Computers have become a vital part of every modern wastewater treatment plant. They can be used for design, analysis, and control of the treatment process. Mathematical modelling and simulation of various process configurations, load conditions, and operational strategies lead to better understanding and improved design and operation. Computer assisted analysis of process performance and automatic control of plant units aid reduce expenses related to energy, chemicals, and man power. Stringent disposal constraints imposed in most modern countries require application of sophisticated computerized control systems to ensure high quality effluents. The sequencing batch reactor system is similar to the conventional activated sludge process in its ability to achieve biological removal of organic carbon and nutrients by a single sludge. However, due to the non-steady-state nature of the process, and to the large substrate and nutrient gradients occurring during the operating cycle, some modifications in the traditional activated sludge waste characterization and process modelling should be considered.