PHYSICAL/CHEMICAL TREATMENT FOR REFINERY WASTEWATER

Environmental compliance is very important to Saudi Arabian refineries and the use of non-traditional treatment methods are being considered to meet constraints imposed by local conditions and facility operational requirements. High concentrations of pollutants, high Total Dissolved Solids (TDS), high temperature and extreme variability in wastewater parameters make traditional biological oxidation a questionable solution for the wastewater treatment needs at some facilities. The high removal efficiencies and less than optimum conditions for biological treatment indicate that alternative treatment schemes utilizing physical/chemical operations rather than biological oxidation could offer a more reliable solution for complying with government discharge standards.Wastewater treatment needs for Saudi Arabian refineries are very challenging. Saudi Arabian discharge standards require that the influent concentrations of phenol and ammonia be reduced to 0.1 and 1 mg/L, respectively. At one refinery, this requires the influent concentration of phenol to be reduced from highs of over 60 mg/L and the ammonia concentration to be reduced from peaks that are over 80 mg/L. The wastewater stream at this same refinery has a temperature that is typically over 50 °C and has a TDS that can rapidly vary from 8,000 to 35,000 mg/L. BOD5 in this wastewater stream is typically low and there are intermittent discharges of contaminants that may be inhibitory or toxic to biological systems.The use of conventional biological oxidation systems at this refinery was questionable under these conditions. Extremely large equalization tanks would be required to buffer the variability of the wastewater contaminant concentrations and cooling would be required to reduce the temperature to a more normal range. After correcting for these needs, the treatment system would sometimes need to, achieve very high removal efficiencies. It is uncertain whether a biological treatment system can achieve the required removal efficiencies under the conditions that exist at this refinery.USFilter was engaged to conduct an engineering study to evaluate alternative wastewater treatment operations for this refinery and determine whether physical/chemical treatment systems could be used to meet compliance requirements with a higher level of reliability than could be expected with biological treatment. An extensive literature survey was conducted to identify potential treatment systems that could be adopted for this application. Many options were evaluated and the best choices were selected for bench scale testing with batches of wastewater from one refinery. The technologies that were identified in the bench scale testing as capable of removing the high ammonia and phenol concentrations were then field pilot tested for several weeks at this refinery. USF then developed a treatment train that utilized only physical/chemical treatment options. A cost analysis of this system determined that it was economically viable, considering the additional mechanical constraints imposed by the feed.The final treatment train utilizes only physical/chemical treatment steps to achieve compliance with government discharge limitations. After conventional free oil removal, the wastewater is fed into columns containing a polymeric resin that can adsorb organic contaminants. This resin was tested and found to be capable of removing the test's organic indicator contaminant (phenol) to approximately 1 mg/L. Test data indicated that the resin was also effective at removing other organic contaminants. Granulated activated carbon columns follow the resin columns and provide polishing to less than the 0.1 mg/L of phenol – the discharge limitation. The ammonia is removed in a venturi stripper to concentrations around the 1 mg/L limitation. The wastewater stream passes through a breakpoint chlorination step to assure that the ammonia meets the discharge limitation. The final discharge was demonstrated to be in compliance with all Saudi Arabian government discharge limitations.