Adsorption-membrane filtration process in boron removal from first stage seawater RO permeate

The paper deals with evaluation of adsorption-membrane filtration (AMF) hybrid process in removal of trace amounts of boron from the first stage RO permeate. Finely ground boron selective resin, Dowex XUS 43594.00, was used as sorbent while polypropylene capillaries with pore dimension of 0.4 mm as the submerged membranes. The process combined delivery of feed and fresh resin suspension with subsequent removal of the loaded sorbent. The effects of such process variables were evaluated: diameter of resin bead, concentration of suspension, rate of suspension replacement and time of the system run. It was found that to reduce boron concentration from 2 mg/L to the WHO recommended level, 1 g/L of resin should be used. During 48 h of process, neither membranes fouling by the sorbent particles nor sedimentation of resin was observed. When resin was subjected to regeneration particle diameter was not changed after 20 alternating immersions in acidic and basic solutions.

Taking into account the efficiency of adsorption-membrane filtration process, it is recommended to use boron selective resin with the small diameter. As a result of using 20-mm particles of Dowex XUS sorbent, the removal of trace amounts of boron appears within 2 Á 3 min of the sorption. To keep the process running safety, it is suggested to use 1 g of powdered sorbent per 1 L of first stage RO permeate. The ratio of suspension delivery to feed flow can be kept as low as 0.05. The AMF system can run in long cycles without any problems caused by sorbent deposition on membrane surface. The ground Dowex XUS resin can be regenerated by alternative immersion in acidic and basic solution and the resin particles do not break to smaller pieces.