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

A biological system for P removal has been developed by using an A/O (anaer obic/aerobic) activated sludge process with a sequencing batch reactor oper ation mode. The effect of three kinds of synthetic wastewater with differen t organic composition has been studied. Evolution of sludge and effluent ch aracteristics from the original sludge to steady state conditions were stud ied, and P and COD profiles during batch A/O cycles were also analysed. A f ast P accumulation in the sludge was detected during the previous acclimati on phases. The presence of higher concentrations of easily biodegradable pr oducts improved the acclimation process and increased the rate at which a c onventional activated sludge was transformed into a phosphorus accumulating microorganism enriched sludge. The steady state P content of the sludge in creased and the VSS concentration decreased in all cases. Acetate in wastew ater 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 s ubstrate used, it is possible that a decrease of Bio-P bacteria number by t he development of another group of microorganisms without P accumulation ac tivity, should be observed. This ratio, and the P sludge content, increased when the wastewater was composed by easier biodegradable products.