Organic Poisoning of Anion Exchange Resins
Until recent years, water treatment by ion exchange was considered as a largely inorganic process and resins were judged solely by their ability to exchange or remove mineral ions. The total organic content of natural water supplies is considerably lower than the inorganic content, and when the standard of water purity required for industrial purposes was 1–2 μS/cm (S = mhos), organic contamination of the input water was rarely sufficient to cause noticeable changes in the quality of the treated water, or the apparent working capacity of the resins. The greater purity requirements of modern boilers, necessitating conductivities of down to 0·1 μS/cm, have converted into severe problems phenomena which were virtually unrecognized until the 1950’s. The nature of the problem is best illustrated in Figure 37 which shows typical results of mixed bed operation under a number of conditions. If the input water contains no organic matter, then results such as Curve B arc readily obtainable, and under ideal conditions, the treated water quality can be as good as in Curve A. Typical results for London water, a mixed and variable supply with about 300 p.p.m. T.D.S, and 1–2 p.p.m. O.A, are given in Curve C, while old mixed beds which have become poisoned will do no better than Curve D. Indeed, some of the thin, organic-loaded waters occurring for example in Wales will rapidly foul a conventional mixed bed to a much greater extent, the conductivities being around 2–3 μS/cm.
Unable to display preview. Download preview PDF.