Evaluation of secondary refinery effluent treatment using ultrafiltration membranes

This paper presents an evaluation of the possibilities of using ultrafiltration as a pre-treatment for reverse osmosis, in a double membrane filtration scheme, in order to recycle biologically treated refinery effluent as cooling water make-up. This study focused on establishing the influence of process conditions for ultrafiltration, i.e. pressure, duration of fouling, frequency and duration of backwashing and chemical cleaning, on the rate of fouling and process efficiency. Two ultrafiltration membranes provided by the same manufacturer, made of polyethersulphone/polyvinylpirollidone, with the same molecular weight cut-off (150,000 Da), but with different coatings have been used. A comparison between their experimental behaviour, under the same process conditions, was made in a laboratory scale system operated in dead-end mode, at constant transmembrane pressure, using as influent secondary refinery wastewater. The effect of reversible/irreversible fouling was studied by means of clean water flux restoration after different cleaning procedures. Experimental results showed that the A-LF (low fouling) membrane was easy to clean by backwashing or enhanced backwashing, having a better 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 have been obtained, for ultrafiltration tests, irrespective of process conditions. The best chemical cleaning agents, considering the results of relative flux restoration, were found to be citric acid and sodium hydroxide.