Study On Denitrification Phosphorus Removal In Sequencing Batch Membrane Bioreactors

Nitrogen and phosphorus are key nutrients that result in water eutrophication. With the rapid development of the industrialization and urbanization, as well as the promotion of comprehensive sewage discharge Standards, it is practical Significance to study and exploit the denitrifying phosphorus removal process which is economical, reliable and effective. Denitrifying phosphorus removal process has many advantages, such as saving of organics, decrease in greenhouse gas emission and less sludge production, in accord with the concept of sustainable development. So this technique has broad development prospects.In this research, sequencing batch membrane bioreactor (SBMBR) was operated in a periodic way to improve the denitrifying phosphorus removal ability by optimizing the operation modes and adjusting operation parameters. The performance of SBMBRs on nitrogen and phosphorous removal, the sludge characteristics and membrane fouling were examined in different operation modes at the same time. The main research conclusions are summarized as follows:1. Simultaneous phosphorus and nitrogen removal performance was investigated by taking a self-designed A²O-MBR, and the removal of N and P was studied in different the load of N while C/N rate in influent was reduced gradually. The results showed that: when the load of N and P were 0.14 kg·m^-3·d^-1 and 0.03kg·m^-3·d^-1, the removal rate of COD, N and P were 90.5%, 80.6% and 67.7%, respectively. The proportion of denitrifying phosphate accumulating organisms (DPAOs) and the rate of denitrifying phosphorous removal were 70% and 69.81%, respectively. The self-designed A²O-MBR simplified the conventional A²O process and membrane filter substituted the secondary sendimentation tank, the laboratory-scale system can obtain good denitrifying phosphorous and nitrogen removal ability without extra nitrate addition, but the nitrate concentration in returned sludge should be limited in a low range to avoid the restraint of phosphorus-release under anaerobic phase, so the process should be improved further.2. The both reactors of MUCT-MBR process modified the above operating mode and avoided the restraint of phosphorus-release under anaerobic phase, the removal rate of NH₄-N and TN were 92% and 79.45% in the system process. Phosphorus-release rate was 24.74 mg/L and TP concentration in effluent was 1.12 mg/L and the removal rate of TP was 86.61% while the NH₄-N load in influent was 0.094 kg·m^-3·d^-1. 3. The analysis of denitrifying phosphate removal showed that anoxic zone in A tank of MUCT-MBR improved denitrifying phosphate removal ability, phosphorus uptake under anoxic zone and the removal rate of phosphorus was 73.88%, A anoxic tank not only avoided the restraint of phosphorus-release but also removed phosphorus. The proportion of denitrifying phosphate accumulating organisms in A tank and B tank were 86.2% and 80.7% respectively, and the denitrifying phosphate removal ability of A tank was better than B tank.4. It was found PHB and poly-p in cells by observation on the activated sludge staining, which validated denitrifying phosphorus uptake under anoxic condition.5. Decrease of sedimentation of activated sludge and increase of Extracellular Polymeric Substances (EPS) concentration led to membrane fouling in operation system, protein as the major components of EPS had strong positive effect on membrane fouling.