Secondary Effluent is Not All Created Equal: Design Considerations for Potable Reuse Facilities

Potable reuse facilities are being planned and designed using effluent from a variety of secondary treatment processes. This evaluation documents higher concentrations and higher variability in non-nitrifying facilities for several key parameters for potable reuse design, including total organic carbon (TOC), ammonia, and nitrite. For non-nitrifying plants, average TOCs ranged from 14 to 27 mg-N/L; nitrifying plants averaged 10 mg-N/L or less. Some non-nitrifying plants routinely reported nitrite concentrations above 2 mg-N/L, and even the fully nitrified facilities occasionally reported nitrite concentrations above 1 mg-N/L and ammonia concentrations above 2 mg-N/L. Plants considering potable reuse should begin monitoring TOC and nitrite to provide data for advanced treatment design. Optimization or upgrades to secondary treatment may be necessary, depending on the advanced treatment goals and requirements.