Effect Of Organic Carbon Source On The Nitrogen Removal By Partial Denitrification And Anammox Coupling Process

Anaerobic ammonia oxidation（anammox）is a new technology which is energy efficient and effective.Nitrite,as the electron acceptor of anammox,is almost absent in wastewater.Nitrite is the intermediate product of the denitrification process and can accumulate stably during the process of denitrifiction.Thus,nitrite could be provided for the anammox through partial denitrification（NO₃^--N→NO₂^--N）.Partial denitrification coupled with Anammox is suitable for treatment of low carbon to nitrogen ratio wastewater.Organic matter is utilized to reduce nitrate to nitrite in partial denitrification process.In order to reduce the cost of wastewater treatment,it is necessary to find a cost-effective organic carbon source.There is a lot of organic matter in the brewery wastewater,including many short-chain fatty acids,which has good biodegradability.The separated and combined PD-Anammox process wases established using brewery wastewater as carbon source in this study.The coupled partial denitrification and anammox coupling processes were started simultaneously with sodium acetate and glucose as the carbon source.The effects of different carbon sources on the nitrogen removal of the partial denitrification and anammox coupling system were compared.Microbial structure was analyzed by high-throughput sequencing technology.The nitrogen removal mechanism of the coupled denitrification-Anammox system was explored with nitrogen removal functional genes.The main conclusions are as follows:（1）When brewery wastewater was used as the carbon source,the separated PD-anammox coupling system could be quickly started up by inoculating the PD sludge and Anammox sludge in PD reactor and anammox reactor,respectively.The initial NO₃^--N concentration in the PD reactor increased from 70 mg/L to 150 mg/L,and the average nitrate-to-nitrite transformation ratio（NTR）reached 80.18%,which could provide adequate NO₂^--N for the anammox reactor.The influent NO₂^--N/NH₄⁺-N ratio of anammox reactor was at around 1.32,the average concentration of NH₄⁺-N、TN and COD_Cr in the effluent were 2.2 mg/L、8.69 mg/L and 34.68 mg/L,respectively,and the maximum removal efficiency of TN reached 98.03%.During the long-term operation,the relative abundance of Thauera in the PD reactor decreased from 72.94%to 55.22%,and it was still the dominant group in the system.The abundance of Candidatus＿Brocadia in the anammox reactor gradually decreased from 30.67%to15.61%,and the abundance of Thauera gradually increased from 0.03%to 15.15%.The abundance of nitrate reductase genes（nar/nap A）in PD reactor was much higher than that of nitrite reductase genes（nir K/nir S）.（2）The combined PD-Anammox coupling reactors were initiated with brewery wastewater,sodium acetate and glucose as carbon source,respectively.The TN removal efficiency of the coupling system gradually increased as denitrifying bacteria gradually enriched in the system.The average TN removal ratio reached 92.96%at the initial COD_Cr:NO₃^--N:NH₄⁺-N of 2.5:1:0.67.In the coupling system fed with brewery wastewater,the average TN removal ratio of the coupling system with sodium acetate as the carbon source reached 94.04%at an initial COD_Cr:NO₃^--N:NH₄⁺-N of 2.2:1:0.67,The average TN removal ratio reached 92.19%at the initial COD_Cr:NO₃^--N:NH₄⁺-N of3.5:1:0.67 in the coupling system fed with glucose as the carbon source.（3）In the combined PD-Anammox coupling system,the relative abundance of denitrifying bacteria gradually increased and the relative abundance of anammox bacteria gradually decreased.On day 110,the relative abundances of Thauera in the coupling systems using brewery wastewater,sodium acetate and glucose as carbon source were 54.29%,44.65%and 18.79%,respectively.While the relative abundances of Candidatus＿Brocadia decreased to 2.08%,4.51%and 2.64%,respectively.The highest abundance of denitrification genes and lower abundance of anaerobic ammonia oxidation genes were found in three coupling systems.The anaerobic ammonia oxidation reaction was the main pathway for TN removal in the three coupling systems.（4）High nitrogen removal performance was obtained in both separated and combined.PD-Anammox coupling systems when brewery wastewater was used as the carbon source.The brewery wastewater is suitable as the carbon source for the PD-Anammox coupling system.