Wastewater treatment will vary depending on the nature, age and size of the refinery; however, figure a typical approach (one that is increasingly encountered) for separating effluent into at least three systems:

• «contaminated» storm water;
• process water;
• deballasting water.

This segregation becomes essential when the objective is to optimise recycling, after processing, of low salinity effluent to cooling, fire water storage and process systems and even to LP or MP – HP boilers.

Process water emanates from refinery units (AD, VD, FCC ,HDS, miscellaneous cracking, visbreaking…). Effluent produced by desalinators and the FCC (catalytic crackers) are the most saline and often polluted with sulphides which justifies a preliminary stripping and/or oxidation treatment before undergoing oil removal by flotation and biological treatment.