Insights into adsorbable organic halogen analysis: Two overlooked factors impacting water quality assessment.

Adsorbable organic halogen (AOX) represents the total amount of halogenated organics that can be adsorbed on activated carbon (AC) from samples. Measuring AOX is crucial for assessing water quality, and any erroneous estimation of AOX risks misleading decision-makers. This study demonstrated two overlooked factors that may introduce biases to AOX measurement. The first one relates to impurities in the gas transfer tubes of AOX combustion system and in the pressurized gas of AOX separation system, which resulted in significant fluctuations and high blank values (8.5-118.0 µg-Cl/L). The solutions of above issues are to warming up the combustor for several runs and replacing the pressurized air with argon gas in the separator, which could drop the blank AOX values to 9.1-10.0 µg-Cl/L. The second one involves coexisting chloride ion (Cl-) during AOX analysis, which interfered with AOX measurements (T. test, p < 0.05) even at low concentration levels (e.g., 10 mg/L Cl- in samples with 100 µg-Cl/L p-chlorophenol). Results show that AC captured 0.02-0.11 % of Cl-, resulting in 17.7-24.5 µg-Cl/L AOX responses in control samples containing 15-130 mg/L Cl- only. Furthermore, a significant mass imbalance of Cl- (3.58-8.39 %) during analysis process suggests a potential impact of residual Cl- on subsequent samples. By comparing synthetic and actual waters, samples with low dissolved organic carbon (DOC) were more susceptible to interference from Cl- on AOX measurement than those with high DOC. These findings underscore the pressing need to optimize existing AOX methods or develop alternative analytical methods to ensure accurate water quality assessment.

Formation of halogenated forms of bisphenol A (BPA) in water: Resolving isomers with ion mobility - mass spectrometry and the role of halogenation position in cellular toxicity.

Halogenated BPA (XBPA) forms resulting from water chlorination can lead to increased toxicity and different biological effects. While previous studies have reported the occurrence of different XBPAs, analytical limitation have hindered the analysis and differentiation of the many potential isomeric forms. Using online solid-phase extraction - liquid chromatography - ion-mobility - high-resolution mass spectrometry (OSPE-LC-IM-HRMS), we demonstrated a rapid analysis method for the analysis of XBPA forms after water chlorination, with a total analysis time of less than 10 min including extraction and concentration and low detection limits (∼5-80 ng/L range). A multi in-vitro bioassay testing approach for the identified products revealed that cytotoxicity and bioenergetics impacts were largely associated with the presence of halogen atoms at positions 2 or 2' and the overall number of halogens incorporated into the BPA molecule. Different XBPA also showed distinct impacts on oxidative stress, peroxisome proliferator-activated receptor gamma - PPARγ, and inflammatory response. While increased DNA damage was observed for chlorinated water samples (4.14 ± 1.21-fold change), the additive effect of the selected 20 XBPA studied could not explain the increased DNA damage observed, indicating that additional species or synergistic effects might be at play.

Transformation of 6PPDQ during disinfection: Kinetics, products, and eco-toxicity assessment.

N-phenyl-N'-(1,3-dimethyl butyl)-p-phenylenediamine-quinone (6PPDQ) currently arouses broad concerns because of its acute lethality to coho salmon and rainbow trout at environmentally relevant concentrations and the wide occurrence in runoff-impacted water. Investigation on the fate and transformation of 6PPDQ in various treatment processes is necessary for its risk assessment and control. Here, we explored the transformation of 6PPDQ during disinfection with its precursor 6PPD as a reference, focusing on kinetics, products, and toxicity variation. 6PPDQ readily reacted with hypochlorite and chlorine dioxide with second-order rate constants of 2580 ± 143 M-1 s-1 and 614 ± 52 M-1 s-1 (pH 7.0 and 25 °C), which are slightly lower than the reactions of 6PPD. We tentatively identified thirteen transformation products for 6PPDQ and eight for 6PPD in reaction with the two disinfectants. It seems that the quinone ring of 6PPDQ and the p-phenylenediamine moiety of 6PPD are reactive sites. The transformation of these compounds probably proceeds through Cl-substitution, ring cleavage, hydroxylation, and amine oxidation and hydrolysis. Tests with zebrafish embryos revealed that the transformation products of 6PPDQ could have higher eco-toxicity than the parent compound, while the toxicity of the 6PPD products remained nearly unchanged. The increased toxicity of 6PPDQ during disinfection highlights the necessity to substantially reduce its content before the disinfection of runoff-impacted water.

CuO Promotes the Formation of Halogenated Disinfection Byproducts during Chlorination via an Enhanced Oxidation Pathway.

Previous studies showed that cupric oxide (CuO) can enhance the formation of trihalomethanes (THMs), haloacetic acids, and bromate during chlorination of bromide-containing waters. In this study, the impact of CuO on the formation kinetics and mechanisms of halogenated disinfection byproducts (DBPs) during chlorination was investigated. CuO does not enhance the formation of DBPs (i.e., 1,1,1-trichloropropanone, chloroform, and trichloroacetaldehyde (TCAL) /dichloroacetonitrile) during chlorination of acetone, 3-oxopentanedioic acid (3-OPA), and aspartic acid, respectively. This indicates that the halogen substitution pathway cannot be enhanced by CuO. Instead, CuO (0.1 g L-1) accelerates the second-order rate constants for reactions of chlorine (HOCl) with TCAL, citric acid, and oxalic acid at pH 8.0 and 21 °C from <0.1 to 29.4, 7.2, and 15.8 M-1 s-1, respectively. Oxidation pathway predominates based on the quantification of oxidation products (e.g., a trichloroacetic acid yield of ∼100% from TCAL) and kinetic modeling. CuO can enhance the formation of DBPs (e.g., THMs, haloacetaldehydes, and haloacetonitriles) during chlorination of model compounds and dissolved organic matter, of which both halogen substitution and oxidation pathways are required. Reaction rate constants of rate-limiting steps (e.g., citric acid to 3-OPA, aromatic ring cleavage) could be enhanced by CuO via an oxidation pathway since CuO-HOCl complex is more oxidative toward a range of substrates than HOCl in water. These findings provide novel insights into the DBP formation pathway in copper-containing distribution systems.

Reaction of Polyamide Membrane Model Monomers with Chlorine Dioxide: Kinetics, Pathways, and Implications.

Aromatic polyamide (PA) based membranes are widely used for reverse osmosis (RO), but they can be degraded by free chlorine used for controlling the biofouling prior to RO treatment. Kinetics and mechanisms for the reactions of PA membrane model monomers, i.e., benzanilide (BA), and acetanilide (AC), with chlorine dioxide (ClO2) were investigated in this study. Rate constants for the reactions of ClO2 with BA and AC at pH 8.3 and 21°C were determined to be (4.1±0.1) × 10-1 M-1.24 s-1 and (6.0±0.1) × 10-3 M-1 s-1, respectively. These reactions are base assisted with a strong pH dependence. The activation energies of BA and AC degradation by ClO2 were 123.7 and 81.0 kJ mol-1, respectively. This indicates a relatively strong temperature dependence in the studied temperature range of 21-35 °C. The presence of bromide and natural organic matter does not promote the degradation of model monomers by ClO2. BA was degraded by ClO2 via two pathways: (1) the attack on the anilide moiety with the formation of benzamide (major pathway) and (2) oxidative hydrolysis to benzoic acid (minor pathway). A kinetic model was developed to simulate the degradation of BA and formation of byproducts during ClO2 pretreatment, and simulations agree well with the experimental data. Half-lives of BA treated by ClO2 were 1-5 orders of magnitude longer than chlorine under typical seawater treatment conditions. These novel findings suggest the potential application of ClO2 for controlling biofouling ahead of RO treatment at desalination treatments.

Biogenic Solution Map Based on the Definition of the Metabolic Correlation Distance between 4-Dimensional Fingerprints.

Accurate discrimination and classification of unknown species are the basis to predict its characteristics or applications to make correct decisions. However, for biogenic solutions that are ubiquitous in nature and our daily lives, direct determination of their similarities and disparities by their molecular compositions remains a scientific challenge. Here, we explore a standard and visualizable ontology, termed "biogenic solution map", that organizes multifarious classes of biogenic solutions into a map of hierarchical structures. To build the map, a novel 4-dimensional (4D) fingerprinting method based on data-independent acquisition data sets of untargeted metabolomics is developed, enabling accurate characterization of complex biogenic solutions. A generic parameter of metabolic correlation distance, calculated based on averaged similarities between 4D fingerprints of sample groups, is able to define "species", "genus", and "family" of each solution in the map. With the help of the "biogenic solution map", species of unknown biogenic solutions can be explicitly defined. Simultaneously, intrinsic correlations and subtle variations among biogenic solutions in the map are accurately illustrated. Moreover, it is worth mentioning that samples of the same analyte but prepared by alternative protocols may have significantly different metabolic compositions and could be classified into different "genera".

UV/chlorine and chlorination of effluent organic matter fractions: Tracing nitrogenous DBPs using FT-ICR mass spectrometry.

UV/chlorine process is a promising advanced treatment to eliminate pathogen and remove refractory micropollutants for reclamation of municipal secondary effluent. However, effluent organic matter (EfOM) featuring high organic nitrogen content serves as a potential precursor for nitrogenous disinfection byproducts (N-DBPs) of health concern. The molecular-level alteration of a hydrophobic (HPO) EfOM fraction and a transphilic (TPI) EfOM fraction isolated from the same municipal effluent and the formation of N-DBPs in the UV/chlorine were tracked by ultrahigh-resolution mass spectrometry. Compared with chlorination, UV/chlorine induced a significantly greater modification on the molecular composition of EfOM and resulted in formation of unique formulae and chlorinated molecules with higher degree of oxidation, lower aromaticity, and less carbon number due to the involvement of reactive radical species. For both EfOM fractions, UV/chlorine formed more diverse DBPs with higher intensity and Cl-incorporation than chlorination. The TPI fraction of EfOM characterized by higher O/C and N/C ratios generated more N-DBPs with higher intensity clustered in the high O/C region than the HPO fraction of EfOM by both UV/chlorine and chlorination. Totally, 207 and 117 nitrogen-containing chlorinated formulae were recorded after UV/chlorine treatment of TPI and HPO, respectively. Precursor tracking found a greater number of DBPs were originated from raw EfOM through electrophilic substitution pathway rather than chlorine addition. Toxicity bioassays demonstrated that DBPs can trigger oxidative stress-induced DNA damage, while HPO fraction of EfOM dominated the induction of cytotoxicity. However, no correlation could be established between the diversity/abundance of N-DBPs and the level of DNA damage. A total of 22 DBPs with a significant rank correlation with DNA damage were identified, while C8H6O5NCl was found as the N-DBP with the strongest correlation. The potential toxic chlorine-containing formula with the most abundant intensity was assigned to C5HO3Cl3. This study suggests that the character and transformation of EfOM and associated toxicity is critical to evaluate the UV/chlorine process toward practical application.

Genotoxic effects of chlorinated disinfection by-products of 1,3-diphenylguanidine (DPG): Cell-based in-vitro testing and formation potential during water disinfection.

1,3-diphenylguanidine (DPG) is a commonly used rubber and polymer additive, that has been found to be one of the main leachate products of tire wear particles and from HDPE pipes. Its introduction to aquatic environments and potentially water supplies lead to further questions regarding the effects of disinfection by-products potentially formed. Using different bioassay approaches and NGS RNA-sequencing, we show that some of the chlorinated by-products of DPG exert significant toxicity. DPG and its chlorinated by-products also can alter cell bioenergetic processes, affecting cellular basal respiration rates and ATP production, moreover, DPG and its two chlorination products, 1,3-bis-(4-chlorophenyl)guanidine (CC04) and 1-(4-chlorophenyl)-3-(2,4-dichlorophenyl)guanidine (CC11), have an impact on mitochondrial proton leak, which is an indicator of mitochondria damage. Evidence of genotoxic effects in the form of DNA double strand breaks (DSBs) was suggested by RNA-sequencing results and further validated by an increased expression of genes associated with DNA damage response (DDR), specifically the canonical non-homologous end joining (c-NHEJ) pathway, as determined by qPCR analysis of different pathway specific genes (XRCC6, PRKDC, LIG4 and XRCC4). Immunofluorescence analysis of phosphorylated histone H2AX, another DSB biomarker, also confirmed the potential genotoxic effects observed for the chlorinated products. In addition, chlorination of DPG leads to the formation of different chlorinated products (CC04, CC05 and CC15), with analysed compounds representing up to 42% of formed products, monochloramine is not able to effectively react with DPG. These findings indicate that DPG reaction with free chlorine doses commonly applied during drinking water treatment or in water distribution networks (0.2-0.5 mg/L) can lead to the formation of toxic and genotoxic chlorinated products.

Molecular-level investigation into UV-induced transformation of hydrophobic aquatic dissolved organic matter.

The ubiquitously present dissolved organic matter (DOM) greatly influence the efficiency of UV-based technologies due to its reactivity to UV irradiation. In this work, UV-induced changes within three hydrophobic DOM fractions isolated from different surface waters were investigated. Analysis on UV absorbance at 254 nm, electron donating capacity, fluorescence intensity and carbon content revealed small changes in DOM bulk properties associated with the UV-induced photochemical reactions. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was further used to explore the modification of the molecular distribution based on H/C and O/C ratios, m/z and DBE. The molecular-level investigation revealed that an average of 296 aromatic and lignin-like molecules were degraded, leading to the production of around 306 new molecules. The UV-reactive community were identified as CHO molecules with higher DBE (>10) and carbon number (>25) which could be readily transformed into smaller saturated molecules. Molecules containing nitrogen (N) or sulfur (S) atom, independent of aromaticity and molecular weight (m/z), were also highly UV susceptible and transformed into molecules with larger DBE and m/z. Possible reaction pathways responsible for the observations were discussed. The results indicated that UV-reactivity and subsequent transformation of DOM are remarkably correlated with its molecular composition and characteristics. Though the changes in bulk properties of DOM following UV irradiation were observed to be very small, the significant alteration in its molecular structures would have a profound impact on the UV-based treatment processes.

Modification Mechanism of Polyamide Reverse Osmosis Membrane by Persulfate: Roles of Hydroxyl and Sulfate Radicals.

Oxidative modification is a facile method to improve the desalination performance of thin-film composite membranes. In this study, we comparatively investigated the modification mechanisms induced by sulfate radical (SO4• -) and hydroxyl radical (HO•) for polyamide reverse osmosis (RO) membrane. The SO4• -- and HO•-based membrane modifications were manipulated by simply adjusting the pH of the thermal-activated persulfate solution. Although both of them improved the water permeability of the RO membrane under certain conditions, the SO4• --modified membrane notably prevailed over the HO•-modified one due to higher permeability, more consistent salt rejection rates over wide pH and salinity ranges, and better stability when exposed to high doses of chlorine. The differences of the membranes modified by the two radical species probably can be related to their distinct surface properties in terms of morphology, hydrophilicity, surface charge, and chemical composition. Further identification of the transformation products of a model polyamide monomer using high-resolution mass spectrometry demonstrated that SO4• - initiated polymerization reactions and produced hydroquinone/benzoquinone and polyaromatic structures; whereas the amide group of the monomer was degraded by HO•, generating hydroxyl, carboxyl, and nitro groups. The results will enlighten effective ways for practical modification of polyamide RO membranes to improve desalination performances and the development of sustainable oxidation-combined membrane processes.

Inputs of disinfection by-products to the marine environment from various industrial activities: Comparison to natural production.

Oxidative treatment of seawater in coastal and shipboard installations is applied to control biofouling and/or minimize the input of noxious or invasive species into the marine environment. This treatment allows a safe and efficient operation of industrial installations and helps to protect human health from infectious diseases and to maintain the biodiversity in the marine environment. On the downside, the application of chemical oxidants generates undesired organic compounds, so-called disinfection by-products (DBPs), which are discharged into the marine environment. This article provides an overview on sources and quantities of DBP inputs, which could serve as basis for hazard analysis for the marine environment, human health and the atmosphere. During oxidation of marine water, mainly brominated DBPs are generated with bromoform (CHBr3) being the major DBP. CHBr3 has been used as an indicator to compare inputs from different sources. Total global annual volumes of treated seawater inputs resulting from cooling processes of coastal power stations, from desalination plants and from ballast water treatment in ships are estimated to be 470-800 × 109 m3, 46 × 109 m3 and 3.5 × 109 m3, respectively. Overall, the total estimated anthropogenic bromoform production and discharge adds up to 13.5-21.8 × 106 kg/a (kg per year) with contributions of 11.8-20.1 × 106 kg/a from cooling water treatment, 0.89 × 106 kg/a from desalination and 0.86 × 106 kg/a from ballast water treatment. This equals approximately 2-6% of the natural bromoform emissions from marine water, which is estimated to be 385-870 × 106 kg/a.

Impact of EfOM in the elimination of PPCPs by UV/chlorine: Radical chemistry and toxicity bioassays.

The UV/chlorine process as a potential tertiary municipal wastewater treatment alternative for removing refractory PPCPs has been widely investigated. However, the role of effluent organic matter (EfOM) on the radical chemistry and toxicity alteration is unclear. The elimination of two model PPCPs, primidone (PRM) and caffeine (CAF), by the co-exposure of UV and free chlorine was investigated to elucidate the impact of EfOM. Experimental results indicated that both •OH and reactive chlorine species (RCS) were importantly involved in the decay of PRM at acidic condition, while ClO• played dominant role at alkaline pH. The decay of CAF was dominated by ClO• under all conditions. Chlorine dose, initial contaminant concentration, solution pH, and water matrix affect the process efficiency at varying degree resulting from their specific effect on the radical speciation in the system. Presence of EfOM isolate remarkably inhibited the decay of PRM and CAF by preferentially scavenging RCS and particularly ClO•. Good correlations (linear for PRM and exponential for CAF) between UV absorbance at 254 nm and the observed pseudo first-order rate constants (k'obs) for all EfOM solutions were obtained, demonstrating the importance of aromatic moieties in inhibiting the degradation of targeted contaminants by UV/chlorine process. Degradation of PRM/CAF in reconstituted effluent spiked with the major effluent constituents (i.e., EfOM isolates, Cl-, HCO3-, and NO3-) was comparable to the results obtained with the real WWTP effluent and fit well to the correlation between k'obs and UV absorbance at 254 nm, suggesting that EfOM isolates can be used to determine the efficiency of UV/chlorine process in real effluent. EfOM serves as the main precursor of adsorbable organic chlorine in the UV/chlorine treatment. Bioassays indicated that chlorine-containing compounds could induce oxidative stress, mitochondrial dysfunction, and increase the cell DNA damage. Among evaluated treatment conditions, the nature of EfOM, hydrophobic versus transphilic fraction, is likely the predominant factor affecting the cytotoxicity. Meanwhile the UV/chlorine treatment can significantly reduce the cytotoxicity of EfOM isolates. However, adding high level of selected contaminants (e.g., PRM and CAF) can inhibit this phenomenon due to the competition with reactive radicals.

Importance of origin and characteristics of biopolymers in reversible and irreversible fouling of ultrafiltration membranes.

The present work compares the chemical properties of isolated biopolymers of different origins and their fouling potential during ultrafiltration (UF). The biopolymers were extracted from secondary wastewater effluent as effluent organic matter (EfOM) and from surface water as natural organic matter (NOM). Multiple analytical techniques were used to characterize the isolates. The characterization results revealed that EfOM biopolymers were more enriched in protein-type structures compared to the NOM organics, and they presented significant differences in the reversibility of membrane fouling. Dissolved in pure water, EfOM biopolymers led to more irreversible fouling than that caused by NOM isolates. Dosing divalent cations (e.g., Ca2+) into the solutions increased the irreversibility of both types of fouling, while aggravating NOM fouling more significantly. Further investigation was conducted to understand the interaction between EfOM and NOM biopolymers during formation of the fouling layer. The results showed that the interaction between these two types of organics was negligible in the absence of salts. These findings highlight the importance of a comprehensive understanding of biopolymers from different origins, considering their chemical properties and water chemistry, which have valuable implications for selecting suitable membrane fouling control strategies for treating water from different origins.

A catalytic ozonation process using MgO/persulfate for degradation of cyanide in industrial wastewater: mechanistic interpretation, kinetics and by-products.

Cyanide-laden wastewaters generated from mining and electroplating industries are extremely toxic and it is of vital importance to treat them prior to discharge to receiving water resources. The present study aims to oxidize cyanide using an ozonation process catalyzed by MgO and persulfate (PS). A MgO nanocatalyst was synthesized using the sol-gel method and characterized. The results show that the synthesized catalyst had a BET surface area of 198.3 m2 g-1 with a nanocrystalline particle size of 7.42 nm. In the present study, the effects of different operational parameters were investigated, and it was found that the MgO/O3/PS process is able to oxidize 100 mg L-1 of cyanide after 30 min under optimum operational conditions. Cyanide degradation mechanisms in the MgO/O3/PS process were completely investigated and the main radical species were identified using scavenging experiments. It was found that sulfate and hydroxyl radicals both contributed to the cyanide degradation in the MgO/O3/PS process. Cyanide degradation by-products were also tracked and it was found that cyanate and ammonium species are primarily generated during the oxidation, but increase of reaction time allowed their conversion to much less toxic compounds such as nitrate and bicarbonate. Cyanide degradation was also conducted in real industrial wastewater containing 173 mg L-1 of cyanide. Although there was a reduction in cyanide removal rate, the MgO/O3/PS process was able to completely oxidize cyanide within 70 min. Finally, it can be concluded that the ozonation process catalyzed by MgO and persulfate is an efficient and reliable advanced oxidation process for removal of cyanide from industrial wastewater.

Effect of copper oxide on monochloramine decomposition in bromide-containing waters.

Copper oxide (CuO), a common corrosion product found in copper pipes, has been shown to catalyse the decay of different oxidants in drinking water, including chlorine, bromine, iodine, and chlorine dioxide. However, its impact on monochloramine (NH2Cl), a disinfectant commonly used in long distribution system worldwide is still unknown. In this study, the effect of CuO on NH2Cl decay in the absence or presence of bromide was investigated. Results showed that in the presence of CuO and the absence of bromide, NH2Cl slightly decayed under acidic conditions. When bromide was present in NH2Cl solutions, the total oxidant concentration (sum of the different bromo-chloro-amines) was significantly decreased by CuO. This was primarily due to the degradation of bromochloramine (NHBrCl) by CuO which was evidenced by membrane inlet mass spectrometry. The decomposition rate of the total oxidant was similar for different CuO dosages (0.02-0.2 g/L) but increased with increasing bromide concentration (0-80 µM) and decreasing pH (6.5-8). An apparent second-order rate constant of 0.73 M-1 s-1 was determined with respect to NH2Cl and bromide concentrations for a CuO concentration of 0.05 g/L. Our findings suggest that, during water transportation in copper pipes or in distribution systems where copper oxide is present, special attention should be given to the stability of chloramines when bromide-containing waters are chloraminated.

Removal of pharmaceutical and personal care products (PPCPs) from wastewater using microalgae: A review.

Pharmaceuticals and personal care products (PPCPs) are a group of emerging micro-pollutants causing detrimental effects on living organisms even at low doses. Previous investigations have confirmed the presence of PPCPs in the environment at hazardous levels, mainly due to the inefficiency of conventional wastewater treatment plants (CWWTPs). Their stable structure induces longer persistence in the environment. Microalgae are currently used to bioremediate numerous pollutants of different characteristics and properties released from the domestic, industrial, agricultural, and farm sectors. CO2 mitigation during culture and the use of biomass as feedstock for biodiesel or biofuel production are, briefly, other benefits of microalgae-mediated treatment over CWWTPs. This review provides a comprehensive summary of recent literature, an overview of approaches and treatment systems, and breakthrough in the field of algal-mediated removal of PPCPs in wastewater treatment processes. The mechanisms involved in phycoremediation, along with their experimental approaches, have been discussed in detail. Factors influencing the removal of PPCPs from aqueous media are comprehensively described and assessed. A comparative study on microalgal strains is analyzed for a more efficient implementation of future processes. The role of microalgae to mitigate the most severe environmental impacts of PPCPs and the generation of antibiotic-resistant bacteria is discussed. Also, a detailed assessment of recent research on potential toxic effects of PPCPs on microalgae was conducted. The current review highlights microalgae as a promising and sustainable approach to efficiently bio-transform or bio-adsorb PPCPs.

Degradation and deactivation of a plasmid-encoded extracellular antibiotic resistance gene during separate and combined exposures to UV254 and radicals.

This study investigated the degradation and deactivation of an extracellular ampicillin resistance gene (ampR) encoded in plasmid pUC19 during exposure to UV254, •OH (generated by UV>290/H2O2), and combined exposure to UV254 and •OH (and/or SO4•-) using UV254/H2O2 and UV254/S2O82-. The degradation rates of ampR measured by quantitative polymerase chain reaction increased with increasing target amplicon length (192-851 bps). The rate constants for the degradation of pUC19 (2686 bps) were calculated as 0.26 cm2/mJ for UV254 and 1.5 × 1011 M-1s-1 for •OH, based on the degradation rates of ampR amplicons and assuming an equal sensitivity of DNA damage across the entire plasmid. DNA repair-proficient Escherichia coli (E. coli) AB1157 strain (wild-type) and its repair-deficient mutants including AB1886 (uvrA-), AB2463 (recA-), AB2480 (uvrA-, recA-), and DH5α (recA-, endA-) were applied as recipient cells in gene transformation assays. Results suggested that the elimination efficiency of transforming activity during UV254 and •OH exposure was dependent on the type of DNA repair genes in recipient E. coli strains. Losses of transforming activity were slower than the degradation of pUC19 by a factor of up to ∼5 (for E. coli DH5α), highlighting the importance of DNA repair in recipient cells. The degradation rates of ampR amplicons were much larger (by a factor of ∼4) in UV254/H2O2 and UV254/S2O82- than UV254 direct photolysis, indicating the significant contribution of •OH and SO4•- to the gene degradation. Not only UV254 and SO4•-, but also •OH contributed to the degradation of ampR during UV254/S2O82-, which was attributed to the conversion of SO4•- to •OH and a 10-fold larger reactivity of •OH towards ampR as compared to SO4•-. However, the enhanced gene degradation by radicals did not lead to a faster elimination of gene transforming activity during UV254/H2O2 and UV254/S2O82-, suggesting that UV254- and radical-induced DNA damage were not additive in their contributions to losses of gene transforming activity. Wastewater effluent organic matter (EfOM) accelerated the degradation of ampR during UV254 irradiation by means of reactive species production through indirect photolysis reactions, whereas EfOM mainly acted as a radical scavenger during UV254/H2O2 and UV254/S2O82- treatments.

Hydroxyl and sulfate radical-based oxidation of RhB dye in UV/H2O2 and UV/persulfate systems: Kinetics, mechanisms, and comparison.

The degradation kinetics and mechanisms of Rhodamine B (RhB) dye by •OH and SO4•- based advanced oxidation processes were investigated. The •OH and SO4•- radicals were generated by UV photolysis of hydrogen peroxide and persulfate (i.e., UV/H2O2 and UV/PS), respectively. The effects of initial solution pH, RhB concentration, oxidant dosage, Fe2+ concentration, and water matrices were examined. The results showed that the degradation of RhB followed pseudo-first-order kinetics in both processes, with the UV/H2O2 process exhibiting better performance than that of the UV/PS process. Acidic conditions were favorable to the degradation of RhB in both systems. Increasing the oxidant dosage or decreasing the contaminant concentration could enhance the degradation of RhB. Photo-Fenton-like processes accelerated the performance when Fe2+ was added into both systems. The removal efficiency of RhB was inhibited upon the addition of humic substances. The addition of Cl- displayed no significant effect and promoted RhB degradation in UV/H2O2 and UV/PS systems, respectively. The presence of NO3- promoted RhB degradation, while H2PO4- and C2O42- showed an inhibitory effect on both UV/H2O2 and UV/PS processes. Radical scavenging tests revealed the dominant role of SO4•- radicals in the UV/PS system. Furthermore, the evolution of low molecular weight organic acids and NH4+ during the degradation of RhB in these two processes were compared. Both UV/H2O2 and UV/PS systems led to similar formation trends of NH4+ and some ring-opening products (e.g., formic acid, acetic acid, and oxalic acid), suggesting some analogies in the decay pathways of RhB by •OH and SO4•--induced oxidation processes.

Impact of DOM source and character on the degradation of primidone by UV/chlorine: Reaction kinetics and disinfection by-product formation.

The presence of Dissolved Organic Matter (DOM) can exert a strong influence on the effectiveness of the UV/chlorine process. This study examined the impact of five DOM isolates with different characteristics on the degradation kinetics of model contaminant primidone (PM) during UV/chlorine treatment. The formation of Disinfection By-Products (DBPs) from DOM after 15-min UV/chlorine treatment followed by 24 h chlorination was investigated and compared with chlorination alone. The use of chemical probes and radical scavengers revealed that •OH and ClO• were the main radical species responsible for the loss of PM at acidic and alkaline conditions, respectively. All tested DOM isolates significantly inhibited the decay of PM. A strong negative correlation (>0.93) was observed between the decay rate constants of PM and SUVA of DOM isolates, except for EfOM isolate, which induced the strongest inhibitory effect due to its higher abundance in sulfur-containing functional groups (i.e., sink of •OH/Cl• radicals). Compared with chlorination, the formation of Adsorbable Organic Chlorine (AOCl) and Trichloromethane (TCM) during the UV/Chlorine process was enhanced and hindered for low SUVA isolates and high SUVA DOM, respectively. However, Dichloroacetonitrile (DCAN) formation was generally lower for all isolates except for Ribou Reservoir DOM at pH 8.4 because of its high reactive nitrogenous DBP precursors at caustic conditions. However, when normalized to the chlorine consumed, the UV/Chlorine process always led to a lower DBPs formation compared with chlorination alone.

Ozone combined with ceramic membranes for water treatment: Impact on HO radical formation and mitigation of bromate.

The beneficial effect of combining ozone with ceramic membrane filtration (CMF) to enhance membrane flux performances during water treatment (e.g., wastewater and drinking water) could be related to the formation of hydroxyl (HO) radicals from the interaction of ozone with ceramic membrane. To explore this effect, para-chlorobenzoic acid was used to probe HO radical activity during a combined ozone/CMF process using a 0.1 µm pore size membrane supplied by Metawater, Japan. Tests were then extended to explore the impact on bromate formation downstream CMF, a well-known undesirable by-product from ozone use in water treatment. Ozone reduction by the membrane and its module appeared to be more associated with physical degassing, but a noticeable formation of HO radicals was observed during the interaction of ozone with the ceramic membrane. CMF treatment of ozonated potable water containing bromide showed a reduced bromate formation of 50% when the water was recirculated to the filtration module containing the ceramic membrane, compared to the experiment performed with an empty module. Single pass experiments showed bromate mitigation of around 10%. The mitigation of bromate formation was attributed to reduced overall ozone exposure by deagassing effect, but also potentially from suppression of the oxidation of Br- and HOBr/BrO- to BrO3- due to the catalytic degradation of ozone via a HO radical pathway.