High recycling efficiency and elemental sulfur purity achieved in a biofilm formed membrane filtration reactor.

Elemental sulfur (S0) is always produced during bio-denitrification and desulfurization process, but the S0 yield and purification quality are too low. Till now, no feasible approach has been carried out to efficiently recover S0. In this study, we report the S0 generation and recovery by a newly designed, compact, biofilm formed membrane filtration reactor (BfMFR), where S0 was generated within a Thauera sp. strain HDD-formed biofilm on membrane surface, and then timely separated from the biofilm through membrane filtration. The high S0 generation efficiency (98% in average) was stably maintained under the operation conditions with the influent acetate, nitrate and sulfide concentration of 115, 120 and 100 mg/L, respectively, an initial inoculum volume of approximate 2.4 × 108 cells, and a membrane pore size of 0.45 μm. Under this condition, the sulfide loading approached 62.5 kg/m3·d, one of the highest compared with the previous reports, demonstrating an efficient sulfide removal and S0 generation capacity. Particular important, a solid analysis of the effluent revealed that the recovered S0 was adulterated with barely microorganisms, extracellular polymeric substances (EPSs), or inorganic chemicals, indicating a fairly high S0 recovery purity. Membrane biofilm analysis revealed that 80.7% of the generated S0 was accomplished within 45-80 μm of biofilm from the membrane surface and while, the complete membrane fouling due to bacteria and EPSs was generally observed after 14-16 days. The in situ generation and timely separation of S0 from the bacterial group by BfMFR, effectively avoids the sulfur circulation (S2- to S0, S0 to SO42-, SO42- to HS-) and guarantees the high S0 recovery efficiency and purity, is considered as a feasible approach for S0 recovery from sulfide- and nitrate-contaminated wastewater.