38    ANAEROBIC DEGRADATION OF CHLORINATED
SOLVENTS
Cecilia Vargas, Graduate Student
Robert C. Ahlert, Professor
Elizabeth E. Abbott, J.J. Slade Scholar
Marshall G. Gayton, J.J. Slade Scholar
Department of Chemical and Biochemical Engineering
Rutgers, The State University
Piscataway, New Jersey 08854
INTRODUCTION
Many environmentally important man-made compounds are halogenated. The list of halogenated
species includes pesticides, plasticizers, plastics, solvents, and trihalomethanes. Of the halogenated
compounds, the best known and most studied are the chlorinated compounds. This is because of the
highly publicized problems associated with DDT, other pesticides, and numerous industrial solvents
[1]. Well contamination by compounds such as chloroform, 1,1,1-trichloroethane, and tetrachlo-
roethylene has been documented [2]. The presence of such compounds in the environment is due to
inadequate disposal techniques and accidental spillage.
Many of these chlorinated compounds are quite persistent in the environment. They are not easily
degraded aerobically and have been found to break through rapidly in granular activated carbon beds
[3]. In contrast to naturally occurring compounds, man-made compounds are less susceptible to
biodegradation. Naturally present organisms often cannot produce the enzymes necessary to bring
about transformation of the original compound to a point at which the resultant intermediates can
enter into common metabolic pathways and be mineralized completely [4].
The metabolic fate of these chemicals under aerobic conditions have been studied widely, and
degradation, if any, or persistence patterns established. Anaerobic studies with halogenated compounds have shown several of these compounds are biodegradable. Methane-producing freshwater
lake sediment was found to dehalogenate iodo-, chloro-, and bromobenzoates by a reductive reaction
[5]. It has been shown that transformations of trihalomethanes can also occur under anaerobic
conditions [2]. Lang et al. reported on the biotransformation of some haloaliphatic compounds,
suggesting a series of reductive dechlorination reactions [2).
The main interest in biodegradation of chlorinated compounds is in anaerobic digestion. Although
there are disadvantages, such as long startup time and incomplete understanding of the microbiology
involved, there is more evidence for biodegradation of chlorinated compounds in anaerobic systems
than in aerobic systems. Recently, researchers have shown that 1- and 2-carbon halogenated aliphatic
organic compounds are biodegradable under methanogenic conditions [2]. There is also field evidence
for the long-term transformation of halogenated compounds under anaerobic conditions [2]. No
specific research has been done to determine the actual degradation mechanism or the affected group
of microorganisms.
In this study, the biodegradability of 1,1,1-trichloroethane (TCA), 1,1-dichloroethane (DCE), and
dichloromethane (DCM) under anaerobic conditions was investigated. Also, the acclimation potential
of a mixed anaerobic culture to these compounds was assessed.
Although other studies with these compounds have been carried out, only the extent of biodegradation has been studied. In addition to biodegradation studies, acclimation and inhibition at different
concentration levels was studied.
Finally, through the variation of conditions to favor certain groups of bacteria, the main population affected by these "toxic" compounds was studied.
339