Abstract: The present invention provides treatment of domestic sewage containing oil. The resulting products will be purified water, dry fertilizer, and fuel (gas and liquid) containing no contaminants that could pollute the environment. After the initial settling process, two parallel flows are created: one containing liquid plus crude sediment (0.2 mm and greater) and the other containing liquid and fine particles (less than 0.2 mm), the latter termed "settled domestic sewage". The two flows are treated separately. The settled domestic sewage after treatment in a low-pressure separator that will separate out liquid fuel, followed by aeration, ultrafiltration, and finally sterilization by ozone or chlorine, results in pure water. The biochemical treatment of the sediments results in the production of gas fuel containing mainly methane gas and solid product that after drying and disinfecting is converted into fertilizer.