In the present contribution, different combinations of control strategies based on PI, MPC and Fuzzy controllers are implemented with a prime concern of improving the quality of the discharge and reducing the operational expenditure in a full scale wastewater treatment plant. The Benchmark Simulation Model No.2 (BSM2) is used as the working platform. The control objective is to maintain the dissolved oxygen concentration in the fourth tank by manipulating the oxygen transfer coefficients of third, fourth and fifth tanks in the biological wastewater treatment. PI and MPC are used at the lower level whereas MPC and Fuzzy controllers are used at the higher level. The effluent violations are reduced for all the proposed control schemes. It is also observed that PI-MPC results in best Effluent Quality Index (EQI) and PI-Fuzzy results in best Operational Cost Index (OCI).