Refinery Wastewater Treatment for 'zero Liquid Discharge'

Entire wastewater from a large refinery was selectively treated for oil removal, then for BOD/COD removal and comingled with freshwater cooling tower blowdown. After equalization of the streams divalent cation were reduced by physical chemical treatment followed by multi-pass multistage Reverse Osmosis membrane process. Reverse Osmosis brine was further treated with falling film thermal evaporator. More than 95% of the water was recovered.