Study On The Effect And Mechanism Of Wastewater Treatment With High Concentration Of Ammonia Nitrogen By Partial Nitrification

The study relies on the operation of partial nitrification and denitrification process in the traditional A/O process.At the initial stage,the experiments were carried out to determine the range of operation with two parameters,pH and dissolved oxygen?DO?,and the results showed that ammonia removal efficiency was best and nitrite?NO₂^--N?accumulation was the most quantified and most stable when the two parameters were controlled at pH 7.6-8.0 and DO 1.6-2.0mg/L.The effect of denitrification on high concentration ammonia wastewater and the effect of high concentration ammonia nitrogen on partial nitrification,activated sludge and functional flora in the system were further studied.The results showed that the removal effect of ammonia reached 99.3%?the average removal efficiency was higher than 95%?.The removal efficiency of total nitrogen?TN?was 71.9%to 78.4%,and the average removal efficiency was 75.3%.Depend on the results of partial nitrification analysis,the concentration of free ammonia(C_FA)in the system of high concentration ammonia was increased from 0.38 mg/L to 17.11mg/L,so that largely affected the activity of nitrite oxidizing bacteria?NOB?,but less effects on ammonia oxidizing bacteria?AOB?,then they were obtaining oxygen easier.Also,in the study of oxygen consumption rate of microorganisms with increase of ammonia concentration,oxygen consumption rate of AOB was decreased from 24.64 mgO2/?MLVSS?h?to 15.66mgO₂/?MLVSS?h?,and the rate of NOB was decreased from 27.4 mgO2/?MLVSS?h?to 1.09mgO₂/?MLVSS?h?,and the reactor was easier to accumulate NO₂^--N under the condition of high level ammonia.By studying the oxidation rate of ammonia?NH₄⁺?and NO₂^--N,increase of ammonia concentration decreased the oxidation rate of NO₂^--N.The simulation results of Monod equation showed that the maximum reaction rate of ammonia increases from 0.24 d^-1to 0.74 d^-11 when ammonia concentration was increased from 40 mg/L to 1000 mg/L,in which it improved that high ammonia nitrogen accelerated the reaction rate of substrates.In the research of sludge,the external mass of the sludge and the microbial colony in the sludge were studied.The results showed that the quantity of sludge increased in the condition of high concentration ammonia,and MLVSS/MLSS was increased from 0.67 to 0.77,so that the biodegradability of active sludge was increased.Also,the concentration of extracellular polymer?EPS?was increased,where polysaccharides were increased from 8.5 mg/gVSS to17.6 mg/gVSS,and proteins were increased from 8.77 mg/gVSS to 14.31 mg/gVSS.The external structures of EPS of sludge were increased,the reaction rate of substrate was increased rapidly.PN/PS reduced strength of sludge,but increased stability of sludge.In the results of SEM scanning under high concentration of ammonia,the layers of internal structure were increased,specific surface area of the sludge was also increased,and the morphology of internal microorganisms was changed.According to the analysis of functional flora,the distance of colony was large and similarity of population was very low in the two reactors,the control group and the experimental group,because the high concentration of ammonia changed the formation of microorganism.Moreover,the microbial abundance could be improved,but the decrease of Simpson and Shannon index indicates that the population diversity of microorganism was decreased.The dominant phylum was changed from Proteobacteria,Planctomycetes,Bacteroidetes and Chloroflexi to Proteobacteria,Bacteroidetes,Chloroflexi and Ignavibacteriae.The quantity of the horizontal denitrifying bacteria,Thauera,was increased greatly,and Nitrosomonas,Phycisphaera and Solitalea were the dominant bacteria.Nitrite oxidizing bacteria,Nitrospira,was not detected in the experimental group,which proved that the increased concentration of ammonia gradually eliminated Nitrospira and inhibited the further transformation of NO₂^--N under high concentration of ammonia.