Perspectives on next-generation secondary wastewater treatment for potable reuse applications

ABSTRACT Flowchart of IPR and DPR pathways with RO- and AC-based AWP options by nitrification need, alongside a treatment plant diagram with open research questions. The growing implementation of indirect and direct potable reuse (IPR and DPR) highlights the need for robust wastewater treatment to strengthen the performance and reliability of downstream advanced water purification facilities (AWPFs). Next-generation secondary wastewater treatment processes are now being considered to enhance compatibility in potable reuse schemes. This perspective analyzes the role of competing next-generation biotechnologies such as integrated fixed-film activated sludge (IFAS) and the moving bed biofilm reactor (MBBR), membrane biofilm reactor (MBfR), Modified Ludzack-Ettinger membrane bioreactor (MLE-MBR) and anaerobic membrane bioreactor (AnMBR) upstream of reverse osmosis (RO)- and activated carbon (AC)-based AWP, and their ability to enhance contaminant removal and improve overall efficiency of AWP. Both MLE-MBR and AnMBR significantly enhance the removal of suspended solids, organics, and microbial contaminants through membrane filtration. AnMBR offers the possibility of net energy-positive operation but does not remove nitrogen, limiting compatibility with AWP. MLE-MBR removes nitrogen but has significantly greater energy demand due to aeration and mixed liquor return pumping. Overall, next-generation biotechnologies provide flexible and effective solutions to enhance secondary effluent quality, supporting safe and regulation-compliant IPR and DPR applications.