Removal of Oil and Grease and Chemical Oxygen Demand from Oily Automotive Wastewater by Adsorption after Chemical De-emulsification

US EPA has proposed new categorical pretreatment standards for the wastewater generated by the Metal Products and Machinery industry, which includes all automotive plants. The oil and grease (O&G) standard (17 mg/L monthly average) is one to two orders of magnitude lower than Ford's current discharge limits. The rationale for this low standard is to remove most organics from the wastewater. Most engine and transmission plants will not meet the standard without modification. Therefore, adsorption was studied as an add-on option to polish the effluent from the existing treatment process, either chemical de-emulsification or ultrafiltration. Five adsorbents (powdered activated carbon, anthracite, and three modified clay adsorbents) were investigated by developing adsorption isotherms for O&G and chemical oxygen demand (COD) using wastewater collected from a Ford plant. Activated carbon had the highest adsorption capacity, whereas anthracite had the lowest. For a typical O&G concentration range (0 to 30 mg/L) expected in the effluent after chemical de-emulsification or ultrafiltration, activated carbon was found to outperform all clay adsorbents studied by over an order of magnitude in terms of both adsorption capacity and costs. The removal of COD via adsorption showed a trend similar to that of O&G.