Increase in the efficiency of phosphorus removal from wastewater is becoming of outmost importance in order to comply with the quality standards foreseen by the international codes. In fact, efficiencies not exceeding 30% are usually ensured by traditional wastewater treatment plants through settling and removal of excess sludge. The Phostrip, Bardenpho and A/O processes, recently developed and implemented in industrial plants, have allowed for substantial improvements in the biological removal of phosphate. Aim of the present paper is to describe how the efficiency of the original A/O process has been optimized in a laboratory-scaled single basin, through an alternate sequence of aerobic and anaerobic phases. Using a ratio of aerobic/anaerobic phases duration of 0.6, phosphorus removal yields higher than 90% have been ensured feeding wastewater containing phosphorus levels up to 100 mg/l.