Purifying Anaerobically Treated Municipal Secondary Wastewater Effluent by a Reverse Osmosis-Based Potable Reuse Treatment Train

Abstract

As a pretreatment to potable reuse trains, anaerobic secondary treatment could reduce the energy demand and footprint compared to aerobic secondary treatment. Long-term pilot tests linked a reverse osmosis (RO)-based potable reuse treatment system to a pilot-scale staged anaerobic fluidized membrane bioreactor (SAF-MBR). A membrane-aerated bioreactor removed sulfide in SAF-MBR effluent prior to RO. The RO operated for ∼120 days at 15 LMH and 67–83% water recovery, with a final feed pressure during each cycle of ∼9–10 bar. When the final pressure increased to ∼12 bar, chemical cleaning reestablished membrane performance, and a membrane autopsy indicated reversible fouling by biomass and phosphate-based minerals. MS2 bacteriophage spiking tests indicated at least 5–6-log removal each by RO and UV/H₂O₂ advanced oxidation process (AOP) treatment at ∼730 mJ/cm² average UV fluence. A 1,100 mJ/cm² average UV fluence met treatment goals for 1,4-dioxane and indicators for other organic contaminants. Halogenated DBPs in the chlorinated final effluent were ∼5-fold lower than potable reuse trains fed by aerobic secondary effluent. N-Nitrosodimethylamine was well below California’s 10 ng/L Notification Limit. An operating cost comparison indicated that a potable reuse train fed by SAF-MBR effluent ($0.69/m³) is cost-competitive to that fed by aerobic secondary effluent ($0.69/m³).