Re/Views in Environmental Science & Bio/Technology 1: 143–167, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands. 143 Review A comprehensive review of the screening methodology for anaerobic biodegradability of surfactants Keith Strevett 1∗ , Irene Davidova 2,3 & Joseph M. Suflita 2,3 1 School of Civil Engineering and Environmental Science; 2 Department of Botany and Microbiology; 3 Institute for Energy and the Environment, The University of Oklahoma, Norman, Oklahoma 73019, USA ( ∗ author for correspondence, e-mail: strevett@ou.edu) Key words: anaerobic, biodegradation, screening protocol, surfactants Abstract A biodegradability assay should mimic in situ conditions as closely as possible. If this is not entirely possible, the assay should at least include inoculum from the site. This review attempts to condense current literature on anaerobic biodegradability assay and propose a clear assessment methodology to determine the fate surfactants in anaerobic environments. It has been well documented that surfactant concentrations toxic to the microflora can lead to unwarranted failure of biodegradability assays. Thus, an important recommendation is to first perform a toxicity evaluation with relevant controls. Based on the results of this evaluation, a Tier 1 biodegradability assay that assesses the rate of formation of reduced endproducts or the consumption of a particular terminal electron acceptor is recommended and supported by current literature. Balanced chemical equations for the complete mineralization of the substrate are then used to compare the amount of transformation that actually occurred with that theoretically expected. When required, results should be confirmed by Tier 2 testing, which includes monitoring of substrate disappearance over time using a variety of analytical tools. These recommended procedures are scientifically defensible and have the potential of providing environmentally relevant information on the fate of surfactant materials in the environment. 1. Introduction There is no doubt that there is a widening appre- ciation for the fate of contaminant materials that enter and reside in anaerobic environments. Instead of being perceived as completely recalcitrant, a myriad of compounds are now known to be susceptible to biodegradation by pure cultures or consortia of anaer- obic microorganisms. This realization has prompted a general reevaluation of the limits associated with the anaerobic bioconversion of many pollutant mate- rials. Any recent search of the literature will reveal that anaerobes are much more metabolically versatile than once believed (Battersby & Wilson 1989; Aeckersberg et al. 1991; Lovley 1997; Caldwell et al. 1998; Rabus et al. 1999; Anderson & Lovley 2000). Attention has now focused on the means for collecting environment- ally realistic anaerobic biodegradation information. To this end, various experimental protocols for assessing the anaerobic biodegradation potential of contaminant chemicals have been used (Suflita et al. 1997; Ulrich et al. 1997; Young 1997). In some countries, such protocols are often an essential step for marketing a commercial product as green or for earning a “biodegradable” advertising label (EEC 1992). However, the underlying opinion is that the majority of surfactants will be degraded under aerobic conditions and therefore anaerobic degradab- ility of these compounds is not as environmentally relevant (Berna et al. 2001). This assumption under- estimates the increasing use of anaerobic treatment options in current wastewater treatment (Wheatley 1990; Ahring 1994), which requires less energy and produces less volumes of sludge. In aerobic treat- ment, surfactants may induce foaming that can impede the performance of wastewater treatment. Moreover,