Operation Characteristics And Pollutants Removal Mechanism Of Vegetation-activated Sludge Process Treating Domestic Wastewater

In order to solve the problems of unstable treatment performance,sensitive treatment efficiency remarkably affected by seasonal fluctuation,and lack of landscaping function in traditional decentralized wastewater treatment processes,an ecological wastewater treatment process involving activated sludge processes(ASP)and wetland vegetation,named as vegetation-activated sludge process(V-ASP)is developed to satisfy the requirement of wastewater treatment and ecological effect.According to the objects,this thesis focused on the configuration of V-ASP,operational characteristics and influence factors,functional microbes,pollutants removal mechanisms,temperature effects and related nitrification enhancement measures at low temperature.The removal efficiencies of typical pollutants,i.e.carbon,nitrogen and phosphorus and the greenhouse gas(GHG)emission behavior were investigated on the base of successful construction of V-ASP.For an in-depth understanding of V-ASP,sludge biomass characteristics,microbial communities and main functional microbes,removal paths and mechanisms of pollutants,include organic,nitrogen and phosphorus,and GHG emission behaviors were carried out,during which a mathematical modeling based on ASM2 D model was established.The effects of temperature and related low temperature nitrification enhancement measures to solve the problem of instable nitrogen removal were also investigated.Firstly,selected decontamination vegetation(Canna indica and Cyperus altrnlifolius,planting density: 50:6)was immersed into ASP(Sequencing Batch Reactor)to form VASP.By compared with ASP,a long-term experimental results evidenced that V-ASP had consistently stable higher removal efficiencies of organic substances and nutrients from domestic wastewater,the average effluent concentrations of COD,NH4+-N,TN and TP were 35.89,1.61,9.29 and 0.32 mg/L,respectively.The removal efficiencies of COD,NH4+-N,TN and TP were improved about 3%,4%,12% and 4%,respectively in constract with ASP.Meanwhile,the results of greenhouse gas emissions displayed that V-ASP has the reduction effect of CH4 and N2 O emissions,and the average emission flux were 7.17 and 0.45 g/(m2·d),respectively.Compared with ASP,the annual CH4 and N2 O emissions reduction proportion of V-ASP was 25.11% and 4.71%,respectively.Secondly,for further analysis the advantage of pollutant removal,the microbial distribution and structure of function microorganisms in V-ASP were studied.The study found that the combination of vegetation increased activated sludge particle size,decreased sludge specific resistance,reduced the contents of sludge extracellular polymers(EPS)and soluble microbial products(SMP),and enhanced SOUR and enzyme activities.The PCR-DGGE was used to compare the diversity,similarity and differences of the samples from ASP,V-ASP and constructed wetlands(CW),and the results showed that the configuration of vegetation had insignificant effects to the diversity of activated sludge in V-ASP.The rhizosphere microorganism was related closely to the activated sludge processes.It also found that the microbial diversity of V-ASP was significantly higher than CWs.The microbial community in V-ASP was also well characterized by using 16 S rRNA gene based high-throughput sequencing,and it was found that Proteobacteria was the most dominant phylum of activated sludge and rhizosphere sludge in V-ASP,and the configuration of vegetation did not have obvious impact on the classification of microorganism in phylum and genus of activated sludge.V-ASPs contained a higher nitrite-oxidizing bacteria(Nitrospira)abundances that resulted in a consistently better nitrogen removal efficiency.Thirdly,in order to provide a basic theory supporting for V-ASP,the removal mechanism was comprehensive studied.The removal mechanism of carbon and nitrogen in V-ASP was traced by Stable Isotope Tracer Technique and phosphorus was determined by mass balance analysis method.The results showed that the activated sludge in V-ASP is the main way to remove pollutants,accounting for about 70% of the total pollutants removal.Under the density of 212 plants/m2 and 30 centimeters of water depth,the direct absorption contribution of the combined vegetation on total carbon,total nitrogen and total phosphorus was 3.67%,6.42% and 14.92%,respectively.After the research on the emission mechanism of GHG in V-ASP,it was found that the main causes of CH4 emissions reduction were relatively low content of methanogens,high content of methane monooxygenase and the directly uptake of organic by vegetation.The major reasons for N2 O emissions reduction were relatively high content of nitrifying bacteria,higher enzymatic(AMO,HAO,N2OR)activities and the directly uptake of nitrogen by vegetation.To guide the design and operation of V-ASP,a mathematical model based on ASM2 d was successfully established by involving related vegetation parameters.The deviations of simulation and measured results were within the acceptable range.Therefore,the mathematical model could used for validation and prediction of the practical operation results.Finally,the ubiquitous problem of unsatisfactory nitrification effect at low temperature was stuided.The allocation of vegetation could improve the temperature shock resistance capability of V-ASP,although its nitrification ability would also be effected by low temperature.The temperature affected the ammonia removal rate by influencing the nitrification rate,enzyme activities and microbial structure.The DGGE results showed that the microbial structure has the great change under 12? and the highest microbial community richness under 15?.The high-throughput sequencing results showed that the low temperature resulted in a decreasing of Proteobacteria and Nitrospira abundance,and the abundance of Proteobacteria was higher in activated sludge compared with rhizosphere sludge.The removal mechanism of nitrogen in V-ASP was not affected by temperature,where the removal pathway also mainly included the assimilation and catabolism by activated sludge and root sludge,and the uptake of vegetation root,stem,and leaf.The low temperature regulation based on mathematical modeling has proved that the adjustment of operation parameters,including SRT and HRT could effectively improve the ammonia nitrogen removal rate of V-ASP.Bioaugmentation by using nitrifying bacteria is one of the effective ways to solve poor nitrification effect at low temperature.Under the optimal dosing quantity of 0.15 g/gSS nitrifying sludge,long-term operation results demonstrated that the bio-augmented VASP exhibited stably high NH4+-N removal at least for 30 days through one-time addition,with the averaged effluent NH4+-N concentration was 1.45 mg/L.