Study On Short-cut Nitrogen Removal Process Of Algal-bacterial Symbiotic Photo-sequencing Biofilm Batch Reactor(PSBBR) For Treating Swine Anaerobic Digestion

At present,the swine wastewater is mainly treated by anaerobic+aerobic biological methods.Due to the high ammonia nitrogen concentration and low C/N ratio of swine anaerobic digestion,traditional biological nitrogen removal technology（BNR）is facing many bottlenecks that needs to be solved urgently.Such as low nitrogen removal rate,large energy consumption for aeration,and high dosage of additional carbon source,etc.The short-cut biological nitrogen removal technology（SBNR）has the advantages of reducing the demand of oxygen and additional carbon source,which has attracted great attention from scholars.The microalgae bioreactor with good removal performance of nitrogen and phosphorus has good application prospects in the treatment and recycling of swine wastewater.In this study,the short-cut biological nitrogen removal technology（BNR）was combined with the emerging technology of microalgae system for treating swine wastewater,making full use of the advantages of two technologies for efficient nitrogen and phosphorus removal.Microalgae and sludge with short-cut nitrificating were combined to construct an algal-bacterial symbiotic photo-sequencing batch biofilm reactor（PSBBR）.To explore its impact factors,effect of short-cut nitrogen removal during long-term operation,and to analyze the nitrogen conversion pathway and bacterial community structure.The mechanism of short-cut nitrogen removal in the algal-bacterial symbiotic PSBBR was preliminarily discussed.The main research contents and conclusions of this thesis are as follows:（1）The sludge acclimation was carried out through using influent with high-concentration NH₄⁺-N and low C/N as well as controling suitable p H（7.5～8.5）and DO（0.8～1.2mg/L）.The studied results demonstrated that the sludge with high NH₄⁺-N removal efficiency and short-cut nitrification was obtained after acclimating for about 50days,and its NH₄⁺-N removal capacity was 12.30 mg NH₄⁺-N/（g MLVSS·h）,the nitrite accumulation rate（NAR）during aerobic process was 92.22%.There were two algal-bacterial adding methods on the construction of algal-bacterial symbiotic PSBBR system were compared,adding sludge first and then microalgae,or sludge and microalgae were added at the same time.The results demonstrated that the former was relatively better on nitrogen and phosphorus removal,especially the advantages of nitrogen removal.（2）Taking removal rate of nitrogen and phosphorus as well as chlorophyll a concentration in effluent as evaluation indexes.The effects of hydraulic retention time（HRT）and light intensity on the nitrogen and phosphorus removal of PSBBR were investigated.The studied results demonstrated that nitrogen and phosphorus removal in system were affected by HRT and light intensity,and the phosphorus removal was significantly affected by HRT.When the HRT was 2d and the light intensity was 5000 lux,the removal effect of nitrogen and phosphorus was good,the daily sewage treatment capacity was large,and the energy consumption was low.The removal rates of NH₄⁺-N,TN and TP reached 97.03%、93.51%and 82.55%,respectively.And the concentration of chlorophyll a in the effluent was 178.96～212.65μg/L.（3）During long-term operation of algal-bacterial symbiotic PSBBR,investigating the removal effect of nitrogen and phosphorus,stability of short-cut nitrification and economics of additional carbon source,and analyzing nitrogen conversion path according to the principle of nitrogen conservation.The studied results demonstrated that when the system was operated at NH₄⁺-N load of 300 mg·L^-1d^-1 for 37 days,the average removal rate of NH₄⁺-N,TN and TP were 96.25%、93.36%and 82.66%,respectively,the system had good effect on nitrogen and phosphorus removal.The average NAR was 91.93%,the system achieved stable short-cut nitrification.The dosage of sodium acetate per unit volume of influent in the denitrification stage was 973.69 mg/L,which was 17.8%less than dosage of carbon source in pure sludge SBBR,and about 60.5%less than dosage of of carbon source in BNR.The main nitrogen removal path of bacteria was as follows,NH₄⁺-N→NH₂OH→NO₂^--N→NO→N₂O→N₂,and the final product of partial denitrification was N₂O.During the stable operation of PSBBR,the average removal rates of NH₄⁺-N and TN were 96.6%and 95.3%,respectively.6.8%of nitrogen was absorbed by the biomass,and 88.5%of nitrogen was removed by short-cut nitrification and denitrification.（4）High-throughput sequencing technology was used to analyze the characteristics of activated sludge in different periods,such as the structure of microorganism community and the abundance changes of functional bacteria,etc.The studied results demonstrated that after the acculturation of the original sludge into sludge with short-cut nitrification,the microbial abundance,diversity and uniformity were reduced.In the activated sludge with short-cut nitrification,the abundance of NH₄⁺-oxidizing bacteria（AOB）was 19.31%,which was mainly Nitrosomonas,and the abundance of NO₂^--oxidizing bacteria（NOB）was less than 0.1%,The AOB/NOB ratio was greater than 193.1.After 37d-operation of PSBBR,the abundance of AOB in the biofilm was 5.65%,and the AOB/NOB ratio was greater than 56.5.The biofilm still had a good function of short-cut nitrification at that time.In addition,Thauera with a relative abundance of 76.61%in the biofilm was beneficial to nitrogen removal in the system.