Abstract
The global demand for petrochemical and petroleum industry products unavoidably generates large volumes of oil refinery wastewater (ORW). The complete treatment, reclamation and disposal of the ORW to an acceptable environmental limit is currently a challenge to most of the petroleum industries. With the current development in conventional treatment methods viz. coagulation, dissolved air flotation (DAF), and biological and membrane separation processes. DAF, which is well-established separation process, effectively employs microbubbles as a carrier phase for separation. Although, DAF is frequently used in combined water and wastewater treatment plants, its fundamental characteristics and operational parameters have not yet been fully investigated for the treatment of ORW. In this study, the correlation and effects of the parameters understudy (coagulant dosage, air saturator pressure, air-water ratio and rising rate) on chemical oxygen demand, soap oil and grease, turbidity and total suspended solids removal from ORW were examined experimentally using a laboratory DAF system. The results showed that increasing the saturator working pressure and the rising rate had less effect on the system, than increasing the air-water ratio. The agglomeration of the oil droplets was found to depend solely on the polyaluminum sulphate (PAS) dosage to destabilize the oil droplets. The DAF treatability performance showed over 80% removal of the contaminants at optimum conditions of pH of 5, PAS dosage of 10 mg/L, rising rate of 15 minutes, air saturator pressure of 300-500 kPa, and air-water ratio of 5-15%. The PAS dosage was found to be the most significant factor. Therefore, a moderate increase of the PAS dosage under these optimum conditions will increase the DAF efficiency in the treatment of ORW.
Highlights
The rational for wastewater treatment, water protection, conservation and reclamation for water usage are vital elements for water management
This study aims to investigate the interfacial effects of the chemical and the oil emulsion on a laboratory dissolved air flotation (DAF) unit, via the influence of coagulation, air bubble generation and oil droplet-air bubble contact time
The air saturator pressure regulator allowed the pressure to be investigated from 200-600 kPa, likewise the air-water ratio varied from 520%
Summary
The rational for wastewater treatment, water protection, conservation and reclamation for water usage are vital elements for water management. In South Africa, the oil refinery industries have a very high specific water intake (SWI). From SWI between 0.51 and 0.67 m3/t crude, as much as 40% of this water is discharge as effluent into the municipal sewer system (Tetteh & Rathilal, 2018). This wastewater is basic with high contents of soap oil and grease (SOG), organics and inorganics compounds and other pollutants, which are non-biodegradable; treatment is essential before discharge(Diya’Uddeen et al, 2011). The amount of oil, which is the main component in oil refinery wastewater (ORW), has been strictly regulated by the South Africa legislation (The National Water Act, 1988)
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