Formation and Fate of Nitromethane in Ozone-Based Water Reuse Processes

Abstract

Ozonation is widely used in wastewater reclamation treatment trains, either for micropollutant control or as a disinfectant and preoxidant in certain reuse processes. We recently found that ozonation of secondary effluent produces nitromethane, which can be efficiently transformed to genotoxic halonitromethanes by chlorination. In this work, the fate of nitromethane through water reuse treatment trains was characterized by analyzing samples from five reuse operations employing ozone. Nitromethane was poorly (<50%) rejected by reserve osmosis (RO), not removed by, and in some cases, increased by ultraviolet/advanced oxidation processes (UV/AOP). Sufficient nitromethane remained after advanced treatment that when chlorine was added to mimic secondary disinfection, halonitromethane formation was consistently observed. In contrast, biological activated carbon removed most (>75%) nitromethane. Bench-scale experiments were conducted to verify low removal by RO in clean systems and with wastewater effluent and to quantify the kinetics of direct and indirect photolysis of nitromethane in UV/AOP. An explanation for increasing nitromethane concentration during AOP is proposed. These results indicate that nitromethane presents a unique hazard to direct potable reuse systems, due to its ubiquitous formation during wastewater ozonation, poor removal by RO and UV/AOP, and facile conversion into genotoxic halonitromethanes upon chlorine addition.

Chloramination of Nitromethane: Incomplete Chlorination and Unexpected Substitution Reaction

“…In our previous work, we demonstrated that ozonation of secondary wastewater effluent forms nitromethane, which is the key and possibly sole intermediate toward chloropicrin during subsequent chlorination, as might occur in direct potable reuse scenarios . We further found that nitromethane formed by ozonation at the inlet of reuse plants persists through the most common advanced treatment processes used in reuse operations, such as reserve osmosis and ultraviolet light advanced oxidation processes . Nitromethane remained in the final effluent water at many plants, although treatment trains employing biofiltration after ozone generally removed nitromethane well .…”

Water Analysis: Emerging Contaminants and Current Issues

“…Shi et al investigated the formation and fate of nitromethane through ozone-based water reuse processes. 155 Nitromethane had been previously found in ozonated wastewater and is a significant precursor in the formation of halonitromethane DBPs. Samples from five reuse operations using ozone were collected.…”

Bubbleless Air Shapes Biofilms and Facilitates Natural Organic Matter Transformation in Biological Activated Carbon

“…Pre-ozonation can facilitate the DOM removal rate of BAC by improving the biodegradability of DOM and elevating the dissolved oxygen concentration (DO) in BAC influents. This combination (O 3 –BAC) has been successfully applied to advanced drinking water treatment and decentralized wastewater reuse. − …”