The oxygen-induced thiosulfate production during Sulfate reduction, Autotrophic denitrification, Nitrification and Anammox (SANIA) integrated process towards next-generation mainstream wastewater treatment

This study proposes a novel integrated process: the oxygen-induced thiosulfate production during S ulfate reduction, A utotrophic denitrification, NI trification and A nammox (SANIA) integrated process, targeting to treat mainstream wastewater after organics capture. Three moving-bed biofilm reactors (MBBRs) were applied for oxygen-induced thiosulfate production during sulfate reduction, mixed sulfide- and thiosulfate-driven partial denitrification and anammox (MSPDA), and nitrification (N), respectively. This study firstly established SANIA with supply of mimic nitrifying effluent to investigated the development of MSPDA (Period I) and subsequently verified SANIA in mainstream condition with implementation of nitrification (Period II). In Period I, the MSPDA-MBBR fed with ERATO-MBBR and mimic nitrifying effluent, was operated for over 300 days. Without inoculation of anammox biomass, the high rates of denitratation and anammox being 2.7 gN/(m 2 ·d) and 2.8 gN/(m 2 ·d), respectively were developed in the bioreactor with the enrichment of anammox bacteria and the coexistence of sulfur-oxidizing bacteria. Batch tests were performed to explore the bioconversion of sulfur and nitrogen compounds in MSPDA with main findings as following: 1) kinetics and pathways of sulfide (S 2- ➔ S 0 ➔ SO 4 2- ) and thiosulfate (S 2 O 3 2- ➔ SO 4 2- ) oxidation were revealed; 2) fast denitrification was achieved during oxidation of sulfide and thiosulfate to S 0 and sulfate, respectively with sufficient nitrite accumulation, supporting the high activity of anammox; 3) nitrite utilization rate of anammox (50.8 mgN/(m 2 ·h)) is higher than sulfur-driven denitritation (12.9−42.6 mgN/(m 2 ·h)), demonstrating the dominance of anammox in nitrogen removal. In Period II, the N-MBBR was set behind MSPDA-MBBR to supply nitrate by recirculation, thus the SANIA system was developed. Afterwards the integrated SANIA system with a short HRT of 4.7 h was continuously operated for over 130 days. Results demonstrated that 90% of COD, 93% of ammonium and 61% of TIN were removed with concentration of COD, ammonium, and TIN below 10 mg/L, 3 mgN/L and 13 mgN/L, respectively in effluent. Combining with organic capture and SANIA for sewage treatment, the energy-neutral and space-efficient treatment of mainstream wastewater is promising. Highlights A new sulfur-cycle process (SANIA) was developed for sewage treatment. High rates of both denitratation and anammox were developed in MSPDA. Oxidation of TdS (to S 0 ) and S 2 O 3 2- (to SO 4 2- ) in MSPDA boosts nitrite buildup. 74−81% of the removed TIN was via anammox in SANIA process. SANIA with a short HRT of 4.7h achieved good effluent qualities for sewage treatment.