Zero liquid discharge: Heading for 99% recovery in nanofiltration and reverse osmosis Original Research Article

Concentrate of nanofiltration and reverse osmosis installations is an increasing problem, especially for inland membrane installations. Introduction of membrane filtration in The Netherlands is severely hindered by the concentrate problem. Two approaches are viable for solving or reducing the concentrate problem: (1) low recovery NF/RO without anti-scalant dosing, (2) Zero liquid discharge. This research focuses on the second option: Zero liquid discharge NF/RO. First and main problem to be solved with zero liquid discharge is to increase the recovery of the membrane installation to its limits, without increasing the costs of water produced. A high recovery (>99%) is necessary to reduce energy consumption and costs for evaporation of the remaining waste stream (<1%). The only possibility to achieve a very high recovery in NF/RO, is removing the scaling components from the feed water. A very important advantage of removing the scaling components is that the nanofiltration or RO can be operated at high fluxes. In this paper the results of two pilot experiments are reported.