The cities of Iraq in general and the city of Al Diwaniyah in particular are characterized by the fact that the majority of households use septic tank to dispose of sewage, leading to contamination of ground and surface water and a disturbance to the environment. The objective of this study is to protect the water and soil sources from the risk of pollution, eliminate the process of perfusion and thus, reduce costs, maintain public health, as well as design and implement the proposed purification unit for domestic wastewater treatment. A domestic wastewater treatment unit has been improved to meet the standard specifications for the quality of the effluent wastewater. In this study, a compact non-electric sewage treatment unit was improved and implemented. Treatment is based on an effective modern biological purification process. Experimental verification and analysis of results were performed to demonstrate the improvement of physical and chemical parameters. The performance of the septic tanks-bioreactor gave satisfactory results. The removal efficiencies of Total Biochemical Oxygen Demand (BOD), Total Chemical Oxygen Demand (COD), NH4-N, Total Nitrogen and Total Suspended Solid (TSS) were 96.9%, 84.6%, 78.8%, 79.9% and 95.3%, respectively.