Pergamon Chemosphere, Vol. 39, No. 11, pp. 1861-1870, 1999 © 1999 Elsevier Science Ltd. All rights reserved 0045-6535/99/$ - see front matter PII: S0045-6535(99)00081-8 TOXIC EFFECT OF SURFACTANTS AND PROBABLE PRODUCTS OF THEIR BIODEGRADATION ON METHANOGENESIS IN AN ANAEROBIC MICROBIAL COMMUNITY Victoria A. Shcherbakova, Kestutis S. Laurinavichius, and Vasily K. Akimenko Skryabin Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, pr. Nauki 5, Pushchino, Moscow oblast, 142292 Russia e-mail: <shcherb@ibpm.serpukhov.su> (Received in Germany 27 December 1998; accepted 8 March 1999) ABSTRACT Surfactants used in household and various industries, are rather toxic; therefore, the accumulation of these compounds in the environment through wastewaters has challenged the problem of their biodegradation. In this research, an attempt was made to assess the toxic effect of various surfactants and the likely products of their biodegradation on the acetoclastic methanogens of an anaerobic microbial community. Among the substances investigated, cationic surfactants were found to be most toxic to methanogens: 154 mg/l alkamon DS and 345 mg/l catamin AB induced a 50% inhibition of methanogenesis. Toxicity studies of some aromatic and cyclic compounds, as the probable products of biodegradation of alkylbenzene sulfonate surfactants, showed that methanogenesis in the microbial community under study are rather tolerant to high concentrations of these compounds. ©1999 Elsevier Science Ltd. All rights reserved INTRODUCTION Surfactants are produced and handled in large amounts in a number of industries. World production of detergents is about 15 million tons per year (Turner and Houston, 1992; Steber and Berger, 1995), most of which is being discharged into the environment through wastewaters. Strong detergents representing alkylbenzene sulfonates with branched alkyl chains were the first class of compounds showing problems of recalcitrant harmful waste in the environment (Leisinger, 1983). On the other hand, other detergents that are readily degradable under aerobic conditions can give rise to aromatic compounds and other xenobiotics (Swisher, 1987), which, when accumulated in the environment, are also hazardous to human health. Of severe risk are some synthetic benzene compounds, which are highly recalcitrant to biodegradation because they are toxic to microorganisms. Detergent-induced foaming in aerotanks reduces their efficiency and the settling ability of sludge; this is particularly the case with the treatment of industrial wastewaters, which may contain up to 300 mg/1 1861