Hybrid membrane processes for micropollutant removal from wastewater

The quality of available water is at risk due to the growing issue of organic micropollutants (OMPs) present in surface waters. These OMPs can be pharmaceuticals, personal care products, per- and polyfluoroalkayl substances (PFAS), industrial chemicals, or pesticides. One pathway for OMPs to enter surface water is through wastewater, since typical wastewater treatment plants (WWTPs) are not designed to remove such compounds. A possible solution to remove OMPs from wastewater is to add additional treatment steps to conventional WWTPs. When nanofiltration (NF) or Reverse Osmosis (RO) membranes are used, the OMPs can be retained by the membrane. This concentrate requires further treatment. This work focuses on treating the concentrate by recirculating it to conventional biological treatment.

The goal of Chapter 2 is to investigate which type of dense membrane has the highest potential for practical application. A model shows that the combination of conventional treatment, membrane filtration and concentrate recirculation can substantially improve the overall removal of OMPs with low bioremoval and high membrane retention. The effects of scale, recovery, flux, crossflow velocity and staging are investigated in detail for the dNF40 hollow fiber nanofiltration (HFNF) membrane in Chapter 3, with a focus on their effect on retention of ions and OMPs and calculated energy consumption. In Chapter 4, the dNF40 membrane is used on pilot scale to investigate the effect of concentrate recirculation on the total treatment system. The combination of biological treatment, the HFNF membrane and concentrate recirculation can increase overall removal compared to only biological treatment for several compounds. The primary focus of Chapter 5 is to achieve a balance between enhancing the transmittance of the membrane permeate, thereby reducing the energy consumption of a subsequent oxidation step, and minimizing the energy required for membrane filtration.