Abstract
By pre-treating reverse osmosis (RO) feed water for process water production with cationic ion-exchange (IEX), scaling on the membrane can be avoided and the water recovery can be increased. Furthermore, by recycling the RO brine for the regeneration of the IEX, the addition of chemicals is avoided. A pilot-scale study of the hybrid IEX-RO system was performed. This study indicates that an RO recovery of 85% can be reached by removing the multivalent cations from the feed. In the IEX, the efficiency of the regeneration with the brine depends on the monovalent:multivalent cation ratio in the feed. In the case of low cation ratios, a minor addition of NaCl to the RO brine is sufficient to fully restore the IEX capacity. The CNK index was developed to predict the efficiency of the hybrid system for a given feed water. An economic analysis indicated that the water revenue for stand-alone RO is 0.52€/m3, while for the hybrid process this revenue increases up to 0.69€/m3, thus resulting in a pay-back time of 2.5years.
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