Formation control of bromate and trihalomethanes during ozonation of bromide-containing water with chemical addition: Hydrogen peroxide or ammonia?

To ensure the safety of drinking water, ozone (O3) has been extensively applied in drinking water treatment plants to further remove natural organic matter (NOM). However, the surface water and groundwater near the coastal areas often contain high concentrations of bromide ion (Br-). Considering the risk of bromate (BrO3-) formation in ozonation of the sand-filtered water, the inhibitory efficiencies of hydrogen peroxide (H2O2) and ammonia (NH3) on BrO3- formation during ozonation process were compared. The addition of H2O2 effectively inhibited BrO3- formation at an initial Br- concentration amended to 350 µg/L. The inhibition efficiencies reached 59.6 and 100% when the mass ratio of H2O2/O3 was 0.25 and > 0.5, respectively. The UV254 and total organic carbon (TOC) also decreased after adding H2O2, while the formation potential of trihalomethanes (THMsFP) increased especially in subsequent chlorination process at a low dose of H2O2. To control the formation of both BrO3- and THMs, a relatively large dose of O3 and a high ratio of H2O2/O3were generally needed. NH3 addition inhibited BrO3- formation when the background ammonia nitrogen (NH3N) concentration was low. There was no significant correlation between BrO3- inhibition efficiency and NH3 dose, and a small amount of NH3N (0.2 mg/L) could obviously inhibit BrO3- formation. The oxidation of NOM seemed unaffected by NH3 addition, and the structure of NOM reflected by synchronous fluorescence (SF) scanning remained almost unchanged before and after adding NH3. Considering the formation of BrO3- and THMs, the optimal dose of NH3 was suggested to be 0.5 mg/L.

Organic Amines Enhance the Formation of Iodinated Trihalomethanes during Chlorination of Iodide-Containing Waters.

The effects of organic amines (OAs) including glycine (Gly), sarcosine (Sar), and triethanolamine (Tea), representing primary, secondary, and tertiary amines, respectively, on iodinated trihalomethanes (I-THMs) formation during chlorination of iodide (I-)-containing waters were investigated. The total concentration of I-THMs formed in the co-presence of an OA and natural organic matter (NOM) was more than 3 times the sum of those formed in the presence of an OA alone and NOM alone, as OAs competed for free chlorine (FC) to form organic chloramines. Taking Gly as an example, the transformation of I- was determined. In the absence of NOM, the yields of iodate (IO3-) were 89%, 60%, and nearly 0 at [Gly]o/[FC]o = 0:1, 3:4, and 1:1, but 0, 2%, and 43% for hypoiodous acid (HOI), respectively. In the presence of NOM, as [Gly]o/[FC]o increased from 0:1 to 1:1, the yield of IO3- decreased from 66% to 0, while that of I-THMs increased from 2.9% to 16.1%. The competition of FC by OAs inhibited the oxidation of HOI to IO3-, and the formed organic chloramines can oxidize I- to HOI, thus promoting I-DBPs formation. Finally, the enhanced I-THMs formation was verified in real waters.

Advancing illicit connection diagnosis of urban stormwater pipes: Comprehensive analysis with EEM fluorescence spectroscopy.

Urban drainage systems are significant contributors to the issue of black-odorous water bodies. The current application of stormwater pipe inspection technologies faces substantial limitations, especially in industrial areas with diverse wastewater. This study introduced an innovative approach using excitation-emission matrix (EEM) fluorescence spectroscopy for rapid and accurate diagnosis, providing a new perspective for diagnosing illicit connections. In single wastewater-type areas like residential zones, the method achieved a remarkable 91.5 % accuracy solely through spectra observation and fluorescence peak intensity comparison, outperforming conventional NH3-N-based techniques, which reached an accuracy of only 68.1 %. For regions with complex wastewater scenarios, after EEM subtraction, the residual spectra can be roughly categorized into four distinctive categories based on characteristics. This provides a preliminary assessment and helps in initially identifying the types and sources of inflowing wastewater. Furthermore, the least squares (LS) method refines diagnosis results, offering calculated coefficients reflecting the probability and severity of suspected wastewater intrusion. Simulation experiments and field sample analyses validated the feasibility and accuracy of the EEM-based method, highlighting its advantages for diagnosing illicit connections in both single and mixed wastewater scenarios. The results can significantly narrow down the investigation scope and enhance the confirmation of wastewater sources, exhibiting promising application prospects.

Tracking the impact of perfluoroalkyl acid emissions on antibiotic resistance gene profiles in receiving water by metagenomic analysis.

The ecological risks posed by perfluoroalkyl acids (PFAAs) to the aquatic environment have recently been of great concern. However, little information was available on the impact of PFAAs on antibiotic resistance genes (ARGs) profiles. In this study, the receiving river of the largest fluoropolymer production facility in China was selected to investigate the effects of PFAAs on ARGs profiles. The highest PFAAs concentration for water samples near the industrial effluent discharge point was 310.9 µg/L, which was thousands times of higher than the average concentration collected at upstream sites. Perfluorooctanoic acid accounted for more than 67.2 % of ∑PFAAs concentration in water samples collected at the downstream sites, followed by perfluorohexanoic acid (3.6 %-15.9 %). 145 ARG subtypes including high-risk ARGs were detected by metagenomic technology. The results indicated that the discharge of PFAA-containing effluents had a significant impact on the abundance and diversity of ARGs in receiving waters, and PFAAs and water quality parameters (e.g., pH, NH3N, CODMn, TP) could largely affect ARG profiles. Specifically, short-chain PFAAs had similar impacts on ARG profiles compared to the restricted long-chain PFAAs. This study confirmed the potential effects of PFAAs on ARGs in aquatic environment and provided more insights into the ecological risk raised by PFAAs.

Accelerated transformation of sodium dodecylbenzene sulfonate surfactant in the UV/chlorine process: Kinetics and formation of chlorinated disinfection by-products.

The degradation kinetics of Sodium dodecylbenzene sulfonate (SDBS) surfactant in the UV/chlorine process was comprehensively investigated, and the formation of chlorinated disinfection by-products (Cl-DBPs) were determined. Results showed that the degradation of SDBS by UV, chlorine and UV/chlorine all followed pseudo-first-order kinetics. The rate constant by UV/chlorine in ultrapure water was approximately 3 times higher than the sum of those by UV and chlorine, and decreased from 0.297 to 0.063 min-1 with pH increasing from 5.0 to 9.0. Water matrices such as NO3-, HCO3- and natural organic matter (NOM) inhibited the degradation efficiency to a certain extent. The second-order rate constant of SDBS with HO• was determined as 2.84 × 109 M-1 s-1. Through using different probes, the main contributors to SDBS degradation were found to be UV, HO• and reactive chlorine species (RCS). Meanwhile, 64.0 µg L-1 trichloromethane (TCM) and 8.7 µg L-1 chloral hydrate (CH) were simultaneously formed within 30 min of UV/chlorine treatment. The concentration of total organic chlorine (TOCl) (424.0 µg L-1) was obviously higher than those of TCM and CH. In addition, 414 unknown by-products formed during UV/chlorine treatment were detected by mass spectrometry at a high confidence level, including 64 monochloro-DBPs and 2 dichloro-DBPs. Although UV/chlorine process accelerated SDBS degradation, the associated DBP formation deserves enough attention.

Reduction of bromate by zero valent iron (ZVI) enhances formation of brominated disinfection by-products during chlorination.

Bromate (BrO3-) is a predominant undesired toxic disinfection by-product (DBP) during ozonation of bromide-containing waters. The reduction of BrO3- by zero valent iron (ZVI) and its effect on formation of organic halogenated DBPs during chlorination were investigated in this study. The presence of ZVI could reduce BrO3- to bromide (Br-), and Br- formed could be transformed to free bromine (HOBr/OBr-) during chlorination, further leading to organic brominated (Br-) DBPs formation. Formation of DBPs during chlorination, including trihalomethanes (THMs) and haloacetonitriles (HANs) was detected under different conditions. The results showed that when ZVI dosage increased from 0 to 1 g L-1, the formation of Br-DBPs (e.g., TBM and DBCM) was significantly improved, while the formation of Cl-DBPs (e.g., TCM, TCAN and DCAN) reduced. Higher ZVI dosage exhibited inhibitory effect on Br-DBPs formation due to the competition between ZVI and free chlorine (HOCl/OCl-). The bromine substitution factor (BSF) of THMs significantly decreased from 0.61 ± 0.06 to 0.22 ± 0.02, as the pH was raised from 5.0 to 9.0. Besides, the increase of initial BrO3- concentration significantly improved the formation of Br-DBPs and decreased the formation of Cl-DBPs, leading to an obvious rise on the BSF of THMs. As the initial concentration of HOCl increased, all THMs and HANs gradually increased. Moreover, the analysis based on the cytotoxicity index (CTI) of the determined DBPs showed that reduction of BrO3- by ZVI during chlorination had certain risks in real water sources, which should be paid attention to in the application.

Dimethoate degradation by VUV/UV process: Kinetics, mechanism and economic feasibility.

Vacuum ultraviolet/ultraviolet (VUV/UV) process has been applied to water treatment recently, but little is known about its efficacy and mechanism for pesticide degradation. This study investigated the degradation kinetics and mechanism of a typical organophosphorus pesticide, dimethoate (DMT) by VUV/UV, and then the economic feasibility was assessed. DMT degradation followed well the pseudo-first-order reaction kinetics at an initial concentration of ≤5.0 mg L-1. DMT was degraded by 97.8% after 10 min of VUV/UV exposure (VUV fluence = 12 mJ cm-2), whereas by only 5.2% after 10 min of UV exposure (UV fluence = 156 mJ cm-2). The apparent quantum yield of DMT degradation by VUV/UV was determined to be 0.19, and at most 50.7% of hydroxyl radicals (HO•) generated from VUV photolysis of water could be utilized for DMT degradation. As the pH increased from 5.0 to 9.0, the DMT degradation rate decreased from 0.43 to 0.23 min-1. DMT degradation pathways in the VUV/UV process were proposed based on identified organic intermediates and inorganic ions. SO42- was first released due to HO• attack on the SP bond of DMT, which governed the DMT degradation efficiency; while the release of PO43- was pertinent to the DMT mineralization efficiency. DMT solution toxicity was significantly reduced after VUV/UV treatment. An electrical energy-per-order (EEO) value of 0.57 kWh m-3 Order-1 demonstrated the economic feasibility of the VUV/UV process for DMT removal in small-scale drinking water treatment.

Accelerated degradation of sulfamethazine in water by VUV/UV photo-Fenton process: Impact of sulfamethazine concentration on reaction mechanism.

The degradation of sulfamethazine (SMN) by VUV/UV photo-Fenton (VPF) process was investigated with a mini-fluidic VUV/UV photoreaction system. Compared with the conventional UV photo-Fenton process, the VPF process significantly enhanced the degradation and mineralization of SMN, because the VUV irradiation photolyzed H2O and accelerated the redox cycle of Fe3+/Fe2+ to generate more reactive oxygen species (ROS). Initial pH and concentrations of SMN, H2O2, Fe3+, inorganic anions (NO3-, HCO3-, and Cl-), and humic acid all considerably impacted SMN degradation in the VPF process. In particular, the initial SMN concentration significantly affected the absorption distributions of UV and VUV photons in the reaction solution, thus inducing a different reaction mechanism. At a lower SMN concentration (1.8µM), most of UV and VUV photons were absorbed by Fe3+ and H2O, respectively, so indirect oxidation by ROS mainly accounted for SMN degradation. However, at a higher SMN concentration (90µM), 89.2% of UV photons and 59.0% of VUV photons were absorbed by SMN, so direct photolysis also played an important role. In addition, HO and HO2 were identified as the main ROS in the VPF process. This study demonstrates that the VPF process can effectively remove organic micropollutants from water.