Study On Simultaneous Nitrification And Denitrification Process Based On SBR Reactor

In the industrial and agricultural fields,high ammonia nitrogen wastewater is relatively common,and its treatment cycle is time-consuming and cost-consuming.This project takes biogas slurry as the object to achieve high-efficiency nitrogen removal process based on the SBR process with suspended fillers which are able to specifically enrich nitrogen removal microorganisms.The main findings are as follows:（1）A simultaneous nitrification and denitrification system was established initially.A SBR reactor was modified:the reactor was divided into aerobic zone,anaerobic zone and anoxic zone by a cuboid-shaped keg,the bottom end of which was opened.So,the nitrification and denitrification reactions could be carried out in a single vessel.Then,suspended fillers were added as biofilm growth carriers,the filling rate of which was 30%and other optimal conditions were:T=30℃,the influent pH=7 to 7.5,HRT=8 h,DO=6.72 mg/L.After 25 days,a stable biofilm structure has been formed on the suspended carriers,and the effluent water quality is stable that the removal rates of COD and NH₄⁺-N are 85%and 63%,respectively.The results of high-throughput sequencing show that the dominant strains on the biofilm are constantly changing at this stage,but the Proteobacteria always shares the largest proportion,the relative abundance of which exceeds 75%.At the genus level,the average abundance of some bacteria which account for 28.97%⁵0.31%of the whole strains is less than 1%,indicating that the bacterial communities of the biofilm change dynamically during this period.Quantitative PCR results show that with the number of AOB gradually increases from 5.235×10⁵ to 4.288×10⁶ copies/g biofilm（dry weight）over time while the quantity of DNB decreases first then rises to 1.105×10⁷copies/g biofilm（dry weight）and the amount of Anammox keeps at a relatively low level.（2）The running process was optimized.After the initial establishment of the system,a 14-day system reconstruction was carried out.The operation process is as follows:T=30℃,the first 7 days are the anoxic period with DO=0.90mg/L,and the next 7 days is aerobic period with DO=6.72mg/L.After one cycle,the effluent NH₄⁺-N,COD and TN removal rate reach 95.12%,90.21%and 55.46%,respectively,while the NO₂^--N accumulation rate is 86.86%which means partial nitrification and denitrification has been achieved.High-throughput sequencing results show that the relative abundance of each bacterial phylum associated with nitrogen cycle is more than 0.5%.Quantitative PCR results showed that the maximum number of AOB is 1.116×10⁷copies/g biofilm（dry weight）,and the maximum quantity of DNB is 9.805×10⁷copies/g biofilm（dry weight）.The number of Anammox has been at a low level,but its content has increased significantly in samples from the period of C/N=8,up to 1.914×10⁶copies/g biofilm（dry weight）.（3）A highly efficient nitrogen removal system was established.In order to further develop microbial structure,a highly efficient anaerobic denitrifying bacteria（A3）was screened from the mature biofilm.The maximum nitrate concentration that the strain can degrade is about 400mg/L TN（in terms of NO₃^--N）,the figure of which can be reduced to 13.15 mg/L within 48h by inoculating a single colony.And it was put to the system according to the dosage of 10⁵ CFU/mL to increase the proportion of denitrifying microorganisms.Combined pre-coagulation pretreatment,after 21 days,the effluent water quality has been stable that the degradation rates of both TN and COD are all over 90%while the number of DNB is 8.327×10⁸ copies/g biofilm（dry weight）.In summary,when the system is applied to the nitrogen removal of biogas slurry that the reaction temperature is 30℃,HRT=8 h,and the system is started with a cycle of oxygen supply for 14 days（no need for an external carbon source）,effluent COD and TN can be maintained at 88 mg/L and 39 mg/L,respectively.