Biological removal of phosphorus from wastewaters by alternating aerobic and anaerobic conditions

A new process alternating aerobic and anaerobic conditions has been tested for continuous removal of phosphorus from wastewaters. Preliminary batch runs have been carried out at different temperatures (5 ÷ 35°C) to study the effect of stress related to changes of temperature, inoculating a synthetic medium with the biomass from the same plant operating in continuous mode. The continuous system, which appeared capable of ensuring phosphorus removals higher than 90% at relatively high phosphate levels, is now studied mainly during the transitions between aerobic and anaerobic stages. The present results show, for the first time, a direct influence of dissolved oxygen level on pH and allow reasonable hypotheses on the mechanisms for both carbon and phosphorus routes.