Application of a carbon dioxide regenerated ion-exchange process for removing sulphate from drinking water: a simple approach to estimate process performance

Abstract

Increasing sulphate concentrations in some German drinking water resources require water suppliers to evaluate the applicability of state-of-the-art water treatment technologies for sulphate removal. In this study, the carbon dioxide regenerated ion exchange process CARIX® was tested in pilot- and lab-scale in one of the largest waterworks in Germany, Berlin-Friedrichshagen. The study's objective was to optimize the process performance in a drinking waterworks of the Berlin Water Company (BWB) and to deduce to what extent laboratory tests with different water quality parameters can predict breakthrough in full-scale ion-exchange plants. The results showed a strong dependence of sulphate removal on influent alkalinity levels. An average 1.29–2.08 mEq L⁻¹ sulphate was removed during the pilot-scale test series, with lower results at decreasing influent alkalinity. In addition to sulphate, 43–59% of the influent dissolved organic carbon (DOC) was also removed during the service cycle. The desorption of only 25–34% of DOC during regeneration indicated an ongoing fouling process on the anion exchanger resin. However, this influence on process performance was not visible within one year of pilot operation. A linear regression analysis revealed linear relationships between the anion and cation exchanger performance as well as the influent and effluent ratio between alkalinity and hardness levels, which can be used to predict process performance based on influent water quality.