Wastewater treatment under low temperature conditions by sulfur redox process and analyses of the biological consortia

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The objective of this research is to make a novel wastewater treatment process activated by a sulfur-redox cycle action of microbe in low temperature conditions. This action is carried out by sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB). The process was comprising of an UASB reactor as pre-treatment and an aerobic downflow hanging sponge (DHS) reactor as post-treatment. As the results of reactor operation, the whole process achieved that over 90% of CODcr removal efficiency, less than 30 mgCODcr/L (less than 15 mgBOD/L) of final effluent, at 12 hr of HRT and at 8 ℃ of UASB reactor temperature. Acetobacterium sp. was detected as predominant species by PCR-DGGE method targeting 16SrDNA with band excision and sequence analysis. In the UASB reactor, various species of sulfate-reducing bacterium, Desulfobulbus sp., Desufovivrio sp., and Desulfomicrobium sp., were found by cloning analysis. In the DHS reactor, Tetracoccus sp. presented as dominant. The proposed sulfur- … More redox action process was considered as an applicable process for low strength wastewater treatment in low temperature conditions.Further more, process performance of the wastewater treatment system was investigated using a pilot-scale reactor system fed with actual sewage for over 600 days. The reactor system was consisted of a denitrification reactor, an UASB reactor, and a DHS reactor with recirculation line. As the results, the total CODcr of 331±117 mg・L^<-1> (total BOD of 128±32 mg・L^<-1>) at influent was reduced desirably to 70±33 mg・L^<-1> of DHS effluent (7±3 mgBOD・L^<-1>) at final effluent with low SS accumulation such as 2-3 % of inlet SS, on the condition of the overall HRT of 24-12 hr and the recirculation ratio of 2-0.3 throughout the experimental period. The final effluent also showed superior quality with respect to low SS, 13±6 mgSS・L^<-1> and high nitrogen removal efficiency, 58±7 % at recirculation ratio 2. Microbial activity test and FISH analysis, it revealed that sulfate-reducing bacteria contributed to degrade of organic matter in the UASB reactor even low temperature condition that it would be less than 10 ℃. Less