Closed circuit reverse osmosis and adsorption: PFAS removal and impact on scaling behaviour

To ensure sufficient clean water production in the future, new approaches to water treatment are required. Closed circuit reverse osmosis is seen as a possible technique to increase water recovery whilst creating pollutant free permeate. Here we operate closed circuit reverse osmosis with an adsorbent bed, formed by cake filtration, in the recirculation stream to treat PFAS containing and calcite scaling prone feed water. Operation to high recovery (99%) with an adsorbent cake was 37% faster compared to operation without an adsorbent cake, due to reduced membrane scaling by CACO 3 precipitation. 10 times more calcium precipitated in the adsorbent cake layer than on the membrane surface. Additionally 58% of PFBA and 99% of other PFAS were removed from the concentrate during operation, reducing the need for further concentrate treatment. • 37% faster at reaching 99% recovery compared to CCRO with no adsorption bed. • Adsorption from the CCRO concentrate allows for high recovery with a clean permeate. • Negligible increase in energy consumption by adsorption bed formed by cake filtration. • Filter cake additionally captures a substantial amount of inorganic scalants.