Evaluation of secondary refinery effluent treatment using ultrafiltration membranes

This paper presents an evaluation of the possibilities of using ultrafiltra tion as a pre-treatment for reverse osmosis, in a double membrane filtratio n scheme, in order to recycle biologically treated refinery effluent as coo ling water make-up. This study focused on establishing the influence of pro cess conditions for ultrafiltration, i.e. pressure, duration of fouling, fr equency and duration of backwashing and chemical cleaning, on the rate of f ouling and process efficiency. Two ultrafiltration membranes provided by th e same manufacturer, made of polyethersulphone/polyvinylpirollidone, with t he same molecular weight cut-off (150,000 Da), but with different coatings have been used. A comparison between their experimental behaviour, under th e same process conditions, was made in a laboratory scale system operared i n dead-end mode, at constant transmembrane pressure, using as influent seco ndary refinery wastewater. The effect of reversible/irreversible fouling wa s studied by means of clean water flux restoration after different cleaning procedures. Experimental results showed that the A-LF (low fouling) membra ne was easy to clean by backwashing or enhanced backwashing, having a bette r flux restoration and a higher efficiency as production and operation than the A membrane. Average removal efficiencies of 98% for turbidity and TSS and 30% for COD h ave been obtained, for ultrafiltration tests, irrespective of process condi tions. The best chemical cleaning agents, considering the results of relati ve flux restoration, were found to be citric acid and sodium hydroxide. (C) 1999 Elsevier Science Ltd. All rights reserved.