Study On The Microbiological Characteristics And Processes Of Denitrifying Phosphorus Removal

Establishment of a healthy social cycle for water utilization is a fundamental way to solve water crisis and achieve sustainable use of water resources in China. According to the strategy of the healthy water cycle, the establishment of the reclaimed water supply system in urban areas is the top priority. The most important issue we faced is to seek an economic and feasible renewable water production technology for wastewater treatment. In recent years the theory of denitrifying phosphorus removal provides us some new ideas and perspectives and attracts more and more people's attention, with its advantage of "dual-use carbon" and "energy conservation and environmental protection". In response to this status, this study focus on the characteristics of denitrifying phosphate-accumulating organisms and the performance of denitrifying phosphorus removal process for treating municipal sewage.A2N process is a typical process of the theory of denitrifying phosphorus removal.In this study, the characteristics of denitrifying phosphate-accumulating organisms was investigated. At the same time, for the existing problems of the A2N process, an improved process was proposed and its performance for treating municipal sewage was investigated in order to seek an economic and feasible technoloty for the renewable wastewater production.Microbial study on A2N process showed that the character and variation of intracellular substances PHB(Poly-β-Hydroxybutyric acid) and Poly-p(Poly-phosphate) were similiar between denitrifying phosphorus accumulating sludge and common aerobic phosphorus accumulating sludge. Two kinds of phosphorus accumulating organisms (PAOs), one used O2 as electron acceptor, the other used O2 or NO3--N, were both found in the anoxic tank of A2N process.To study the characteristic and diversity of denitrifying phosphorus accumulating organisms (DPAOs), three phosphorus removal reactors with different electron acceptors of O2, NO3--N and NO2--N were carried out respecitively. The results showed that nitrite inhibits both aerobic and anoxic phosphorus uptake, and the threshold for aerobic and anoxic phosphate uptake were 0.88mgN/gVSS, 6.72 mgN/gVSS, respectively. With a stepwise increasing of NO2--N concentration in the influent, DPAOs were gradually accommodated to utilize NO2--N as electron acceptor, but its phosphorus removal efficiency was lower than that of O2 and NO3--N as electron acceptors. The results of DGGE targeting 16SrRNA gene indicated a significant shift in microbial community with different electron acceptor conditions.Furthermore, batch experiments were carried out to study the factors affecting the denitrifying phosphorus removal. Carbon sources had a great effect on phosphorus removal. Long-term experiments showed that propionate-fed system had similar phosphorus removal efficiency with acetate-fed system, when glucose was used as the sole carbon source, it would result in the deterioration of the phosphorus removal system. DGGE analysis showed that propionate-fed system had similar biological community structure with acetate-fed system, glucose as the sole carbon source caused the biological community structure changed radically and a novel glycogen accumulating organisms (GAOs), Micropruina glycogenica have proliferated. DPAOs were low-temperature-resistant bacteria, short-term temperature changes had little effect on denitrifying phosphorus removal. With the increase of MLSS, the quantity and rate of denitrifying phosphorus removal increased, while the specific phosphorous uptake quantity decreased.Long-term experiments showed that modified A2N process was applicable for low C/N wastewater treatment. When the influent C/N ratio ranged among 3.5~5.5, the mean removal efficiency of COD,NH4+-N,TN and TP were 80.93%,97.44%,81.46% and 68.2%, respectively. The COD,NH4+-N and TN removal were excellent in the modified A2N process, which met the standards of urban wastewater treatment plant pollutant discharge (GB18918-2002) - level A discharge standards, and achieved the reclaimed water demand. The mean final effluent TP concentration was 0.94 mg/L,achieved level B discharge standards, and the TP removal efficiency could be further improved.As compared with the traditional A2N process, the modified A2N process was simpler and more efficient on NH4+-N and TN removal. NH4 +-N could even achieve zero discharge at most of the time. When the nitrified recycle ratio was constant, TN removal rate was stable and efficient because of the nitrogen loss in the biofilter. However, due to the poor stability and "the second phosphorus release" in the biofilter, the phosphorus removal efficiency in modified A2N process was lower than that of the former A2N process.