Abstract
Activated sludge which had been subjected to an anaerobic-aerobic cycle showed high rates of anaerobic release of phosphate, followed by excess phosphate uptake under aerobic conditions. Addition of carbon and energy sources was essential to anaerobic release of phosphate, and no significant release of phosphate occurred in the absence of added substrates. Heating activated sludge (90°C for 2min) strongly inhibited anaerobic release of phosphate. Treatment of activated sludge with chemical reagents including sodium hypochlorite, benzalkonium chloride and ethanol greatly inhibited phosphate release. Increasing the osmotic pressure in the medium adding sodium chloride and sucrose also inhibited the release. These results showed that the anaerobic release of phosphate from activated sludge which had been acclimated to an anaerobic-aerobic cycle is principally attributable to a biological mechanism.
