The role of metal cations in enhanced biological phosphorus removal (EBPR) from wastewater by activated sludge was investigated. Potassium and magnesium were simultaneously required for efficient EBPR. Neither potassium nor magnesium could induce enhanced phosphorus uptake on its own.

Cations were co-transported with phosphorus during anaerobic release and aerobic uptake. With every mole of phosphorus, between 0.23 and 0.43 moles of potassium and between 0.25 and 0.36 moles of magnesium were co-transported. Calcium appeared to be involved in EBPR to a limited extent, and did not seem to chemically co-precipitate with phosphorus.

For every gram of chemical oxygen demand (COD) consumed by the sludge in the anaerobic zone of the experimental systems, 0.22 grams of phosphorus were released at a 15 d mean cell residence time and 20°C. Approximately 20 mgCOD/L were taken up by the sludge before any phosphorus was released. Phosphorus release could be described by first order kinetics.

Phosphorus uptake under aerobic conditions could also be described by first order kinetics. The total phosphorus uptake in the anoxic and aerobic zones of the experimental systems was proportional to the total phosphorus release in the anaerobic zone. For every gram of phosphorus released, between 1.1 and 1.2 grams of phosphorus were taken up by the sludge regardless of the operating conditions. Phosphorus uptake by the sludge in the aerobic phase was hindered by the presence of acetate in solution. Uptake commenced only after all of the available acetate was first consumed by the sludge.

Distilled water, 0.85 percent sodium chloride, and 5 mM and 50 mM ethylene diamine tetra-acetic acid were used to extract chemically precipitated phosphorus from EBPR sludge. Each of the washing media seemed to cause some cell lysis, suggested by the extraction of non-reactive phosphorus. The duration of wash seemed to affect the extent of cell lysis.

Phosphorus fractionation extracts were assayed for deoxyribonucleic acid to determine whether cell lysis occurred. The assay was apparently not affected by the contents of the sludge supernatant.