UV-based advanced oxidation processes (AOPs) effectively degrade N-nitrosodimethylamine (NDMA) passing through reverse osmosis (RO) units within advanced treatment trains for the potable reuse of municipal wastewater. However, certain utilities have observed the re-formation of NDMA after the AOP from reactions between residual chloramines and NDMA precursors in the AOP product water. Using kinetic modeling and bench-scale RO experiments, we demonstrate that the low pH in the RO permeate (∼5.5) coupled with the effective rejection of NH promotes conversion of the residual monochloramine (NHCl) in the permeate to dichloramine (NHCl) via the reaction: 2 NHCl + H ↔ NHCl + NH. Dichloramine is the chloramine species known to react with NDMA precursors to form NDMA. After UV/AOP, utilities generally use lime or other techniques to increase the pH of the finished water to prevent distribution system corrosion. Modeling indicated that, while the increase in pH halts dichloramine formation, it converts amine-based NDMA precursors to their more reactive, neutral forms. With modeling, and experiments at both bench-scale and field-scale, we demonstrate that reducing the time interval between RO treatment and final pH adjustment can significantly reduce NDMA re-formation by minimizing the amount of dichloramine formed prior to reaching the final target pH.

This study investigated the use of ultra-low-pressure reverse osmosis (ULPRO) and nanofiltration (NF) membranes for water reuse applications where lower operating pressures and a high permeate quality are desired. A laboratory-scale investigation was performed to compare the rejection and operational performance of RO, ULPRO, and NF membranes and to select two membranes for testing at a California water facility. A ULPRO membrane and an NF membrane were then tested at pilot and full scale at a water recycling plant and monitored for operational performance and rejection of total organic carbon, total nitrogen, and regulated and unregulated organic micropollutants. Pilot-and full-scale testing of the best-performing membranes demonstrated that both ULPRO and NF membranes could be used to meet potable water quality requirements. The presumed advantage of using ULPRO and NF membranes diminished as fouling occurred, resulting in operating pressures only slightly lower than or similar to those found for traditional RO membranes. n increasing number of municipalities are using surface water that has been affected by wastewater discharges or reclaimed water for drinking water augmentation. For groundwater injection projects in the United States that use reclaimed water, treatment using an integrated membrane system such as microfiltration (M F) pretreatment followed by reverse osmosis (RO ) is the industry standard (N RC, 2004). RO membranes are favored for these applications because of their high removal efficiencies for total dissolved solids, pathogens, and unregulated trace organic chemicals. For direct injection into a potable aquifer in California, the California Department of Public H ealth (CDPH ) draft regulations for groundwater recharge with reclaimed water require RO treatment and effluent water quality of < 0.5 mg/L total organic carbon (TO C) and < 5 mg/L total nitrogen (TN ; CDPH , 2007). Currently, there is the potential to lower operating pressures and costs by implementing newer types of membrane processes such as nanofiltration (N F) and ultra low-pressure RO (ULPRO ) for these types of applications. H owever, an understanding of the advantages and disadvantages of using ULPRO and N F compared with conventional RO membranes in terms of operational performance and permeate water quality is lacking.

No abstract

Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary influent, primary effluent, and secondary effluent of a wastewater treatment plant producing water destined for potable reuse. Results showed the most N-Nitrosodimethylamine (NDMA) production from primary effluent, and the recycle streams entering the primary clarifiers were identified as the main source of NDMA precursors. The degradation of aminomethylated polyacrylamide (Mannich) polymer used for sludge treatment was a significant cause of precursor occurrence. A strong correlation between NDMA formation and ammonia concentration was found suggesting an important role of ammonia oxidation on NDMA production. During ozonation tests in DI water using dimethylamine (DMA) as model precursor, the NDMA yield significantly increased in the presence of ammonia and bromide due to the formation of hydroxylamine and brominated nitrogenous oxidants. In addition, NDMA formation during ozonation of dimethylformamide (DMF), the other model precursor used in this study, occurred only in the presence of ammonia, and it was attributable to the oxidation of DMF by hydroxyl radicals. Filtered wastewater samples (0.7 μm) produced more NDMA than unfiltered samples, suggesting that ozone reacted with dissolved precursors and supporting the hypothesis of polymer degradation. Particularly, the total suspended solids content similarly affected NDMA formation and the UV absorbance decrease during ozonation due to the different ozone demand created in filtered and unfiltered samples.

No abstract