Effect Of Activated Sludge Exchange(Circulation) On Nitrification And Denitrification Rate

The main operating mode of the A/O or A~2O is that the sewage first enters the anaerobic(anoxic)tank,then enters the aerobic tank,and after that about 200%-300%of the muddy water is returned to the anaerobic(anoxic)tank.Alternate nitrification and denitrification can effectively remove nitrogen in sewage.However,there are some shortcomings in this sewage recycling method.In the recycling process,the abundance of nitrifying bacteria and denitrifying bacteria in the anaerobic tank and aerobic tank is very close with this cycle,resulting in the decrease of nitrification and denitrification efficiency.To this end,this research focuses on the impact of wastewater recycling methods on the efficiency of nitrification and denitrification.That is,the activated sludge method is used to carry out nitrification and denitrification reactions,and then different mud-water exchange methods are used to compare the nitrification and denitrification experiments under the conditions of different mud-water exchange ratios,and to explore different ratios of sludge exchange and nitrification and denitrification.The relationship between the nitrification rate was compared with the method without sludge exchange.Subsequently,based on the research results,a set of sieve plate tower bioreactor system for clean water exchange was developed and used for actual urban sewage treatment.The specific experimental process and results are as follows:(1)The sludge taken from the aerobic and anaerobic tanks of a wastewater treatment plant.The sludge is domesticated by nitrate and ammonium to obtain highly efficient nitrification and denitrification sludge;(2)Transfer the domesticated nitrification sludge to a measuring cylinder with a volume of 1-L,and add ammonia-nitrogen-containing solution to carry out a nitrification experiment.The initial ammonia nitrogen concentration is set to about 40mg N/L.(3)Add the domesticated denitrification sludge into an Erlenmeyer flask with a volume of 1-L,and then add the nitrate-containing effluent generated by the nitrification reaction into the Erlenmeyer flask for the denitrification reaction.(4)In the above experiment,we compared the nitrification and denitrification rate under different sludge exchange methods.Among them,the sludge exchange volume is 0%,20%,30%and 50%respectively.(5)Compared with the sludge exchange volume of 50%,without sludge exchange,the nitrification rate is increased by 30%,and the denitrification rate is increased by 50%.(6)High-throughput sequencing experiments were performed on sludge samples without biomass exchange and with biomass exchange,as well as the sludge from a wastewater treatment plant with A~2O treatment.The results showed that none of the key bacterial genera for nitrification and denitrification became the dominant bacteria in the anoxic(denitrification)and aerobic(nitrification)sludges with sludge exchange.,Venn diagram figure shows that in their microbial community distribution,the same microbial population reaches more than 32%,while in the microbial community without sludge exchange,only 1%of the microbial population is the same.(7)The Vertical Baffled Bioreactor Reactor(VBBR)developed according to the patented technology is applied to the actual municipal sewage treatment.Under the same A1 effluent standard of the national municipal wastewater treatment plant conditions the hydraulic retention time is shortened from 13hours to 9 hours.