In the past year Vitens, The Netherlands' largest water supply company, and Witteveen+Bos, have prepared the preliminary, basic and detailed design for a full-scale ion exchange plant reducing colour in drinking water to a value of less than 10 mg/l PtCo. Current pilot study shows that the results are even better than expected. The plant will be built in 2004 and start-up is scheduled for mid 2005. The introduction of ion exchange at WTP (Water Treatment Plant) Oldeholtpade is part of a larger project, also including softening in pellet reactors, preceded by counter-current aeration and renovation of the existing treatment plant.
The colour content present in groundwater is caused by peat layers. In contrast with conventional ion exchange processes, previous pilot studies showed that the exchange capacity of the resin for organics is much larger than expected. The excellent results can be explained by assuming the simultaneous occurrence of adsorption and ion exchange processes on the resin. It can be concluded that optimising operating conditions, such as higher exchange capacity (as KMnO4/liter resin), higher superficial velocity, shorter contact time and longer filter run cycle clearly affect resin volume as well as the required amount of regenerant.
Vitens has started additional experiments at WTP Spannenburg to confirm the innovative design parameters. Aim of the research is the relation between adsorption and ion exchange during filtration, in order to clarify the achieved results. Furthermore the relationship between the specific water type (characterisation of organic compounds) and the operational results of ion exchange will be studied.
In order to minimise the waste regenerant, treatment towards recycling is studied by dead end nanofiltration. With nanofiltration it is possible to concentrate the waste stream to a maximum of 10% of the original waste stream. The recovered regenerant can be recycled for regeneration of the resin.