The efficiency of a Waste Water Treatment Plant (WWTP) can be estimated using process simulation. Process simulators (software) used for biological waste water treatment are Activated Sludge Simulation (ASIM), Sewage Treatment Operation and Analysis Over Time (STOAT), and GPS-X. A comparative chart on these software are assessed. Based on the ease-to-use, ASIM was selected to find out Chemical Oxygen Demand (COD) removal efficiency of a biological waste water treatment. This paper reviews the methodology utilized to find out the COD removal efficiency. The average COD removal efficiency of the treatment is found to be 62.734%. To further improve its efficiency, few suggestions were suggested. Instead of using a large volume of reactor, small number of reactors cascading its volume can be in use. Coupling membrane technology with activated sludge is an expensive method. Bardpheno process, where anoxic-aerobic stages are placed in an alternative manner, can also improve the COD removal efficiency of a biological waste water treatment.