The use of the drainage gradient method for evaluating reverse osmosis membrane anti-scalants

This paper describes the use of the drainage gradient method for assessing the relative inhibitory effectiveness of various reverse osmosis (RO) anti-scalants. Five different anti-scalants were selected for the examination of the drainage gradient method's feasibility for evaluating their relative inhibitory effectiveness. The results show that pH, ΔKCa (increase in cycles of concentration) and Langelier's saturation index (LSI) can be used as indicators and that ΔKCa is the most suitable indicator. The sensitivities of the three indicators from greatest to least are: ΔKCa > LSI ≫ pH, with relative standard deviations (RSD) which are 38.39%, 14.22%, and 1.45%, respectively. The order of the scale suppression effectiveness of the five tested anti-scalants, based on the three judgment indicators, is D > E > B > C > A.