Nairobi city has experienced a speedy urban increase in the populace in the last few years as a result of rural-urban migration as well as natural growth. As a result, social amenities have been overburdened due to increased demand. Emerging challenges in wastewater treatment and increased knowledge about the consequences of water pollution have led to a common desire and need for better water quality. To maintain acceptable water quality standards, conventional wastewater treatment plants are required to meet both local and international standards, before discharging to reduce negative impacts on the receiving river systems. Discharging of effluents that meet regulatory discharge standards subsequently, promotes the protection of diminishing freshwater resources. Kariobangi Sewage Treatment Works is a conventional wastewater treatment plant and is one of the two main sewage treatment works serving Nairobi city. The plant plagued with severe pressure from industrialization, urbanization and rapid population resulted in the treatment works not being able to accommodate the waste generated from the city centre and the areas channelling their wastes to the plant which resulted in the wastewater being discharged directly into the rivers. Due to the myriad of problems that arose the Government of Kenya with the funding assistance of the African Development Bank decided to undertake a project that included the restoration and rehabilitation of the plant. The study is therefore aimed at establishing the treatment efficiency of the plant after undergoing rehabilitation