Effect of wastewater composition on the development of an activated sludge biological phosphorus removal system

A biological system for P removal has been developed by using an A/O (anaerobic/aerobic) activated sludge process with a sequencing batch reactor operation mode. The effect of three kinds of synthetic wastewater with different organic composition has been studied. Evolution of sludge and effluent characteristics from the original sludge to steady state conditions were studied, and P and COD profiles during batch A/O cycles were also analysed. A fast P accumulation in the sludge was detected during the previous acclimation phases. The presence of higher concentrations of easily biodegradable products improved the acclimation process and increased the rate at which a conventional activated sludge was transformed into a phosphorus accumulating microorganism enriched sludge. The steady state P content of the sludge increased and the VSS concentration decreased in all cases. Acetate in wastewater caused bad sludge settling and soluble starch caused slow evolution to steady state conditions. Different stoichiometric ratios of mg P released per mg COD removed in the anaerobic phase were observed. Depending on the substrate used, it is possible that a decrease of Bio-P bacteria number by the development of another group of microorganisms without P accumulation activity, should be observed. This ratio, and the P sludge content, increased when the wastewater was composed by easier biodegradable products.