INFLUENCE OF NUTRIENT CONCENTRATION IN NEW OPERATING CRITERIA FOR BIOLOGICAL REMOVAL OF PHOSPHORUS FROM WASTEWATERS

The actual practicability of biological treatment of effluents heavily polluted by phosphoric compounds is evaluated in this paper. Preliminary batch tests have shown that high COD levels inhibit phosphorus release during anaerobic conditions but allow, at the same time, a more efficacious removal during the subsequent aerobic stage. Removal yields exceeding 60% have been calculated for an influent COD level of about 840 mg/l. The A/O process, suitably modified so as to alternate aerobic and anaerobic phases in the same reactor, has been tested for the biological removal of phosphorus in synthetic wastewaters with high phosphate concentrations. The start-up phase, carried out with a synthetic solution having a starting phosphorus concentration of 10 mg/l, showed average phosphate and COD removals of 78 and 90%, respectively. The results obtained after reaching steady-state conditions, by feeding P concentrations up to 100 mg/l, seem to indicate this process as an excellent means of reducing phosphorus emissions into the environment and therefore may contribute to the solution of eutrophication-related problems. Removals higher than 90% have been assured for wastewaters containing phosphate levels up to 70 mg/l; at higher concentrations, the system proved capable of tolerating phosphate overloading for no more than 10 days; yield then rapidly fell to zero.