Anaerobic bioventing of unsaturated zone contaminated with DDT and DNT J.K. Shah * , G. D. Sayles ** , M.T. Suidan * , P. Mihopoulos * , S. Kaskassian * *Department of Civil and Environmental Engineering, University of Cincinnati, Cincinnati, OH 45221–0071, USA ** US Environmental Protection Agency, National Risk and Management Research Laboratory, Dr. Martin Luther King Rd., Cincinnati, OH 45268 USA Abstract Initial degradation of highly chlorinated compounds and nitroaromatic compounds found in munition waste streams is accelerated under anaerobic conditions followed by aerobic treatment of the degradation products. The establishment of anaerobic environment in a vadose zone can be accomplished by feeding appropriate anaerobic gas mixture, i.e., “anaerobic bioventing”. The gas mixture contains an electron donor for the reduction of these compounds. Lab scale study was conducted to evaluate potential of anaerobic bioventing for the treatment of an unsaturated zone contaminated with 1,1,1-trichloro -2,2- bis(p-chlorophenyl)ethane (DDT) and 2,4-dinitrotoluene (DNT). Hydrogen was used as the electron donor. Using the soil columns innoculate with anaerobic microorganisms, it was observed that by feeding a gas mixture of 1% hydrogen, 1% carbon dioxide and nitrogen, methanogenic conditions were established and DDT was reductively dechlorinated. 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD) accumulated as the intermediate product. The half life of DDT was calculated to be 8.5 months. DNT completely disappeared after six months of operation and no intermediates could be detected. Keywords Anaerobic bioventing; DDT; DNT; munition wastes; pesticides; vadose zone Introduction Introduction and large scale production of synthetic halogenated organic chemicals over the last few decades has resulted in a widespread contamination of these compounds. These compounds exhibit very low solubility, and high toxicity coupled with a tendency to accu- mulate in food chains, make them particularly relevant targets for remediation activities. Halogenated compounds are relatively oxidized by the presence of halogen substituents, which are highly electronegative and thus more susceptible to reduction. Similarly, due to the electron withdrawing nature of nitro, nitroaromatic compounds are electron deficient impeding electrophilic attack by aerobic bacteria (Rieger and Knackmuss, 1995). The degradation of these compounds thus requires the presence of strong anaerobic conditions for degradation. Bioventing is an in situ process appropriate for bioremediation in the unsaturated zone. It is the use of induced gas movement through unsaturated soils, with or without the addi- tion of nutrients, to stimulate the growth of indigenous microbes that are capable of con- verting organic contaminants to less hazardous substances. It is an innovative technology for clean up of hazardous compounds in the vadose zone. Existing soil vapor extraction facilities can be easily converted to establish aerobic conditions promoting biodegradation. Bioventing has been successfully applied to remove a wide range of contaminants, espe- cially petroleum hydrocarbons and BTEX compounds (Du Pont, 1993). It offers a cost- effective remediation technology as the required flow rates are much lower and the system rarely requires emission permitting or expensive off gas treatment (Ratz et al., 1997). Using the same gas delivery system as employed in aerobic bioventing, anaerobic gas mix- ture can be introduced to the unsaturated zone to establish anaerobic conditions and provide Water Science and Technology Vol 43 No2 pp 35–42 © IWA Publishing 2001 35 Downloaded from https://iwaponline.com/wst/article-pdf/43/2/35/429149/35.pdf by guest on 22 November 2018