Oxidation-reduction potential (ORP), pH and dissolved oxygen (DO) can be used to monitor and control biological nutrient removal process in an Sequencing Batch Reactor (SBR) reactor. The objective of this study was to establish control strategies for biological phosphorus and nitrogen removal using ORP, DO and pH profiles. A lab scale SBR system was used. It was observed that when nitrate was fully consumed in the anoxic phase, ORP values were more negative (-55 mV). However, after the consumption of nitrates, phosphate release was observed in the anoxic phase with the provision of true anaerobic conditions. This shows that the anoxic phase was characterized by denitrification and phosphorus release. The break point in the pH and ORP curve in the anoxic period coincided with the end of denitrifying activity at about 10 min of the anoxic phase. The change in the ORP and pH appears to be related to nitrate concentration and these parameters show a nitrate "knee" and the ammonia "valley" during the operation. Therefore, the experimental study showed that pH and ORP values can be used as control parameters for denitrification and biological phosphorus removal. However, it is observed that pH profile provide much information during the oxic phase, whereas ORP in the anoxic phase. (c) 2005 Elsevier Ltd. All rights reserved.