Potassium removal accompanied by enhanced biological phosphate removal

Abstract

The effects of potassium on excess uptake of phosphate in an aerobic-anaerobic activated sludge process were examined by the fill-and-draw procedure. The presence of sufficient potassium was necessary for excess uptake to occur. The contents of potassium and phosphate in the sludge at the end of each cycle of the process were correlated with each other by a non-linear equation, with some scattering. However, the sum of the molar ion valences of magnesium ( Mg) and potassium ( K), 2 Mg + K, was well correlated by a linear equation with the moles of P expressed as mmol/g-VSS, with a correlation coefficient of 0.993. When the potassium concentration was insufficient for the enhanced uptake of phosphate, its concentration in treated water was of the order of 0.1 mg/ l. In the first anaerobic period phosphate was released into the liquid phase, but potassium was released after initial instantaneous removal, and in the successive aerobic period they were both taken up again.