ELSEVIER

Environmental Pollution 86 (1994) 337-340 © 1994 Elsevier Science Limited

Printed in Great Britain. All rights reserved 0269-7491/94/$07.00

ANAEROBIC DIGESTION OF A MIXTURE OF CHEESE WHEY, POULTRY WASTE A N D CATTLE DUNG:

A STUDY OF THE USE OF ADSORBENTS TO IMPROVE DIGESTER PERFORMANCE

M a n i k Desa i & D a t t a M a d a m w a r *

Post-Graduate Department of Biosciences, Sardar Patel University, Vallabh Vidyanagar--388 120, Gujarat, India

(Received 10 June 1993; accepted 29 November 1993)

Abstract This paper-describes the results of a study aimed at im- proving the efficiency of anaerobic digestion of a mixture of cattle dung, poultry waste and cheese whey at a ratio of 2 : 1 : 3 (w/w on dry weight basis) in terms of total gas production, methane content and process stability by adding various adsorbents. The adsorbents appeared to improve the digester performance, for example about a two-fold enhancement in total gas production with 17% enriched methane content were achieved with the addition of 4 g litre i of silica gel.

Keywords: cheese whey, poultry waste, cattle dung, adsorbents, anaerobic digestion, methane, energy.

INTRODUCTION

Cheese whey, a by-product of cheese production, is generated in an enormous quantity in India due to the increased production of cheese. Whey typically con- tains about 4% lactose, 1% protein, 1% salt and 0.1- 0.8% lactic acid. Recovery of whey proteins has be- come a relatively well established process (Moulin & Galzy, 1984). However, the lactose stream (whey per- meate) having a biological oxygen demand of greater than 30 000 mg litre i, remains a major disposal prob- lem. The anaerobic digestion process offers a solution to the problem from both energy conservation and pol- lution control considerations, since it can reduce the BOD considerably with the production of fuel in the form of methane (Clanton et al., 1985; Yan et al., 1988). However, it has not gained popularity.

Cheese whey contains high levels of carbohydrates, which promote the growth of acid forming bacteria, but have negative effects on methane producing bacteria (Hanson, 1982). This problem can be overcome by adding poultry waste, which is also a major problem for disposal. The addition of poultry waste increases the nitrogen content of the digester and supports the growth of methanogens. As such, poultry waste is difficult to handle by anaerobic digestion systems due to heavy ammonia toxification.

* To whom correspondence should be addressed.

Previous work has shown improved gas production with enriched methane content when a mixture of cattle dung, poultry waste and cheese whey in the ratio 2 : 1 : 3 (w/w on dry weight basis) was used as a sub- strate (Desai et al., 1994). There is a further growing interest in maximizing the extraction of methane for energy recovery from cheese whey and poultry waste.

It has been reported that the addition of powdered activated carbon results in an increase in total gas pro- duction with high methane content and stabilizes anaerobic process performance (McConville & Maier, 1978). Similar results were obtained with other adsor- bents (Madamwar & Mithal, 1986; Patel et al., 1992). Based on a review of the literature, it is evident that adsorbents are responsible for improved digestion. The surface of the adsorbent provides sites where substrate can accumulate thereby providing high localised sub- strate concentrations. These areas of adsorption provide a more favourable growth environment for the bacterial substrate system. However, so far, no detailed study seems to have been done on the effect of activated carbon and other adsorbents, such as silica gel, bentonite, aluminium powder, gelatin and pectin, on the anaerobic digestion of cheese whey, poultry waste, and cattle dung mixtures. This study was undertaken with the aim of improving the gas production and methane content through the appropriate use of adsorbents.

337

MATERIALS AND METHODS

Resources All chemicals used were of analytical grade. All adsor- bents were obtained from LOBA Chemie, India and they were of analytical grade. Poultry waste was collected from Bakrol poultry farm, Bakrol, India, and the cheese whey was collected from AMUL Dairy Anand, India. Fresh cattle dung was always obtained locally.

Anaerobic digestion Several bench-scale anaerobic digesters were used. Each vessel consisted of a 5-1itre glass reaction bottle, having a working volume of 3 litres and containing 6% total

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Fig. 1. Steady state profile of anaerobic digestion of cheese whey/poultry waste/cattle dung mixture in the presence of adsorbents. Operating conditions: temperature, 40°C; retention time, 10 days; loading rate, 6.0 g total solid litre -~ of digester day -I using a mixture of cattle dung/poultry waste/cheese whey, in the ratio of 2 : 1 : 3 w/w on dry weight basis. (Gas production, A; methane

content, I'-1; COD, Q).)

solids (mixture of cattle dung, poultry waste and cheese whey, 2 : 1 : 3 (w/w on dry weight basis). Digesters were maintained at 40 + I°C in a thermostat. Gas was collected and measured by displacement of an acidified saturated salt-solution and the results have been cor- rected for atmospheric pressure and temperature. The digesters were fed on a semi-continuous basis (once per day) with the mixture of cattle dung, poultry waste and cheese whey and a retention time of 10 days with a solids loading rate of 6 g total solids litre -~ of digester day 1 (Desai et aL, 1994). Prior to feeding, an equal quantity of sludge was withdrawn from the bottom of the digester. Adsorbents were incorporated with the feed sludge. A steady state condition was decided upon by a fairly constant mean gas production rate and con- stant BOD/COD values. Experiments were carried out in triplicate for each adsorbent and for each concentra- tion, and average data are presented in Fig. 1.

Analysis Gas composition was analysed with a CIC gas chro- matogram with a stainless steel Chromosorb 2 column and a thermal conductivity detector (Varel et al., 1980). Feed and effluent slurry were routinely analysed for

pH, volatile acids, biochemical oxygen demand (BOD), chemical oxygen demand (COD), total solids, and volatile solids, using standard procedures (APHA, 1976).

RESULTS AND DISCUSSION

A summary of the steady state profiles of the anaerobic digesters, in the presence of various adsorbents under different concentrations is presented in Fig. 1 and Table 1. The effects of adsorbents (silica gel, activated carbon, bentonite, aluminium powder, gelatin and pectin) were evaluated using several anaerobic reactors operating at different dosages at 40°C with a retention time of 10 days and a loading rate of 6 g total solids (w/v) litre -~ of digester day -l. In general, all digesters dosed with adsorbents up to a limit of about 4 g litre 1 showed an increase in gas production, with enriched methane content.

Figure 1 shows enhanced gas production with in- creasing amount of adsorbents. Maximum enhance- ment (two-fold) was achieved, for example, with the addition of 4 g litre -~ of silica gel (Fig. 1). In addition to increasing total gas production silica gel was respon-

A study of the use of adsorbents to improve digester performance 339

Table 1. Steady-state profile of anaerobic digestion of cheese whey/ponltry waste/cattle dung in the presence of adsorbents

Adsorbent COD removal Volatile acids Volatile solids dose (%) (g litre -1) (g %)

(g litre l)

Control 72-00 + 0.518 0.81 1.99

Silica gel

0.5 72-85 ± 0-56 0.74 1.82 1-0 74.89 ± 0.63 0.63 1.59 2-0 76.50 ± 1.90 0.57 1.32 3-0 77.52 ± 0-38 0.52 1.07 4.0 78.54 ± 1.10 0.51 0.87

Powdered activated charcoal 0.5 72.41 + 1.07 0.78 1.88 1.0 73.72 + 0.34 0.70 1.77 2-0 75.33 + 0.47 0.62 1.48 4.0 76.21 + 0.77 0.60 1.39 6.0 74.31 + 1.09 0.67 1.64

Bentonite 0.5 72.26 + 0.47 0.80 1.96 1.0 72.70 ± 1.15 0-75 1.83 2.0 73.29 ± 0.95 0-71 1.79 3.0 75.48 ± 1.34 0.62 1.42 4.0 77.08 ± 1.04 0-54 1.17

Aluminium powder 0.5 72.12 ± 0.49 0.82 1.97 1.0 72.56 ± 0.93 0.79 1.89 2.0 74.16 ± 0.84 0-68 1-65 3.0 76.64 ± 0.67 0-59 1-28 4.0 75.04 ± 0.78 0-64 1-58

Gelatin 0.5 72.41 ± 0.55 0.79 1.87 1.0 72.70 ± 0.31 0.75 1.81 2.0 73.58 ± 0.53 0.71 1.76 4.0 75.77 ± 0.65 0.62 1.43 6-0 75.18 ± 1.10 0.64 1.47

Pectin 0.1 71.97 ± 0.88 0-80 1.97 0.5 73.29 ± 0.92 0.73 1.80 1.0 74.02 ± 0.92 0.68 1.65 2.0 75.62 ± 1.59 0.61 1.43 4.0 75.48 ± 1.22 0.63 1.49

Operating conditions: temperature, 40°C; retention time, 10 days; loading rate, 6-0 g total solid litre t of digester day-l; using a mixture of cattle dung/poultry waste/cheese whey, at the ratio of 2 : l : 3 w/w on dry weight basis.

sible for a higher methane content in the digester gas. As shown in Fig. 1, as much as 72.8% methane was present in the total gas at a dose of 4 g litre -I of silica gel, as compared with 62% for the control digester without adsorbent.

The data also indicate that adsorbents are responsible for improved efficiency in the conversion of organic matter to volatile acids and then to methane. Organic matter was reduced with increased dose of adsorbent (as given in Table 1 in terms of volatile solids). Process stability, as evidenced by lower volatile acids (McConville & Maier, 1978), consistently increased with increased levels of silica gel (Fig. 1). This indicates that volatile acids are consumed at a faster rate than in

the control experiment, where no adsorbent is used. It is well documented that protein- and carbohydrate- fermenting bacteria grow rapidly, and the substrates are rapidly degraded to fatty acids, even at retention times of less than 1 day (McCarty, 1971; Mclnerney & Bryant, 1981). However, fermentation of fatty acids to methane is a slower process due to the slow growth of the fatty acid-fermenting bacteria and is therefore, a rate limiting step (Mclnerney et aL, 1979; Boone & Bryant, 1980; Mclnerney & Bryant, 1981). Methano- genic bacteria catabolise mainly acetate, carbon dioxide and hydrogen to the terminal products. The main- tenance of a very low concentration of hydrogen in the digester by methanogens is essential for efficient fermentation, because it maintains a low production of propionate and other reduced products (Mclnerney et aL, 1979). Only a slight increase in hydrogen can lead to the accumulation of propionate and carbon dioxide. In our studies propionate and carbon dioxide were found to accumulate in larger quantities in a control digester (data not given), than in those receiving silica gel. From Fig. 1 it can be seen that the presence of adsorbents boost the methane-forming step of the digestion process. The average acid concentration ranged from 0.81g litre -l in the digester with no adsor- bent to 0.51 g litre -1 in the digester dosed with 4 g litre -l of silica gel. High average acid concentration in the control digester indicates an imbalance between acidifying bacteria and methanogenic bacteria (Kugelman & Chin, 1971).

Process performance can also be judged by chemical oxygen demand (COD) values, which indicate the extent of biodegradation that has taken place under steady state conditions (Gossett & McCarty, 1975; Hills & Roberts, 1981). Silica gel resulted in the lower COD value at a dosage of 4 g litre l, indicating greater biodegradation and high process performance. The COD was 14.7 g litre t with the silica gel (4 g litre -1) digester compared to a value of COD of 19-11 g litre in the control reactor (Fig. 1). Table 1 also gives data on COD removal. This parameter is important because the values suggest bacterial efficiency, thereby increas- ing biodegradability. A 78.5% COD reduction occurred with a silica gel dosage of 4 g litre -t, whereas the COD reduction was only 72% in the control digester.

Other adsorbents tested also showed increased gas production with enriched methane content (up to a limit) indicating that adsorbents in general enhance the con- version efficiency. Addition of these adsorbents resulted in higher process stability, as shown by the lower values of volatile acids, and increased rates of decomposition, giving reduced values of effluent COD and higher % COD removal in the adsorbent-dosed digesters.

From these studies it seems that contact between substrate and bacteria is enhanced by adsorbents. Analysis of the data shows that adsorbents provide sites for the anaerobic reaction to occur, that is adsor- bents may be providing higher localized substrate con- centrations. These areas of adsorption provide a more favourable growth environment for the bacteria-sub-

340 Manik DesaL Datta Madamwar

strate system. Similar observations have been made by other workers, while working with powdered activated carbon (McConville & Maier, 1978; Spencer, 1978). Adsorbent presence may be responsible for reducing the inhibitory concentration of certain components present in the digester,

Adsorbents, such as gelatin and pectin, may also have additional effects, such as stimulating fatty acid production and degrading bacteria by serving as good nitrogen and carbon sources. However, this needs detailed investigation.

REFERENCES

American Public Health Association (1989). Standard Methods for the Examination of Water and Waste Water, 17th edn. American Public Health Association, Washington, DC.

Boone, D. R. & Bryant, M. P. (1980). Propionate degrading bacterium Syntrophobacter wolinii sps. nov. gen. nov., from methanogenic ecosystem. Appl. Environ. Microbiol., 40, 626-32.

Clanton, C. J., Goodrich, P. R. Morris, H. A. & Backus, B. D. (1985). Anaerobic digestion of cheese whey. In Proceed- ings of the Fifth International Symposium on Agricultural Wastes. ASAE, St Joseph, MI, pp. 475-82.

Desai, M., Patel, V. & Madamwar, D. (1994). Effect of temperature and retention time on biomethanation of cheese whey-poultry waste-cattle dung. Environ. Poll. 83, 311-5.

Gossett, J. M. & McCarty, P. L. (1975). Heat refuse for increasing anaerobic biodegradation. Symposium: Cellu- lose--A Variable Resources. Paper presented at the 68th Annual Meeting, American Institute of Chemical Engineering, Los Angeles, CA, Nov. 16-20.

Hanson, G. (1982). End product inhibition in methane fermentation. Process Biochem., 17, 45-9.

Hills, D. J. & Roberts, D. W. (1981). Anaerobic digestion of dairy manure and field crop residues. Agric. Wastes, 3, 179-89.

Kugelman, I. J. & Chin, K. K. (1971). Toxicity Synergism and Antagonism in Anaerobic Waste Treatment Processes. ed. R. F. Gould. Advances in Chemistry Series 105, American Chemical Society, Washington, DC, pp. 55-90.

Madamwar, D. B. & Mithal, B. M. (1986). Effect of pectin on anaerobic digestion of cattle dung. Biotechnol. Bio- engng, 28, 624-6.

McCarty, P. L. (1971). Energetics and Kinetics of Anaerobic Treatment, ed. R. F. Gould. Advances in Chemistry Series, 105, American Chemical Society, Washington, DC, pp. 91-107.

McConville, T. & Maier, W. J. (1978). Use of powdered activated carbon to enhance methane production in sludge digestion. Biotechnol. Bioengng Syrup., 8, 243-59.

McInerney, M. J. & Bryant, M. P. (1981). Biomass Conver- sion Process or Energy and Fuel, ed. S. S. Sorer & O. P. Zaborsky. Plenum Press, New York, pp. 277-96.

McInerney, M. J., Bryant, M. P. & Pfenning, N. (1979). Anaerobic bacterium that degrades fatty acids in syntrophic association with methanogens. Arch. Microbiol., 122, 129-35.

Moulin, G. & Galzy, P. (1984). Whey, a potential substrate for biotechnology. Biotechnol. Genetic Engng Rev., 1, 347-74.

Patel, V., Patel, A. & Madamwar, D. (1992). Effects of adsor- bents on anaerobic digestion of water hyacinth-cattle dung. Bioresource Technol., 40, 179-81.

Spencer, R. R. (1978). Enhancement of methane production in the anaerobic digestion of sewage sludge. Paper pre- sented at the symposium on Biotechnology in Energy Pro- duction and Conservation, Gatlinburg, TN, May 10-12.

Varel, V. H., Hahimoto, A. G. & Chen, Y. R. (1980). Effect of temperature and retention time on methane production from beef cattle waste. Appl. Environ. Microbiol., 40, 217-22.

Yan, J. Q., Liao, P. H. & Lo, K. V. (1988). Methane produc- tion from cheese whey. Biomass, 17, 203-11.