Denitrifying Phosphorus Removal In Anaerobic-Anoxic-Nitrification Double Sludge System

Eutrophication is mainly caused by nitrogen and phosphate discharged into the water body. With the severe eutrophication occurred, the process design of the municipal wastewater water treatment plant should expand its function from pure organic matter removal to nitrogen and phosphate removal. However, traditional nitrogen and phosphate removal processes have the disadvantages of longer process, more area and higher construction and operation cost. High efficiency nitrogen and phosphate removal technique has become the focus of the research field. Denitrifying phosphate removal technique is a noval, promising biological wastewater treatment technique and draws widely attention of the field. A2N double sludge process is based on this new technique, which can decrease oxygen and external organic supply greatly, reduce the waste sludge production and the volume of the reactor to some extent. These advantages make it significant for the treatment of the lower C/N ratio municipal wastewater. At present, studies on denitrifying phosphate removal are always executed using pure substrate cultivation and synthetic wastewater. However, the real wastewater treatment is an open, dynamic system, during which influent water quality and quantity change instantaneously. These make it rather hard to simulate and reappearance the real process. Simultaneously, most of the studies focused on mechanism and theory can not give a definite range of the key parameters for the operation. This obstacles the generalization and application of the technique into practice. In this paper, the effect of HRT (hydraulic retention time) on denitrifying phosphorous removal process was investigated by applying a continuous flow, two sludge anaerobic/anoxic/nitrification (A2N) process combined with SBR batch test in which real domestic wastewater was treated. Also, the feasibility of using nitrite as electron acceptor is also investigated. The main conclusions from these experiments are as follows. Anaerobic stage is the key step of A2N process. It is critical for both nitrogen and phosphorous removal. Under long anaerobic HRT, although the total amount of released dissolved phosphate increased, the phosphate uptake and the nitrogen removed by denitrifying during anoxic stage are not increased proportionally. Some of the dissolved phosphate released under anaerobic stage is"noneffective", it is useless for both nitrogen and phosphorous removal under succeeding anoxic stage. Under shorter anaerobic HRT, denitrifying phosphorous removal bacteria can not absorb the readily biodegradable COD in the influent completely; this result in decrease of anoxic phosphate luxury uptake and at the same time, denitrifying activities of DPB are also limited. When treat with real domestic wastewater, Anaerobic HRT of 2 hours can meet both the nitrogen and phosphorous removal requirements perfectly.Biofilm in the nitrification stage can bear severe impact load. But the HRT has obvious effects on SND. Under constant aeration rate, longer HRT leads to higher TN removal efficiency in this stage,...