In the face of escalating water scarcity, direct potable reuse (DPR) is emerging as a critical solution, particularly in regions where water resources are stretched thin. However, this approach isn’t without its challenges. A recent study published in *Voda za istraživanje X* (Water Research X) sheds light on innovative strategies to tackle one of the most pressing issues in DPR: the intermittent passage of low molecular weight (LMW) volatile organic compounds (VOCs) through reverse osmosis (RO) and advanced oxidation processes (AOP). These compounds pose significant public health concerns, and finding effective mitigation strategies is crucial for the energy sector, which relies heavily on consistent and safe water supplies.
The study, led by George William Kajjumba of the Water Quality Research and Development Division at the Southern Nevada Water Authority, explored two potential add-on treatment strategies: granular activated carbon (GAC) treatment after RO/AOP and ozonation followed by biological activated carbon (O3/BAC) treatment before RO/AOP. The findings offer promising insights into how these technologies can be optimized to address VOC peaking events in potable water schemes.
Kajjumba and his team conducted rapid small-scale column tests (RSSCTs) to simulate GAC performance with intermittent spiking events of individual LMW VOCs—acetone, formaldehyde, methyl tert-butyl ether (MTBE), 1,2-dichloroethane, and 1,2,3-trichloropropane—in RO/AOP product water. The results were compelling. GAC RSSCTs achieved higher reductions of haloalkanes (>98%), MTBE (>98%), and acetone (47%) compared to O3/BAC. However, formaldehyde proved to be a different story. “Formaldehyde was effectively removed by O3/BAC (>98%) via biotransformation, while GAC had limited efficacy (<30%)", Kajjumba noted. This disparity highlights the importance of tailoring treatment strategies to the specific VOCs present in the water. The study also evaluated a pilot-scale O3/BAC system treating tertiary-filtered wastewater under similar spiking conditions. While spiked VOCs temporarily reduced N-nitrosodimethylamine removal in the O3/BAC system, baseline performance recovered, indicating the system's resilience. These preliminary results suggest that GAC post-RO can mitigate haloalkane and ether-like VOC peaks, although real-world monitoring and long-term pilot testing are needed. O3/BAC, on the other hand, is well-suited for removing biodegradable compounds like formaldehyde but may require optimization. The implications of this research are significant for the energy sector, which often relies on large-scale water treatment facilities to ensure a consistent and safe water supply. As water scarcity becomes an increasingly pressing issue, the ability to effectively mitigate VOC peaking events in potable reuse schemes will be crucial. The findings from Kajjumba's study offer a roadmap for optimizing treatment strategies, potentially paving the way for more reliable and efficient water treatment processes. Looking ahead, the study suggests that additional strategies, such as air stripping, activated sludge pretreatment, and blending, should be further explored to address LMW chemical peaking in potable reuse schemes. As the field continues to evolve, the insights gained from this research will undoubtedly shape future developments, ensuring that water treatment technologies keep pace with the growing demands of a water-scarce world.