Influence of sulfate reduction on the microbial dechlorination of pentachloroaniline in a mixed anaerobic culture |
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Authors: | Zainab Z Ismail Spyros G Pavlostathis |
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Institution: | (1) School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0512, USA;(2) Present address: Department of Environmental Engineering, University of Baghdad, Baghdad, Iraq |
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Abstract: | The reductive dechlorination of pentachloroaniline (PCA) was investigated in the absence and presence of sulfate in batch
assays using a PCA-dechlorinating mixed anaerobic culture with methanol as the external electron donor at neutral pH and 22°C.
PCA at an initial concentration of 7.8 μM was sequentially dechlorinated to dichlorinated anilines in the sulfate-free culture
and the culture amended with 300 mg sulfate-S/L. At an initial concentration of 890 mg sulfate-S/L, a higher sulfate reduction
rate was achieved, but PCA dechlorination was not observed until the sulfate concentration dropped to about 100 mg S/L. The
transient inhibition of PCA is attributed to competition between sulfate reducing and dechlorinating species for electron
donor, more likely for H2 resulting from methanol fermentation. A long-term (118 days) PCA dechlorination assay with the sulfate-amended culture, which
included five feeding cycles, resulted in accumulation of both sulfide (886 mg S/L) and acetate (1,900 mg COD/L). Under these
conditions, the sulfate reducers were inhibited, while the rate and pathway of PCA dechlorination were not affected. The results
of this study show that the rate of sulfate reduction rather than the sulfate concentration alone dictates the outcome of
the competition between sulfate reducers and either dechlorinators or methanogens. The findings of the present study have
significant implications relative to the fate and transport of PCA and its dechlorination products in sulfate-laden subsurface
systems. |
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Keywords: | |
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