Experiment series in environmental engineering: Experiment 5 (NUS ChBE, AY 2004/2005, Semester 1)

High hardness concentration in areas where groundwater is extensively used is a significant problem due to its tendency to form scale on the heating elements of industrial boilers and the clogging of pipes due to the deposition of calcium carbonate. It is also a major problem in the water that is to be used by the semi-conductor industry. Ion exchange has been extensively used in the water treatment industry to soften the hard water. Ion exchange works by using a polystyrene-divinylbenzene sulphonated strong acid cation resin presaturated with sodium as the counter ion to remove the calcium ions from the hard water by exchanging it with the sodium counter ion at the sulphonic (-SO₃^-) acid exchange sites. Most ion exchange resins in the industry are operated in the downflow packed mode. As the treatment process progresses, the number of available ion exchange sites decreases. Thus there will be a point where the number of ion exchange sites available is unable to ensure that the treated water meets a predetermined water quality and this is the breakthrough point. The resin would then be regenerated, rinsed and backwashed and then re-entered into service. Due to cost and time considerations, there is a compromise between regeneration efficiency and column utilization where 50% is the target set for both processes. A critical parameter in the determination of regeneration efficiency is the theoretical exchange capacity. <p> This experiment is designed to illustrate the major parts of the industrial ion exchange service cycle and to introduce the EDTA-Hardness titration method to determine hardness. The objective of the experiment is to determine the exchange capacity of the cationic exchange resin used. The theoretical exchange capacity of the resin is 74176.08 mg as CaCO₃/ l resin which concurs with that reported in the literature for polystyrene-divinylbenzene resin. The regeneration efficiency is determined to be 53.6% which also agrees with that in the literature. In conclusion, the objective of the experiment is successfully accomplished. Done by: Luo Jinjing, Lian Juan, and Ng Wenfa<br>