Are TOC and COD Limits Appropriate for Regulating Potable Reuse? Analyzing Organics through the Domestic Water Cycle: Results from WE&RF Project-15-04

Secondary effluent contains a vast number of organic chemicals used in everyday life, such as pharmaceuticals and personal care products, that are not regulated and do not have extensive monitoring data. Complete characterization of these myriad organic compounds, and their associated health relevance, is not practical. Consequently, various regulatory approaches incorporating surrogate bulk carbon measurements, such as total organic carbon (TOC) and chemical oxygen demand (COD), have been applied to potable reuse projects in an attempt to control potentially hazardous organic chemicals. These regulatory approaches range from a TOC limit of 0.5 mg/L in California for direct groundwater injection to COD limits of 10 mg/L and 18 mg/L in Virginia and Georgia, respectively for surface water augmentation. In some cases, these limits are significantly lower than the conventional water supplies in the same region. In addition, regulating to an extremely low TOC or COD limit for potable reuse can produce significant unintended consequences, without necessarily improving the protection of public health. For example, recent research showed that mandating a TOC limit of 0.5 mg/L, which has driven the adoption of reverse osmosis (RO) technology, increases the net present value costs for a 20-mgd potable reuse plant at an inland location by more than 200% because of the high cost of concentrate disposal. Consequently, as potable reuse continues to grow, practical, yet safe, guidance regarding organics removal is desperately needed by those considering its application. The Water Research Foundation Project 15-04 (Reuse-15-04) was funded to begin development of this guidance.