| Nitrogen and phosphorus are the main influencing factors of eutrophication. Sincenitrogen can be auto-synthesized by aquatic plants and animals, and phosphorus isthe exogenous input, the control of phosphorus is more important than nitrogen control.According to the GB18918-2002"Cities Sewage Treatment Plant Pollutant DischargeStandard" promulgated in2006, urban sewage treatment plant effluent must not behigher than0.5mg/L (level A) since January1,2006. However, it cannot approach theLevel A standard by the usage of biological phosphorus removal due to the influence ofinflow water quality, environmental factors and management. Therefore, sewagetreatment plants have adopted the chemical method (addition of coagulant) to enhancethe effect of phosphorus removal.Based on the previse research, FeSO4has been selected as the preferredauxiliary medicament of phosphorus removal in SBR. The characteristics of phosphorusremoval and subsequent effects were concluded as the following:（1）The optimal operation mode of SBR process: water infection-anaerobic stirring (1hour)-aeration (4hours)-anoxic (1.5hours)-staticprecipitation (1hour)-drainage mud (0.25hours). CODcr, NH3-N and total nitrogen(TN) removal rate reached90%,87%and75%, respectively. However, the totalphosphorus (TP) removal efficiency of the system is not ideal, the influentTP concentration was6.2~7.6mg/L, and TP in the effluent is within the range of2.7~3.7mg/L. By adding ferrous sulfate at the end of the aeration based on Fe/TP molarratio of1.5, the0.2~0.5mg/L of effluent phosphorus can reach the "Cities SewageTreatment Plant Pollutant Discharge Standard" level A standard. After addingmedicament, pH value decreased from7.63to7.46which is still in the neutral rangeand is suitable for microbial activity in sludge; MLSS increased6.6%and the amount ofsludge increased; SVI value decreased5.3%with a better sludge settlingperformance, which is more easily through the0.45m membrane filter.（2）Iron phosphate in the wastewater can be dissolved around30%in anaerobic stage,Fe3+of the dissolution was reduced to Fe2+. The concentration of PO43+at the end of theanaerobic period was higher than that in water infection due to the dissolution of PO43+.Due to the uncompleted precipitated in the aeration; there was a phosphorus Over-abundance with an increase of iron phosphate content. （3）Antagonistic effects will be produced on potassium uptake of activated sludgewhen the content of iron phosphate in the sludge increased to a certain degree, leadingto a lower efficiency on phosphorus removal. Therefore, it is necessary to control thecontent of iron phosphate in the system. Moreover,30%potassium ion in waste wateris absorbed by iron phosphate. |
PDF Full Text Request