Influence of high acetate concentrations on enhanced biological phosphorus removal

The effect of increased acetate concentration on the process of enhanced biological phosphorus removal was investigated in a sequential batch bioreactor treating synthetic wastewater in a 6-h cycle. Anhydrous sodium acetate was used as the sole carbon source during the experiment and corresponded to a chemical oxygen demand concentration. The phosphate-accumulating organisms were initially cultured for 70 days and the chemical oxygen demand concentration was gradually increased to the final concentration of 1800 mgO₂ L⁻¹ under conditions suitable for the growth of the phosphate-accumulating organisms. Successful cultivation of the phosphate-accumulating organisms was only possible if the acetate concentration in the influent did not lead to an excessive concentration of residues in the sludge after the anaerobic phase (estimated at a chemical oxygen demand concentration of 100 mgO₂ L⁻¹), which then passed into the aerobic phase. Cultivation continued for the next 67 days. During this time, the sludge was exposed five times to high acetate loading at different concentrations (corresponding to a chemical oxygen demand concentration of 250–1000 mgO₂ L⁻¹) to test the performance of the enhanced biological phosphorus removal. High acetate concentrations had no effect on the anaerobic phase of enhanced biological phosphorus removal, as the phosphate-accumulating organisms performed well in anaerobic phosphorus release and acetate assimilation in all five tests. However, the effect of residual acetate in the aerobic phase was detrimental to the aerobic phase of enhanced biological phosphorus removal, as the phosphate-accumulating organisms were prevented from assimilating phosphorus in the aerobic phase.