Addressing Low Molecular Weight Chemical Peaking Events During Direct Potable Reuse by Granular and Biological Activated Carbon

Direct Potable Reuse (DPR) is an innovative solution designed to address water scarcity by treating wastewater to directly produce safe drinking water. As droughts and water shortages become more frequent, DPR offers a sustainable and localized water supply by incorporating advanced treatment processes. DPR systems typically rely on a combination of technologies such as ozone followed by biological activated carbon (O3/BAC), reverse osmosis (RO), and advanced oxidation processes (AOPs) to remove a wide range of contaminants. However, low molecular weight organic compounds (LMWCs), particularly volatile organic compounds, can sometimes pass through RO membranes and AOP systems.California's DPR regulations currently adopt these advanced treatment techniques to maintain the highest water quality standards, but opportunities exist to optimize treatment processes for enhanced removal of LMWCs. This study investigates the potential for altering the treatment train by replacing O3/BAC (deployed pre RO) and changing the process location (post RO) with granular activated carbon (GAC) or BAC to better target LMWCs. Both coconut shell- and coal-based GACs were tested with RO permeate through isotherm experiments for their efficacy in the removal of 1,2-dichloroethane (1,2-DCA) Additionally, rapid small-scale column tests (RSSCTs) were conducted over a 20-month period, during which LMWCs, including acetone, formaldehyde, methyl tert-butyl ether (MTBE), 1,2- DCA, and 1,2,3-trichloropropane (1,2,3-TCP), were intermittently spiked at ~5,000, ~17,000, and ~42,000 bed volumes with concentrations ranging from 50 to 300 g/L. Coconut shell-based GACs proved to have higher adsorption performance on the LMWCs based on isotherm testing. RSSCTs results indicated that GAC is effective at removing MTBE, 1,2-DCA, and 1,2,3-TCP, with removal rates exceeding 99%. Conversely, highly hydrophilic compounds like acetone and formaldehyde were less effectively removed by GAC alone. The conversion of the GAC to BAC (post RO) demonstrated the removal of biodegradable LMWCs, i.e., acetone and formaldehyde, suggesting that the GAC to BAC conversion could provide removal for a broader range of LMWCs. Optimizing treatment trains by integrating both GAC and BAC technologies post RO has the potential to enhance the reliability and sustainability of DPR systems, ensuring safer drinking water and promoting more efficient resource use in the context of increasing water scarcity, and should be investigated for future work.