SURFACTANTS IN ANAEROBIC DIGESTION OF CHEESE WHEY, POULTRY WASTE, AND CATTLE DUNG FOR IMPROVED BIOMETHANATION M. Desai, D. Madamwar ABSTRACT. TO obtain enriched methane content and improve the anaerobic digestion of a mixture of cattle dung f poultry waste and cheese whey, with enriched methane content, the effect of various surfactants was studied. Among the surfactants tested, Tween 80 and sodium lauryl sulphate showed the maximum enhancement in gas production as well as methane content, indicating better process performance. The Tween 80 dosed digester (300 JJL/L) produced about 3.5 L gas/L of digester/d with 70% methane. Results also indicated increased percent COD reduction in the presence of Tween 80. Keywords. Surfactants, Cheese whey, Poultry waste, Cattle dung, Anaerobic digestion, Biomethanation. T he worldwide production of fluid whey by the cheese and casein industries is over 100 billion tons annually, with the production of 1 ton of cheese resulting in the production of 8 tons of liquid whey (Kosaric and Wieczorek, 1975). This whey contains about 4% lactose, \% protein, 1% salts, and 0.1 to 0.8% lactic acid and is not effectively utilized. It has a very high biological oxygen demand (above 30 000 mg/L); therefore, its disposal creates a tremendous pollution load. Whey represents potential energy source and poses several advantages if it is subjected to anaerobic digestion. During the past several years there has been considerable interest in anaerobic digestion of cheese whey (Hill et al., 1987). Anaerobic digestion of whey offers an excellent approach from both energy conservation and pollution control considerations (Clanton et al., 1985; Yan et al., 1988). Previous work has shown that cheese whey contains a high level of carbohydrates which promotes the growth of acid-forming bacteria, but has a negative effect on methane-producing bacteria (Hanson, 1982). However, addition of poultry wastes increases the nitrogen content of the digester and supports the growth of methanogens (Desai et al., 1994). By itself, poultry waste is difficult to handle by anaerobic digestion systems due to heavy ammonia toxicity. We found improved gas production with enriched methane content when a mixture of cattle dung, poultry waste, and cheese whey in the ratio of 2:1:3 (dry weight basis) was used as substrate (Desai et al., 1994). There is growing interest in maximizing the extraction of methane for energy recovery from cheese whey and poultry waste. It has been reported that surfactants increase the productivity of anaerobic digesters (Madamwar et al., 1991). Surfactants are especially noted for their wetting qualities. They improve enzyme production and enhance Article was submitted for publication in September 1993; reviewed and approved for publication by the Emerging Technologies Div. of ASAE in February 1994. The authors are Manik Desai, Research Student, and Datta Madamwar, Reader, Post Graduate Dept. of Biosciences, Sardar Patel University, Vallabh Vidyanagar, Gujarat, India. enzyme activity (Elworth et al., 1968). The purpose of our study was to elucidate the effect of different types of surfactants on the anaerobic digestion of a mixture of cattle dung, poultry waste, and cheese whey with the ultimate aim of improving gas production and methane content. MATERIALS AND METHODS RESOURCES Poultry waste was collected from the Bakrol Poultry Farm, Bakrol, India. Cheese whey was collected from AMUL Dairy, Anand, India. All chemicals used were of analytical grade. The following surfactants were used in our study, and they were obtained from Central Drug House (CDH), India. Tween 20 (Polyoxyethylene sorbitan monolauerate) Tween 60 (Polyoxyethylene sorbitan monostearate) Tween 80 (Polyoxyethylene sorbitan monooleate) Sodium lauryl sulphate Triton-X 100 (Iso-octylphenoxy-polyethoxy-ethanol) Caprylic acid Cetrimide (Tetradecyl trimethyl ammonium bromide, myristyl trimethyl ammonium bromide) ANAEROBIC DIGESTION Several anaerobic digesters were used. Each digester consisted of a 5-L glass bottle, having a working volume of 3 L and containing 6% of total solids with mixtures of cattle dung, poultry waste, and cheese whey, 2:1:3 (dry weight basis) were maintained at 40° C in a thermostat. Gas was collected and measured by displacement of acidified saturated salt solution making due correction for atmospheric pressure and temperature. The digesters were fed on a semicontinuous basis (once per day) with the mixture of cattle dung, poultry waste, and cheese whey. The digesters were intermittently stirred with magnetic stirrers (total duration 4 h/day at 120 rpm). A retention time of 10 days at a loading rate of 6 g TS/L/day was used based on a previous study (Desai et al., 1994). Prior Transactions of the ASAE VOL. 37(3):959-962 © 1994 American Society of Agricultural Engineers 0001-2351 / 94/ 3703-0959 959