BIOLOGICAL PHOSPHORUS UPTAKE UNDER ANOXIC AND AEROBIC CONDITIONS

Biological phosphorus removal was investigated under anoxic and aerobic conditions. Tests were made to establish whether phosphorus accumulating bacteria can take up phosphate under anoxic conditions and thus utilise nitrate as oxidant. Furthermore, it was tested how the amount of organic matter taken up by the phosphorus accumulating bacteria during the anaerobic phase affects the total denitrification rate, as well as the rate at which the phosphorus accumulating bacteria take up phosphate under anoxic conditions. The tests were conducted as batch experiments in 21. reactors with activated sludge from two different pilot plants incorporating phosphorus removal. The results showed that the phosphorus accumulating bacteria can be divided into two groups in respect of process: one group capable of utilising only oxygen as oxidant and another group capable of utilising both oxygen and nitrate as oxidant. The phosphorus uptake was more rapid under aerobic conditions than under anoxic conditions. The explanation of this is that all phosphorus accumulating bacteria take up phosphate under aerobic conditions, whereas only part of the phosphorus accumulating bacteria take up phosphate under anoxic conditions. There was a linear relationship between the amount of acetate taken up in the anaerobic phase, the denitrification rate and the phosphorus uptake rate.