Research On Start-up,operation And Optimization Strategy Of New Partial Nitritation Process Based On Alternate Treatment Of FNA And Heat Shock

Water ecological environment protection is one of the priorities of the“14th Five-Year Plan”.Improving the quality of the water environment has become the top priority of social sustainable development.Compared with the traditional biological nitrogen removal process,the partial nitritation process has the advantages of saving about 25%of aeration,40%of external carbon source,low sludge output,short process flow and energy consumption.Partial nitritation process is the front-end process to realize partial nitritation coupled with anammox（PN/A）,and it is also a key and restrictive step.Therefore,this project mainly took wastewater of artificial simulation as the treatment object,and initiated and realized the partial nitritation process based on sequencing batch reactor（SBR）.According to the characteristics of partial nitritation process,a novel process of alternating treatment of FNA and heat shock based on linear regression method is proposed to inhibit the activity of NOB and realize the enrichment of AOB,so as to realize the method of stable nitritation of sludge,in order to provide stable substrate support for the anaerobic ammonia oxidation process.（1）Experimental were conducted at different temperatures（25,30,35℃）,the results showed that the nitrite accumulation rate and effluent nitrite concentration at 30°C were higher than 25 and 35°C,the effluent nitrate concentration was lower,the stabilization time was longer,and the effluent nitrite concentration was the highest reached 42.59 mg/L.However,whether it was the better 30°C or the other two temperature conditions,the nitrate concentration in the effluent increased significantly after running for a long time.This may be due to the strong adaptability of NOB,that is,the recovery of NOB activity affects the stability of partial nitritation.Therefore,a batch test of heat shock was carried out to explore the effect of heat shock on the rapid start-up partial nitritation.Results revealed that heat shocked at 60℃for 20 minutes,NOB was inhibited while AOB still had certain activity.As a result,the accumulation of nitrite can be realized,which provides a certain theoretical basis for the subsequent alternate treatment of FNA and heat shock.（2）After the optimal conditions for heat shock treatment were obtained,a batch test was carried out with the model obtained by the response surface method,and variance analysis was carried out according to the obtained the batch test results.The regression equation can quantitatively describe the effects of FNA concentration,FNA exposure time,FNA treatment ratio and their interactions on the response function（NAR and AOB activity）.The linear regression equation of response surface methodology showed that the interaction of FNA concentration with treatment ratio and exposure time had a significant effect on AOB activity,and the interaction of FNA concentration with treatment ratio had a significant effect on nitrite accumulation rate.Results revealed that the FNA concentration was 2.20 mg HNO₂-N/L,the exposure time was 24 h,and the treatment ratio was 20%could inhibit NOB activity to the greatest extent and maintain the maximum AOB activity,which also provides a certain theoretical basis for the subsequent alternate treatment of FNA and heat shock.（3）According to the batch test of heat shock,the best treatment time and temperature of heat shock treatment were heat shocked at 60℃for 20 minutes.And the best optimization conditions obtained from FNA batch test and response surface methodology analysis:the FNA concentration was 2.20 mg HNO₂-N/L,the exposure time was 24 h,and the treatment ratio was 20%.The optimal conditions of FNA were used to start the continuous-flow SBR partial nitritation reactor.A novel process of alternating treatment of FNA and heat shock to realize stable partial nitritation of sludge was explored.Microbial community analysis was carried out in order to solve the problems of partial nitritation instability and slowly start-up,FNA and heat shock were alternately treated to obtain more sustained and stable NOB inhibition and to provide a stable substrate for subsequent Anammox.The results showed that the FNA and heat shock were used to treat nitrification sludge alternately,which can solve the problem of NOB adaptation at a single FNA or heat shock treatment.The microbial community analysis showed that multiple alternations could achieve AOB（Nitrosomonas）genus dominance and inhibit NOB（Nitrospira）.The NO₂^--N accumulation rate could reached more than 90%,so as to achieved long-term stability of sludge nitritation.The proportion of NOB（Nitrospira）after FNA/heat shock alternate treatment was lower than the FNA single treatment and heat shock single treatment,indicating that with inhibition in the alternating FNA/heat shock treatment being better than the single FNA treatment and the single heat shock treatment.The abundance of AOB（Nitrosomonas）was also higher after alternating FNA/heat shock treatment.These results may indicate that alternating FNA/heat shock treatment can inhibit NOB while maintaining a high AOB abundance.Thus,the novel process of alternating FNA/heat shock treatment can realize stable partial nitritation and provide substrate for Anammox.The activated sludge after alternating FNA/heat shock treatment could be adapted to different environmental factors,as well as to other types of sewage treatment without strict process control,making the application range of this nitritation process more extensive.