Optimization Of Denitrification Performance And Mechanism Of CANON Process For Treating Digested Piggery Wastewater

The start-up of CANON(Completely autotrophic nitrogen removal over nitrite)process by changing the process parameters was investigated to treat piggery wastewater by inoculating the sludge with anaerobic ammonium oxidation function in Continuous-flow reactor.The effects of hydraulic retention time(HRT),temperature and NH4+-N concentration on the denitrification performance of CANON process were investigated.Based on this,the response surface method was used to optimize the denitrification performance of the reactor.Sequencing technology was used to analyze the biological population of sludge samples,and the denitrification mechanism of CANON process for treating piggery wastewater was discussed by means of denitrification activity kinetics,nitrogen balance analysis,quantitative PCR(qPCR)and sludge sample characterization.The main contents and conclusions are summarized as follows:(1)By gradually increasing the NH4+-N concentration,reducing dissolved oxygen,and prolonging the HRT,the CANON process successfully realized the rapid start of the actual pig farm biogas slurry after 52 days.After successful start-up,the influent NH4+-N concentration was 400 mg/L,and the average removal rates of NH4+-N and TN in the reactor were 74.60%and 64.59%,respectively;? NO3--N/? NH4+-N was stable at the theoretical value of 0.11.During the start-up process,the biomass in the reactor increased,and the amount of the membrane of the filler was 6.78 mg/piece.The sponge filler in the reactor was full and the biofilm on the filler was reddish brown.(2)The results of single factor experiments show that HRT,temperature and NH4+-N concentration have significant effects on the denitrification efficiency of the reactor.Based on the single factor test,the model optimized by response surface is extremely significant.The optimal nitrogen removal conditions are HRT 1.35 d,temperature 34.4?,ammonia nitrogen concentration 415 mg/L,NH4+-N removal rate and TN removal rate were 81.91%and 72.12%,respectively.The verification experiment was carried out under the conditions obtained after the response surface optimization.The average NH4+-N effluent reached 74.68 mg/L,the NH4+-N removal rate reached 83.05%,the average TN effluent reached 108.28 mg/L,and the TN removal rate reached 73.91%.The NH4+-N and COD effluent is lower than the maximum allowable daily average concentration of intensive poultry farming in the livestock and poultry industry pollutant discharge standard(GB18596-2001).(3)High-throughput sequencing technology was used to analyze the DNA sequencing of 10 sludge samples under different working conditions.The results showed that the sequencing depth was reasonable,and HRT was inversely proportional to the ace index and chao index,indicating that the community richness was consistent with HRT.The Shannon index is the highest at the temperature of 35?,and the Simpson index is the lowest,indicating that the microbial diversity is the highest at this temperature;the ace index and the chao index are higher and the Shannon index is higher at the ammonia nitrogen concentrations of 400 mg/L and 500 mg/L.Higher,Simpson index is lower,indicating that the community richness and microbial diversity are at a higher level under this condition.The dominant bacteria in the sample are Proteobacteria,Planctomycete and Chloroflexi.The relative abundance of Proteobacteria shows a decreasing trend with the increase of HRT.Growth at 29?35 0C and ammonia nitrogen concentration of 400 mg/L;while the fungi were higher in HRT,higher temperature and lower ammonia nitrogen concentration;The impact of the change is small.The AOB bacteria detected in the system are Nitrosomonas,the ANAMMOX bacteria are Candidatus_Kuenenia and Candidatus_Brocadia,the NOB bacteria are Nitrospira,and the denitrifying bacteria are norank_o_Xanthomonadales,Denittrasoma and Comamonas.When HRT is longer(greater than 1.2d),Candidatus_Brocadia and Candidatus_Kuenenia have higher abundance in the system.Nitrosomonas only appears under 1.2d and 1.4d conditions;with the decrease of temperature,the abundance of Candidatus_Kuenenia gradually increases,and the abundance of Candidatus_Brocadia The degree is gradually decreased,and Nitrosomonas is detected only under the condition of 35?;the abundance of Candidatus_Kuenenia decreases with the increase of ammonia nitrogen concentration,and the abundance of Nitrosomonas at the concentration of ammonia nitrogen at 300 mg/L and 400 mg/L Higher,and abundance is higher at 400 mg/L than at 300 mg/L.(4)Static experiments were carried out on the relevant denitrifying bacteria under the optimal conditions of response surface simulation.The results showed that the activities of anammox bacteria(ANAMMOX)and ammonia oxidizing bacteria(AOB)reached 5.17 mg/(g·h),respectively.And 3.19 mg/(g·h),which is at a higher level in the activity of related denitrifying bacteria;the activity of NOB bacteria is 0.4 mg/(g·h);the activity of denitrifying bacteria is 1.17 mg/(g·h).Similarly,by analyzing the nitrogen balance of the water in the reactor under the working conditions,it was found that the proportion of NH4+-N removed by short-cut nitrification accounted for 44.97%,and that of NH4+-N removed by anaerobic ammonium oxidation accounted for 33.63%.The anaerobic ammonium oxidation process dominated the TN removal,and 69.02%of TN was removed,indicating that the short-range nitrification and anaerobic ammonium oxidation processes dominated by AOB and ANAMMOX were frequent in this system.(5)Real-time qPCR results showed that the gene copy number of AN AMMOX and AOB on the optimal working condition sponge filler was 1.02 × 109copies/gDNA and 7.56 × 107copies/gDNA,respectively,and the abundance of these two denitrifying bacteria in the system The highest abundance on the filler is higher than that of the flocculent sludge.The SEM characterization of the combined sludge shows that the microbial species in the sludge are abundant,the sludge shows coarse and agglomerated,and the amount of cocci on the filler is found to be flocculated.More in the sludge indicates that the conditions and fillers are suitable for the growth of these two types of denitrifying bacteria.