids separation,aerobic polishing of digester effluents, and biological nutrient removal. This review discusses the presentand future role of anaerobic processes in piggery waste treatment with emphasis on reactor design,operating and performance parameters, and effluent processing.

INTRODUCTION

The swine industry is growing rapidly as more people in developing countries can afford and acquire ataste for more meat in their diet, including pork. In the past 16 years, the annual global production of swine has increased from 790 million to 926 million with most of that increase occurring in China, India,and other emerging countries (FAO, 1990, 1991, 1995, 1996). In past years, piggeries were small(hundreds or less animals) and wastes were disposed of on the same land used to grow the feed, servingas fertilizer and soil conditioner. The increased demand for pork has resulted in establishment of larger centralized piggeries with herds frequently exceeding 1,000 and sometimes more than 10,000 head(Hatfield et. al, 1998). Wastes from these facilities exceed the capacity for direct land disposal withoutsevere environmental impacts, including odor, attraction of rodents, insects and other pests, and releaseof animal pathogens, atmospheric methane and ammonia, nitrogen, phosphorus, and other nutrients intoground and surface waters.

The characteristics of swine wastes vary with a number of factors, including the age and diet of the pigs,type of housing or confinement, and waste removal and pre-processing (Day & Funk, 1998; USDA, 1992;Zhang & Felmann, 1997). The wastes are either scraped or hydraulically flushed into a holding basin,after which they are treated directly or after solids separation. Commonly used systems for removal of organic matter include aerobic and anaerobic lagoons, oxidation ditches, and anaerobic digestion. More

advanced systems include tertiary treatment operations, such as oxidation ponds, aquatic plants,wetlands, and denitrification units.

This review addresses the current and future role of anaerobic processes for swine waste management.Anaerobic digestion has been applied in a variety of forms and scales to stabilize the organic matter inthese wastes. This process results in effective organic matter and pathogen reduction with production of a useful fuel and compost. Properly operated anaerobic digesters result in reduction of odors associatedwith these wastes (Wilkie, 1998). Anaerobic treatment may also play an important role in nutrientremoval. Following aerobic oxidation of ammonia to nitrate, nitrogen may be removed by anaerobicdenitrification. Phosphorus removal may also be enhanced by anaerobic pretreatment, which results information of organic acids that enhance phosphorus uptake in aerobic processes. Algae ponds andwetlands have also been applied for effluent polishing and nutrient removal.

The review summarizes the characteristics of piggery wastes, the role of anaerobic treatment of organicmatter, the role of anaerobic digestion in reduction of pathogens and gaseous emissions, and anaerobictreatment of nitrogen and phosphorus. It also discusses integrated treatment systems that use anaerobicprocesses and future trends in utilization of anaerobic treatment of piggery wastes.

CHARACTERISTICS OF PIGGERY WASTES

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Global Production

Worldwide swine populations by region and select countries for the periods of 1979-81, 1989-91, and1996 are presented in Table 1. The number of pigs in the world are about one billion, or one

Table 1. World Population of Swine (1000 Head; FAO, 1990,1991, 1995, 1996 1995, 1996)

REGIONS 1979-81 1989-91 1996World 779,506 854,213 927,354Asia 368,702 433,194 535,844

Europe 173,384 182,930 166,963North and Cent. America 97,327 87,012 96,644

South America 51,722 52,378 56,122Africa 10,155 16,522 21,652

COUNTRIESChina 313,660 360,247 452,198

USA 64,045 54,557 60,190Brazil 34,102 33,643 35,350Germany 34,468 33,350 24,698Mexico 16,895 15,715 18,000

Viet Nam -- 12,225 17,200France 11,472 12,233 14,523Canada 9,709 10,505 12,043

India 9,433 11,193 11,900Denmark 9,669 9,390 10,709

Korea -- 8,007 10,300Japan 9,851 11,673 10,200

Philippines 7,712 7,968 8,941Italy 8,885 9,150 7,984

per six persons. By region, the largest numbers are in Asia, followed by North and Central America,South America, and Africa. By country, the largest numbers are in China followed by the U.S., Brazil, andGermany. The most significant increases in numbers have occurred in certain emerging countries suchas China, Vietnam, Korea, and India while numbers have decreased in several developed countries,including the U.S., Germany, and Italy. These trends may be attributed to a number of factors, such asimproved economies resulting in higher meat consumption and export by emerging countries, andreduced meat consumption and environmental regulations in developed countries. Estimates of globalproduction of swine wastes are presented in Table 2.

Future Trends in Wastes Production

The numbers of swine and associated quantities of wastes are likely to increase greatly over the nextseveral decades due to the projected increase in human population and the trend of developing countries,with the highest rates of population increase, to shift to diets with a higher meat content. This will beoffset to some extent by reduced red meat (including pork) consumption by the more developedcountries. For example, in the U.S., the market share of red meat has decreased from 74% in 1970 to59% in 1994 (Zhang & Felmann, 1997). The projected world human population increase of 27% by 2020(US, 1997) should result in at least the same increase in numbers of swine.

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Table 2. World Swine Waste Production by Region (Safley et al., 1992)

Region Total Manure,Mt/day (wet)

Volatile Solids,Mt/day

Asia and Far East 1,663,466 168,010

Eastern Europe 788,722 77,641Western Europe 570,932 57,664North America 345,490 34,960Latin America 320,415 32,362

Africa 52,519 5,286Oceania 24,079 2,432

Near East and Mediterranean 830 84Total 3,746,273 378,439

.Swine Production Facilities

The trend in developed and developing countries is to change from small piggeries, where the feed isgrown and wastes are land applied locally, to fewer piggeries with greater numbers per facility and importof feed. This results in large quantities of wastes which must now be treated in order to prevent major environmental impact. Also, odors from larger facilities are objectionable to nearby communities. Swineoperations are often separated into feeder pig producers (up to 18 kg; 60 days) and feeder pig finishing(98 kg or larger; 150-160 days). The traditional operators raise a pig from birth to death (farrow to finish).The trend in swine housing is confinement in open feedlots or slanted floor units (Day & Funk, 1998;Zhang & Felmann, 1997). Manure is collected by scraping and land applied (with or without prior treatment), or hydraulically flushed from slanted or slatted floor housing where the diluted waste is storedunder the house or transported to storage tanks, lagoons, or other waste treatment systems. In somecases, treated wastewater is reused for flushing. Table 3 indicates that liquid flush systems prevail indeveloped countries, while dry storage and drylot systems are more common in emerging countries.

Physical and Chemical Characteristics

Typical values for swine waste characteristics as excreted and as collected in storage tanks and lagoonsand of runoff water and sludges from feedlots are presented in Tables 4, 5, 6, and 7 (Day & Funk, 1998;USDA, 1992; Zhang & Felmann, 1997). These data are useful in predicting environmental impact anddesigning systems for waste treatment.

Environmental Impact

In past years, swine herds were small and wastes could be applied to land used to produce feed andother crops. In contemporary concentrated piggeries with large herds, wastes may exceed the carryingcapacity of local ecosystems and are a potential cause of a number of pollution and health problemsrelated to their organic matter, nutrients, pathogens, odors, dust, and airborne microorganisms (Zhangand Felmann, 1997).

Table 3. Global Swine Waste Management System Usage (percent) (Safley et al., 1992)

Region AnaerobicLagoons

LiquidSystems a

DailySpread

Dry Storageand Drylot

Other Systems b

Asia 1 38 1 53 0Eastern Europe 8 39 0 52 1Western Europe 0 77 0 23 6

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North America 25 50 0 18 6Latin America 0 8 2 51 40

Africa 0 7 0 93 0Oceania 55 0 0 0 28

Near East and Mediterranean 0 32 0 68 0Global Average 5 42 1 45 5

a

Includes liquid/slurry and pit storagebIncludes deep pit stacks, litter, and other

Table 4. Typical Body Mass and Waste Production andCharacteristics per day per 1000kg of Swine (Day & Funk, 1998)

Table 5. Production and Characteristics of Fresh Manure by Pigs (Zhang & Felmann, 1997)

Parameter Nursery Growing Finishing GestationSow

Sow andLitter

Boar

Size, kg 15.9 29.5 68.1 125 170 159Manure, kg/day 1.0 1.9 4.4 4.0 14.9 5.0

TS, kg/day 0.091 0.18 0.41 0.36 1.36 0.45VS, kg/day 0.077 0.14 0.33 0.30 1.09 0.420

BOD 5 0.032 0.059 0.14 0.12 0.45 0.16N, kg/day 0.007 0.013 0.031 0.028 0.10 0.035

P 2O 5, kg/day 0.005 0.010 0.023 0.022 0.078 0.027K2O, kg/day 0.005 0.11 0.024 0.022 0.082 0.028

Table 6. Swine Waste Characteristics From Storage TanksUnder Slats (USDA, 1992)

Component Farrow Nursery Finish BreedingMoisture, % 96.5 96.0 91.0 97.0TS, % w.b. 3.50 4.00 9.00 3.00VS, % w.b. 2.28 2.79 6.74 1.80FS, % w.b. 1.22 1.71 2.26 1.20

N, g/L 3.6 4.8 6.3 3.0

Parameter Mean Std. Dev.Live Weight, kg 61 --

Total Manure, kg 84 24Urine, kg 39 4.8

Density, kg/m 3 990 24Total Solids, kg 11 6.3

Volatile Solids. kg 8.5 0.66BOD 5, kg 3.1 0.72COD, kg 8.4 3.7

pH 7.5 0.57TKN, kg* 0.52 0.21

Ammonia-N, kg* 0.29 0.10Total P, kg 0.18 0.10Ortho-P, kg 0.12 --

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NH4-N, g/L 2.8 4.0 - -P, g/L 1.8 1.6 2.7 1.2K, g/L 2.8 1.6 2.2 2.1

C:N Ratio 4 3 6 3

Table 7. Swine Waste Characteristics From Storage/Treatment Facilities (USDA, 1992)

Anaerobic Lagoon Feedlot*Component Sludge Supernatant Settled Sludge Runoff Water Moisture, % 92.4 99.8 88.8 98.5TS, % w.b. 7.60 0.25 11.2 1.5VS, % w.b. 4.68 0.12 90.7** --FS, % w.b. 2.92 0.13 21.3** --BOD 5, g/L -- 0.40 -- --COD, g/L 64.6 1.2 -- --

N, g/L 3.0 0.35 5.6** 2.0**NH4-N, g/L 0.76 0.22 4.5** 1.2**

P, g/L 2.7 0.13 2.2** 0.38**K, g/L 7.6 0.38 10.0** 1.10**

C:N Ratio 8 2 -- -- *Semi-humid climate (76 cm annual rainfall); annual sludge removal**kg/d/1000kg animal weight

Organic matter is concentrated and undergoes anaerobic decomposition producing odors related tohydrogen sulfide, ammonia, volatile acids, and other compounds. The highly biodegradable organicmatter also attracts pests, including insects and rodents. Organic matter may also cause oxygendepletion in surface waters and other undesired effects related to color, turbidity, and taste and odor.When organic matter undergoes decomposition under highly anaerobic conditions, methane (a major greenhouse gas) is released into the atmosphere (Safley et al., 1992; USEPA, 1993).

Nutrients each have their own impacts on surface and ground water. Nitrogen may be released asammonia into the atmosphere, where it acts as a greenhouse gas and contributes to acid rain in itsoxidized form. Ammonia may also react with nitrate in the atmosphere to form ammonium nitrateparticles which contribute to smog and health problems. High ammonia levels in swine houses may alsocause eye irritation, respiratory problems, and illness in workers and animals. The recommendedmaximum acceptable level for human and animal occupancy is 10 ppm (Morrison et al., 1991).

In surface waters, nitrogen in the form of ammonia or nitrates causes blooms of algae and aquatic plantswhich contribute to eutrophication and their decomposition may lead to anaerobic conditions. Theseblooms, caused also by phosphorus, may consist of highly toxic algae ( Pfiesteria ) in brackish waters andhave been implicated in kills of fish and other aquatic life, and as a cause of adverse health effects onhumans and animals (Lusk, 1998). Ammonia is toxic to life in surface waters (Zhang & Felmann, 1997).Concentrations as low as 0.08 mg/L have been shown to cause trout kills. Runoff from swine raisingoperations and manure-fertilized fields commonly contains 200-200 mg/L ammonia which is well abovethe recommended USEPA standard of 0.02 mg/L (USDA, 1992). Nitrates in groundwater may causesignificant health problems in human and animal development leading to methemoglobinemia, a diseasecausing oxygen starvation of developing tissues and possible death. The USEPA drinking water standardfor nitrate-N is 10 mg/L (USDA, 1992). At elevated levels, nitrates are also toxic to fish and other aquaticorganisms.

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Sulfides are generated from degradation of protein and other sulfur-containing compounds in swinewastes. These may be toxic to aquatic organisms and cause odors and toxicity in swine-housing(Donham, 1991; Morrison et al., 1991). Hydrogen sulfide, detectable as an odor at concentrations as lowas 0.005 ppm, causes loss of appetite, vomiting, and nausea at 50-500 ppm, and is lethal at 1000 ppm.

Swine wastes contain pathogens and coliform bacteria and other microbial indicators of fecal pollution(CAST, 1996; Zhang & Felmann, 1997). Although the pathogens are mainly host specific, certaindiseases such as salmonellosis, Q fever, Newcastle disease, histoplasmosis, cryptosporidiosis, andgardiasis may be transmitted by swine waste. Fecal indicator organisms originating from swine wastesmake it impossible to distinguish the presence of animal or human fecal pollution. Pathogens in thewastewater may also result in cross-infection of the swine.

Dust and bioaerosols from animal feed and manure may cause health problems in animals and workers if not controlled by ventilation and other means (Morrison et al., 1991; Zhang & Felmann, 1997). They maycause infectious and respiratory diseases, reduced immune response, allergies, and discomfort.

Odors are a major environmental problem with large piggeries (Davidson et al., 1995; Wilkie et al.,1995a). These are caused by numerous volatile compounds such as ammonia, amines, volatile fattyacids, mercaptans, carbonyls, phenols, and indoles. Odor threshold concentrations are very low and area major factor limiting location of these facilities.

Laws, Regulations, Policy

In response to the increased environmental impact of intensive rearing facilities for swine and other livestock, several laws, regulations, and policies designed to protect public health and the environmentare being called into enforcement as they apply to these industries in the U.S. (Weitman, 1995).

Control of methane, ammonia, and dust emissions may fall under the jurisdiction of agencies chargedwith enforcing the Clean Air Act which addresses the air quality of the nation.

The Clean Water Act regulates animal feeding operations considered to be point sources of pollution byrequiring permits issued by the National Pollution Discharge Elimination System (NDPES). Whether apiggery or other operation falls under the jurisdiction of this Act depends on the number of animal units

(1000 animal units equals 2,500 swine), type of confinement, days of operation, and nature of the water receiving discharge. For example, Category 1 includes operations with over 1,000 animal units; confines,feeds, or maintains animals for a total of 45 days or more in a year; and does not sustain any crops,vegetative forage, or harvest residues. The NDPES permit for this category stipulates that there must bea storage facility to contain all of the manure plus processing water and runoff from a 25-year, 24-hour storm event. Monitoring is required at least once per year and a plan for nutrient management must beapproved and implemented. Smaller facilities must submit plans based on Best Available Technology(BAT) that is economically achievable and Best Conventional Pollutant Control Technology (BCPCT)based on professional judgment. The Clean Water Act also regulates non-point source pollution byrequiring states to devise a comprehensive plan that addresses contributors. This involves voluntaryadoption of Best Management Practices (BMPs) which are encouraged by educational programs, training,financial and technical assistance, and demonstration projects.

The Coastal Zone Act Reauthorization Amendments (CZARA) of 1990 regulates animal operations in35 states which have coastal area watersheds. These facilities are regulated exclusive of those under theClean Water Act. These regulations require storage and treatment of wastewater and stormwater, wastetreatment, and nutrient management. Existing facilities in the U.S. under these regulations for swine have100-200 head. Odor problems are becoming more prevalent due to the increased scale of intensivelivestock operations and urban encroachment into rural areas; these problems are subject to the commonlaws of nuisance. Farmers are still protected to some extent from these complaints by the Right-to-Farmlaws. Federal and state incentives are alternatives to regulation. For example, the Environmental Quality

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Incentives Program (EQIP) provides cost sharing of up to 75% of the costs of pollution preventionpractices.

Ultimately, the tax payer, consumer, and producer must pay the price for maintenance of environmentalquality. The cost of environmental pollution is difficult to assess as the effects are usually indirect andlong-term. Whatever the case, human activities, including animal production must strive for sustainablitywhich will cost more.

ANAEROBIC DIGESTION OF ORGANIC MATTER

Anaerobic digestion may be defined as the engineered methanogenic anaerobic decomposition of organicmatter. This process, occurring naturally in anaerobic environments such as sediments, soils, and animalguts, involves a mixed consortium of different species of anaerobic microoganisms that function in concertto degrade organic matter and complete the carbon cycle for a large fraction of organic matter (Chynoweth, 1996). Non-methanogenic populations depolymerize organic polymers and ferment them toacetate (sometimes via other acids and fermentation products), hydrogen, and carbon dioxide. Differentmethanogenic bacteria convert acetic acid, hydrogen, and carbon dioxide to methane (Boone et al., 1993;Smith & Frank, 1988). Most, but not all organic matter can be decomposed by this fermentation withoutchemical or physical pretreatment. Lignin is the major natural compound that is refractory to anaerobicdecomposition. Other organics, such as cellulose, may be resistant to degradation when complexedtightly with lignin (e.g., in pine wood) or contained in biomass that contains methanogenic inhibitors (e.g.,in eucalyptus wood).

Anaerobic digestion has been applied for decades for treatment of domestic sludges, animal wastes,industrial wastes (McCarty, 1992), and more recently for the organic fraction of municipal solid wastes(Chynoweth & Isaacson, 1987). It has also been the subject of research for production of substitutenatural gas (SNG) from wastes, energy crops, including terrestrial herbaceous and woody energy crops,and aquatic (freshwater and marine) energy crops (Chynoweth & Pullammanappallil, 1996; Legrand,1993; Smith et al., 1988; Smith et al., 1992). Whatever the application, anaerobic digestion produces auseful energy form (methane) and a stabilized residue that can be subsequently applied to land as a soilamendment. Currently, its most common applications are treatment of domestic sludges, industrialwastes, and animal wastes. Its wider use has been hampered by the low cost of fossil-based energy,limited regulations on waste processing, a history of process instability, and greater knowledge and

popularity of aerobic processes. However, the climate is changing for this technology with incentives toreplace fossil fuels with renewable greener energy forms and stricter regulations on management of organic wastes that will require more costly in-vessel systems compared to land application, landfilling, or crude open lagoons.

A typical swine waste treatment system is shown in Figure 1. The wastes are transported directly or after

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Figure 1. Illustration of Collection and Management Options for Piggery Wastes

concentration into a digestion vessel which may vary in design from a lagoon to a mixed,non-mixed plug-flow, or attached film reactor. The operating temperature may be ambient, mesophilic(35 oC), or thermophilic (55 oC). The effluent is stored and land applied on a seasonal basis. Thesupernatant may be further treated for nutrient removal prior to discharge into receiving waters. Thebiogas is used either directly for heating or for operation of internal combustion engines to run equipmentor generate electricity.

Feed CharacteristicsDesign and operating parameters of anaerobic treatment systems are largely dependent upon the influenttotal solids (TS) concentration (Chynoweth, 1987; Chynoweth & Isaacson, 1987). For swine wastes, theexcreted concentration is about 10% and becomes diluted with urine and further diluted with flush water (in liquid systems), or concentrated when bedding is used in dry storage systems (Day & Funk, 1998;Sweeten et al., 1981; Zhang & Felmann, 1997). A typical concentration for tanks under slats is 3-4%.For a specific organic loading rate, the hydraulic retention time (HRT) of conventional stirred tank reactor

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(CSTR) anaerobic digesters increases inversely with the total solids concentration. At very lowconcentrations (

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straw (Llabres-Luengo & Mata-Alvarez, 1987), corn stover (Fujita et al., 1980), algae and water hyacinth(Campos & d'Almeida Duarte, 1992), and sewage sludge (Wong, 1990). Wong (1989) investigated avariety of agro-industrial additives, including cardboard, newspaper, sawdust, and sugarcane wastes.Mixtures of swine waste with sawdust or cardboard gave the highest methane yields. Residues fromsugarcane blends with pig wastes exhibited the highest fertilizer value. Wastes from pigs fed different

sources of fiber (oat hulls, maize hulls, lupin hulls, maize cobs, soya bean hulls, pea hulls, wheat bran,lucerne stems, and lucerne leaves) exhibited different extents and rates of biodegradability duringanaerobic digestion (Stanogias et al., 1985) . Volatile solids destruction ranged from 45% for wastes fromthe lucerne leaf diet to 80.4% from the maize hull diet.

Reactor Designs

The goals in selecting an appropriate anaerobic digester design are to maximize volatile solids (VS)conversion and associated methane yields, increase conversion rates and process stability, decreaseprocess energy requirements, and ultimately achieve a reliable system with the lowest possibleinstallation and operating costs. Odor control may also be a primary concern. No single reactor design issuitable for all applications in treatment of piggery wastes. Major factors influencing selection include:

chemical characteristics of feed concentration of feed biodegradable matter concentration of feed particulate solids density of raw and digested feed scale of application continuity of feed availability desired products site

The designs most commonly used for treatment of swine wastes are lagoon, batch, fed-batch,completely-mixed, and plug-flow. Several new high-rate designs have been developed to retain solidsand microorganisms and are particularly suitable for treatment of dilute wastes from flush systems or liquid fractions of separated wastes (Wilkie & Colleran, 1989). The principles of these various reactor designs are discussed below, and operating and performance data for several different reactor configurations are summarized in Table 9.

Component Influent % DestroyedTS, % 6.9 52

VS, %TS 82.6 60COD, g/L 73.8 58

total N, g/L 3.9 --protein, %TS 19.3 47

hemicellulose, %TS 20.1 65cellulose, %TS 12.4 64

lipids 14.8 69starch 1.6 94lignin 4.4 3

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Table 9. Operating and performance data for different digester designs (CSTR)

Reference (Hashimoto,1983)

(Hashimoto,1983)

(Stevens &Schulte, 1979)

(Mills, 1977) (Fischer et al.,1979)

(Zhang et al.,1990)

(Iannotti et al.,1979)

Operational DataReactor type CSTR CSTR CSTR CSTR CSTR CSTR CSTR

Volume, m 3 0.004 0.004 2.500 13.500 140.000 199.000 0.420Temp, oC 55 35 22.5 35 35 35 35

Type of waste whole whole whole flushed farrow-finish Whole finishingInfl. TS, % w.b. 6.36% 6.36% 5.48% 4.30% 3.00% 6.88%Infl. VS, % w.b. 5.04% 5.04% 3.57% 1.50% 2.38% 5.69%Infl. COD, g L -1 52.10 52.10 74.30 74.30 41.35 0.07

OLR, kg VS m -3 d -1 10.08 10.08 1.80 1.30 1.70 3.78OLR, kg COD m -3 d -1 7.43

HRT, d 5.00 5.00 20.00 10.00 14.00 15.00

Performance DataMY, m 3 kg VS added -1 0.31 0.26 0.29

MY, m 3 kg COD added -1 0.14MPR, m 3 m -3 d -1 3.12 2.69 0.52 0.79 0.57 0.52

VS redn., % 50.2 43.7 22.4 60.0 66.0 60.0COD redn., % 35.7 51.0 73.0 58.0Effl. N, g L -1 3.34 3.29 3.66 2.24 0.38 2.25 3.97Effl. P, g L -1

Gas Quality, % CH 4 61.1 64.2 63.0 60.0 64.0 59.0

Table 9. Operating and performance data for different digester designs (CSTR and two-phase)

Reference (van Velsen,1977)

(van Velsen et al.,1979)

(Petersen, 1982) (Cavallero &Genon, 1984)

(Maekawa et al.,1995)

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Operational DataReactor type CSTR CSTR CSTR CSTR two-phaseVolume, m 3 0.240 6.000 40.000 0.050 1.300

Temp, oC 32 30 37 35 38Type of waste whole whole whole supernatant whole dilutedInfl. TS, % w.b. 7.50 5.83 2.30 4.00Infl. VS, % w.b. 5.40 4.39 5.53 1.38Infl. COD, g L -1 80.30 51.75 32.09

OLR, kg VS m -3 d -1 4.50 2.64 2.12 4.74OLR, kg COD m -3 d -1 6.70 2.57

HRT, d 12.00 27.00 12.50 6.75

Performance DataMY, m 3 kg VS added -1 0.35 0.29

MY, m 3 kg COD added -1

MPR, m 3 m -3 d -1 0.90 0.61 0.72 1.41VS redn., % 38.3 46.0 41.2

COD redn., % 40.3 34.2Effl. N, g L -1 2.32Effl. P, g L -1

Gas Quality, % CH 4 76.3 63.3 78.5 60.1

Table 9. Operating and performance data for different digester designs (attached-film)

Reference (Chou et al., 1997) (Bolte et al., 1986) (Bolte et al., 1986) (Nordstedt &Thomas, 1985)

(Hill & Bolte,1988)

(Hill & Bolte,1986)

OPERATIONAL DATAReactor type AF upflow immobile

cellsAF, nylon mesh &

polyurethane foamAF, nylon mesh &

polyurethane foamAF, oak wood

blocksAF, polyester felt AF, nylon mesh

Volume, m 3 0.014 0.005 0.005 0.005 0.300 0.300

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Temp, oC 37 35 55 31.1 35 35Type of waste screened, diluted flushed, screened flushed, screened settled supernatent flushed screened flushed screenedInfl. TS, % w.b. 1.33 1.42 2.02 1.88 1.89Infl. VS, % w.b. 1.03 1.13 1.43 1.50 1.56Infl. COD, g L -1 7.50 16.11 17.80 33.47 19.69 21.10

OLR, kg VS m -3 d -1 3.44 11.34 7.22 7.50 7.80OLR, kg COD m -3 d -1 7.50

HRT, d 1.00 3.00 1.00 2.00 2.00 2.00

PERFORMANCE DATAMY, m 3 kg VS added -1 0.30 0.22 0.23 0.37 0.27

MY, m 3 kg COD added -1 0.12 0.29 0.20MPR, m 3 m -3 d -1 0.90 1.03 2.43 1.68 2.80 2.15

VS redn., % 46.5 40.6 38.4 51.0 42.9COD redn., % 61.0 49.7 34.5 51.7 46.2 42.1Effl. N, g L -1 0.97 0.98 0.87 0.82Effl. P, g L -1

Gas Quality, % CH 4 77.0 71.0 67.7 79.2 62.5 60.5

Table 9. Operating and performance data for different digester designs (attached-film) Reference (Wilkie &

Colleran, 1986)(Wilkie &

Colleran, 1986)(Sorlini et al.,

1990)(Sorlini et al.,

1990)(Sorlini et al.,

1990)(Hasheider &

Sievers, 1983)OPERATIONAL

DATAReactor type AF, polypropylene

ringsAF, polypropylene

ringsAF, wood chips AF, PVC AF, expanded

clayAF, limestone

Volume, m 3 2.800 2.800 0.015 0.015 0.015 0.003Temp, oC 25 35 30 30 30 35

Type of waste settledsupernatent

settled supernatent whole whole whole screened diluted

Infl. TS, % w.b. 1.33 1.45 0.62 0.62 0.62

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Infl. VS, % w.b. 0.87 0.96 0.40 0.40 0.40 0.60Infl. COD, g L -1 25.20 29.60 5.73 5.73 5.73

OLR, kg VS m -3 d -1 6.00OLR, kg COD m -3

d -18.40 9.90 0.73 1.18 0.54

HRT, d 3.00 3.00 7.89 4.84 10.71 1.00

PERFORMANCEDATA

MY, m 3 kg VS

added -10.21 0.14 0.03 0.23

MY, m 3 kg CODadded -1

0.17 0.22

MPR, m 3 m -3 d -1 1.47 2.18 0.21 0.21 0.21 0.90VS redn., % 60.0 64.7 13.5 41.9

COD redn., % 52.0 60.0Effl. N, g L -1 0.41Effl. P, g L -1

Gas Quality, %CH 4

87.0 87.0 72.0 77.0 68.0 71.0

Table 9. Operating and performance data for different digester designs(attached-film and UASB)

Reference (Ng & Chin, 1988) (Wilkie & Colleran,1984)

(Lo et al., 1994) (Foresti & deOliveira, 1995)

(Owens, 1988)

OPERATIONAL DATAReactor type AF, activated carbon AF, clay UASB UASB UASBVolume, m 3 0.004 0.180 0.015 0.011 0.002

Temp, oC na 33 25 25 20.7Type of waste whole settled supernatent screened diluted screened diluted flushed screenedInfl. TS, % w.b. 0.40 1.51Infl. VS, % w.b.Infl. COD, g L -1 7.80 30.05 12.00 3.73 8.84

OLR, kg VS m -3 d -1

OLR, kg COD m -3 d -1 14.20 5.00 3.58 4.50 4.40

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HRT, d 0.75 6.00 3.28 0.83 2.00

PERFORMANCE DATAMY, m 3 kg VS added -1 0.05

MY, m 3 kg COD added -1 0.39MPR, m 3 m -3 d -1 0.46 1.93 0.71 0.13

VS redn., % 57.0 44.4COD redn., % 78.0 73.3 87.0 53.6Effl. N, g L -1 0.23

Effl. P, g L -1Gas Quality, % CH 4 84.3 87.0 67.0 80.0

Table 9. Operating and performance data for different digester designs (plug-flow, baffle-flow, lagoons)

Reference [Yang, 1985a #89] (Floyd & Hawkes,1986)

(Boopathy &Sievers, 1991)

(Yang & Chou,1985)

(Chandler et al.,1983)

(Safley &Westerman, 1988)

OPERATIONALDATA

Reactor type plug-flow withrecycle Tubular ABR ABR Anaerobic Lagoon Anaerobic LagoonVolume, m 3 11.500 0.013 0.010 0.020 19,000

Temp, oC 26 30 35 30 ambientType of waste whole diluted whole whole settled supernatent flushedInfl. TS, % w.b. 5.30 5.17 0.7Infl. VS, % w.b. 0.79 3.88 3.86 0.09Infl. COD, g L -1 58.50 1.77

OLR, kg VS m -3 d -1 5.27 4.00 1.75 0.11 0.16OLR, kg COD m -3

d -13.53

HRT, d 1.50 10.00 15.00 0.50 53-60

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PERFORMANCEDATA

MY, m 3 kg VSadded -1

0.14 0.25 0.50 0.23

MY, m 3 kg CODadded -1

0.07 0.04 0.11

MPR, m 3 m -3 d -1 0.71 0.96 2.01 0.04-0.05 0.03 (biogas)VS redn., % 88.7 61.0 75

COD redn., % 62.0 28.8Effl. N, g L -1 1.10 0.14 0.24Effl. P, g L -1

Gas Quality, %CH 4

67.5 63.0 62.0 69

Table 9. Operating and performance data for different digester designs (sequencing batch reactors)

Reference (Zhang et al.,1997)

(Zhang et al.,1997)

(Masse et al., 1993) (Hill et al., 1985)

OPERATIONAL DATAReactor type SBR SBR SBR SBRVolume, m 3 0.012 0.012 0.025 0.454

Temp, oC 25 25 20 35Type of waste screened diluted screened diluted screened whole, scrapedInfl. TS, % w.b. 4.80% 12.77%Infl. VS, % w.b. 0.90% 3.30% 3.00% 10.82%

Infl. COD, g L-1

84.00OLR, kg VS m -3 d -1 4.50 5.50 0.02

OLR, kg COD m -3 d -1 1.20HRT, d 2.00 6.00 78.00 60.00

PERFORMANCE DATAMY, m 3 kg VS added -1 0.24 0.23 0.76 0.33

MY, m 3 kg COD added -1

MPR, m 3 m -3 d -1 1.08 1.28VS redn., % 39.0% 40.0% 56.0% 46.4%

COD redn., % 73.0%

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Effl. N, g L -1 0.89 2.47Effl. P, g L -1

Gas Quality, % CH 4 72.0% 61.0% 63.0% 59.8%

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(anaerobic lagoon)

An anaerobic lagoon is a deep pond (~5 meters) with steep sides which is not aerated and operateslargely under anaerobic conditions. The surface may be covered (Chandler et al., 1983; Safley &Westerman, 1989) to facilitate biogas collection and odor reduction. Lagoons operate at ambienttemperature, receive dilute swine waste slurries, and serve as reactors for treatment and reservoirs for storage. Biogas production rate from a swine waste lagoon was 0.05 m 3/m3 per day and 0.13 m 3/m2 per day. Production of biogas was found to be a function of VS loading and lagoon temperature (Cullimore etal., 1985; Safley & Westerman, 1989; Safley & Westerman, 1988). Lagoons may be inexpensive, butrequire large areas and are often associated with odors.

(batch)

Batch reactors consisting of large circular or rectangular tanks are fed waste along with an inoculum, anddegradation is permitted to startup and proceed to completion. These reactors are often unstable andrequire careful attention to the inoculum-to-feed ratio; VS conversion is erratic.

(completely mixed)

The continuously-stirred tank reactor (CSTR) is the most common design used in wastewater and farmapplications treating feeds with >3% solids. This design is usually heated, mixed constantly, and usuallyfed intermittently rather than continuously. The major disadvantage is the loss of inoculum andundigested solids at high loading rates.

(anaerobic contact)

This design employs a CSTR followed by a settling operation to concentrate washed out microorganismsand undigested solids for recycle back to the CSTR. This results in increased solids retention time (SRT)and reduced digester volume and is used for dilute wastewater applications.

(plug-flow)

The plug-flow reactor is non-mixed and the feed passes through a trench or cylinder (Floyd & Hawkes,

1986; Gorecki, 1993). These systems are often covered with a balloon plastic cover (Taiwan, 1993). TheSRT may also be increased using sludge recycle (Yang and Nagano, 1985). Best performance wasobtained at an HRT of 2 days and SRT of 3.25 days. In the baffled modification of this design, internalbaffles facilitate mixing and result in extended retention of microorganisms and solids (Boopathy &Sievers, 1991; Yang & Chou, 1985; Yang & Moengangongo, 1987). These designs result in moreconversion and higher conversion rates than CSTR or batch reactors.

(continuously expanding/sequential batch)(fed-batch)

Some batch reactors, such as the continuously expanding (Hill et al., 1985) or anaerobic sequential batch(Dague et al., 1992; Zhang et al., 1997), are intermittently fed, allowing the solids to settle, andsupernatant is withdrawn between feeding intervals. Solids are also removed on an intermittent basis.These reactors may or may not be heated (Masse et al., 1993). They promote longer solids than liquid

retention times and substantially improve process kinetics over batch and CSTR designs.(attached-film)

Several designs use various inert media for attachment of bacteria, forming biofilms, and thus preventingtheir washout at high hydraulic loadings (Wilkie & Colleran, 1989). These designs are applicable for feedstocks with low suspended solids (

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an expanded or fluidized state of the biofilm coated medium. One of the most popular designs, the upflowanaerobic sludge blanket (UASB), takes advantage of the formation of granules consisting of denseconsortia of microorganisms which are formed under carefully controlled conditions. Specialized gas/flocseparators are employed to prevent washout of these granules.

Lo (1994) showed that performance of UASB digesters treating screened swine waste could be improvedby incorporation of a rope matrix for attachment of microorganisms in the mid-section of the reactor.Chou (1997) immobilized inoculum in cellulose triacetate for use in a packed bed reactor. Very lowhydraulic retention times were achieved in this system without sacrifice in performance.

Other successful media for microbial attachment have included nylon cuboid and polyurethane foam(Bolte et al., 1986; Bossier et al., 1986), wood blocks (Nordstedt & Thomas, 1985), nylon mesh (Hill &Bolte, 1986), polypropylene cascade mini-rings(Wilkie & Colleran, 1986), limestone (Hasheider & Sievers,1983), sand and activated carbon (Ng & Chin, 1988). Wilkie and Colleran (1984) compared severalmedia including clay, coral, mussel shell, and plastic pall-ring support materials, finding similar performance in upflow filters.

(high solids)

Swine wastes may be mixed with bedding or other wastes, such as the organic fraction of municipal solidwastes, to produce high-solids feedstocks exceeding 20% total solids. Several reactor designs havebeen recently developed to accommodate high-solids feeds without dilution. One group includes mixeddigesters operated at solids concentrations as high as 35%. These include vertical reactors, with feedmixing with inoculum only during feeding, or intermittent mixing of reactor contents during operation asdescribed by Chynoweth (1996). Some designs have horizontal reactors mixed by slow rpm mixers.The sequential batch anaerobic composting design (Chynoweth et al., 1991) uses batch leachbedreactors which are started up by interacting leachate between new and mature reactor solids beds toinoculate the new batch and convey fatty acids to a mature reactor during startup. Others interactleachbeds with methane-phase digesters during startup and operation. Advantages of high-solidssystems include reduced odors, easier nutrient management, and reduced reactor size.

(staged)

Several designs involve one or more stages (usually two) where depolymerization and fermentation toorganic acids occur in the first stage and degradation of acids and methanogenesis is accomplished inthe second stage, in conventional or high-rate attached-film digesters. Actually in most piggeries, this firstacid-forming stage occurs fortuitously during waste storage prior to treatment in anaerobic digesters.There are three major advantages to multi-phase designs (Chynoweth & Pullammanappallil, 1996). Thefirst involves improved stability. In a single, combined-phase digester, overloading and inhibition result inaccumulation of volatile organic acids for which resident populations are not present in sufficient numbersto metabolize. Enrichment for these organisms can take several weeks. In a two-phase system,formation of acids is encouraged in the first, or acid phase; therefore, the second methane phase isconstantly receiving acids to encourage high populations of acid-utilizing organisms. In other words, theacid-phase is an intentionally imbalanced digester which is resistant to further imbalances resulting fromoverloading or inhibitors. The second advantage is that the slow-growing populations of microorganisms(acid utilizers and methanogens) can be concentrated in biofilms, thus permitting short retention times for

the second-phase reactor. This reduces the overall reactor volume requirement, including both stages.The third advantage is that most of the biogas is produced in the methane-phase digester and themethane content of this gas is higher because of the prior release of much of the carbon dioxide in the

acid phase. This advantage facilitates biogas utilization by localizing its production and increasing itsmethane content.

Yang (1995) proposed a three-stage digester design for undiluted pig wastes (TS 8-10%). With anorganic loading rate of 2.95 g VS/L per day, a methane yield of 0.42 L/g VS and VS reduction of 69.9%

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was achieved. Tseng (1992) observed improved digestion of swine wastes employing the first stagereactor to perform solids sedimentation and acidification, and a second tank to perform methanogenesis.

Operating Parameters

(loading rate)

The most meaningful parameter for describing the feed rate is loading rate which is the feedconcentration divided by the HRT (Chynoweth & Pullammanappallil, 1996). Loading rate is expressed asweight of organic matter (VS or COD) per culture or bed volume per day (e.g., kg VS/m 3/day). Thisparameter (corrected for head space) describes the reactor volume needed for a particular feed rate.Other parameters, such as solids concentration and retention time (hydraulic or solids), are misleadingand do not provide a valid basis for comparison of digester costs.

Aside from influencing digester size, solids concentration has a significant effect on digester design andperformance, and on materials handling. Feeds with low concentrations of suspended solids (15 days for mesophilictemperature) or some mechanism for retaining suspended solids, such as solids recycle or concentrationof solids within the reactor, as in the sequential batch, upflow sludge blanket, or baffle-flow designs. Inthe case of feed blends (discussed below), feed solids may exceed 10%, allowing for the use of high-solids designs with reactor solids concentrations up to 35%. Advantages of these designs include higher loading rates, lower heating energy requirements, and less water as a waste product (Wujick & Jewell,1980). It has also been shown that cellulolytic enzyme activity per unit reactor volume is higher in high-solids systems (Rivard et al., 1994). High solids systems have a unique set of advantages and limitationswith respect to materials handling related to feed addition, mixing, and effluent removal.

(start-up)

Effective digester startup is dependent upon the quality and quantity of inoculum (Chynoweth &Pullammanappallil, 1996). In conventional CSTR digesters, the inoculum-to-feed ratio (VS basis) istypically greater than 10. In designs where washout of critical organisms is a concern, suspended solids

in the effluent may be settled and recycled. With batch and plug-flow designs, inoculum is obtained fromprevious runs or by effluent recycle. Baffled systems trap inoculum throughout the reactor and inoculatethe feed as it passes through. Attached-film reactors often take months to fully start up but have theadvantage of inoculum retention during the course of operation. Under-inoculation of a digester results inimbalanced performance due to the more rapid growth of acid formers than methane formers leading toaccumulation of organic acids and consequent pH reduction.

(temperature)

Biological methanogenesis has been reported at temperatures ranging from 2 oC (in marine sediments) toover 100 oC (in geothermal areas)(Zinder, 1993). Most applications of this fermentation have beenperformed under either ambient (15 to 25 oC), mesophilic (30 to 40 oC), or thermophilic (50 to 60 oC)temperatures. In general, the overall process kinetics double for every 10 oC increase in operating

temperature up to some critical temperature (about 60o

C) above which a rapid dropoff in microbialactivityoccurs (Harmon et al., 1993). The populations operating in the thermophilic range are geneticallyunique (Zinder, 1993), do not survive at lower temperatures, and are more sensitive to temperaturefluctuations outside of their optimum range. Digesters with lower temperatures are more stable andrequire less process energy, but require larger volumes. Thermophilic digesters have lower volumerequirements but have higher energy requirements and are less stable. Ammonia is also more toxic inthese digesters because the more toxic free ammonia is favored (Hansen et al., 1998).

Typically, most digesters are operated at mesophilic or ambient temperatures. Several researchers haveinvestigated psychrophilic anaerobic digestion of swine wastes (Safley & Westerman, 1990; Stevens &

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Schulte, 1979; van Velsen et al., 1979; Zeeman et al., 1988). Digestion proceeds at temperatures as lowas 10 oC, requires longer retention times, and requires a low-temperature inoculum for effective startup.Mesophilic operation seems to be the most preferred because of the possibility for control of temperaturefluctuations (not possible for ambient temperature operation) and the higher energy costs for thermophilicdigestion. Thermophilic operation is practiced in circumstances when the reduced reactor sizes and theeffective pathogen kill justify higher energy requirements and extra effort to ensure stable performance.

(nutrients)

Nitrogen and phosphorus are the major nutrients required for anaerobic digestion. These elements arebuilding blocks for cell synthesis and are directly related to microbial growth requirements in anaerobicdigesters. An average empirical formula for an anaerobic bacterium is C 5H7O2NP 0.06 (Speece, 1997).Thus, the nitrogen and phosphorus requirements for cell growth are 12% and 2%, respectively, of thevolatile solids converted to cell biomass (about 10% of the total volatile solids converted); this would beequivalent to 1.2% and 0.024% of the biodegradable volatile solids, respectively, for nitrogen andphosphorus.

Previous studies have identified critical feedstock C/N ratios of 15 for seaweed (Chynoweth et al., 1987)and 15-19 for swine waste (Sievers & Brune, 1978), above which nitrogen was limiting. In fact, nutrientlimitations are better related to concentrations; e.g., a value of 700 mg/L was recently reported for theoptimum NH 4-N concentration in high-solids anaerobic digestion of the organic fraction of municipal solidwaste (Kayhanian, 1994). Nutrients may also be concentrated by certain design and operating practices.For example, designs that concentrate solids (Chynoweth, 1987) or reuse supernatant or leachate fromprocess effluent (Chen & Chynoweth, 1990; Chynoweth et al., 1991), concentrate nutrients extracted fromthe feedstock. Ammonia is also an important contributor to the buffering capacity in digesters but mayalso be toxic to processing in high solids digesters. Ammonia toxicity was exhibited from feeds that hadnormal C/N ratios because ammonia became concentrated in the supernatant as digestion proceeded(Jewell et al., 1993).

Other nutrients needed in intermediate concentrations, include sodium, potassium, calcium, magnesium,chlorine, and sulfur. Requirements for several micronutrients have also been identified, including iron,copper, manganese, zinc, molybdenum, cobalt, nickel, selenium, and vanadium (Speece, 1997; Wilkie etal., 1986). Available forms of these nutrients may be limiting because of their ease of precipitation and

removal by reactions with phosphate and sulfide. Limitations of these micronutrients have beendemonstrated in reactors where the analytical procedures failed to distinguish between available andsequestered forms (Jewell et al., 1993).

(mixing)

Mixing is traditionally thought to be required for optimized digestion to enhance interaction between feedand cells (inoculation) and remove inhibitory metabolic products from the cells. Mixing is also practiced tobreak up floating scum and foam layers which are typical with some feedstocks, such as domestic sludge.Therefore, conventional digesters include mixing, which is accomplished by mechanical stirring, liquidrecycle, or gas recycle. Mixed digesters have been referred to as microbial torture chambers based onresearch observations (J.G. Ferry, personal communication) that metabolism of certain compounds (e.g.,benzoate) is inhibited by mixing and efficient consortia function well in UASB digesters employing

granules or other biofilms (Switzenbaum, 1991). One explanation for this inhibition is that microbialconsortia existing in clumps are disrupted from that optimum arrangement by mixing. Chynoweth (1987)also demonstrated that a nonmixed solids-concentrating reactor design exhibited more rapid kinetics,lower nutrient requirements, and greater stability than a CSTR design. This improved performance wasattributed to reduction in washout of solids and critical organisms. The practice of mixing in swine wastedigesters varies depending on the design and was previously addressed under the discussion of reactor options. However, the energy requirement related to mixing can require as much as 14 percent of themethane energy product in conventional low solids designs (see below under energy requirements).

(inhibition)

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Biomethanogenesis is sensitive to several groups of inhibitors, including alternate electron acceptors(oxygen, nitrate, and sulfate), sulfides, heavy metals, halogenated hydrocarbons, volatile organic acids,ammonia, and cations (Speece, 1996). The toxic effect of an inhibitory compound depends upon itsconcentration and the ability of the bacteria to acclimate to its effects. The inhibitory concentrationdepends upon different variables, including pH, HRT, temperature, and the ratio of the toxic substanceconcentration to the bacterial mass concentration. Antagonistic and synergistic effects are also common.Methanogenic populations are usually influenced by dramatic changes in their environment, but can beacclimated to otherwise toxic concentrations of many compounds.

Inhibition in anaerobic digesters is reflected by accumulation of volatile acids (related to overloading or toxic feed components), high ammonia levels (related to nitrogenous feeds), or toxic feed components.Normal and inhibited turnover rates of volatile acids are discussed by Winter (1984). When theconcentration of total volatile organic acids is in the range of 2,000 mg/L or higher, the onset of imbalanceis indicated. Digesters, e.g., acid-phase systems, can acclimate to concentrations as high as 10,000mg/L. This tolerance is related to alkalinity levels which are influenced by ammonia and bicarbonate.

Swine wastes have a high nitrogen content, resulting in high ammonia concentrations during anaerobicdigestion. Concentrations in the range of 3,000 mg/L or higher have traditionally been thought to beinhibitory to anaerobic digestion (Braun et al., 1981), especially in combination with high pH that favorsthe volatile NH 3 form. Some researchers have found that acclimated digester cultures can functionnormally at much higher concentrations, even as high as 6,000 mg/L (Hansen et al., 1998; van Velsen,1977). Cintoli (1995) evaluated use of zeolite to reduce ammonia in piggery wastes to sub-inhibitorylevels (1500 to 300 mg/L) prior to treatment in a UASB digester.

Swine and other animals are fed antibiotics and other drugs to prevent infectious diseases and promotegrowth. In general, results have shown that some antibiotics (e.g., monensin and chlorotetracycline)inhibit digestion (Varel & Hashimoto, 1981; Varel & Hashimoto, 1982) but acclimation is possible, andothers (e.g. arsanilic acid, roxarsone, and avilamycin) either stimulated digestion or had no observableeffect (Brumm & and Sutton, 1979; Brumm et al., 1980; Brumm et al., 1979; Brumm et al., 1977; Sutton etal., 1989). Camprubi (1988) evaluated different concentrations of antibiotics added to swine waste,including furazolidone, chloramphenicol, chlorotetracycline tylosin, erythromycin, carbadox, and copper sulfate. Chloramphenicol was the most potent inhibitor of anaerobic digestion.

Performance Parameters

(Gas and Methane Yields, Rates, and Reduction in Organic Matter)

Total biogas and methane production, when related to organic matter, are directly influenced by theextent and rate of conversion. Biogas yields are related to organic matter fed which is expressed asvolatile solids (VS) or chemical oxygen demand (COD). These data are typically reported as gas volume(m3) per weight (kg) VS or COD added. Methane yield is preferred over gas yield because pH changes inthe reactor can cause changes in release or uptake of carbon dioxide that are unrelated to degradation.Use of VS permits calculation of a materials balance between the feed, effluent solids, and gas. Use of COD allows for calculation of an oxidation-reduction balance between the feeds and products. In thecontext of materials balances, the reduction in organic matter may be calculated as reduction in VS or

COD. A typical methane yield for the organic fraction of swine waste is 0.3 m3

/kg VS (Table 9) whichcorresponds to a volatile solids reduction of 50%.

Methane production rate is a measure of process kinetics and is determined as volume of methane per volume of reactor per day (m 3/m3/day). This parameter is the product of loading rate (kg/m 3/day) andmethane yield (m 3/kg VS added). Values for piggery waste digestion have been reported in the range of 0.04 to 3.0 m 3/m3/day.

Methane content of the biogas is also a good indicator of stability. Under normal circumstances, thisvalue is a function of the H/C ratio of the biodegradable fraction and is normally in the range of 50-60%

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(Owens & Chynoweth, 1993). Since lowered methanogenic activity is the key factor leading to imbalance,a reduction of methane gas content is a key performance parameter and has been employed as an on-line control parameter (Chynoweth et al., 1994). The biochemical methane potential (BMP) assay(Chynoweth et al., 1993; Owen et al., 1979; Owens & Chynoweth, 1993) is useful for estimating theultimate methane yield and relative conversion rates of feed samples, specific feed components, andremaining biodegradable matter in process residues. This assay may also be used to determine toxicityof feed components. In general, the test is conducted with miniature digesters (200 mL) which areoptimized for conversion in terms of inoculum, feed concentration, nutrients, and buffer. These miniaturebatch digesters are incubated until no further gas production is observed. Measurements include gasproduction and composition of influent and effluent organic matter.

(Organic Acids, pH, and Alkalinity)

Organic acids, pH, and alkalinity are related parameters that influence digester performance (McCarty,1964; WPCF, 1987). Under conditions of overloading and the presence of inhibitors, methanogenicactivity cannot remove hydrogen and organic acids as fast as they are produced. The result isaccumulation of acids, depletion of buffer, and depression of pH. If uncorrected via pH control andreduction in feeding, pH will drop to levels which stop the fermentation. Independent of pH, extremelyhigh volatile acid levels (>10,000 mg/L) also inhibit performance. The major alkalis contributing toalkalinity are ammonia and bicarbonate. A normal healthy volatile acid-to-alkalinity ratio is 0.1. Increasesto ratios of 0.5 indicate the onset of failure and a ratio of 1.0 or greater is associated with total failure. Themost common chemicals for pH control are lime and sodium bicarbonate. Lime produces calciumbicarbonate up to the point of solubility of 1,000 mg/L. Sodium bicarbonate adds directly to thebicarbonate alkalinity without reaction with carbon dioxide. However, precautions must be taken not toadd this chemical to a level of sodium toxicity (>3500 mg/L). The alkalinity needed to neutralize volatileacids (VFA) is calculated by multiplying 0.833 times VFA concentration (mg/L as acetic acid) (WPCF,1987).

Certain volatile fatty acids are particularly associated with the onset of digester failure, including propionicand higher numbered acids (Gourdon & Vermande, 1987; Hill, 1988; Wilkie and Smith, 1989).Accumulation of these acids results from a backup of hydrogen (or electron) flow and their formation asan alternative to methanogenesis for hydrogen utilization. Useful parameters based on this principle arethe ratio of these acids to acetic acid (Hill et al., 1987) and the concentrations of iso-volatile acids (Hill &

Holmbert, 1988).

Modeling

Numerous models have been developed to provide a theoretical understanding of microbial populationsand their interactions with the physical and chemical environment. Models use mathematical expressionsto describe the interactions between various microbial populations involved in the process, includingsubstrate utilization rates, microbial growth rates, product formation rates, and physico-chemicalequilibrium relationships. More simplified anaerobic digestion models can be used for optimizing process

design and operation and for process control. These usually incorporate four major steps, includingdepolymerization and solubilization, acidogenesis, methanogenesis, and inhibition.

The following equations based on the Contois Model have been used to describe the kinetics of anaerobic digestion of swine waste at steady state (Chen, 1983; Hashimoto, 1984):

B B K

K om

= +

11

(1)

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= +

B L K

K om

11

(2)

Where: = methane yield, m 3/kg VS

Bo = ultimate methane yield at infinite retention time, m3

/kg VSK = kinetic parameter (inversely related to digester performance;values

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A discussion of anaerobic treatment of swine wastes would not be complete without mentioning its role inbiological nutrient removal. Per 1000 head in a finishing piggery, 18.6 tons per year (tpy) of nitrogen areingested and 11.5 tpy excreted; the intake for phosphorus is 4.7 tpy, 4.5 tpy of which is excreted(Kephart, 1996). Anaerobic processes may play an important role in removal of nitrogen and phosphorus(Ekama & Wentzel, 1997). For nitrogen removal, ammonia nitrogen resulting from metabolism of nitrogenous organic compounds must be oxidized aerobically after which nitrogen may be removedanaerobically by denitrification. This is accomplished by recycle of aerobic effluent back through ananaerobic denitrification process. Biological removal of phosphorus is sometimes accomplished by theuse of anaerobic prefermenters which produce volatile acids which then enhance uptake of phosphorusby bacteria in subsequent aerobic operations. This may be accomplished in a sequencing batch reactor that is alternated between aerobic and anaerobic conditions (Bortone et al., 1992). Algae, aquatic plants,and wetlands may also be used for nutrient removal from digester effluents (Lincoln & Earle, 1990; Yang& H., 1994; Zhang & Felmann, 1997).

Gaseous Emissions

Gaseous emissions from piggery wastes are of concern because of their potential health hazards to theanimals and farm workers, their contribution to greenhouses gases related to global warming, and as thecause of odors which are objectionable to piggery workers and nearby residents. Over 75 compounds(including ammonia, hydrogen sulfide, volatile organic acids, amines, mercaptans, and heterocyclicnitrogen compounds) have been identified in animal waste emissions which contribute to odors and arelargely a result of partial anaerobic decomposition of these wastes (Barth & Melvin, 1984). Under totallyaerobic conditions, these compounds would not form as they would be converted to carbon dioxide,water, and oxides of sulfur and nitrogen, all of which are odorless. Under conditions of highconcentrations of organic matter (such as animal wastes), oxygen is depleted and an imbalancedanaerobic decomposition occurs giving rise to these products. Many uncontrolled environments wheremanure is accumulated (manure piles, collection pits or tanks, etc.) have imbalanced anaerobicdecomposition (Wilkie et al. 1995b). In a balanced methanogenic decomposition, the gases are limitedprimarily to methane, carbon dioxide, hydrogen sulfide, and ammonia. Levels of hydrogen sulfide andammonia are high for swine wastes, compared to other animal wastes, because of the high proteincontent.

As discussed above, ammonia and hydrogen sulfide cause discomfort and represent health risks toconfined animals and workers.

Methane is produced during the anaerobic decay of organic matter in manure. Worldwide emissions fromthis source range from 10 to 18 teragrams (Tg) per year, or 2 to 5% of global anthropogenicemissions(Safley et al., 1992; USEPA, 1993). Swine account for 40% of the emissions from animalwastes. No information could be found on the contribution of swine-waste ammonia emissions toatmospheric nitrous oxides.

The influence of anaerobic digestion on odors from swine and other animal wastes can be significant(Powers et al., 1997; Wilkie, 1998). Anaerobic treatment is conducted in closed vessels and under conditions that lead to a balanced decomposition. Thus, volatile acids and other reduced compoundsfound under imbalanced conditions do not accumulate. Organic matter that would lead to production of

odors is further decomposed leaving a stable residue that can be applied to fields without generating anodor nuisance. Although the biogas may be odorous due to hydrogen sulfide, the gas is usually encloseduntil it is burned or treated for hydrogen sulfide removal prior to use. The problem with most aerobicprocesses treating animal wastes (e.g. composting and oxidation ditches), is that oxygen becomeslimiting and the processes become partially anaerobic leading to volatile gases that are transported to theatmosphere by the aeration process. Other methods to control odors include, solids separation, aerationof anaerobic lagoon surfaces, and ventilation of housing gases through biofilters.

Commercial Systems and Economics

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Sweeten (1981) reviewed the technical and economic considerations for systems for production of methane from swine manure. Using 1980 prices, their construction costs ranged from $22-$36 per 68 kghog. This is equivalent to $214-$357 per m 3 digester volume. They concluded that treatment of concentrated wastes (8-10% TS) would be more economical than treatment of diluted flush wastes (2-3%TS). Chandler (1983) reported that a $89,000 75kw covered lagoon effectively treated wastes from a1,000 sow (farrow to finish) piggery with an internal return of 34% and a payback period of 3 years.

Yang (1995) used lab-scale data to determine the cost of three-stage anaerobic digestion of undiluted pigwaste. The cost in Hawaii for treatment with this system was $3.73 per head per year for a 300-herd farmwith a profit of $3.01 per head for a 1,000-herd farm.

Oleszkiewicz (1983) compared nine full-scale waste treatment schemes for treatment of large-herdpiggeries (>10,000 animals) with water-flushed slurry wastes in a developed country. It was found thatsome of the systems practiced, including extended aeration, chemical coagulation, series of lagoons, andsystems featuring land disposal, are not cost effective. Systems with high-rate anaerobic and aerobic unitoperations could treat the wastes more effectively at one-third to one/half the cost of more traditionalsystems. Anaerobic digestion in cost-effective schemes was used for secondary treatment of wastewater and settled sludges and for denitrification. Aerobic treatment was used to polish digester effluent and for biological nutrient removal. Durand (1988) presented the results of an economic system model for anaerobic treatment of confined swine wastes. The best configuration, of 12 evaluated, included flushingmanure collection, thermophilic anaerobic digestion with effluent heat recovery, and direct combustion of gas. The economics were most sensitive to digester size, energy price, and efficiency of energyconversion.

Table 10 summarizes data from several commercial swine waste digester systems in the U.S., includingdigester type and volume, gas production, electricity production (if applicable), and capital costs. Asoftware package is available from a U.S. government program (AgSTAR) that facilitates determination of design and economics of different animal waste treatment systems based on anaerobic processes.

Table 10. Summary of Economics of Anaerobic Digestion Treatment Systems for Swine Wastes

Herd

Size

Feed

Type

Digester

Type

Dig.

Vol.,m 3

Gas

Prodn.

Elect.

Prodn.,annual

Cost Country Ref.

1,150 flush non-mixedslurrytank

207 $20,000(materials);

US (Lusk,1998)

16,500 flush coveredlagoon

29,400 1,960m3/d

700,000kwh

$220,000 US (Lusk,1998)

13,000 flush plusdairyproc.

wastes

plug-flow 1,302 1,680 1.0 millionkwh

$525,000 US (Lusk,1998)

11,500 flush covered

lagoon

26,180 980

(1960 infuture)

600,000

possible

$191,500 US (Lusk,

1998)

3,000 flush coveredlagoon

10,892 336 175estimated

$85,000 US (Lusk,1998)

? flush coveredlagoon

30,000 40,000 625,000 $232,500 US (Lusk,1998)

1,000 scraped(TS 8-10%)

three-stagebatch

100 131 $67,558 Hawaii (Yang &Kuroshima 1995)

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storageplus 2

CSTRs3,200 scraped CSTR 88 197 supplies

all farmenergy

requiremts.

$62,375 US (Fischer et al.,1979)

The economics of swine waste treatment systems are highly site specific and dependent upon severalfactors, including land and labor costs, effluent discharge regulations, and energy prices.

INTEGRATED SYSTEMS USING ANAEROBIC PROCESSES

With over eight million hogs raised in Taiwan, the Taiwan Livestock Research Institute(Taiwan, 1993)developed a standardized waste treatment system that is used in over 90% of the piggeries. This systeminvolves a complex combination of solids/liquid separation, composting, activated sludge, and anaerobicdigestion operations. Redmud plastic-covered plug-flow digesters are employed to treat the overflowdilute fraction. The effluent is polished by activated sludge treatment. Solids are treated by composting.Chou (1995) evaluated automated control of this system. In Denmark, animal wastes are blended withthe organic fraction of solid and industrial wastes for anaerobic digestion. The biogas is utilized primarilyfor heating and generation of electricity (Tafdrup, 1995).

Effluent Processing

Fong and Yuen (1986) reported on a lab-scale process for concentrating piggery digester effluent as apotential animal feed. The effluent contained 14% protein. Yang (1994) evaluated a combined fixed-filmand aquatic plant system for treatment of diluted piggery waste digester effluent. The system effected90% COD reduction, 95% reduction of TKN-N, and 99% suspended solids reduction at an estimated cost$2.95 per pig per year for a farm with 1000 head. Camarero (1996) investigated final treatments for effluents from piggery digesters. Coarser fractions separated by flocculation were further digested ashigh-solids feeds; finer fractions were treated by aerobic digestion and chemical oxidation. De la Noue(1989), Lincoln et al. (1993) and Lincoln et al. (1996) investigated nutrient removal using variousmicroalgae. Chlorella achieved the highest removal rates but Phormidium and Spirulina would be easier to harvest. Effective removal of nutrients by Phormidium was confirmed in laboratory experiments(Canizares-Villanueva et al., 1994; Lincoln & Earle, 1990)

Biogas Utilization

Figure 2 shows various options for utilization of biogas on farms (Ross & Drake, 1996)). The mostefficient use of biogas is direct combustion for heat. Commonly, biogas is used directly with minimalcleanup (hydrogen sulfide and moisture removal) for electrical generation. The heat from generator

engines may be captured with heat exchangers for digester heating or other uses. Biogas as produced istypically 60% methane and 40% carbon dioxide, but the methane content can be as high as 80% inattached-film digesters. The heating value is about 14.8-17.8 kJ/m 3. The hydrogen sulfide is typically1%. Iron sponges or iron-impregnated wood chips are often used for hydrogen sulfide removal.Upgrading biogas by removal of carbon dioxide is possible, and necessary for uses requiringcompression, but is not economic for the small quantities generated by piggeries. Ross (1996) presents adetailed discussion of properties, conversion, handling and storage, instrumentation and controls, health,safety, and environmental considerations, and economics related to biogas use..Net Energy Considerations

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Process energy requirements should influence design and operating conditions selected for treatment of swine wastes and other feedstocks in digesters. For CSTR digesters, the components in order of their relative importance are feed heating, reactor heat losses, and mixing (Chen, 1983; Chen & Hashimoto,1981; Srivastava, 1987). The total requirements can range from about 10% to over 100% of the methaneproduct energy depending upon the design, feed solids concentration, loading rate, mixing regime,operating temperature, and ambient temperature. Since feed heating is the major requirement, therequirements are high for colder climates and higher digester operating temperatures. There is a strongincentive for ambient temperature operation for high-rate digesters receiving dilute waste streams. This isrelated to the high energy requirements to heat the dilute feed and the rapid kinetics of these designs atlow temperatures. On the other hand, (Legrand, 1993) has calculated that high-solids digesters may beself-heating in tropical and sub-tropical climates.

FUTURE OF ANAEROBIC PROCESSES IN SWINE WASTE MANAGEMENT

Several demographic trends will influence swine waste management into the twenty-first century:

increase in human population increase in swine meat consumption in developing countries decrease in swine meat consumption in developed countries centralization of swine production with herds in the tens of thousands

stricter local and global environmental regulations with respect to gaseous, liquid, and solidsemissions public health regulations with respect to animal and worker comfort and health

Anaerobic DigestBiogas

Biogas Stor (low pressure)

Scrub H2S Scrub H2S + C02

low pressure storag high pressure stora

Heating:Process heating (hot water,steam,etc.)

Space heating

Dom estic heatinDomestic cookin

Stationary enginMechanical powElectrical power

Transport engin

Biogas Utilization on Far

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Figure 2. Biogas Utilization Options

In developed nations like the United States and the European Union, piggeries will be treated like other industries, with emphasis on clean sustainable animal raising operations. Wastes will be rapidly removedfrom their site of production to minimize effects on animals and workers and treated with much the sameobjectives as for human and industrial wastes, i.e., removal of solids, organic matter, nutrients, andpathogens. The trend continues to be toward flushed systems which will be followed by combinations of operations for separation, anaerobic and aerobic organic matter reduction, nutrient removal, anddisinfection. Anaerobic treatment should play an important role in future swine waste management for treatment of organics with its minimum biological sludge production, production of a useful methane fuel,emerging developments for biological removal of nitrogen and phosphorus, and its capacity to reducepathogens. There are strong arguments in favor of minimizing water use in management of thesewastes, and in fact to further increase solids by use of straw and other high-solids wastes for bedding.High-solids management not only reduces required reactor sizes, but also odors and water requirements.

In developing countries, the trends will be the same, but piggeries will be smaller on the average andemphasis on environmental pollution control will be slower to develop. High level of treatment of piggerywastes will probably coincide with the emergence of effective treatment of human wastes.

In general, it makes the most sense to grow swine in the vicinity of their feed production. This wouldfacilitate a sustainable cycle for nutrient management. A modern approach to evaluation of systems

involving anaerobic digestion of wastes from swine, or any feedstock, is life cycle assessment (LCA).LCA (IEA, 1997) involves the systematic identification of all materials, energy, and economic inputs andoutputs of a system from cradle to grave, i.e., from the extraction of raw materials from the environmentto their eventual assimilation back into the environment. The flows are assessed in terms of their potential to contribute to specific environmental impacts. For swine waste systems, this would involveassessment of feed production and processing, waste collection and storage, waste transport, air emissions, water emissions, net energy consumption, compost, and wastes.

ACKNOWLEDGEMENTS

The authors acknowledge several colleagues who promptly responded by sending recent reviews andpapers on the subject matter, including R. Zhang, P. Lusk, and C.Y. Chou. They also gratefullyacknowledge Gloria Chynoweth, who located references and entered them into a database.

LITERATURE CITED

Andreadakis, A. D. (1992). Anaerobic digestion of piggery wastes. Wat. Sci. Technol. , 25(1), 9-16.Barth, C. L. & Melvin, S. W. (1984). Agriculture and the environment: an examination of critical issues for

food policy - part 4: Odor. Ag. Eng. , 65(4), 20-22.Bendixen, H. J. (1994). Safeguards against pathogens in Danish biogas plants. Wat. Sci. Tech., 30(12),

171-180.Bolte, J. P., Hill, D. T. & Wood, T. H. (1986). Anaerobic digestion of screened swine waste liquids in

suspended particle-attachment growth reactors. Trans. ASAE , 29(2), 543-549.

31

8/4/2019 ADSW_fin

32/38

Boone, D. R., Chynoweth, D. P., Mah, R. A., Smith, P. H. & Wilkie, A. C. (1993). Ecology andmicrobiology of biogasification. Biomass and Bioenergy , 5, 191-202.

Boopathy, R. & Sievers, D. M. (1991). Performance of a modified anaerobic baffled reactor to treat swinewaste. Trans. ASAE , 34(6), 2573-2578.

Bortone, G., Gemelli, S., Rambaldi, A. & Tilche, A. (1992). Nitrification, denitrification and biologialphosphorus removal in sequencing batch reactors treating piggery wastewater. Wat. Sci. Technol. ,26(5-6), 977-985.

Bossier, P., Poels, J., Van Assche, P. & Verstraete, W. (1986). Influence of the dimensionalcharacteristics of polyurethane foam on high rate anaerobic digestion of piggery manure. Biotechnol.Lett. , 8(12), 901-906.Braun, R., Huber, P. & Meyrath, J. (1981). Ammonia toxicity in liquid piggerymanure digestion. Biotechnol. Lett. , 3(4), 159-164.

Brumm, M. C. & Sutton, A. L. (1979). Effect of copper in swine diets on fresh waste composition andanaerobic decomposition. J. Anim. Sci. , 49, 20-25.

Brumm, M. C., Sutton, A.L. & Jones, D. D. (1980). Effect of dietary arsonic acids on perfromancecharacteristics of swine waste anaerobic digesters. J. Anim. Sci. , 51, 544-549.

Brumm, M. C., Sutton, A. L., Mayrose, V. B. & Krider, J. L. (1979). Effect of dietary arsonic acid on freshswine waste composition and anaerobic decomposition. J. Anim. Sci. , 48, 1305-1311.

Brumm, M. C., Sutton, A. L., Mayrose, V. B., Nye, J. C. & Jones, H. W. (1977). Effect of arsanilic acid inswine diets on fresh waste production, composition and anaerobic decomposition. J. Anim. Sci. , 44,521-531.

Brumm, M. C., Sutton, A. L., Mayrose, V. B., Nye, J. C. & Jones, H. W. (1977). Effect of arsanilic acidlevel in swine diets and waste loading rate on model anaerobic lagoon performance. Trans. ASAE ,20, 498-501.

Camarero, L., Diaz, J. M. & Romero, F. (1996). Final treatments for anaerobically digested piggery slurryeffluents. Biomass and Bioenergy , 11(6), 483-489.

Campos, L. & d'Almeida Duarte, E. F. (1992). Increasing of biogas production rate by addition of algaeand water hyacinth to pig manure. International Symposium on Anaerobic Digestion of Solid Waste ,April 14-17, 1992, Venice, Italy. 469-471.

Camprubi, M., Paris, J. M. & Casas, C. (1988). Effects of antimicrobial agents and feed additives on theperformance of piggery waste anaerobic treatment. Anaerobic Digestion 1988 - 5th International Symposium on Anaerobic Digestion , May 22-26, 1988, Bologna, Italy. Pergamon Press. 239-248.

Canizares-Villanueva, R. O., Corona, A. I., Monroy, O., De La Torre, M., Gomez-Lojero, C. & Travieso, L.(1994). Phormidium treatment of anaerobically treated swine wastewater. Wat. Res. , 28(9), 1891-

1895.CAST. (1996). Integrated Animal Waste Management . Council for Agricultural Science and Technology.#128.

Cavallero, C. & Genon, G. (1984). Digestion tests of dilute piggery wastes. Ag. Wastes , 11, 227-233.Chandler, J. A., Hermes, S. K. & Smith, K. D. (1983). A low cost 75 kw covered lagoon biogas system. In

Energy From Biomass and Wastes VII , ed. D. Klass, Institute of Gas Technology, Chicago, IL. LakeBuena Vista, FL, pp. 627-646.

Chen, T., Chynoweth, D. P., & Biljetina, R. (1990). Anaerobic digestion of municipal solid waste in anonmixed solids-concentrating digester. Appl. Biochem. Biotechnol. , 24/25, 533-544.

Chen, Y. R. (1983). Kinetic analysis of anaerobic digestion of pig manure and its design implications. Ag.Wastes , 8, 65-81.

Chen, Y. R. & Hashimoto, A. G. (1981). Energy requirements for anaerobic fermentation of livestockwastes. In Livestock Waste: A Renewable Resource , ASAE. St. Joseph, MI, pp. 117-121.

Chou, C. Y., Hu, Y. Y. & Huang, J. C. (1995). Automatic control for swine wastewater treatment systems.Seventh Intern. Symp. on Ag. and Food Processing Wastes (ISAFPW95) , Chicago, Illinois. ASAE.137-143.

Chou, C. Y., Liu, A. C. & Yang, P. Y. (1997). Anaerobic digestion of swine wastewater by applying theimmobilized cell. Proc. Internat. Symp. Ag.-Mech. and Automation , Taipai, Taiwan. Chinese Inst. of Agricultural Machinery. 287-292.

Chynoweth, D. C., Bosch, G., Earle, J. F. K., Legrand, R. & Liu, K. (1991). A novel process for anaerobiccomposting of municipal solid waste. Appl. Biochem. Biotech. , 28/29, 421-432.

32

8/4/2019 ADSW_fin

33/38

Chynoweth, D. C., Svoronos, S. A., Lyberatos, G., Harmon, J. L., Pullammanappallil, P., Owens, J. M. &Peck, M. J. (1994). Real-time expert system control of anaerobic digestion. Water Sci. Tech ., 30(12),21-30.

Chynoweth, D. P. (1987). Biomass Conversion Options. Magnolia Publishers, Orlando, Fl, 621-642.Chynoweth, D. P. (1996). Environmental impact of biomethanogenesis. Envir. Monitor. Assess. 42, 3-18.Chynoweth, D. P., Fannin, K. F. & Srivastava, V. J. (1987). Biological Gasification of Marine Algae. In

Seaweed Cultivation for Renewable Resources , eds. K. Bird and P. Benson Elsevier AppliedScience, New York, 285-303.

Chynoweth, D. P. & Isaacson, H. R. eds. (1987). Anaerobic Digestion of Biomass. Elsevier AppliedScience , New York .

Chynoweth, D. P. & Pullammanappallil, P. (1996). Anaerobic Digestion of Solid Wastes. In Microbiology of Solid Waste , ed. A. C. Palmisano & M. A. Barlaz, CRC Press, Inc. Boca Raton, 71-113.

Chynoweth, D. P., Turick, C. E., Owens, J. M., Jerger, D. E. & Peck, M. W. (1993). Biochemical methanepotential of biomass and waste feedstocks. Biomass Bioenergy , 5, 95-111.

Cintoli, R., Di Sabatino, B., Galeotti, L. & Bruno, G. (1995). Ammonium uptake by zeolite and treatment inUASB reactor of piggery wastewater. Wat. Sci. Tech. , 32(12), 73-81.

Cullimore, D. R., Maule, A. & Mansuy, N. (1985). Ambient temperature methanogenesis for pig manurewaste lagoons: thermal gradient incubator studies. Ag. Wastes , 12(2), 147-57.

Dague, R. R., Habben, C. E. & Pidaparti, S. R. (1992). Initial studies on the anaerobic sequencing batchreactor. Wat. Sci. Tech. , 26(9-11), 2429-2432.

Davidson, K. D., Westermann, P. W., Safley, L. M. & Barker, J. C. (1995). Relative odor levels from swineproduction facilities and lagoons. Seventh Intern. Symp. on Ag. and Food Processing Wastes(ISAFPW95) , Chicago, IL. ASAE. 616-626.

Day, D. L. & Funk, T. L. (1998). Processing manure: physical, chemical and biological treatment. In Animal waste utilization: effective use of manure as a soil resource , eds. J. L. Hatfield & B. A.Stewart, Ann Arbor Press. Chelsea, pp. 243-282.

De la Noue, J. & Basseres, A. (1989). Biotreatment of anaerobically treated swine manure withmicroalgae. Biol. Waste , 29, 17-31.

Donham, K. J. (1991). Health concerns from the air environment in intensive swine housing: where havewe come from and where are we going? Making Swine Buildings a Better Place to Work . Nat. PorkProducers Council and Nat. Pork Board, Des Moines, IA.

Duarte, E. A., Mendes, B. & Oliviera, J. S. (1992). Removal of salmonella, streptococci, and coliforms inpig breeding effluent by anaerobic mesophilic digestion. Wat. Sci. Tech. , 26(9-11), 2169-2172.

Durand, J. H., Fischer, J. R., Jannotti, E. L. & Miles, J. B. (1988). Development of an economic systemmodel to optimize the performance of a swine waste digestion system. Biomass , 14, 45-65.Ekama, G. A. & Wentzel, M. C. (1997). Difficulties and developments in biological nutrient removal

technology and modelling. IN Proc. 3 rd AWWA/IAWQ BNR Conf, Brisbane, Aus, 3-13.Engeli, H., Edelmann, W., Fuchs, J. & Rottermann, K. (1993). Survival of plant pathogens and weeds

during anaerobic digestion. Wat. Sci. Tech. , 27, 69-76.FAO. (1990, 1991, 1995, 1996). FAO Food Production Yearbook . FAO.Fischer, J. R., Meador, N. F., Sievers, D. M., Fulhage, C. D. & Iannotti, E. L. (1979). Design and operation

of a farm anaerobic digester for swine manure. Trans. ASAE , 22(5), 1129-1136.Fischer, J. R., Osborn, D. D., Meador, N. F. & Fulhage, C. D. (1979). Economics of a swine anaerobic

digester. ASAE 1979 Winter Conference , December 11-14, 1979, New Orleans, LA. ASAE,13 pp.Floyd, J. R. S. & Hawkes, R. R. (1986). Operation of a laboratory tubular digester on piggery wastes. Ag.

Wastes , 18, 36-60.

Fong, J. C. L. S., Morrissette, D. & Yuen, R. T. H. (1986). Integrated production of biogas and proteinbiomass from piggery manure. Biotechnol. Lett. , 8(4), 299-302.Foresti, E. & de Oliveira, R. A. (1995). Anaerobic treatment of piggery wastewater in UASB reactors.

Seventh Intern. Symp. on Ag. and Food Processing Wastes (ISAFPW95) , Chicago, Illinois. ASAE.309-19.

Fujita, M., Scharer, J. M. & Moo-Young, M. (1980). Effect of corn stover addition on the anaerobicdigestion of swine manure. Ag. Wastes , 2(3), 177-184.

Gorecki, J., Bortone, G., and Tilche, A. (1993). Anaerobic treatment of the centrifuged solid fraction of piggery wastewater in an inclined plug flow reactor. Wat. Sci. Tech. , 28(2), 107-114.

33

8/4/2019 ADSW_fin

34/38

Gourdon, R. & Vermande, P. (1987). Effects of propionic acid concentration on ananerobic digestion of pig manure. Biomass , 13, 1-12.

Hansen, K. H., Angelidaki, I. & Ahring, B. K. (1998). Anaerobic digestion of swine manure: inhibition byammonia. Wat. Res. , 32, 5-11.

Harmon, J. L., Svoronos, S. A., Lyberatos, G. & Chynoweth, D. P. (1993). Adaptive temperatureoptimization of continuous anaerobic digesters. Biomass and Bioenergy , 5, 279-288.

Hasheider, R. J. & Sievers, D. M. (1983). Limestone bed anaerobic filter for swine manure. 1983 ASAE Summer Conference , June 26-29, 1983, Montana State University, Bozeman, MT.

Hashimoto, A. G. (1984). Methane from swine manure: effect of temperature and influent substrateconcentration on kinetic parameter (k). Ag. Wastes , 9, 299-308.

Hashimoto, A. G. (1983). Thermophylic and mesophilic anaerobic fermentation of swine manure. Ag.Wastes , 6, 175-191.

Hill, D. T. (1983). Design parameters and operating characteristics of animal waste anaerobic digestionsystems - swine and poultry. Ag. Wastes , 5, 157-178.

Hill, D. T. (1984). Economically optimized design of methane fermentation systems for swine productionfacilities. Trans. ASAE , 27(2), 525-529.

Hill, D. T. (1988). Long chain volatile fatty acid relationships in anaerobic digestion of swine waste. Biol.Wastes , 23, 195-214.

Hill, D. T. (1985). Practical and theoretical aspects of engineering modeling of anaerobic digestion for livestock waste utilization systems. Trans. ASAE , 28(1), 850-855.

Hill, D. T. & Bolte, J. P. (1984). Characteristics of screened-flushed swine waste as a methane substrate.1984 ASAE Conference , June 24-27, 1984, University of Tennessee, Knoxville, TN. ASAE. 1-20.

Hill, D. T. & Bolte, J. P. (1986). Evaluation of suspended particle-attached growth ferments treating liquidswine waste. Trans. ASAE , 29(6), 1733-1788.

Hill, D. T. & Bolte, J. P. (1988). Synthetic fixed media reactor performance treating screened swine wasteliquids. Trans. ASAE , 31(5), 1525-1531.

Hill, D. T. & Cobb, S. A. (1996). Simulation of process steady-state in livestock waste methanogenesis.Trans. ASAE , 39(2), 565-573.

Hill, D. T., Cobb, S. A. & Bolte, J. B. (1987). Using volatile fatty acid relationships to predict anaerobicdigester failure. ASAE Trans. , 30, 496-501.

Hill, D. T. & Holmbert, R. D. (1988). Long chain fatty acid relationships in anaerobic digestion of swinewaste. Biol. Waste , 23, 195-214.

Hill, D. T., Prince, T. J. & Holmberg, R. D. (1985). Continuously expanding digestor performance using a

swine waste s