ELSEVIER P I I : S 0 9 6 0 - 8 5 2 4 ( 9 7 ) O 0 1 7 8 - 8

Bioresource Technology 64 (1998) 1-6 O 1998 Elsevier Science Ltd. All rights reserved

Printed in Great Britain 0960-8524/98 $19.00

BIOLOGICAL TREATMENT OF SWINE WASTE USING ANAEROBIC BAFFLED REACTORS

Ramaraj Boopathy Environmental Research Division, Building 203, Argonne National Laboratory, Argonne, IL 60439, USA

(Received 5 August 1997; revised version received 19 November 1997; accepted 21 November 1997)

Abstract Four laboratory-scale anaerobic baffled reactors (with two, three, four, and five chambers, respectively) were used to successfully treat whole swine waste. The baffled reactors did an excellent job of trapping the small diameter, methane-containing particles of proteins, cellulose, hemicellulose, and lipids. Solids retention times of 25, 30, 36, and 42 days were achieved with a corresponding hydraulic retention time of 14 days for two-, three-, four- and five-chamber anaerobic baffled reactors, respectively. COD reduc- tions ranged from 70 to 78% among all the reactors studied. Maximum methane production was observed in the reactors with four and five chambers with a value of 0.59 and 0.62 l/g of volatile solids added at a loading of 4 g VS/l/day, respectively. 0 1998Elsevier Science Ltd. All rights reserved.

Key words: Anaerobic digestion, anaerobic baffled reactor, swine manure, retention time, COD.

INTRODUCTION

The primary advantages of anaerobic treatment are the reduction of high solids wastes and recovery of methane. Swine waste is a good candidate for anaerobic treatment because of its high solids content and oxygen demand. The major difficulty associated with anaerobic digestion of livestock waste is maintaining a high solids retention time (SRT) in the reactor while keeping the hydraulic retention time (HRT) to a minimum. Minimum HRT results in a smaller reactor size and econom- ical savings.

The organic fraction (volatile solids) of swine waste contains a large portion of small diameter particles (dia <0.21 mm) (Boopathy and Sievers, 1991). The biochemical constituents of these small particles include protein, lipids, and cellulose. These chemical fractions account for more than 50% of the

potentially available methane in swine waste (Sievers et al., 1980). If methane recovery from swine waste is to be maximized, this fraction of small diameter particles must be maintained in the digester long enough for degradation to occur. There are two problems with accomplishing this. One, the smaller diameter particles do not settle by gravity either in pretreatment (settling basins) (Sievers et al., 1980) or in the digester. Secondly, the particles require long SRTs to digest (Sievers et al., 1986). Thus, the anaerobic reactors must be designed in such a way to trap these small particles in the digester for a sufficiently long SRT to extract the potential methane. In the past, various reactor designs have been used, including a fiber-wall reactor (Jones et al., 1977), upflow anaerobic filters (Hasheider and Sievers, 1984) and fixed-film reactors (Bolte et al., 1986). Yang and Moengangongo (1987) have successfully used a modified version of a baffled reactor to treat diluted swine waste. Boopathy and Sievers (1991) demonstrated the particle-trapping efficiency of two- and three-chamber modified baffled reactors treating swine manure. The baffled digester design was modified in an attempt to trap more small diameter particles inside the reactor. The objectives of this study were to document the overall performance of the anaerobic baffled reactors in digesting whole swine waste and to deter- mine the reactor's ability to trap small particles.

METHODS

Anaerobic baffled reactor (ABR) Four anaerobic baffled reactors (ABR) were constructed from thin sheet plastic (Fig. 1). The only difference among the four reactors was the number of chambers (two, three, four and five). The total volume of the reactors was 15 1. The baffles were angled at 40 ° to the horizontal to reduce entrance velocities and direct incoming material to the center of the chamber. Two small, plastic-tube (20 cm dia)

2 R. Boopathy

Effluent

[]

Underflow baffle

8cm I

Influent

Gas outlets

,,s, ,s, V__ WL

) ( 3cm

2 ~.__. Overflow baffle

ABR2

Gas outlets

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/

I

i

/

._11. II II I t

' llol [] []11o

JlJlJ ABR3 ABR4

Fig. 1. Anaerobic baffled reactors with various chambers.

I

[ ]

/

I I I I I

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ABR5

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settlers were used at the discharge end of the ABRs. All the reactors were operated at 35°C (by keeping them in a temperature-controlled room) and at a hydraulic retention time (HRT) of 14 days. Biogas production was measured with wet tip gas meters.

Swine waste A single batch of swine manure was collected from a concrete feeding floor, thoroughly mixed, and frozen until used. Characteristics of the waste are given in Table 1.

Reactor start-up and loading All ABRs were started with inoculum obtained from an operating pilot-scale swine manure digeste r . The total and volatile solids of the inoculum were 8966 and 4341 mg/1, respectively. Initial loading was 1 g VS/l/day and gradually increased to 4 g VS/1/day over a period of 57 days. After 220 days, the loading was increased gradually to 8 g VS/1/day. The reactors were operated for 28 days at this high loading rate. All reactors were loaded 6 days per week.

Table 1. Characteristics of swine waste used in ABR experiments

Components Average unit S.D.

Total solids (g/l) 52.4 6.1 Volatile solids (g/l) 39.1 4.3 Ammonia nitrogen (mg/l) 1682 66 Total organic nitrogen (mg/l) 3800 79 COD total (mg/l) 59 400 237 Total volatile fatty acids (mg/1) 3712 112 Protein (% dry matter) 21.78 2.1 Fat (% dry matter) 12.76 1.3 Cellulose (% dry matter) 5.97 0.5 Hemicellulose (% dry matter) 28.11 3.6

S,D., standard deviation of triplicate analyses of samples.

Analyses Total solids (TS), volatile solids (MS), chemical oxygen demand (COD), alkalinity, pH, kjheldhal nitrogen, and volatile fatty acids were determined according to standard methods (APHA, 1982). Ammonia nitrogen was quantified with an ammonia probe (Orion model 95-10). Carbon dioxide and methane were quantitated by gas chromatography (GC) using a Fisher model 25 gas partitioner (Boopathy and Sievers, 1991).

At the conclusion of the 4 g VS/1 loading study, samples of the solids in each chamber of all the reactors were taken at three depths below the liquid surface (10, 20 and 30 cm). It was assumed that the solids at these depths were representative of their surrounding chamber volume. One fraction of the sample was dried (55°C) and used for the analysis of cellulose, hemicellulose, protein (Goering and Van Soest, 1970), and total lipids (Folch et al., 1957). A second fraction of the sample was passed through a Microtrac II particle size analyzer (Leeds and Northrup, Model No. 7997) to determine particle size distribution.

Chromium as a stable element marker was used to estimate the solids retention time (SRT). Sesqui chromic oxide (Cr203) was used as a source of hexavalent chromium and was attached to the influent solids. Forty-five milligrams of chromic oxide was dissolved in 1 1 of reactor influent, filtered through Whatman No. 41 filter paper and retained solids collected. The retained solids were then resus- pended in 1 1 of distilled water and loaded into the reactors. Each day an effluent sample was collected and analyzed for chromium concentration using atomic absorption spectrophotometry (Perkin Elmer model 360). The sampling and analyses were performed until 100% of the chromium was recovered. The log of the percent chromium accumulated was plotted against time (days) (Fig. 2).

The inverse of the slope of the semi-log plot was the SRT (Hungate, 1966).

RESULTS AND DISCUSSION

Initial loading phase Over the first 50 days of operation, the organic loading rate was gradually increased to 2 g VS/1/day,

120"

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~1 O0

E

80 2 e= o

60 "D

0 a

~ 40

U

'~ 20

The biological treatment o f swine waste 3

0 10 20 30 40 50

Days

Fig. 2. Accumulated chromium in effluent of all ABRs.

where it was maintained until day 60. The objective of this low loading rate was to develop a suitable biomass of flocculent organisms in the reactor before higher loading rates were tried (Fischer et al., 1981). The success of the low loading in achieving its objective was indicated by the appearance of floc in all chambers of the reactors. During this start-up phase of operation, days 1-60, gas production increased from 0.8 to 5.2 l/day in the three-chamber ABR. Similar increases in gas production were observed in all the other reactors.

Loading at 4 g VS/l/day On day 61, the VS loading rate was increased from 2 to 4 g VS/1/day. This period represents the transi- tion from the establishment of a flocculent biomass to a commercially acceptable loading rate. The transitional phase (from 2 to 4g VS/l/day) was typified by signs of a healthy reactor. Methane production increased steadily to 0.48 l/g VS added (ABR with two chambers), 0.52 l/g VS added (ABR with three chambers), 0.59 l/g VS added (ABR with four chambers), and 0.62 l/g VS added (ABR with five chambers), whereas methane and CO2 contents of the gas remained uniform at approximately 65 and 30%, respectively, in all the reactors. The pH varied from 6.8 to 7.2 throughout the study in all the reactors. Performance characteristics for all the

Table 2. ABR characteristics during 4 g VS/l/day loading rate a

Characteristics ABR 2 ABR 3 ABR 4 ABR 5

COD (mg/1) 16 234 15 000 13 675 12100 Alkalinity (mg/1) 4555 3890 3436 3410 pH 7.0-7.3 7.0-7.2 7.0-7.3 6.9-7.2 Volatile fatty acids (mg/1) 101 112 124 131 Ammonia nitrogen (mg/1) 922 856 996 1011 Total Kjheldhal nitrogen (mg/1) 1618 1820 1600 1935 Total solids (mg/l) 22 900 18 434 16 789 l 5 600 Volatile solids (rag/l) 12160 9976 8790 7255 CH4 (l/g VS added) 0.48 0.52 0.59 0.62 SRT (days) 25 30 36 42

aAll analyses were carried out in triplicate and the percentage deviation was within 5% (95% confidence level).

Table 3. A review of biogas production from swine wastes

Temp HRT Org. loading Digester Gas production Reference (°C) (days) (g VS/l/day) (l/g VS added) (1/g VS added)

35 10 1.4-4.5 Conventional 0.43 Hobson et al., 1980 35 15-30 1.05-2.1 Conventional 0.62-0.82 Kroeker et al., 1975 35 15 4 Conventional 0.55 Fischer et al., 1979 35 26.5 2.4 Conventional 0.36-0.42 Haga et al., 1979 33 10-15 1.92-3.85 Conventional 0.26-0.45 Gramms et al., 1971 35 3-9 4 Ana. filter 0.33-0.42 Hasheider and Sievers, 1984 35 5-25 2.5-12.5 Conventional 0.41-0.77 Hashimoto, 1983 35 1-5 3.7-16.0 Attached 0.23-0.56 Hill and Bolte, 1986 35 15 4.0-8.0 Baffled reactor 0.68-0.96 Boopathy and Sievers, 1991 35 14 4.0-8.0 ABR 2 0.72-1.18 This study 35 14 4.0-8.0 ABR 3 0.79-1.29 This study 35 14 4.0-8.0 ABR 4 0.87-1.40 This study 35 14 4.0-8.0 ABR 5 0.94-1.46 This study

4 R. Boopathy

reactors operating at 4 g VS/1/day are summarized in Table 2. All the reactors operated with consistent results. Biogas production compared favorably (higher in many cases) with values reported in the literature (Table 3). ABRs with four and five chambers outperformed ABRs with two and three chambers. Although all reactors had equivalent HRT (14 days), the chromium studies (Fig. 2) indicated that ABR with five chambers had an SRT 6 days greater than the ABR with four chambers

Table 4. Mass reductions for ABRs (days 150-200)

and 12 days greater than the ABR with three chambers. The additional chambers i n - an ABR make a significant difference to particle retention.

On a mass reduction basis, ABR with three, four and five chambers appeared to be doing a better job of reducing organic matter than ABR with two chambers (Table 4). Methane production in all units varied from 0.48 to 0.621 CH4/g VS added. The ABR with five chambers, having more baffles, is efficient in converting trapped organic materials to methane.

Parameter % Reduction

ABR 2 ABR 3 ABR 4 ABR5

Total solids 54 60 64 65 Volatile solids 65 71 75 77 COD 70 74 75 78 Total Kjheldhal nitrogen 52 48 50 55 Ammonia nitrogen 40 38 40 44

Loading at 8 g VS/I/day On day 220, loading in each ABR was increased to 6 g VS/1/day and on day 250 to 8 g VS/1/day. Loading at 8 g VS/l/day was continued for 28 days when the experiment was ended. Throughout the 28 days of operation, all the normal parameters of digestion (pH, alkalinity, and gas production) remained consistent. Methane production was 0.60, 0.66, 0.69,

Table 5. % Distribution of particle size at various depths of ABRs

Sampling point Particle size (micron)

<0.2 2.0 3.5 7.0 20 31 60 90 > 100

ABR 2 Chamber 1

10 cm 2.0 11 14 20 10 16 5.0 9.0 20 cm 4.0 16 10 11 8.0 7.0 22 5.0 30 cm 7.0 6.0 22 10 5.0 3.0 10 15

Chamber 2 10 cm 5.0 6.0 15 20 30 16 2.0 1.0 20 cm 1.0 4.0 10 11 10 20 20 22 30 cm 8.0 7.0 5.0 14 6.0 8.0 30 12

ABR 3 Chamber 1

10 cm 3.0 5.0 12 11 5.0 2.0 25 20 20 cm 5.0 6.0 8.0 10 22 15 15 9.0 30 cm 10 11 9.0 6.0 12 8.0 26 13

Chamber 2 10 cm 32 5.0 3.0 12 8.0 13 10 5.0 20 cm 25 8.0 7.0 11 7.0 20 5.0 11 30 cm 37 12 6.0 10 15 5.0 10 5.0

Chamber 3 10 cm 11 12 15 12 5.0 6.0 20 10 20 cm 14 15 5.0 6.0 10 8.0 10 15 30 cm 22 20 10 10 8.0 10 5.0 10

ABR 4 Chamber 1

10 cm 6.0 5.0 8.0 7.0 9.0 2.0 25 20 20 cm 10 3.0 9.0 10 12 25 15 9.0 30 cm 5.0 12 10 10 8.0 8.0 26 13

Chamber 2 10 cm 11 5.0 7.0 20 8.0 13 16 15 20 cm 15 10 7.0 11 7.0 20 5.0 11 30 cm 14 12 6.0 10 15 5.0 10 5.0

Chamber 3 10 cm 33 5.0 5.0 10 5.0 6.0 20 10 20 cm 25 6.0 4.0 6.0 10 4.0 10 15 30 cm 38 2.0 10 10 8.0 10 5.0 10

Chamber 4 10 cm 13 18 10 12 15 8.0 16 6.0 20 cm 7.0 12 11 15 5.0 22 12 10 30 cm 5.0 6.0 6.0 22 11 10 10 11

12 17 22

4.0 3.0 10

19 10 11

6.0 5.0 2.0

10 18 5.0

19 10 11

10 5.0 15

10 15 7.0

4.0 6.0 20

The biological treatment of swine waste 5

and 0.71 l/g VS added for ABRs with two, three, four and five chambers, respectively, at this loading (data not shown).

Particle analyses Most of the solids (TS, VS) were found at the middle (20 cm) and bottom (30 cm) depths of the baffled chambers in all the reactors (data not shown), which indicates that the baffles were trapping most solids. The distribution of particle sizes (Table 5) was quite uniform for two- and three- chamber reactors, with the exception of the top 10 cm of chamber 2 in ABR 2. Here a rather large fraction of particles in the 3.5-31 micron diameter range was found. However, this fraction contained little potential methane, as the nutrient content of that fraction appeared to be small (Fig. 3). Large amounts of small diameter particles (<0.2 microns diameter) were trapped in the second chamber of ABR 3 and the third chamber of ABR 4 (Table 5). The particle size distribution in ABR 5 was similar to ABR 4 (data not shown). These small particles consisted largely of proteins, lipids, and cellulose (Fig. 3). These chemical fractions account for greater than 50% of the potentially available methane in swine manure (Sievers et al., 1980).

Proteins and fats accumulated in the middle and bottom (20, 30 cm) of all chambers. These fractions are high in potential methane but also have been shown to be slow to degrade (E. L. Iannotti, R. Mueller and D. M. Sievers, unpublished results). Very few nutrients were located in the top volume of the last chamber of all reactors. Fig. 3 indicates good trapping of these particular nutrient fractions and explains the excellent biogas production values obtained from the ABRs (Table 2). The ABRs were trapping a larger fraction of the methane-containing particles compared with conventional digesters. There are two reasons for this: (i) the modifications of the baffle design reduce the movement of small particles due to flow velocity under the baffle; and (ii) feeding whole waste into the first chamber of each ABR establishes an excellent natural filter for trapping small particles.

As suggested by nutrient analysis (Fig. 3), proteins were accumulating more than any compound in the lower depths, and hence, a large fraction of the potential methane was effectively being trapped. Lipids were accumulating least.

On day 256, the particle size distribution of efflu- ents from ABRs was determined. The largest fraction being lost from the reactors was in the 10-80 micron diameter range (46% for ABR 2, 58%

30 30 ABR 3

I ABR 2

2 0 ' 20

10'

0 0 . . . .

(:;1-10 C1-20SampllngC1-30 PolntsC2"10 C2-20 e 2 - 3 0 ~ l ~ M I l ~ P o k l t s 0 C$20 C l l 0

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ABR4

, 1 0 . . . . 0 . . . . . . . . . . . . . . . .

: 1 - 10 C 1 - 20 C 1 - 30 C 2- I 0 C2~20 C2-30 C3-10 C3-20 C3- 30 G4 - ! 0 G4.20 C4 -30 C! - |0G| -~C! -~la C2- ] 0G2-20C2-$0C3- ! 0C$-20C3-~C4- ICC4-2004-34C5-| 0C5-24CS.30

Sampling Points SamplMg Points

Fig. 3. Nutrient content of the solids accumulated in each ABR chamber. C1, C2, C3, C4, and C5 refer to chamber 1, 2, 3, 4, and 5 respectively. The numbers 10, 20, and 30 refer to the depth of samples taken from 10, 20, and 30 cm from the

surface, respectively. [], protein; I~, cellulose; It, hemicellulose; ~, fat.

6 R. Boopathy

for ABR 3, 62% for ABR 4, and 66% for ABR 5). Losses of the smallest diameter particles ( < 10 micron) were minimal in all the reactors (14, 8, 6 and 4% for ABR with two, three, four, and five chambers, respectively), while each reactor lost a similar amount (approx. 35%) of particles with larger diameters ( > 100 micron) (data not shown).

The anaerobic baffled reactor shows excellent promise for treating swine waste. It combines the advantages of the anaerobic filter, which has high stability and reliability, and the upflow anaerobic sludge process in which microbial mass itself functions as the support medium.

The ABR's construction avoids certain limitations of these other reactors. Specifically, the risk of clogging and the risk of sludge-bed expansion with resulting high microbial biomass losses are minimized. The ABR maintains a high void volume without the need for expensive filter media, work- intensive gas collection systems or sludge separation systems. The under- and over-liquid flow reduces bacterial washout considerably and does not require unusual settling properties for the microbial culture.

Biogas production in the ABRs was equal to, or greater than, other digester designs reported in the literature (Table 3). This is attributed to the ability of the baffled reactor to effectively trap the small diameter methane-containing particles and maintain a high SRT. The four- and five-chamber ABRs appeared to be slightly more efficient in converting solids to biogas, compared with the two- and three- chamber ABRs. Based on this study, the four- or five-chamber ABR is recommended for the most efficient treatment of swine waste and maximum production of methane from swine manure.

REFERENCES

APHA (1982). Standard Methods for the Examination of Water and Wastewater, 15th edn. American Public Health Association, Washington DC.

Bolte, J. P., Hill, D. T. & Wood, T. H. (1986). Anaerobic digestion of screened swine waste liquids in suspended particle-attached growth reactors Transactions of the ASAE, 29, 543-549.

Boopathy, R. & Sievers, D. M. (1991). Performance of a modified anaerobic baffled reactor to treat swine waste. Transactions of the ASAE, 34, 2572-2578.

Fischer, J. R., Iannotti, E. L., Porter, J. H. & Garcia, A. (1979). Producing methane gas from swine manure in a pilot size digester. Transactions of the ASAE, 22, 370-374.

Fischer, J.R., Iannotti, E.L. & Sievers, D.M. (1981). Anaerobic digestion of manure from swine fed various diets Agric. Wastes, 3, 201-204.

Folch, J., Lees, M. & Stanley, G. H. S. (1957). A simple method for the isolation and purification of total lipids from animal tissues J. Biol. Chem., 226, 497-509.

Goering, H. K. and Van Soest, P. J. (1970). Forage Fiber Analysis. Agricultural Handbook No. 379. USDA Agricultural Research Service, Washington DC.

Gramms, L. C., Polkowski, L. B. & Witzel, S. A. (1971). Anaerobic digestion of farm animal wastes, Transactions oftheASAE, 14, 7-11.

Haga, K., Tanaka, H. & Higaki, S. (1979). Methane production from animal wastes and its prospects in Japan. Agric. Wastes, 1, 45-56.

Hasheider, R. J. & Sievers, D. M. (1984). Limestone bed anaerobic filter for swine manure - - laboratory study. Transactions of the ASAE, 27, 834-839.

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

Hill, D. T. & Bolte, J. P. (1986). Evaluation of suspended particle-attached growth fermenter treating swine waste. Transactions of the ASAE, 6, 1733-1738.

Hobson, P. N., Bousefleld, S. and Summers, R. (1980). Anaerobic digestion of piggery and poultry wastes. In: D. A. Stafford, B. I. Wheatley, and D. E. Hughes (Eds). Anaerobic Digestion. Applied Science, London.

Hungate, R. E. (1966). The Rumen and its Microbes. Academic Press, New York, pp. 56-68.

Jones, D. D., Dale, A. C., Nye, J. C. and Harrington, R. B. (1977). Fiber wall reactor digestion of dairy cattle manure. ASAE paper No. 77-4054. ASAE, St. Joseph, MI.

Kroeker, E. J., Lapp, H. M. and Schulte, D. D. (1975). Cold weather energy recovery from anaerobic digestion of swine manure. Paper presented at the Conference on Energy, Agriculture and Waste Management, 16-18 May 1975, Ann Arbor, MI.

Sievers, D. M., Huff, H. and Iannotti, E. L. (1980). Poten- tial methane production of the clarified liquids from a settling basin. Paper presented at the 4th International Symposium of Livestock Waste, 22-28 May, 1980, Amarillo, TX.

Sievers, D. M., Mueller, R. E. and Iannotti, E. L. (1986). Potential methane in manure particulates. Paper presented at the Summer Meeting of Agricultural Wastes Conference, 10-14 May 1986, San Luis Obisdo, CA.

Yang, P. Y. & Moengangongo, T. H. (1987). Operational stability of a horizontally baffled-anaerobic reactor for diluted swine waste water in the tropics Transactions of the ASAE, 30, 1105-1110.