Research On Denitrification Of Saline Wastewater By Denitrifying Anaerobic Methane Oxidation Coupled With Anaerobic Ammonia Oxidation System

Denitrifying anaerobic methane oxidation(DAMO)process coupled with anaerobic ammonium oxidation(Anammox)links the carbon and nitrogen biogeochemical cycles,this process could achieve anaerobic methane oxidation and nitrogen removal from wastewater.Marine Anammox bacteria(MAB)has great potential in saline wastewater treatment because MAB could exhibit a stable Anammox activity in saline conditions.In this work,three sequencing batch reactors were inoculated with activated sludge dominated by MAB.The SBR was fed with saline wastewater(35.0‰)containing ammonium and nitrate,and methane was provided with different supply frequencies.The aim is to achieve nitrogen removal from saline wastewater through DAMO-Anammox process and analyze the effect of aeration frequency on nitrogen removal performance and microbial diversity.After 270 d long-term operation,simultaneous ammonium and nitrate removal from saline wastewater through DAMO-Anammox process was achieved.Ammonium and nitrate removal performance under different methane supply frequencies(R1,R2,and R3 with aeration 1,2,and 3 times a day,respectively)was also studied.The results showed that the ammonium removal rate was negatively correlated with aeration frequency,while nitrate removal rate was positively correlated with methane aeration frequency.However,the maximum total nitrogen removal efficiency was reached in R2,and the molar ratio of consumed nitrate to ammonium(1.06 ± 0.15)was close to the theoretical value of 1.06.High throughput sequencing results showed that the relative abundance of Candidatus Scalindua and Candidatus Methanoperedens increased with the increased methane aeration frequency.Microbial Alpha and Beta diversity analysis suggested that high methane aeration frequency is beneficial to the community abundance,while not to the microbial community diversity.Also,compared with community abundance,the influence of methane aeration frequency on community diversity is more significant.Key modules and enzymes of methane and nitrogen metabolism in DAMOAnammox system were analyzed with metagenomic sequencing.Methanogenesis module accounts for 13.45% of methane metabolism and the key enzymes involved in the methanogenesis module have a high abundance,such as methyl-coenzyme M reductase(17580 hits),which indicated that methane was anaerobic oxidized based on the reverse-methanogenesis pathway.With regard to nitrogen metabolism,the denitrification module and nitrate reduction module account high proportion(45.07%and 32.93%,respectively).Nitrate reductase with high abundance(61623 hits)also supported the existence of nitrate reduction reaction.Key enzymes involved in Anammox process,such as nitrite reductase(19238 hits),hydrazine synthase(18622hits),and hydrazine dehydrogenase(8896 hits),also have a high abundance.DAMO process provides electrons for nitrate reduction with carbon dioxide and nitrite as the product.Nitrite produced and ammonium present in the wastewater could be used directly by MAB to achieve nitrogen removal from saline wastewater.