Australian Journal of Basic and Applied Sciences, 5(8): 446-455, 2011 ISSN 1991-8178 Corresponding Author: M. F. Rahmat, Department of Control and Instrumentation Engineering, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Malaysia. 446 Control Strategies of Wastewater Treatment Plants 1 M.F. Rahmat, 2 S.I. Samsudin, 1 N.A. Wahab, 3 Sy Najib Sy Salim, 1 M.S. Gaya, 1 Department of Control and Instrumentation Engineering, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Malaysia. 2 Department of Industrial Electronics, Faculty of Electrical and Electronics, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka Malaysia 3 Department of Control,Instrumentation and Automation Department, Faculty of Electrical Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka Malaysia. Abstract: The objective of the current study is to investigate various control strategies implemented to wastewater treatment plants. The paper starts with discussion in modeling part of wastewater system and continues with designation of control objectives and control parameters. Subsequently, the implementations of common control structures including feedback, feedforward-feedback, supervisory and hierarchical controls are explained. The study is exclusively emphasized on four control techniques. Model predictive control performs superior control in optimizing nitrogen removal based on predictions of future behavior of wastewater systems. The performances of PID control in dissolve oxygen and nitrate control is improved significantly with multivariable configuration. Similar results achieved by data-driven approach compared to default PI simulation. Finally, artificial neural networks are commonly suggested for modeling and prediction purposes. A study is emphasized on Benchmark Simulation Model No. 1. The paper serve as a reference and for future research improvements in developing new advanced control techniques for wastewater field that aims in achieving stringent effluent quality standards. Key words: Wastewater treatment plant, control strategies, BSM1 benchmark. INTRODUCTION Wastewater treatment plants (WWTPs) are mainly affected by large disturbances and uncertainties related to the influent wastewater’s composition. The plants naturally aim to remove suspended substances, organic material and phosphate from the water before releasing it to the recipient. Generally, there are three different steps involve in the WWTPs include mechanical treatment, biological treatment and chemical treatment. The best technology available to control the discharge of pollutants proved in biological process. Activated sludge process (ASP) becomes a frequent concepts for biological process in which microorganism are oxidized to organic matter. The organic material is then transformed to carbon dioxide and some is incorporated into new cell mass. The new cell mass forms sludge that contains both living and death microorganisms and thus contains organic material, but also some phosphorous and nitrogen (Anders, 2000). In wastewater, there are several forms of nitrogen components include ammonia (NH 3 ), ammonium (NH 4+ ), nitrate (NH 3! ), nitrite (NO 2! ) and organic matter (Wahab, 2009). Nitrogen is an essential nutrient for biological growth and acts as one of the main constituents in all living organisms. The presence of higher nitrogen in effluent wastewater invites a numbers of problems (Barnes and Bliss 1983). Initially, the increased numbers of aquatic plants and algae are originated from nitrogen and this leads to oxygen shortage because of degrading process. Next, high concentrations of ammonium in the effluent possible to reduce the oxygen stored in the recipient. It is noted that oxygen is heavily consumed to oxidize ammonia to nitrate. Thus, minimization of nitrogen level in the incoming wastewater is strongly demanded. As a result, two biological processes are proposed. The most common one is called a nitrification or ammonium removal, where ammonium in aerobic conditions is converted into nitrate by autotrophic bacteria. Secondy, a denitrification process or nitrate removal where nitrate is converted to nitrogen gas by heterotrophic bacteria under anoxic conditions with the aids of COD as reducing agent (Sotomayor et al., 2001).