Purification of biologically treated Tehran refinery oily wastewater using reverse osmosis

In this paper, results of an experimental study on separation of oil from industrial oily wastewaters with combined biologically method/reverse osmosis (RO) process for purification of Tehran refinery oily wastewater is presented. The effects of different operating parameters on permeation flux and TDS rejection were investigated. Taguchi method (L-9 orthogonal array (OA)) was used initially to plan a minimum number of experiments. Analysis of variance (ANOVA) was applied to calculate sum of square, variance, ratio of factor variance to error variance and contribution percentage of each factor on response. The results showed that TMP and temperature have significant effects on the response. Permeation flux was found to increase with increasing transmembrane pressure (TMP), cross flow velocity (CFV) and feed temperature at constant feed concentration but rejection slightly decreases. The pH effects were found to be complex. By increasing acidic and basic nature of the feed, permeation flux was found to increase but rejection decrease. At original oily wastewater composition, high rejection of TDS (87%), COD (95%), BOD 5 (95%), TOC (90%), turbidity (82%) and oil and grease content (87%) along with complete rejection of color, free oil and TSS were achieved with a reasonably high permeation flux of 50 L/m(2) h. Also, the results show that cake filtration model can well predict the flux decline.