Concerns about water scarcity, especially in California which has recently experienced serious drought, has increased interest in potable reuse of wastewater. Increasing numbers of full-scale and pilot-scale reuse plants currently in use around the United States and worldwide. In order to produce high quality water to meet regulations for potable reuse, advanced treatment processes are needed such as reverse osmosis (RO), ultraviolet light/advanced oxidation process (UV/AOP), and ozone/biological activated carbon (O<sub>3</sub>/BAC). Ozone is widely used in water reuse both as a pre-oxidant prior to membrane processes and a disinfectant. A highly effective oxidant, ozone is effective at oxidizing micropollutants such as pharmaceutical compounds. Unfortunately, previous research indicates that ozonation increases the formation potential of halonitromethanes, which are highly toxic disinfection byproducts previously observed in drinking water and recycled wastewater, during subsequent secondary disinfection with chlorine, as would occur in direct potable reuse systems. Recent research has suggested that nitromethane is the immediate precursors for halonitromethanes formed during ozonation of wastewater. We hypothesized that nitromethane formed during ozonation of wastewater might be resistant to subsequent advanced treatment in reuse systems, because of its polarity, size, and electron deficiency.In this project, water samples were obtained along the treatment trains of five different full-scale or pilot-scale wastewater reuse plants employing ozone. We found that nitromethane is not substantially removed by microfiltration or reserve osmosis. UV/AOP with hydrogen peroxide failed to decrease nitromethane concentrations, and in some case increased nitromethane concentration. The reasons behind poor removal by RO and AOP were investigated at bench scale. In contrast, BAC removed most nitromethane formed by ozone. In all cases, halonitromethanes are detectable during secondary disinfection with chlorine, whether at the plant or at bench scale to simulate final disinfection in a direct potable reuse project. Although nitromethane itself is not particularly harmful, it posts a unique threat for direct potable reuse because of its resistance to advanced treatment and facile conversion to toxic byproducts.

Fate and transformation of nitromethanes during wastewater reuse processes

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.