Integrated membrane pilot plant for refinery wastewater treatment in order to produce boiler feedwater

Treatment of Tehran refinery effluent, high in oil and grease (O&G), total organic carbon (TOC), and total dissolved solids (TDS), as boiler feedwater was proposed by a treatment scheme comprising microfiltration (MF), ultrafiltration (UF), and reverse osmosis (RO). To find optimum conditions for each membrane operation, effects of operating parameters such as transmembrane pressure (TMP), flow rate (Q), and temperature on permeation flux and TOC or TDS removal efficiencies were investigated. A tubular ceramic MF (α-Al2O3) membrane module was employed for treatment of oily wastewater before UF. The optimum operating condition was found as TMP of 1.25 bar, Q of 32.5 L min-1, and temperature of 32.5°C. MF reduced turbidity and solid particles content of the wastewater for UF. UF was investigated in this study to reduce turbidity and O&G of the wastewater prior to RO, which was necessary to reduce salinity to an acceptable level for using as boiler feedwater. The optimum UF experiments were found at TMP of 2 bar, temperature of 25°C, and Q of 12 L min-1; using a spiral wound polyacrylonitrile membrane module. UF reduced O&G and turbidity almost completely. Another spiral wound Polyamide RO membrane module was used to finally treat the wastewater. The optimum condition was found as TMP of 15 bar, temperature of 30°C, and Q of 10 L min-1. Analysis of the oily wastewater treated by the MF–UF–RO integrated membrane system exhibited 100% reduction in total suspended solids (TSS), 99.43% reduction in turbidity, 99.87% reduction in O&G, 97.43% reduction in TOC, and 97.93% reduction in TDS. As a result, the effluent of MF–UF–RO integrated membrane system could be recommended as boiler feedwater.