This document describes upgrades to Attock Refinery Ltd.'s effluent treatment plant (ETP) to enhance its capacity and comply with environmental regulations. The upgrades include: 1) Adding secondary treatment with an activated sludge system and clarifier after primary treatment via dissolved air flotation. 2) Upgrading API separators with scrapers to remove solids, oil skimmers to remove oil, and oil coalescers. 3) Expanding effluent treatment capacity from 100 to 200 gallons per minute and adding biological secondary treatment to remove more contaminants like BOD, COD, and oil/grease.