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 SO4 2- , SO4 2- 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.