Bioresource Technology 37 ( 1991 ) 157-160 (', ~., • ?, Effects of Various Surfactants on Anaerobic Digestion of Water Hyacinth-Cattle Dung Datta Madamwar, Anami Patel & Vikram Patel Department of Biosciences, Sardar Patel University, Vallabh Vidyanagar -- 388 120, Gujarat, India (Received 25 August 1990; revised version received 23 September 1990; accepted 29 September 1990) Abstract In an effort to improve the anaerobic digestion pro- cess of water hyacinth-cattle dung, the effects of various doses of different surfactants: Tween 20, Tween 60, Tween 80, sodium lauryl sulphate, Tego- prens 42, Tegoprens 43, Tegoprens 47, Tegoprens 51, Tegoprens 52, Tegoprens 63, have been evalu- ated in bench-scale digesters. Increasing concentra- tions of surfactants produced maxima or minima in the various parameters measured. Amongst the surfactants tested, Tegoprens 43 showed a maxi- mum of more than 114% increase in gas produc- tion with a 6.25% higher methane content. Key words: Water h3)acinth, cow dung, anaerobic digestion, methane, energy, surfactants, biogas. INTRODUCTION In India, a large number of water bodies have been damaged due to the excessive growth of aquatic weeds, particularly water hyacinth (Eich- hornia crassipes), to the extent that they are of no further use. Today, utilization is considered an important part of weed management. Therefore, the anaerobic digestion of water hyacinth (WH), resulting in the production of biogas, a valuable source of energy, has recently attracted universal attention (Obeid, 1975; Gupta & Lamba, 1976; Wolverton & McDonald, 1976; Saraswat & Khanna, 1986; Annachhatre & Khanna, 1987). There is also a growing interest in maximizing the extraction of methane for energy recovery from water hyacinth. Unfortunately, operating experi- ences with anaerobic digesters and their cost effectiveness has not been consistently good. Digesters are susceptible to malfunctioning due to shock loading and a variety of toxic substances. 157 Bioresource Technolog3' 0960-8524/91/S03.50 © 1991 Great Britain Malfunctioning manifests itself in terms of reduced gas production, reduced degradation of organic materials and a simultaneous increase in acidity. Researchers have shown the need for pH control and the advantages of mixing. However, further process improvements are needed. Surfactants are amongst the most versatile of the products of the chemical industry and are used in diverse forms. Of late, surfactants have become sub- jects of intense investigation in the field of chemical kinetics and biochemistry because of the unusual properties of the polymeric forms (micelles) of these materials. They show unusual catalysis of organic reactions (Fendler & Fendler, 1975) and show similar behaviour with biological reactions; for example, surfactants improve enzyme activity (Elworthy et al., 1968; Fendler & Fendler, 1975; Rosen, 1978; Naik & Rastogi, 1983). Surfactants are used in detergents and biocides and may adversely affect digesters. No study, however, seems to have been made so far on the effects of surfactants on the anaerobic digestion of water hyacinth and cattle dung with the objective of improving both the performance stability and the rate of decomposition, with improved gas produc- tion, by adding various surfactants. METHODS Resources All chemicals used were of analytical grade. All Tegoprens were obtained from Gold Schmidt AG, Essen, FRG. Cattle dung and water hyacinth were obtained locally. Anaerobic digestion Several bench-scale anaerobic digesters were used. Each vessel consisted of a 10-1itre glass reaction bottle, having a working volume of 6 litres and con- Elsevier Science Publishers Ltd, England. Printed in