Modelling of stimulus response experiments in the feed channel of spiral-wound reverse osmosis membranes

Reverse osmosis is commonly used to produce ultrapure water which is necess ary in hemodialysis to prepare the dialyzing liquid. We have managed to tes t some spiral-wound FT30-4040 membranes by analyzing their response to a st imulus injection of tracer, The shape of the distribution of the tracer in the rejection side is compared for different membranes, a new and two used ones, and different tracers in order to study the evolution of the interact ions between the solutes and the membrane with wear. We used three tracing solutions: sodium chloride solution (1.5M), hydrochloric acid (1.2M) and so dium hydroxide (1.5M) to reach acid or basic pH. The distributions of trace r detected in the rejection side are unimodal with a tail which is greater in the case of the hydrochloric tracing. These results enable us to establi sh an increasing affinity for NaOH, NaCl and HCl with the membrane. We repr esent the feed channel between the sheet of membranes by a series of perfec t mixing cells with exchange. The modelling of the space between the membra ne sheets by a series of perfect mixing cells with exchange, the dead zone representing the membrane, gives good results. It gives prominence to the e xistence of excursions of the solute in the membrane.