Effect of hydrocarbon contaminants on the performance of RO membranes

This paper is related to potential problems associated with the desalination performance of reverse osmosis (RO) units in conditions when the feed may be contaminated with crude oil and fuel oil spillages. The work has involved the examination of the behaviour of polyamide seawater membranes and brackish water membranes with feedwater comprising NaCl/water solutions of 2000–35000 mg/l concentration. The effect of a range of contaminants on RO membrane performance was assessed by comparing the water flux and salt rejection of membrane samples before and after their exposure to the oil-based media which comprised crude oil, crude oil/water mixtures, diesel and diesel/water mixtures. Also included in the study were hexane and hexane/water mixtures. The results demonstrated serious degradation of desalination performance after exposure to some, but not all, of the contaminating fluids. The “pure” hydrocarbons, and also when they are in emulsion form with water, cause extremely severe reductions of RO membrane performance as opposed to the situation when they are in solution in the aqueous phase.

Contact of TFC polyamide membranes with the products of crude oil and fuel spillages can cause catastrophic reductions in the desalination performance. Diesel contamination is especially dangerous with a capacity to reduce membrane fluxes to zero if present in large concentrations for even short periods of time. Hexane, which is one of lighter crude oil fractions can also cause serious deterioration of the performance of RO membranes when in contact in pure or emulsified form. The damage is worse in more concentrated hydrocarbon mixtures and at longer exposure times. Within the scope of the experiments conducted in this project, hydrocarbons retained in solution in water were not found to exhibit damaging effects of the performance of the RO membranes.