Effects And Mechanism Of External Carbon Sources On The Thiosulfate-driven Autotrophic Denitration Coupled With Anammox System

Sulfur autotrophic denitrification and Anammox techniques were efficient and economical novel wastewater denitrification techniques.Thiosulfate-driven autotrophic denitration coupled with Anammox system（SDDA）overcame the insufficient nitrite supply and nitrate accumulation during Anammox with no requirement of organic carbon source due to its autotrophic process.However,some complex organic matter often exists in the actual nitrogen-containing wastewater,which affects the biological denitrification efficiency,so it was significant for practical engineering application to study the influence of organic matter on SDDA.In this paper,we successfully constructed the SDDA coupling system,and investigated the effects of different concentrations of COD on nitrogen removal,its conversion mechanism and microbial community structures in the SDDA system.Firstly,the upflow anaerobic sludge suspending bed（UASB）was usded as the reactor to enrich the Anammox bacteria.After 180 days domestication,Anammox reactor start up successfully with the total nitrogen removal volumetric loading rate reaching 0.39 kg-N/m³·d,and the removed ratios ofΔNO₂^--N/ΔNH₄⁺-N andΔNO₃^--N/ΔNH₄⁺-N stabilized at 1.28 and0.23,respectively.The sludge morphology gradually changed from black floc sludge to irregular red granular sludge.In addition,the relative abundance and diversity of microbial communities in the reactor were reduced,and the Planctomycetes was increased from 0.42%to22.45%.Batch tests showed that the optimal temperature and p H were around 35°C and 7.5-8.0 for An AOB,the concentrations of free ammonia（FA）and free nitrite acid（FNA）changed with the change of p H in the solution,which affected the An AOB activity.The SDDA process was constructed with activated sludge and An AOB sludge asinoculated sludge,and the influence of organic matter on the denitrification performance in SDDA was investigated.Long-term experiments showed that low concentration of organic carbon（COD<140 mg/L）could promote the removal of total nitrogen,and the best total nitrogen removal efficiency was 92.8%,in which Anammox accounted for the largest proportion（32.7-64.6%）.Moreover,organics addition can promote not only the heterotrophic denitrification,but also the transformation of thiosulfate/sulfur to sulfide by sulfate reducing bacteria.The produced sulfides would react with the elemental sulfur with low solubility to form the biocompatible polysulfides,which promoted the production of nitrite in the sulfur autotrophic denitrification process,eventually improving the Anammox activity.The addition of appropriate organic carbon source was beneficial to the development of microbial community richness and diversity in SDDA,and the activities among sulfate reducing bacteria,sulfur oxidizing bacteria,heterotrophic denitrifying bacteria and Anammox bacteria could maintain a balance in the SDDA system.