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

Elemental sulfur (S) is always produced during bio-denitrification and desulfurization process, but the S yield and purification quality are too low. Till now, no feasible approach has been carried out to efficiently recover S. In this study, we report the S generation and recovery by a newly designed, compact, biofilm formed membrane filtration reactor (BfMFR), where S 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 S 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 × 10 cells, and a membrane pore size of 0.45 μm. Under this condition, the sulfide loading approached 62.5 kg/m·d, one of the highest compared with the previous reports, demonstrating an efficient sulfide removal and S generation capacity. Particular important, a solid analysis of the effluent revealed that the recovered S was adulterated with barely microorganisms, extracellular polymeric substances (EPSs), or inorganic chemicals, indicating a fairly high S recovery purity. Membrane biofilm analysis revealed that 80.7% of the generated S 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 S from the bacterial group by BfMFR, effectively avoids the sulfur circulation (S to S, S to SO, SO to HS) and guarantees the high S recovery efficiency and purity, is considered as a feasible approach for S recovery from sulfide- and nitrate-contaminated wastewater.