Quick Start Of Partial Nitrification And Denitrification In Municipal Wastewater Treatment Process By A Novel Anaerobic/ Pulse Washout (APW) Approach

Partial nitrification and denitrification technology is a biological treatment process with low carbon source and energy consumption requirements,which is suitable for treating low-carbon source municipal wastewater.At present,the denitrification effect of partial nitrification and denitrification on low-carbon source wastewater has been verified.However,due to the close physiological characteristics between ammonia oxidizing bacteria?AOB?and nitrite oxidizing bacteria?NOB?,the NO₂^--N accumulated during partial nitrification was converted into NO₃^--N by NOB frequently.Therefore,the partial nitrification and denitrification technology has the problems of long start-up time and difficulty in stable operation in practical application.Based on the inhibitory effect of anaerobic conditions on NOB,a quick start method of partial nitrification and denitrification by a novel anaerobic/pulse washout?APW?was proposed.It provided theoretical basis and technical support for the efficient nitrogen removal of activated sludge systems treating low-carbon source municipal wastewater.APW significantly inhibited the quantity and activity of NOB,while the original weakly competitive AOB quickly became the dominant population by controlling the activated sludge system under alternating long-term anaerobic and short-term aerobic dissolved oxygen conditions in the early stage of partial nitrification and denitrification.Thereby,the quick start of partial nitrification and denitrification of activated sludge system was achieved.The results showed that APW with appropriate duration could significantly inhibit the activity of nob.After 5 days of APW,NO₃^--N in the effluent decreased by 76.03%,NO₂^--N increased by 5.14 times,and the nitrite accumulation rate?NAR?was 31.76%,increased by 5.30 times.For partial nitrification reactor,the system using APW realized the startup of partial Nitrification on the 20th day,and the startup rate was significantly higher than the system without APW?45 days?.In addition,based on the characteristics of APW process,the microbial community structure and the directional changes of extracellular polymeric substances?EPS?and intracellular polymers in the process of partial nitrification were studied,and the mechanism of accelerating the process of partial nitrification by APW was analyzed.The results show that,after APW,the enrichment of Proteobacteria and Nitrosomonas was accelerated,and the growth of Nitrospirae and Nitrospira was inhibited rapidly.The growth rate of AOB activity(3.94mgN·L^-1d^-2)and the increase rate of AOB relative abundance?86.13%on the 20th day?after APW were also significantly higher than those without APW(1.83 mgN·L^-1d^-2;63.35%on the 45th day).At the same time,APW has accelerated the directional changes of tyrosine and tryptophan content and the secondary structure of proteins in extracellular polymeric substances and intracellular polymers of microorganisms during the partial nitrification of the reactor.As a result,AOB became the dominant bacteria faster,and then accelerated the start-up of partial nitrification in activated sludge system.In treating low-carbon source domestic sewage?C/N=3.5?,APW also accelerated the same directional changes of EPS and intracellular polymers in partial nitrification,which may affect the activity changes of AOB and NOB,and NOB was effectively inhibited,so that NAR has gone up and the realization of partial nitrification was accelerated.When the efficiency of partial nitrification was reduced,the activated sludge system can quickly resume the partial nitrification and denitrification through short-term APW.The quick start and stable operation of partial nitrification and denitrification under the condition of low carbon source were guaranteed.