Industrial wastewater is wastewater that originates from industrial processes and often contains specific contaminants that are not found in domestic wastewater. It may contain chemicals, heavy metals, organic compounds, oils, greases and other pollutants resulting from the production or cleaning of industrial plants. The composition of industrial wastewater varies depending on the industry (e.g. chemicals, food, metal processing) and usually needs to be treated before being discharged into the public sewage system or watercourses. Treatment often involves special processes such as chemical precipitation, flotation, filtration or biological degradation processes to remove pollutants.