| In this study,a new two-sludge denitrifying phosphorus removal process-A2/O-Biological Contact Oxidation(BCO)was used.This process separates polyphosphate bacteria and nitrifying bacteria in different reactors,and they can be in the most favorable growth conditions,so as to achieve energy saving and deep nitrogen and phosphorus removal.In the BCO reactor,polypropylene suspendedcarriers were used as the microbial attachment material,and N1,N2 and N3 were operated in series to realize the efficient nitrification,the screening of nitrifying bacteria and the continuous optimization of bacteria structure.In this thesis,the reactor startup and trial operation were completed through the domestic sewage(low C/N)in Yangzijin campus.After that,artificial low C/N wastewater was used.Through long-term operation and batch experiments,the factors,mechanism and microbial community structure that affect the efficient utilization of carbon source and denitrifying phosphorus removal were explored.The main research contents and conclusions are as follows:(1)The natural membrane hanging of BCO reactor was basically completed in 20 days without adding activated sludge,and the biomass and membrane thickness of N1,N2 and N3 were different.The biofilm color was obviously different in each stage.The maximum biomass was 993.26mg/L,and the average biofilm thickness was 93.33 um,69.81 um and 51.41 um,respectively,where AOB was the main nitrifying bacteria.The sludge settleability in A2/O reactor has been greatly improved.SV increased from 24%to 33%,and SVI decreased from 158 ml/gMLSS to 97 ml/gMLSS with VSS/MLSS increased from 0.60 to 0.80.During the start-up period,the reactor could realize the simultaneous and efficient removal of COD,N and P.The removal rates of COD and TN were 83.6%-96.5%and 71.6%-81.6%,respectively.The removal rates of PO43--P fluctuated greatly,and the highest removal rate after stabilization was 100%.(2)During the different phases of sodium acetate/sodium propionate ratios,the average removals rate of COD and NH4+-N were 89.1%-92.1%and 91.4%-100%,and the average removal rate of TN was 76.1%,80.7%,84.7%,82.5%and 81.6%,respectively.The ratio of carbon source exerted a negligible effect on the final removal of COD and ammonia nitrogen.However,it proved a significant impact on the anaerobic COD absorption.The consumption of COD in the anaerobic stage was 155.0,154.8,239.5,206.3 and 204.6 mg/L respectively.When sodium acetate:sodium propionate=1:1,the absorption effect of COD in the anaerobic stage was the best,and the release of phosphorus in this stage reached the maximum(30.58 mg/L).Even so,the effect of phosphorus removal still needed to be strengthened due to various influence factors.(3)The specific phosphorus release rate(SPRR),specific phosphorus absorption rate(SPAR)and specific denitrification rate(SDNR)increased with the increase of temperature.At 25?,the specific rates were 18.8 mg PO43--P/(g MLSSˇh),11 mg PO43--P/(g MLSSˇh)and 9.6 mgNO3--N/(g MLSSˇh),respectively.At this time,the phosphorus removal effect was the best,and the phosphorus effluent concentration was less than 0.5 mg/L.The temperature coefficients of specific phosphorus release rate and specific phosphorus absorption rate affected by temperature were 1.073 and 1.044,respectively.(4)When SRT was shortened to 6 days,the P concentration in effluent decreased to almost 0.Based on EDS element quantitative analysis,the wt%of anoxic sludge P was 11.63%.At the same time,PHB staining showed that the synthesis of PHB occurred in anaerobic phosphorus release stage;Ploy-P staining showed that there was a large amount of phosphorus uptake by microorganisms in anoxic stage.(5)The transformation process of external carbon source such as COD and internal carbon source including PHB,Gly were closely related to the degradation characteristics of organic matter,nitrogen,phosphorus and other substrates.The change process of each substrate reflected the metabolic pathway with denitrifying phosphorus removal as the main body.After long-term operation,DPAOs accounted for 60.71%-86.86%of PAOs,which was much higher than inoculated sludge of 3.26%,and DPAOs accounted for the highest proportion when sodium acetate:sodium propionate=1:1.(6)In the kinetic model of COD removal established in this study,the COD removal rate constant was KAn?0.000921/g h.The calculation model of anaerobic effluent concentration wasCAn=(Cinf+rCeff)/(0.00092XAntAn+1+r,and the final calculation model of effluent concentration was Ceff=((0.00092XAntAn+1+r)CAn-Cinf)/r.(7)After acclimation,the diversity and richness of bacteria decreased,but the enrichment of bacteria increased.In A2/O reactor,the proportions of some bacteria with denitrifying and phosphorus accumulating function such as Pseudomonas,Decloromonas,Thauera,Flavobacterium,unclassified_rhodococcaceae,norank_Acinetobact?Candidatus_Microthrix increased with a total percentage from 3.63%(seed sludge)to 10.08%(Phase ?),13.09%(Phase ?),13.19%(Phase ?),12.51%(Phase ?),17.87%(Phase ?).The proportions of nitrifying bacteria in the three compartments of BCO reactor were 4.28%,28.30%and 17.61%respectively.In addition,the bacteria groups with external denitrification function such as Thauera,Comamonaas,Zoogloea and Azospira decreased from the initial 24.96%to 6.23%-13.58%. |
PDF Full Text Request