Catalytic hydrolysis: A novel role of zero-valent iron in haloacetonitrile degradation and transformation in unbuffered systems.

Efforts to remove highly toxic haloacetonitriles (HANs) is an important step to reduce health risks associated with disinfection by product exposure. Zero valent iron (ZVI) is a versatile material, whose reductant, sorbent and coagulant role has been well understood. However, their catalytic role is less known. In this study, the degradation and transformation of HANs in ZVI system were investigated. Significant decreases of the four HANs in ZVI system were observed, and haloacetamides and haloacetic acids (hydrolysis products of HANs) were the dominant transformation products of HANs. However dehalogenated HANs, Fe (II) and Fe (III) were rarely detected after reaction, indicating that the ZVI acted as a catalyst to promote the hydrolysis of HANs, rather than other previously reported causes (dehalogenation or redox reaction). The HAN degradation rates were dramatically affected by the initial pH, ZVI doses and initial HAN concentration. Kinetic analysis indicated that HAN removal was enhanced with the increase of initial pH (5-9), ZVI doses (1-10 g/L), and initial HAN concentration (25-200 µg/L). ZVI induced the transformation of HANs to haloacetamides, haloacetic acids and other de-halogenated compounds, which reduced the cytotoxicity and genotoxicity by 88% and 85%, respectively. This study helped to understand the fate of HAN during the transmission in cast iron pipes, and provided a theoretical foundation for future HAN control and monitoring efforts.

Modification of regenerated cellulose ultrafiltration membranes with multi-walled carbon nanotubes for enhanced antifouling ability: Field test and mechanism study.

Although ultrafiltration (UF) has been extensively employed for drinking water purification, it is crucial to further develop novel membrane materials to improve the antifouling capacity and satisfy the practical usage. Multi-walled carbon nanotubes (MWCNTs) have characteristics that could potentially improve the membrane antifouling performance. Therefore, in this study, modified cellulose UF membranes were prepared using MWCNTs of various outer diameters ranging from 10 to 20 nm to 40-60 nm. The antifouling properties of the modified membrane and natural organic matter (NOM) removal mechanism were investigated while treating water from a local drinking water source river. Overall, the antifouling ability increased by more than one-fold when the nascent cellulose membrane was coated with MWCNTs (outer diameter of 40-60 nm) at a loading of 17.4 g/m2. The molecular weight distribution profiles of the NOM in the raw water and permeates suggest the superior performance of the modified membranes in removing two major NOM fractions with molecular weights ranging from approximately 5 k-30 k and 500 k-1000 k. Based on its hydrophobicity, the NOM of the raw water was fractionated into the strong hydrophobic (SHPO), the weak hydrophobic, the strong hydrophilic and the moderately hydrophilic (MHPI) fractions. The WHPO fraction caused the highest fouling compared with the other fractions under consistent experimental conditions. Meanwhile, the modified membranes showed a preference for removing the MHPI and SHPO fractions. These results imply that MWCNTs can be employed to improve the antifouling property of cellulose UF membranes and have the potential to selectively remove moderately hydrophilic contaminants from water.

New insights into interaction of proteins in extracellular polymeric substances of activated sludge with ciprofloxacin using quartz crystal microbalance with dissipation.

Proteins in extracellular polymeric substances play a vital role in adsorbing organic contaminants in biological wastewater treatment processes, but there is still lack of a fast and effective approach to monitor their interaction. Quartz crystal microbalance with dissipation (QCM-D) was used to investigate the binding and viscoelastic properties of ciprofloxacin (CIP) on extracellular proteins from activated sludge by a two-step sequential deposition method. A saturated viscoelastic monolayer of proteins was formed on the crystal by injecting 500 mg L-1 extracellular proteins. Binding of CIP with the extracellular proteins film followed the pseudo-first-order kinetic equation and Langmuir model, with the maximum binding capacity of 172.4 mg g-1. The binding mass, energy dissipation, and reaction rate constant increased with increasing CIP concentration. A strong binding was obtained at pH 5, suggesting electrostatic interactions as the dominating binding mechanism. Cations inhibited CIP binding with extracellular proteins, probably due to cations competition. Two binding periods were distinguished according to the viscoelastic properties of CIP layer: viscous binding in the initial period and elastic towards binding saturation. Results highlighted QCM-D as an effective and real-time technique to evaluate the role of extracellular proteins in contaminants removal.

Has the formation of disinfection by-products been overestimated? Membrane leakage from syringe filter heads serves as unexpected precursors.

Syringe filters are widely used for sample pretreatments in laboratories. This study found that, surprisingly, these filters can leak dissolved organic carbon (DOC) that can potentially serve as precursors of disinfection by-products (DBPs). Nine common types of syringe filters were assessed. The results showed that the DOC of ultrapure water increased after syringe filtration. The DOC shed from filter membranes was characterized, whose spectra showed that the main compounds exhibited a low apparent molecular weight. Five classes of DBPs were investigated including trihalomethanes, haloacetaldehydes, haloacetonitriles, haloacetamides and halonitromethanes, among which trichloromethane (TCM), dichloroacetaldehyde (DCAL), trichloroacetaldehyde (TCAL), dichloroacetonitrile (DCAN), and trichloronitromethane (TCNM) were principally detected. The DBP formation was affected by chlorination time and membrane types. In general, the use of the poly vinylidene fluoride membrane resulted in the highest formation of TCM and TCAL, whereas nylon and mixed cellulose esters membranes contributed significantly to the formation of DCAN and TCNM, respectively. The shedding DOC and the formation of TCM, DCAL and TCAL from filter membranes were mitigated effectively by pre-washing; however, the contribution of membrane leakage to DCAN and TCNM formation was still notable, even with a pre-wash volume of 50 mL. When unwashed syringe filters were used for a real water sample, the DBP formation increased by up to 73.2% compared to the pre-washed ones; particularly for TCNM it was always over 15%. Therefore, for better quality control in laboratories, more attention should be paid to the syringe filters during sample pre-treatments, particularly when DBP formation is being investigated.

Interaction of ciprofloxacin with the activated sludge of the sewage treatment plant.

Interaction of ciprofloxacin with the activated sludge of the sewage treatment plant is of importance for the ciprofloxacin migration and risk control. More than 96.0% ciprofloxacin was removed through the sludge adsorption. The sludge surface charge varied little with ciprofloxacin since most ciprofloxacin was dissociated into the neutral one. No obvious shift was observed for the soluble carbohydrate concentration and composition with the addition of ciprofloxacin, indicating the weak interaction between the carbohydrates and ciprofloxacin. The introduction of ciprofloxacin resulted in a reduction of the soluble protein concentration, a marked increase of the extracellular protein fluorescence intensities, and a dramatic emergence of new extracellular proteins. The alteration of the proteins highlights the strong interaction between the extracellular proteins and ciprofloxacin, and the consequent integration of certain soluble proteins and original unextractable inner layer extracellular proteins into the extractable extracellular proteins. Different types of interactions are suggested to dominate between the extracellular proteins and the differently dissociated ciprofloxacin.

Distribution and fate modeling of 4-nonylphenol, 4-t-octylphenol, and bisphenol A in the Yong River of China.

In this study, the concentrations of 4-nonylphenol (4-NP), 4-tert-octylphenol (4-t-OP), and bisphenol A (BPA) in the water column of the Yong River were investigated and found to be in the range of 140-3948, 6-828, and 15-1415 ng L-1, respectively. A fate and transport model coupled with the Water Quality Analysis Simulation Program (WASP) was developed. After model calibration and validation, the distributions of 4-NP, 4-t-OP, and BPA in the Yong River were modeled for the duration of 2015. The total contaminant loads from the upstream boundary, four tributaries and two wastewater treatment plants were determined to be 2318 kg yr-1 for 4-NP, 506 kg yr-1 for 4-t-OP, and 970 kg yr-1 for BPA. Both measured and modeled results reported higher concentrations of the selected contaminants near river confluences and at the outfalls of the wastewater treatment plants. Peak concentrations were found to always appear in months with relatively reduced precipitation. The influences of adsorption and degradation on the dissolved concentrations of the selected chemicals were also modeled. The combined effects of adsorption and degradation were found to reduce dissolved concentrations of 4-NP, 4-t-OP, and BPA by 17.9%, 30.7%, and 12.1%, respectively. Adsorption was shown to reduce 4-NP concentrations in the Yong River more than degradation. Conversely, adsorption and degradation caused almost equal reductions in the dissolved concentrations of 4-t-OP and degradation caused larger decreases than adsorption in the dissolved concentrations of BPA.