Study On Process Optimization And Bioaugmentation Of Simultaneous Nitrification And Denitrification Phosphorus Removal System In High-altitude Aera

At present,the biological treatment process operating in high altitude areas is affected by the unfavorable natural environment of low temperature,low pressure and low oxygen,and there are common problems such as difficulty in sludge cultivation,low microbial activity and high energy consumption of aeration.Simultaneous nitrification,denitrification and phosphorus removal process(SNDPR),as a new type of simultaneous nitrogen and phosphorus removal process in recent years,has the advantages of high efficiency,stability,and energy saving.Compared with the traditional sewage biological treatment process,its demand for dissolved oxygen is lower and it can save carbon sources,and it may be suitable for the characteristics of low temperature,low pressure,low oxygen and low organic matter concentration in high altitude areas.This study applies the SNDPR system to urban domestic sewage treatment in high-altitude areas.The applicability of the SNDPR system under low atmospheric pressure and low influent COD concentration was verified through experiments,and the process optimization and bioaugmentation of the SNDPR system under low atmospheric pressure were carried out by optimizing anaerobic/aerobic time parameters and adding microbial strains.This study provided a scientific basis for the practical application of the SNDPR system in high altitude areas.Here are key research findings:1)The influence of different influent COD concentrations on the pollutant removal performance of the SNDPR system under low atmospheric pressureThe SNDPR system was operated under normal atmospheric pressure of 100 kPa and low pressure of 72 kPa respectively.The results showed that at 72 kPa,when the influent COD was reduced from 300 mg/L to 200 mg/L,the concentration of NH4+-N was 30 mg/L and the TP concentration is 5 mg/L,the SNDPR system shows good COD and TP removal performance,while the TIN removal performance drops from 81.21%to 72.86%,and the SND drops from 59.48%to 31.95%.Compared with the SNDPR system operating under normal pressure,the SNDPR system operating under 72 kPa has a better TIN removal performance.Periodic experiments also show that as the atmosphere pressure drops from 100 kPa to 72 kPa,the DO concentration in the aerobic phase drops from 6.47 mg/L to 5.46 mg/L,and the ammonia oxidation rate in the SNDPR system also decreases,indicating that the SNDPR system is suitable for Characteristics of urban sewage in high-altitude areas with low atmospheric pressure and low influent COD concentration.2)The effect of adjusting the anaerobic/aerobic duration time under low atmosphere pressure on the nutrient removal performance of the SNDPR systemThe experiment runs 4 reactors,one of which is placed under normal atmosphere pressure of 100 kPa(L1),the anaerobic/aerobic time is 120 min/210 min,and the remaining three are placed under low atmosphere pressure of 72 kPa,anaerobic/aerobic time 120-180 min/210-150 min(referred to H1,H2 and H3 respectively).The results show that when the influent COD is 200 mg/L,the NH4+-N is 30 mg/L,and the TP is 5 mg/L,H1,H2,and H3 all show good COD and TP removal performance at 72 kPa.Which was similar as L1 running at 100 kPa.There are differences in the TIN removal rate,the TIN removal rate in L1 is the lowest(67.54%).With the adjustment of anaerobic/aerobic time duration,the removal rate of TIN in H1,H2 and H3 gradually increased to 76.33%.This is because the drop of atmospheric pressure and the shortening of aerobic time provided an anoxic environment in the system,thus promoting denitrification process.As a result,the removal efficiency of TIN was improved.3)Analysis of key enzyme activities related to denitrification process and microbial community structure in the in the SNDPR system under low atmosphere pressureThe activity measurement results of denitrification-related enzymes show that under low atmospheric pressure,the AMO and HAO enzyme activities related to the process NH4+→NH2OH→NO2-are inhibited,while the process NO2-→NO3-related enzyme NXR On the contrary,the activity increased.During the denitrification process,the activity of the NIR enzyme related to NO3-→NO2-was enhanced,while the activity of the NAR enzyme responsible for the process of NO2-→NO was inhibited.Microbial community analysis showed that with the decrease of atmosphere pressure,the dominant bacterial genera in the SNDPR system changed,and the abundance of key ammonia oxidizing bacteria(AOB)related bacterial genera decreased.This is consistent with the result of the decrease in ammonia oxidation rate at low atmospheric pressure.Under low atmospheric pressure conditions,with the change of the anaerobic/aerobic time ratio,denitrifying phosphorus accumulating bacteria(DPAOs),phosphorus accumulating bacteria(PAOs)and related denitrifying bacteria(DNB)in the SNDPR system are enriched,thereby Ensure the system’s highefficiency nitrogen and phosphorus removal performance.4)The enhanced effect of adding high-efficiency microorganisms to the processing efficiency of the SNDPR system under low atmospheric pressureFive strains with high efficiency of nitrification or denitrification were screened from activated sludge of sewage treatment plant operating at high-altitude areas.The 16S rDNA identification showed that the related bacteria had nitrification or denitrification function.The results showed that both of the two ways improved the treatment efficiency of COD and TIN in SNDPR system.The concentration of NO3--N in effluent was the lowest and the removal rate of TIN was the highest in the SNDPR system strengthened by immobilized bacteria.Therefore,the enhanced effect of immobilized bacteria was the better way.