Effects Of Chemical-aid Phosphorus Removal Drug On The Activated Sludge Of The Biological Treatment System

Currently, eutrophication and harmful algae blooms have become increasinglysevere in China. With biological methods as the main treatment, carbon source of waterinflow in urban wastewater treatment plants is usually difficult to meet the demand forbiological nutrient removal, resulting in low efficiency of phosphorus removal. Inaddition, the poor resistance to impact load from the external environment has alsocaused unsatisfactory phosphorus removal. In recent years, in order to solving theproblem that total phosphorus concentration exceeds the discharge standard, wastewatertreatment plants commonly use dosage of the chemical agents to aid in the biologicalphosphorus removal. The combination of chemical phosphorus removal and biologicalphosphorus removal is the future trends of wastewater phosphorus removal process.At present, there are few information about chemically enhanced phosphorusremoval and process operation, and the effect of the dosing point and dosage forchemically enhanced phosphorus removal effects for biological phosphorus removalcapacity of the sludge system are uncertain, as well as the performance of sludge andcapacity of system recovery after stoping dosing. The study will provide technicalsupport for phosphorus removal difficulties solving and design and operation ofchemically enhanced phosphorus removal process in wastewater treatment plant.Through the optimization of coagulant dosage analysis, which also means the typesof chemicals dosing and the dosage, as well as means of dosing, Fe based coagulantswas found to be best by SBR operating. The common wastewater quality parametersand the parameters of sludge performance and microorganism features were discussedwhen dosing Fe based coagulants in different operation stage of SBR and the recoveryability of sludge system was also focused. The conclusions were as below:①The Al and Fe based coagulant can significantly improve total phosphorusremoval efficiency and partly improve the COD removal. The efficency of Fe basedcoagulant was better on phosphorus removal than their counterparts.②The best operation parameters of SBR system was found to be as below: sludgeretention time14d with26℃and pH at7.2as well as DO2-3.5mg/L. The SBRoperation mode was to be hinflow（0.5h）-anarobic（1.5h）-aerobic（4h）-precipitation（1h）-free（1h）, under the condition of which the removal ofphosphorus and other organic matters was considerable effecitive. ③Dosing of ferric and ferrous coagulant improved the removal efficiency ofCOD and PO₄^3--P. This effiency of ferric coagulant was better than ferrous coagulantand the results for post-recovery return. These two coagulants had less influence on theefficency of NH₄⁺-N removal and had a significant effect for SS.④The figure for MLSS, EPS rose and the figure for SVI, the floc size decreasedafter dosing. Chemical agents improved the morphology of the sludge floc, thepromotion of bio-flocculation, sludge settleability. The impacts of adding ferric andferrous coagulant were different on the performance of the sludge: the whole sludgesystem got shocked but its precipitation degree was better in Fe （II） reactor, while theperformance of activated sludge in the reactor of Fe （III） can be quickly recovered afterstop dosing.⑤The activities of nitrifying bacteria and nitrification bacteria were found to beaffected by adding Fe based salts and the impaction in Fe （II） reactor is more serious.