Capillary nanofiltration under anoxic conditions as post-treatment after bank filtration – improvement of chemical cleaning and removal of sulphate and organic micropollutants
Bank filtration schemes for the production of drinking water are increasingly affected by constituents such as sulphate and organic micropollutants (OMP) in the source water. Within the European project AquaNES, the combination of bank filtration followed by capillary nanofiltration (NF) is being demonstrated as a potential solution for these challenges at pilot scale. As the bank filtration process reliably reduces total and dissolved organic carbon (TOC/DOC), biopolymers, algae and particles, membrane fouling is reduced resulting in a long term stability of operation of the NF. With the new developed membrane module for capillary NF a reduction of sulphate, selected micropollutants (depending on size & charge) and hardness can be achieved together with further removal of DOC. Dissolved iron and manganese concentrations in bank filtrate were not a problem for the capillary NF under anoxic conditions with a good cleaning concept including backwash with anoxic permeate, forward flush and chemical cleaning.