Adama Science and Technology University (ASTU) wastewater treatment plant (WWTP) is one of thirteen university constructed by The Project “University Capacity Building (UCBP)” managed by GIZ IS Ethiopia. The plant has activated sludge technology with anaerobic sludge digestion and it has the capability to treat 3125 cubic meters per day of domestic wastewater. The main goal of this research was to evaluate the efficiency of the treatment plant and Optimization of the plant for better effluent quality. To evaluate the effluent quality, Laboratory analysis and existing data was used as a main source to determine the characteristic of the existing treatment. The commencement of this research, the effluent from ASTU’s treatment plant only complied with the Biological Oxygen Demand (BOD5) and Chemical Oxygen Demand (COD) standards set by the environmental authority, while the Total Suspended Solids (TSS), Total Kjeldahl Nitrogen (TKN), Ammonia-nitrogen (NH3-N) parameters exceeded the permissible maximum limits. It was evident from the outset that optimization was necessary to ensure all parameters fell within acceptable levels. The optimization process was carried out using a combination of laboratory and field work, along with a computer simulation program known as GPS-X. The thesis details the application of several methods to optimize the process. The first method involved adjusting the treatment parameters on-site based on laboratory test results by adjusting waste activated sludge flow rate of the treatment plant. A significant decrease in TSS (from 205 to 2.49), COD (from 149.5 to 59.71), BOD (from 69.33 to 11.50) was observed after adjusting on-site waste activated sludge flow rate. The second method included the addition of extra plant accessories such as an equalization tank and sand filter, which resulted in improvements in parameters like TSS (from 205 to 1.21), COD (from149.5 to 49.12), BOD (from 69.33 to 4.16). The most significant improvement was observed when the Membrane Bio Reactor (MBR) was replaced with secondary clarifier by considering cost and operation difficulties the recommended three options can be applied for a better effluent quality. Keyword: Performance Evaluation, optimization, secondary clarifier, Membrane Bio Reactor