A variety of environments are contaminated with chlorinated benzenes. Therefore, investigating the biodegradation of chlorobenzenes in different types of soils is useful in assessing the feasibility of bioremediation. One mineral-dominated soil: PPI (Petro Processors Inc. site) soil, and three organic matter-dominated soils (natural wetland soil, constructed wetland soil (a mixture of peat, compost and sand), and river sediment) were used to investigate anaerobic biodegradation of 1,2,3,4-Tetrachlorobenzene (1,2,3,4-TeCB) using laboratory microcosms. To determine whether methanogens were directly responsible for dechlorination, a comparative study using 2-bromoethanesulfonic acid (BES) for inhibition of methanogenesis was conducted. Hydrogen and methane concentrations, and microbial diversities were analyzed. The results of the present study showed that 1,2,3,4-TeCB was completely biodegraded in all test soils with different microbial communities. The most dominant dechlorination pathway was: 1,2,3,4-TeCB à 1,2,3-TCB à 1,2-DCB + 1,4-DCB + 1,3-DCB à monochlorobenezene + benzene. The test chemical was biodegraded at rates ranging from 0.023 day-1 (half-life time of 30.5 days) to 1.108 day-1 (half-life time of 0.6 days), with lag periods varied between 1 and 72 days. Dechlorination kinetics of chlorobenzenes was found to depend on many factors other than organic carbon content. DGGE banding profile, methane concentration and dechlorination activities suggest that BES probably changed the compositions of bacteria consortia, and partly inhibited methanogenesis and chlorobenzene dechlorination. Moreover, methanogens were probably not directly responsible for dechlorination of chlorobenzenes.
Rhizosphere of some plants can enhance rhizodegradation of organic contaminants. Thus, the present study also investigated the effects of Typha latifolia L. roots on anaerobic degradation of 1,2,3,4-TeCB. Biodegradation rate constant of 1,2,3,4-TeCB was observed to increase with increasing amounts of roots, indicating that Typha, a native wetland plant, could be a very promising vegetation for application in phytoremediation. Due to root matter, higher concentrations of organic acids and hydrogen were observed in treatments with roots compared with the treatment without roots, which probably caused higher dechlorination activities in root-amended microcosms.