Enhanced elementary sulfur recovery with sequential sulfate-reducing, denitrifying sulfide-oxidizing processes in a cylindrical-type anaerobic baffled reactor.

Simultaneous removal of COD, SO4(2-) and NO3(-) and recovery of elemental sulfur (S(0)) were evaluated in a four-compartment anaerobic baffled reactor (ABR) with separated functional units of sulfate reduction (SR) and denitrifying sulfide removal (DSR). Optimal SO4(2-)-S/NO3(-)-N ratio was evaluated as 5:5, with a substantial improvement of S(0) recovery maintained at 79.1%, one of the highest level ever reported; meanwhile, removal rates of COD, SO4(2-) and NO3(-) were approached at 71.9%, 92.9% and 98.6%, respectively. Nitrate served as a key factor to control the shift of SR and DSR related populations, with the possible involvement of Thauera sp. during SR and Sulfurovum sp. or Acidiferrobacter sp. during DSR, respectively. DsrB and aprA genes were the most abundant during SR and DSR processes, respectively. Cylindrical-type ABR with the improved elemental sulfur recovery was recommended to deal with sulfate and nitrate-laden wastewater under the optimized SO4(2-)/NO3(-) ratio.