Effect of concentrate recycle on anti-scalant performance

A convenient reverse osmosis (RO) laboratory technique for rapid initial screening of anti-scalant performance is based on full recycling of concentrate and permeate to the feed vessel and observing the scale suppression effectiveness under different operating conditions. Once-through flow tests in which both permeate and concentrate are continuously withdrawn from the RO system simulate more closely actual plant conditions but are usually impractical as they require a large inventory of the feed solution. In the recycle mode of operation, the residence time of the anti-scalant in the system is increased. The objective of the present study was to investigate if the increased residence time leads to a deviation between results measured by the simple recycle technique with those obtained by the more elaborate once-through technique. A comparison between inhibition results observed in full recycle and once-through tests respectively was carried out in a continuous flow pilot RO system. Tests were performed w...