| With the large-scale development of industry and agriculture,industrial wastewater,agricultural wastewater and domestic sewage have increased significantly in China.I Although,the treatment rate of industrial and agricultural wastewater and domestic sewage reached about 90%,and the concentration of wastewater treatment plant(WWTP)effluent has reached the relevant discharge standards.However the total amount of pollutants emissioned by the WWTP still causes serious pollution on rivers and lakes,and others surface waterwater,which lead to water quality deteriorates,seriously environmental damage,and human health problems.Since microorganisms have the characteristics that it can forming biofilm under low nutrient conditions,which make it become one of the main techniques for treating micro-polluted water.In Biofilm Sewage Treatment Technology,the characteristics of biofilm carrieres and operating conditions in Biofilm Sewage Treatment Technology can affect the removal of COD,nitrogen,phosphorus and other pollutants.Choosing the biofilm carrieres and finding suitable operating conditions are the keies to the stable operation of bio film system.In this experiment,a Sequencing Batch Biofilm Reactor(SBBR)with a polypropylene suspension pellets as carrieres and a Sequencing batch reactor(SBR)without carrieres were used as controls.Under different aeration strategies and C/N(5,8 and 11),the nitrogen removal effect of a new SBBR with polyvinyl alcohol gels(PVA)as carrieres were studied through treating WWTP effluent.By comparing the removal effects of COD,total nitrogen(TN),ammonia nitrogen(NH4+-N),nitrate nitrogen(NO3--N)and total phosphorus(TP),the operating conditions were optimized.At the same time,the microbial communities of the 2 carriers in SBBR and water bodies in SBR under optimal conditions were tested.The analysis and comparison of microorganisms related to nitrogen removal in the community were carried out.The nitrogen removal efficiency of PVA gels in WWTP effluent was evaluated and the following conclusions were drawn:(1)By investigating and comparing the effects of different aeration strategies on nitrogen removal in aerobic zone,the results show that the NH4+-N removal rates of the SBBR with suspension pellets and the SBBR PVA gel are 37?96%,54?99%and 0?15%,respectively.In the optimal aeration strategy S3(2 hours aeration after the water inflow 15 h),the removal rate of NH4+-N in the PVA gel was as high as 99%,while the removal rates of NH4+-N in the SBBR with suspension pellets and the SBR without carrieres were 63%and 6%,respectively.Therefore,the PVA gel has the best NH4+-N removal effect.(2)In the anaerobic zone,the No3--N removal rates of the SBBR with polypropylene suspension pellets,PVA gel as the filler and the SBR without fillers are 100%,100%and 96%,respectively;and the effluent concentrations were 0 mg/L,0 mg/L and 0 mg/L,respectively.Therefore,the effect of NO3--N removal of anaerobic zone in the three reactors was similar.(3)By changing the influent load and hydraulic retention time(HRT),the stability of denitrification effect of the three reactors investigated.After changing the influent load,the average TN removal rate of the SBBR with suspension pellets and the SBR without carrier was decreased from 50%to 37%and increased from 30%to 48%.However,the average TN removal rate of the SBBR with PVA gel was stabilized at 55%?57%.Therefore,the PVA gel has the strongest resistance to fluctuations in the influent load.(4)By changing carbon-nitrogen ratios(C/N=5,8 and 11),the effects of C/N on nitrogen removal was investigating.When the C/N increased from 5 to 11,the effluent TN concentration in the SBBR with suspension pellets,the SBBR with PVA gels and the SBR without carriers are 3.9?6.3 mg/L,1.6?4.5 mg/L and 4.3?5.2 mg/L,respectively,and the removal rates were 37%?62%,55%?84%and 41%?57%.Under the optimal C/N(C/N=8),the effluent TN concentration of the SBBR with suspension pellets and the SBR without carriers were 3.9 mg/L and 4.3 mg/L,and removal rates were 62%and 47%,respectively.Meanwhile,the effluent TN concentration and removal rate of SBBR with PVA gels was 1.6 mg/L and 84%,which can meet the requirements of surface V water.Therefore,the PVA gel has better denitrification ability.(5)By detecting the microbial community composition the 2 carriers in SBBR and water in SBR under the optimal working conditions,the results showed that the first dominant bacteria in the PVA gels is Proteobacteria(35.4%),followed by Nitrospirae(27.0%).In the PVA gels the proportion of microorganisms related to denitrificationw was as high as 39.4%,while the proportion in suspended pellets and the water in SBR was 29.65%and 22.85%,respectively.Therefore,the proportion of microorganisms associated with denitrification in the PVA gels is significantly higher than that of the suspended pellets and the water in SBR. |
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