Membranes have an increasingly important role in alleviating water scarcity and the pollution of aquatic environments. Promising molecular-level design approaches are reviewed for membrane materials, focusing on how these materials address the urgent requirements of water treatment applications.

Materials for next-generation desalination and water purification membranes

Interest in the formation of nitrogenous disinfection byproducts (N-DBPs) has increased because toxicological research has indicated that they are often more genotoxic, cytotoxic, or carcinogenic than many of the carbonaceous disinfection byproducts (C-DBPs) that have been a focus for previous research. Moreover, population growth has forced utilities to exploit source waters impaired by wastewater effluents or algal blooms. Both waters feature higher levels of organic nitrogen, that might serve as N-DBP precursors. Utilities are exploring new disinfectant combinations to reduce the formation of regulated trihalomethanes and haloacetic acids. As some of these new combinations may promote N-DBP formation, characterization of N-DBP formation pathways is needed. Formation pathways for halonitroalkanes, halonitriles, haloamides, and N-nitrosamines associated with chlorine, ozone, chlorine dioxide, UV, and chloramine disinfection are critically reviewed. Several important themes emerge from the review. First, ...

Halonitroalkanes, Halonitriles, Haloamides, and N-Nitrosamines: A Critical Review of Nitrogenous Disinfection Byproduct Formation Pathways

Desalination membranes are essential for the treatment of unconventional water sources, such as seawater and wastewater, to alleviate water scarcity. Promising research efforts on novel membrane materials may yield significant performance gains over state-of-the-art thin-film composite (TFC) membranes, which are constrained by the permeability–selectivity trade-off. However, little guidance currently exists on the practical impact of such performance gains, namely enhanced water permeability or enhanced water–solute selectivity. In this critical review, we first discuss the performance of current TFC membranes. We then highlight and provide context for recent module-scale modeling studies that have found limited impact of increased water permeability on the efficiency of desalination processes. Next we cover several important examples of water treatment processes in which inadequate membrane selectivity hinders process efficacy. We conclude with a brief discussion of how the need for enhanced selectivity ...

The Critical Need for Increased Selectivity, Not Increased Water Permeability, for Desalination Membranes

Formation, precursors, control, and occurrence of nitrosamines in drinking water: a review.

Characterization of intracellular & extracellular algae organic matters (AOM) of Microcystic aeruginosa and formation of AOM-associated disinfection byproducts and odor & taste compounds.

Recent studies indicated that water treatment polymers such as poly(epichlorohydrin dimethylamine) (polyamine) and poly(diallyldimethylammonium chloride) (polyDADMAC) may form N-nitrosodimethylamine (NDMA) when in contact with chloramine water disinfectants. To minimize such potential risk and improve the polymer products, the mechanisms of how the polymers behave as NDMA precursors need to be elucidated. Direct chloramination of polymers and intermediate monomers in reagent water was conducted to probe the predominant mechanisms. The impact of polymer properties including polymer purity, polymer molecular weight and structure, residual dimethylamine (DMA), and other intermediate compounds involved in polymer synthesis, and reaction conditions such as pH, oxidant dose, and contact time on the NDMA formation potential (NDMA-FP) was investigated. Polymer degradation after reaction with chloramines was monitored at the molecular level using FT-IR and Raman spectroscopy. Overall, polyamines have greater NDMA-...

Degradation of amine-based water treatment polymers during chloramination as N-nitrosodimethylamine (NDMA) precursors.

Rejection of selected N -nitrosamines, a group of probable human carcinogens, and their precursors by nanofiltration (NF) and brackish water reverse osmosis (BWRO) membranes was evaluated using a bench-scale cross-flow filtration apparatus. The tested nitrosamines included N -nitrosodimethylamine, N -nitrosomethylethylamine, N -nitrosopyrrolidine, N -nitrosodiethylamine, N -nitrosodi- n -propylamine, and N -nitrosodi- n -butylamine. The target nitrosamine precursors included secondary amines such as dimethylamine, methylethylamine, diethylamine, and dipropylamine. Rejection of nitrosamines varied greatly depending on the tested membranes (9–75% for NF membranes and 54–97% for BWRO membranes) and the molecular weight of nitrosamines. Experimental data obtained with the BWRO membranes matched well with an irreversible thermodynamic model coupled with film theory. The model further suggested that effective diffusion of nitrosamines through the BWRO membranes is responsible for the relatively low rejections o...

Removal of N -Nitrosamines and Their Precursors by Nanofiltration and Reverse Osmosis Membranes

The NDMA formation potential (NDMA FP) of four commonly used amine-based cationic water treatment polymers was assessed in reactions with chlorine-based oxidants (free chlorine, monochloramine and chlorine dioxide) and nitrosifying agents (nitrite and nitrate). Relatively high dosages of polymers were directly exposed to oxidants for long reaction times in the FP tests to assess the potential to form NDMA and obtain mechanistic insight. Results show that the NDMA FP of the polymers generally follows the trend of aminomethylated polyacrylamide (Mannich polymer)>>poly(epichlorohydrin-dimethylamine) (polyamine) > poly(diallyldimethylammonium chloride) (polyDADMAC) > cationic polyacrylamide copolymer (cationic PAM). The high NDMA FP of Mannich polymer was largely due to the high amount of dimethylamine (DMA) residue in the polymer solution. For the other three polymers, the DMA concentration was increased after oxidation, indicating polymer degradation, and the trend of DMA increase agreed with that of NDMA FP. Among the oxidants, NDMA formation followed the order of monochloramine > free chlorine > chlorine dioxide, despite that the DMA release from the polymers caused by the oxidant followed the opposite order. At equal dosages, nitrite and nitrate generated NDMA from the polymers at levels comparable to those by free chlorine and chlorine dioxide; even so, the nitrosifying agents are unlikely to contribute significantly to NDMA formation due to expected lower concentrations in drinking water treatment systems. Jar tests followed by monochloramination of real water samples using conditions in line with those at potable water treatment plants generally showed relatively small contributions from polyamines and polyDADMACs to the overall NDMA formation.

Potential N-nitrosodimethylamine (NDMA) formation from amine-based water treatment polymers in the reactions with chlorine-based oxidants and nitrosifying agents

Sang-Hyuck Park

Papers

Degradation of amine-based water treatment polymers during chloramination as N-nitrosodimethylamine (NDMA) precursors.

Removal of N -Nitrosamines and Their Precursors by Nanofiltration and Reverse Osmosis Membranes

Potential N-nitrosodimethylamine (NDMA) formation from amine-based water treatment polymers in the reactions with chlorine-based oxidants and nitrosifying agents