Effect of activated carbon on BOD and COD removal in a dissolved air flotation unit treating refinery wastewater

The effects of powdered activated carbon (PAC) on the performance of a pilot-scale laboratory dissolved air flotation (DAF) unit were investigated. Refinery wastewater of different pollutant concentrations was treated and the effects of different operating parameters on the removal efficiency of pollutants in terms of biological oxygen demand (BOD) and chemical oxygen demand (COD) were studied. A circular pilot-scale DAF unit with conical bottom was used and the operating parameters investigated included flow rate, recycle ratio, saturation pressure and the concentration of PAC added. It was found that for dosages of activated carbon in the range of 50–150 mg/l, the removal efficiencies for BOD increased from 27–70% to 76–94% while those for COD increased from 16–64% to 72–92.5% for inlet values of 45–95 mg/l and 110–200 mg/l for BOD and COD respectively. Such findings represent considerable improvement in the performance of the dissolved air flotation unit.