PAOs Population Dynamics And Phosphorus Distribution In A Coupling Anaerobic-aerobic Biofilm Reactor

The purpose of this study was to established a coupling anaerobic-aerobic biofilm reactor(CAABR)using a semi-suspended bio-carrier to reveal the distribution of phosphorus and population dynamics of “Polyphosphate-accumulating organisms(PAOs)”.The start-up operation of this experimental reactor was divided into two phases: Phase I,the influent concentrations of P were controlled at 1 mg/L from the reactor started to run to 54 th day;Phase II,the reactor was from the 55 th days run to 78 days,which increases the influent concentration of P to 1.5 mg/L.The effect of CAABR on artificial simulated synthetic wastewater was investigated by measuring the influent and effluent conventional indicators(COD,NH4+-N,NO2--N,NO3--N,and PO4--P)of the reactor.Furthermore,chemical methods were used to determine the distribution of aqueous phase,EPS(Extracellular Polymeric Substances)and intracellular phosphorus in the reactors at each stage.In addition,the micro-electrode was used to measure the change of oxygen concentration in the biofilm.Finally,the high-throughput sequencing method was used to study the population dynamics of polyphosphate-accumulating organisms(PAOs)in the reactor.The main findings are as follows:The CAABR system started by rapid-sludge method form biofilm,with a sludge concentration of 1000 mg/L at startup and a hydraulic retention time(HRT)of 24 h.The system was continuously run for 78 days,which there was not have excess sludge discharge in the whole operation stage.The experimental results show that in phase I and II,the COD removal rate remains stable at 88±7.54%,the NH4+-N effluent concentration is maintained at less than 1 mg/L.The effluent concentration of phosphorus was lower than 1 mg/L,and it was the lowest at 0.02 mg/L when it was stable at stage I.The removal rate of phosphorus was up to 97.89 %,and the average removal rate was 69±22 %.Moreover,phosphorus removal rate in Phase II decreased but remained at 64.56±11.08%.The semi-suspended bio-carriers in CAABR are manufactured using 3D printing technology,which forms a biofilm on the surface of the reactor during its operation.The study found that a significant oxygen concentration gradient was gradually formed in the biofilm,which confirmed the successful formation of micro-anaerobic/aerobic biofilm on the surface of the semi-suspended bio-carriers.The coupled anaerobic-aerobic microenvironment in biofilms is more conducive to PAOs release more phosphorus in anaerobic environment,and provide enough energy for phosphorus removal in aerobic environment.The experimental results demonstrated that the percent of phosphorus relative concentration in Intracellular was the maximum,around 66%-83%,EPS take second place,around 16%-34%,and the minimum of aqueous phase as little as 0.4%.Phosphorus is transferred from the aqueous phase to the EPS and eventually stored in Intracellular as polyphosphates by the PAOs,resulting in the highest intracellular phosphorus content.The CAABR system has significant differences in microbial populations in Phase I and Phase II.The results showed that the relative abundance of Proteobacteria,Chloroflexi and Bacterioidetes gradually decreased as the CAABR system prolonged,and Actinobacteria gradually became a dominant species,about 47.5-57.4 %.Meanwhile,there are 13 PAOs species in CAABR,and the abundance of Candidatus Accumulibacter as important PAOs gradually decreases with the operation of the reactor,from the highest period of 71.2% to 0.6%;Zoogloea ramigera gradually became a dominant species,and its relative abundance increased from the initial 7.5 % to 93.1 %.In summary,from the aspects of phosphorus removal,dissolved oxygen distribution in biofilms,P metabolism,and PAOs population succession,the dynamics of PAOs and the distribution of phosphorus in coupled anaerobic-aerobic biofilm reactors were systematically studied.It was clarified that the CAABR system had good ability of removing phosphorus,and there was an anaerobic-aerobic micro-environment in the biofilm.It was found that the distribution of phosphorus in the system was influenced by the ability of PAOs to accumulate phosphorus.It was also learned that Arthrobacter aurescens and Zoogloea ramigera are major populations of phosphorus removal in CAABR.The results of this study will help to better understand the mechanism of phosphorus removal in CAABR system and the population changes of PAOs,and provide a theoretical basis for the practical application of coupled biofilm reactors.