Optimal Operation And Automatic Control Of The Chemical Phosphorus Removal In Municipal WWTP

Chemical-aid phosphorus removal process is widely used recently in order to meet much more stringent requirement for the TP in municipal wastewater treatment plants (WWTPs) in China. However, the chemical coagulant dosage was often given based on experiences in most of chinese WWTPs and that brings a lot of problems such as chemical-waste, sludge production increase and endanger for biological phosphorus removal process. The object of this research is that : to develop opration optimization and on-line control system of Chemical-aid phosphorus removal process based on laboratory and real WWTPs investigation; to support effective operation of Chemical-aid phosphorus removal process. The results was following :(1) The properties of coagulants was very important for the phosphorus removal efficiency. The addition coefficientβvalue depends on the type of coagulants, It should be taken to obtain individiual value by specifical tests before real addition. theβvalue of Poly - aluminum iron is in the range of 1.0~5.0 in this research.(2) Control model included timing control, flow feed-forward control, load feed-forward control and PID feed-back control. The results show that the traditional method of excessive constant dosing cannot ensure to meet the discharge standard steadily, and that would induce chemicals-waste. When the optimal constant control dosage was 0.26 mgFe/L, the effluent orthophosphate-p concentration was below 1.0 mg/L stably. When the dosage was 0.40 mgFe/L, the effluent orthophosphate-p concentration droped below 0.5 mg/L. The timing control model would be a better pattern in case of staedily water quantity and water quality. Many factors such as fluctuation of water quality and quantity, biological sludge concentration in the pool need to be considered in feed-forward control, prediction dosing could be established by this way. PID feed-back control could ensure the effluent orthophosphate-p concentration under 1.0 mg/L, almost 0.5 mg/L, when the dosage was 0.27 mgFe/L. In a word , PID feed-back control was the best control model in this research. (3) Chemical coagulants bring some negative effects to the biological phosphorus removal process. Al3+ has stronger inhibitory effects than Fe3+ on the activated sludge OUR. Al3+ shows different inhibitory effects on ntrosobacterica and heterotroph in biological process and almost no notabale effects on nitrobacteria was founded.