pollutant contributions may come from both direct and indirect point sources direct point sources discharge wastewater directly into a water body whereas indirect point sources discharge wastewater to a publicly owned treatment works which in turn discharges directly to surface waters to reduce pollutants in influent wastewater the industrial pretreatment is required the influent wastewater with the chemical oxygen demand lower than biological oxygen demand is required to have the pretreatment to lower the value of biological oxygen demand for the wastewater with high total organic carbon the removal of total dissolved ions is required as additional step of pretreatment process