Study Of Treating Low-nitrogenous Wastewater By Coupling ANAMMOX With Partial Denitrification

Anaerobic Ammonium Oxidation?ANAMMOX?has been regarded as a new promising process due to its advantages of energy saving,low sludge yield,and high nitrogen removal efficiency.It has been successfully applied to the treatment of high-strength wastewater such as sludge water and leachate,but how to apply ANAMMOX to the treatment of municipal wastewater is a hot topic at home and abroad,and the coupling of partial denitrification?PD?and anaerobic ammonia oxidation is a possible approach.In this study,sodium acetate was used as the carbon source to enrich the microorganisms with partial denitrification function under the conditions of low carbon to nitrogen ratio?COD/NO₃^--N=2.5?.Then,the feed-batch feeding pattern was operated to culture ANAMMOX bacterica in an anaerobic sequencing batch reactor.Finally,the cultured partical denitrifying bacteria and anaerobic ammonia oxidizing bacteria were coupled to explore the feasibility of anaerobic ammonia oxidation combined with partial denitrification treatment of low concentration ammonia nitrogen wastewater.Main results are as follows:?1?Partial denitrification?NO₃^--N?NO₂^--N?could be achieved by controlling both reaction time and sludge retention time at low carbon to nitrate ratio?COD/NO₃^--N=2.5?condition,stable accumulation of NO₂^--N was achieved.The accumulation rate of NO₂^--N during the stable operation was as high as 94.98%,and the maximum reduction rate of nitrate was 240.02 mg·gVSS^-1h^-1.The maximum accumulation rate of nitrite was235.86 mg·gVSS^-1h^-1.?2?The total nitrogen?TN?loading during the ANAMMOX reactor operation ranged from 2.39 to 2.76 kg·?m³·d?^-1,corresponding to a removal rate of 99.23%±3.02%,99.31%±3.05%and 89.70%±3.18%for NH₄⁺-N,NO₂^--N and TN,respectively.The stoichiometric molar ratios of nitrite consumption and nitrate production to ammonium consumption were calculated to be 1.32:0.21:0.04.The appearance of ANAMMOX sludge was red,almost ellipsoidal,indicating that it was rough and had a good granulation.Fluorescence in situ hybridization?FISH?showed that the dominant bacteria in the sludge was ANAMMOX bacteria.?3?Intermittent experiments showed that the coupling reaction could be achieved in the range of influent NO₃^--N/NH₄⁺-N ratios were 0.8 to 1.6,but different NO₃^--N/NH₄⁺-N ratios corresponding to different TN removal rates when NO₃^--N/NH₄⁺-N ratios were 0.8,1.0,1.2,and 1.6,the TN removal rates were 73.20%,87.89%,96.42%,and 91.98%,respectively.The optimum value of NO₃^--N/NH₄⁺-N ratio was 1.2.?4?The continuous experiment with the optimum NO₃^--N/NH₄⁺-N ratio showed that the advanced nitrogen removal could be obtained by the coupling system integrating ANAMMOX and partial denitrification.During the operation,the concentration of influent NH₄⁺-N was 20 to 40 mg·L^-1,the average removal rates of NH₄⁺-N,NO₃^--N,and TN were 86.5%,95.2%,and 94.88%,respectively.In addition to partical denitrification bacteria and anammox bacteria,there are also heterotrophic nitrite-reducing bacteria in the sludge,and they compete with anammox bacteria for NO₂^--N produced by partical denitrification bacteria.The relationship between heterotrophic denitrification bacteria and ANAMMOX bacteria is cooperative and competitive in the system while 84.3%of the total NO₃^{-_</sup>N in the influent is removed by ANAMMOX approach and the rest of 15.7%by heterotrophic denitrification pathway based on the mass balance.}