| Based on the latest research findings on simultaneous phosphorus and nitrogen removal from wastewater—denitrifying dephosphatation,this paper sudied a new process to realize simultaneous phosphorus and nitrogen removal.First, this study investigated the fraction of three groups of phosphate-accumulating organisms (PAOs) in total PAOs in A/O-SBR.The three groups of PAOs could be proposed as follows: the first group is those capable of utilizing only oxygen as electron accepor, the second group is those capable of utilizing both oxygen and nitrate(but not nitrite) as electron accepor; the third group is those capable of utilizing oxygen , nitrate and nitrite as electron accepor. The results of long-term operation showed that COD and phosphorus can be removed efficiently, the average removal rate of COD and phosphorus is 88 %,90%,the average of TN removal rate is 56%.The fraction of DPB in total PAOs was reached 18%, and the fraction of PO, PON and PONn were 82%,7%,11% respectively.The results also suggested that nitrate and nitrite were not inhinitor to phosphorus removal process.Instead, its are alternative electron acceptors to oxytgen.The second, an anaerobic/aerobic/anoxic process (referred to as an AOA process) using a SBR was proposed for simultaneous phosphorus and nitrogen removal from wastewater.The selection and dominance of DPB,which are caperble of utilizing nitrate or nitrite as electron acceptor, was the key prolem in this process. The AOA process was stably operated over more than two months when a certain amount of carbon substrate (12.8~17.2mgCOD/gMLSS) was supplemented to inhibit aerobic phosphate uptake. The average TN and phosphorus removal efficiencies were 85.5% and 91.4% respectively. It was also demonstrated that phosphate- accumulating organisms (PAOs) capable of utilizing nitrite as an electron acceptor, DPB could exist in the AOA process. Further research revealed that the pH profile in a cycle was regular and could be linked to the variation of nitrogen and phosphorus in the wastewater, which might be used for prediction of the end of phosphate release, ammonia conversion and phosphate uptake, based upon the pH monitoring. In conclusion, the AOA process allows DPB to take an active part in simultaneous nitrogen and phosphorus removal in an SBR when a suitable amount of carbon substrate is supplied at the start of aerobic conditions. To use DPB for simultaneous nitrogen and phosphorus removal in the SBR, the AOA sludge had a better performance than AO sludge in terms of phosphorus and nitrogen removal.What is more important, the DPB take up and store phosphate using nitrate or nitrite as electron acceptor, then the organic carbon substrate can be used simultaneously for both phosphorus and nitrogen removal. This is of significance since organic carbon content in most municipal wastewaters is too limited in order to achieve both phosphorus and nitrogen removal. Employing DPB in the biological nutrient processes also makes it possible to reduce sludge production and aeration demand and this will make a significant impact on the engineering practice of phosphorus and nitrogen removal process from wastewater. |
