Phosphorus requirement in high-rate anaerobic wastewater treatment

Abstract

In this study the effect of phosphate limitation on reactor performance and on methanogenic activity was examined. Laboratory scale UASB reactors were fed with gelatin or volatile fatty acids as COD substrate while the phosphorus content of the substrate was varied. Phosphate uptake was investigated using the granular sludge which was developed in the phosphorus-deficient reactors. Phosphorus deficiency reduces methanogenic activity in UASB reactors to 50% of the control. This reduction was found to be reversible by dosage of phosphate. In batch experiments a complete recovery of the maximal methanogenic activity was observed by a dosage of 5 mg PO 4-PI −1. At low concentrations (0.1 g PO 4-Pl −1) phosphate dosage is also profitable. When the applied sludge loading rate was below the methanogenic activity of the sludge under phosphorus-limiting conditions, the treatment efficiency was not affected. The sludge growth however was slightly reduced. Overdosage of phosphate, which in practice is related to high effluent phosphate concentrations, was found to be unprofitable.