Study On Start-up And Stable Operation Of CANON Process For Treating Medium And Low Concentration Nitrogenous Wastewater

In recent years,the CANON process based on short-range nitrification and anaerobic ammonia oxidation has been widely researched and applied in the field of denitrification of high ammonia nitrogen wastewater for the advantages in that it has a short process flow,no additional carbon source,alkali consumption,oxygen consumption,low infrastructure cost,and low residual sludge output.The field of denitrification of high ammonia nitrogen wastewater has been widely researched and applied.However,this process still has many constraints when treating low-and medium-concentration ammonia nitrogen wastewater(500 mg·L-1 or less),including long start-up time,poor system stability,and suppression of organic matter in wastewater.This paper sets up two reactors R1 and R2,compares the difference between the denitrification performance and stability of the CANON process started by the two methods in the treatment of low-and medium-concentration ammonia nitrogen wastewater,in order to find a suitable mode for the efficient and stable operation of the CANON process to treate low-and medium-concentration ammonia nitrogen wastewater.The whole test is mainly divided into two stages.In Phase ?(R1:1-170 d,R2:1-120 d),exploring the start-up strategy of the CANON process in the R1 and R2 reactors with an influent NH4+-N concentration of 200 mg·L-1.The reactor to achieve the "low concentration and high flux" start-up by the "three adjustments and one increase"(gradual adjustment and shortening of HRT,adjustment of aeration,adjustment of reflux ratio and increase of ammonia nitrogen volume load).The nitrogen removal in the system during the start-up phase and the changes in the parameters along the way were investigated,thereby comparing the nitrogen removal efficiency of the CANON process in the two reactors.The results are as follows:(1)The R1 reactor is an upflow sludge bed reactor.The CANON process took 170 days to complete the sludge granulation culture.When the start-up is completed,this system achieved an average NH4+-N removal rate of 93%and an average TN removal rate of 81%,and the effluent NH4+-N and TN concentrations are below 15 mg·L-1 and 42 mg·L-1,respectively,maintaining relatively stable state.In the reaction system,the sludge coexists in two ways:particles and flocs,and the average particle size exceed 668.725 ?m.(2)The R2 reactor is an upflow biofilm reactor(with built-in packing).After 120 days,the CANON process was started.During stable operation,HRT is 5h,NIL is 0.902 kg·(m3·d)-1,the effluent NH4+-N and TN were below 6 mg·L-1 and 30 mg·L-1,respectively,achieving an average NH4+-N removal rate of 97.18%and an average TN removal rate of 85.87%.The sludge system integrates three forms of flocs,particles,and biofilm on the filler,and has strong stability.(3)During stage I,the species abundance of AOB and AnAOB in the R1 and R2 reactors showed an increasing trend,NOB and other non-functional bacterial groups were continuously eliminated at this stage due to the domestication of sludge.When the start of CANON is completed,the proportions of AOB and AnAOB in the R1 reactor rise to 6.16%and 13.83%respectively,and the proportion of DeNOB is only 1.21%.The proportion of three kinds of bacteria AOB,AnAOB,and DeNOB participating in the denitrification reaction in the R2 reactor is much higher than that in R1,which is 20.22%,32.65%,3.55%.Among them,the dominant genuses of AOB and AnAOB at this stage are Nitrosomonas and Candidatus_Jettenia,respectively.In phase ?(R1:171-248 d,R2:121-248 d),further explore the tolerance threshold of the CANON system initiated by the two methods to organic matter,with a view to establishing a system for simultaneous removal of nitrogen and carbon from low-and medium-concentration ammonia nitrogen wastewater.Maintain the temperature,pH,and HRT at the end of stage I,and gradually increase the COD concentration of the influent and adjust the oxygen demand to investigate the effect of organic matter concentration on the nitrogen removal capacity and microbial morphology of the CANON system.The results of the two reactors are as follows:(1)The COD of the R1 reactor inlet water gradually increases from 30 mg·L-1 to 80 mg·L-1.When it exceeds 50 mg·L-1,the system's nitrogen removal capacity decreases and particulate sludge begins to disintegrate.In the later period,the water intake stops adding COD to restore the system stability.From the point of view of nitrogen removal capacity and sludge status,the R1 reactor can be used to treat low-and medium-concentration ammonia nitrogen wastewater with a COD concentration of less than 50 mg·L-1.(2)The COD concentration in the inlet water of the R2 reactor gradually increased from 50 mg·L-1 to 200 mg·L-1,which has better adaptability to the change of water quality than the R1 reactor,and successfully completed the CANON coupling denitrification process,And the optimal C/N ratio of the R2 reactor is 0.5.Under the optimal C/N ratio,the highest average removal efficiency of the R2 reactor for NH4+-N and TN reaches 97.09%and 93.67%,respectively,and the highest COD removal rate 95.88%,meeting the needs of simultaneous nitrogen and carbon removal.(3)The excessively high organic matter concentration in the simulated wastewater mainly inhibits the biological activity of the anaerobic ammonia oxidizing bacteria,which is mainly reflected in the reduction of the removal rate of NH4+-N by AnAOB,and the impact on the R1 reactor is greater than that of the R2 reactor;The organic carbon source provided by water promotes the continuous improvement of the biological activity of DeNOB.The final removal rate of DeNOB in the R1 and R2 reaction systems is 10.95 mg(g·h)-1 and 10.36 mg(g·h)-1 respectively.(4)In the late stage ?,the diversity and abundance of the dominant genus of bacteria involved in the denitrification process have clearly evolved.Candidatus_Kuenenia in AnAOB,Comamonadaceae and Xanthomonadaceae in Denitrification have been added.Among them,the overall proportion of AOB and AnAOB in R1 and R2 is suddenly reduced by the concentration of organic matter,while the species abundance of DeNOB increased significantly at this stage,and the proportions in R1 and R2 systems reached 4.25%and 8.34%,respectively.The difference in denitrification performance in the reactor is positively correlated.