What wastewater treatment processes are used in refineries?

Refinery wastewater treatment: Primary treatment - API separator removes free oil by gravity (density difference), CPI (corrugated plate interceptor) for improved separation, dissolved air flotation (DAF) for emulsified oil. Secondary treatment - biological treatment using activated sludge or fixed film to remove dissolved organics (BOD, COD), phenols, and ammonia. May need equalization for shock loads. Tertiary treatment - sand filtration for suspended solids, activated carbon for residual organics, membrane processes for reuse quality. Sour water stripping - removes H2S and NH3 from sour water before discharge to biological treatment. Effluent limits: COD <100-150 mg/L, oil <10 mg/L, phenol <0.5 mg/L, sulfide <0.5 mg/L typically. Zero liquid discharge (ZLD) increasingly required in water-stressed regions.