Study on the performance of CAST process for phosphate removal under conventional operation mode

The cyclic activated sludge technology(CAST) process was operated under the conventional mode to investigate its performance for phosphate removal. The variation of phosphate concentration in biologic selector and reaction zone were examined in the typical cycle. In addition,the pathway of phosphorous removal and its limiting factors were analyzed,based on which,the proportion of denitrifying phosphate accumulating organisms(DNPAOs) in biomass was measured. The results showed that the average phosphate concentration in effluent of stable CAST system was 1.9 mg/L,giving the phosphate removal rate of 62%. Phosphorous removal in this system was accomplished with the combined action of polyphosphate accumulationg organisms(PAOs) and DNPAOs. Analysis demonstrated that the percentage of DNPAOs in phosphate accumulating organisms was 81.1%.