Oxidation kinetics of selected taste and odor compounds during ozonation of drinking water

Oxidation processes and me

This publication summarizes my journey in the field of chemical oxidation processes for water treatment over the last 30+ years. Initially, the efficiency of the application of chemical oxidants for micropollutant abatement was assessed by the abatement of the target compounds only. This is controlled by reaction kinetics and therefore, second-order rate constant for these reactions are the pre-requisite to assess the efficiency and feasibility of such processes. Due to the tremendous efforts in this area, we currently have a good experimental data base for second-order rate constants for many chemical oxidants, including radicals. Based on this, predictions can be made for compounds without experimental data with Quantitative Structure Activity Relationships with Hammet/Taft constants or energies of highest occupied molecular orbitals from quantum chemical computations. Chemical oxidation in water treatment has to be economically feasible and therefore, the extent of transformation of micropollutants is often limited and mineralization of target compounds cannot be achieved under realistic conditions. The formation of transformation products from the reactions of the target compounds with chemical oxidants is inherent to oxidation processes and the following questions have evolved over the years: Are the formed transformation products biologically less active than the target compounds? Is there a new toxicity associated with transformation products? Are transformation products more biodegradable than the corresponding target compounds? In addition to the positive effects on water quality related to abatement of micropollutants, chemical oxidants react mainly with water matrix components such as the dissolved organic matter (DOM), bromide and iodide. As a matter of fact, the fraction of oxidants consumed by the DOM is typically > 99%, which makes such processes inherently inefficient. The consequences are loss of oxidation capacity and the formation of organic and inorganic disinfection byproducts also involving bromide and iodide, which can be oxidized to reactive bromine and iodine with their ensuing reactions with DOM. Overall, it has turned out in the last three decades, that chemical oxidation processes are complex to understand and to manage. However, the tremendous research efforts have led to a good understanding of the underlying processes and allow a widespread and optimized application of such processes in water treatment practice such as drinking water, municipal and industrial wastewater and water reuse systems.

Removal characteristics of 53 micropollutants during ozonation, chlorination, and UV/H2O2 processes used in drinking water treatment plant

The removal of 53 emerging micropollutants (MPs), including 10 per- and polyfluorinated substances (PFASs), 25 pharmaceuticals and personal care products (PPCPs), 7 pesticides, 5 endocrine disrupters (EDCs), 3 nitrosamines, and 3 taste and odor compounds (T&Os), by chlorination, ozonation, and UV/H2O2 treatment was examined in deionized water and surface waters used as the raw waters in drinking water treatment plants (DWTPs) in South Korea. The UV/H2O2 treatment was effective in the removal of most MPs, whereas chlorination was selectively effective for 19 MPs, including EDCs (>70 %). MPs containing aromatic ring with electron-donating functional group, or primary and secondary amines were effectively removed by chlorination immediately upon reaction initiation. The removal of MPs by ozonation was generally lower than that of the other two processes at a low ozone dose (1 mg L-1), but higher than chlorination at a high ozone dose (3 mg L-1), particularly for 16 MPs, including T&Os. Compared in deionized water, the removals of MPs in the raw water samples were lower in all three processes. The regression models predicting the rate constants (kobs) of 53 MPs showed good agreement between modeled and measured value for UV/H2O2 treatment (R2 = 0.948) and chlorination (R2 = 0.973), despite using only dissolved organic carbon (DOC) and oxidant concentration as variables, whereas the ozonation model showed a variation (R2 = 0.943). Our results can provide the resources for determining which oxidative process is suitable for treating specific MPs present in the raw waters of DWTPs.

Comparison of four pre-oxidants coupled powdered activated carbon adsorption for odor compounds and algae removal: Kinetics, process optimization, and formation of disinfection byproducts

Pre-oxidation and powdered activate carbon (PAC) are usually used to remove algae and odorants in drinking waterworks. However, the influence of interaction between oxidants and PAC on the treatment performance are scarcely known. This study systematically investigated the combination schemes of four oxidants (KMnO4, NaClO, ClO2, and O3) and PAC on the inactivation of Microcystis aeruginosa cells and removal of four frequently detected odorants in raw water (diethyl disulfide (DEDS), 2,2'-oxybis(1chloropropane) (DCIP), 2-methylisoborneol (2-MIB) and geosmin (GSM)). O3 showed highest pseudo-first-order removal rate for all four compounds and NaClO exhibited highest inactivation rates for the cell viability and Chlorophyll a (Chl-a). The Freundlich model fitted well for the adsorption of DEDS and DCIP by PAC. When treated by combined oxidation/PAC, the removal ratio of algae cells and odorants were lower (at least 1.6 times) than the sum of removal ratios obtained in oxidation or PAC adsorption alone. Among these four oxidants, the highest synchronous control efficiency of odorants (52 %) and algae (66 %) was achieved by NaClO/PAC. Prolonging the dosage time interval promoted the removal rates. The pre-PAC/post-oxidation processes possessed comparable efficiency for the removal of odorants and algae cells comparing with pre-oxidation/post-PAC process, but significantly inhibited formation of disinfection byproducts (DBPs), especially for the formation of C-DBPs (for NaClO and ClO2), bromate (for O3) and chlorate/chlorite (for ClO2). This study could provide a better understanding of improving in-situ operation of the combined pre-treatments of oxidation and PAC for source water.

Constructed electron-dense Mn sites in nitrogen-doped Mn3O4 for efficient catalytic ozonation of pyrazines: Degradation and odor elimination

In this study, N-doped Mn3O4 catalysts (Mn-nN) with electron-dense Mn sites were synthesized and employed in heterogeneous catalytic ozonation (HCO). These catalysts demonstrated excellent performance in pyrazines degradation and odor elimination. The synthesis of Mn-nN was achieved through a facile urea-assisted heat treatment method. Experimental characterization and theoretical analyses revealed that the MnN structures in Mn-nN, played a crucial role in facilitating the formation of electron-dense Mn sites that served as the primary active sites for ozone activation. In particular, Mn-1N exhibited excellent performance in the HCO system, demonstrating the highest 2,5-dimethylpyrazine (2,5-DMP) degradation efficiency. •OH was confirmed as the primary reactive oxygen species involved in the HCO process. The second-order rate constants for 2,5-DMP degradation with O3 and •OH, were determined to be (3.75 ± 0.018) × 10-1 and (6.29 ± 0.844) × 109 M-1 s-1, respectively. Seventeen intermediates were identified through GC-MS analysis during the degradation of 2,5-DMP via HCO process with Mn-1N. The degradation pathways were subsequently proposed by considering these identified intermediates. This study introduces a novel approach to synthesize N-doped Mn3O4 catalysts and demonstrates their efficacy in HCO for the degradation of pyrazines and the elimination of associated odors. The results show that the catalysts are promising for addressing odor-related environmental issues and provide valuable insights about the broader significance of catalytic ozonation processes.

Electronic nose application for detecting different odorants in source water: Possibility and scenario

The problem of taste and odor (T&O) in drinking water is a widespread societal concern and highlights substantial challenges related to the detection and evaluation of odor in water. In this study, the portable electronic nose PEN3, which is equipped with ten different heated metal sensors, was applied to analyze its applicability, feasibility and application scenarios for the detection of typical odorants, such as 2-methylisobornel (2-MIB), geosmin (GSM), β-cyclocitral, β-ionone, and other T&O compounds in source water, while avoiding uncertainties and instability related to manual inspection. All the T&O compounds could be effectively differentiated by principal component analysis (PCA). Linear discriminant analysis (LDA) showed that the odors varied greatly between different samples and could be effectively distinguished. As the odorant concentration increased, the sensor response intensity of the primary identification sensors R6 and R8 increased with a significant positive correlation. For Microcystis aeruginosa, an algae that produces odorants, PCA could distinguish the odors of algae at a series of densities at different concentrations. The responses of R10 showed a significant increase with increasing algae density, implying the production of more aliphatic hydrocarbons and other odor compounds. The results indicated that the electronic nose could provide a promising alternative to traditional unstable and complex detection methods for the detection of odorous substances in surface water and early warning of odor events. This study aimed to provide technical support for rapid monitoring and early warning of odorants in source water management.

Bacillus cereus WL08 immobilized on tobacco stem charcoal eliminates butylated hydroxytoluene in soils and alleviates the continuous cropping obstacle of Pinellia ternata

Butylated hydroxytoluene (BHT), as an emerging contaminant in ecosystems, has potential influences on animals, aquatic organisms, and public health, and has been proven to be a major allelochemical of Pinellia ternata. In this study, Bacillus cereus WL08 was used to rapidly degrade BHT in liquid culture. Strain WL08 immobilized on tobacco stem charcoal (TSC) particles notably accelerated BHT removal in contract to its free cells, and exhibited excellent reutilization and storage capacities. The optimal removal parameters of TSC WL08 were ascertained to be pH 7.0, 30 °C, 50 mg L^-1 BHT and 0.14 mg L^-1 TSC WL08. Moreover, TSC WL08 significantly accelerated the degradation of 50 mg L^-1 BHT in sterile and non-sterile soils compared to that of free WL08 or natural dissipation, and notably shortened their half-lives by 2.47- or 362.14- fold, and 2.20- or 14.99- fold, respectively. Simultaneously, TSC WL08 was introduced into the continuous cropping soils of P. ternata, which accelerated the elimination of allelochemical BHT, and notably enhanced the photosynthesis, growth, yield, and quality of P. ternata. This study provides new insights and strategies for the rapid in situ remediation of BHT-polluted soils and effective alleviation of P. ternata cropping obstacles.

Degradation of odorous 2,4,6-trichloroanisole in chlorinated water by UV-LED/chlorination: kinetics and influence factors

2,4,6-Trichloroanisole (2,4,6-TCA) has aroused a special concern for their odor problem and potential threats. In this study, the degradation of 2,4,6-TCA by UV/chlorination with different UV sources was compared, including low-pressure mercury lamp (LPUV, 254 nm) and ultraviolet light-emitting diode (UV-LED, 275 and 285 nm). The maximum removal of 2,4,6-TCA can be achieved by 275-nm UV-LED/chlorination in neutral and alkaline conditions which was 80.0%. The reaction, kinetics, and water matrix parameters on 2,4,6-TCA degradation were also evaluated. During UV-LED (275 nm)/chlorination, 2,4,6-TCA degradation was mainly caused by direct UV photolysis and indirect hydroxyl radical (HO·) oxidation, while reactive chlorine radicals (RCSs) had a negligible contribution. The second-order rate constant between HO· and 2,4,6-TCA was determined as 3.1 × 10⁹ M^-1 s^-1. Increasing initial chlorine dosage and decreasing 2,4,6-TCA concentration or pH value significantly promoted 2,4,6-TCA degradation during UV/chlorination process. The presence of natural organic matter (NOM) and bicarbonate (HCO₃^-) can inhibit 2,4,6-TCA degradation, while chloride ion (Cl^-) had a negligible effect. The kinetic model for 2,4,6-TCA degradation was established and validated, and the degradation pathways were proposed based on the identified intermediates. Furthermore, UV-LED (275 nm)/chlorination also exhibited a promising effect on 2,4,6-TCA removal in real water, which can be used to control 2,4,6-TCA pollution and odor problems.

Effective catalytic hydrodechlorination removal of chloroanisole odorants in water using palladium catalyst confined in zeolite Y

Chloroanisoles is a class of odorous pollutants commonly identified in drinking water. In the present study, we confined noble metal palladium (Pd) in the micropores of zeolite Y (ie-Pd@Y) using an ion exchange method, and applied it for the catalytic hydrodechlorination removal of chloroanisoles (represented by 2,4,6-trichloroanisole/TCA) in water. Pd supported on zeolite Y surface (im-Pd/Y, prepared by conventional impregnation method) was used as the benchmarking catalyst. The characterization results revealed that ie-Pd@Y had smaller Pd particle size and higher Pdⁿ⁺/Pd⁰ ratio than im-Pd/Y. The catalytic hydrodechlorination of TCA followed a concerted dechlorination pathway and the Langmuir-Hinshelwood model. The ie-Pd@Y catalysts with different Pd loadings exhibit excellent catalytic activities with more than 95% of TCA removed within 30 min, which is far superior to the im-Pd/Y catalysts (27-70%). Moreover, due to the confinement effect of zeolite Y, ie-Pd@Y displayed enhanced catalytic stability as compared with im-Pd/Y. The initial activity of ie-Pd@Y was more than 20 times higher than that of im-Pd/Y after five reaction cycles. Additionally, with the assistance of sieving effect, ie-Pd@Y displayed much stronger capability against the interference from dissolved organic matter than im-Pd/Y. The present results demonstrate that the confined catalysts ie-Pd@Y can be applied in liquid phase catalytic hydrogenation to effectively eliminate halogenated odorants in waters.

Degradation of geosmin and 2-methylisoborneol in UV-based AOPs for photoreactors with reflective inner surfaces: Kinetics and transformation products

Geosmin (GSM) and 2-methylisoborneol (2-MIB) are representative musty/earthy odor compounds commonly present in surface water. In present study, the degradation of GSM and 2-MIB subject to different UV-based advanced oxidation processes (AOPs), including UV/H₂O₂, UV/S₂O₈^2-, UV/chlorine, and UV/chloramine, in a phosphate-buffered saline (PBS) was conducted in a photoreactor with reflective inner surfaces and compared with that in an environmental water sample. A dynamic model to predict the degradation of GSM and 2-MIB in the photoreactor with reflective inner surfaces in the four UV-based AOPs was developed applying the second-order rate constants for the GSM and 2-MIB with primary reactive species (i.e., •OH, •Cl, and •SO₄^-) determined in this study. The model was proven to successfully simulate the degradation of GSM and 2-MIB. In addition, 8, 7, 8, and 11 degradation intermediates were detected from UV/H₂O₂, UV/S₂O₈^2-, UV/chlorine, and UV/chloramine in this study, and possible degradation pathways were proposed. This study is the first to report the degradation kinetics and formation products of GSM and 2-MIB in UV/chloramine. Research based on photoreactors with reflective inner surfaces may provide some guidance for eliminating GSM and 2-MIB in UV-based AOPs for full-scale engineering applications.

Odor-producing response pattern by four typical freshwater algae under stress: Acute microplastic exposure as an example

Algae-induced odor problems in water have been repeatedly occurred concerns for drinking water quality. However, present researches mostly focus on the odor-producing pattern of algae in normal growth, and there is scarce discussion on those under stress. Microplastics (MPs) pollution have been global concern for their negative ecological impacts and frequently co-occurs with odor-producing algal bloom in freshwaters. Thus, this study aimed to elucidate the effects and mechanisms of MPs as an environmental stress on algal odorant production for good illustration of odor-producing response pattern under stress. Variation in MP size (polystyrene microspheres; 100 nm, 1000 nm and 10 μm) had significant effects on odorant formation (β-cycloidal, 2-methylisopropanol, 2,4-heptandienal and 2,4-decadienal) by four freshwater algae (Microcystis aeruginosa, Pseudanabaena sp., Cyclotella meneghiniana and Melosira varians). The size ratio of MPs over cells (SRMC) was proposed to categorize the size-ratio dependent effects on the algal odorant production. Interestingly, when SRMC was in the range of 0.1-1, there were always promoting effects; when SRMC < 0.1 or SRMC > 1, there exhibited inhibiting effects, and the inhibiting effects of SRMC < 0.1 were far more severe than those of SRMC > 1. The promotion on odorant production in the SRMC range of 0.1-1 was mainly attributed to the increase in cellular yield, which was related to the increased odorant precursors derived from the oxidation products of reactive oxygen species (ROS). Alternatively, the inhibition of odorant production caused by MPs with SRMC < 0.1 was the results of simultaneously inhibiting cellular density and cellular yield, which might be attributed to the cellular internalization of MPs, inducing the extensive toxic effects. This study illustrated the possibilities of MPs in impairing the esthetics of the source water and provided guidance for the future algal odor issues under stress.

Ozonation of organic compounds in water and wastewater: A critical review

Ozonation has been applied in water treatment for more than a century, first for disinfection, later for oxidation of inorganic and organic pollutants. In recent years, ozone has been increasingly applied for enhanced municipal wastewater treatment for ecosystem protection and for potable water reuse. These applications triggered significant research efforts on the abatement efficiency of organic contaminants and the ensuing formation of transformation products. This endeavor was accompanied by developments in analytical and computational chemistry, which allowed to improve the mechanistic understanding of ozone reactions. This critical review assesses the challenges of ozonation of impaired water qualities such as wastewaters and provides an up-to-date compilation of the recent kinetic and mechanistic findings of ozone reactions with dissolved organic matter, various functional groups (olefins, aromatic compounds, heterocyclic compounds, aliphatic nitrogen-containing compounds, sulfur-containing compounds, hydrocarbons, carbanions, β-diketones) and antibiotic resistance genes.

Kinetic and mechanistic investigation of geosmin and 2-methylisoborneol degradation using UV-assisted photoelectrochemical

The taste and odor (T&O) problem represented by 2-methylisoborneol (2-MIB) and geosmin (GSM) in water is the multiple undesirable substances in the drinking water and the aquatic industry. In this study, the UV-assisted photoelectrochemical, a prospective advanced oxidation process (AOP), was evaluated for the degradation of 2-MIB and GSM. In contrast to UV photochemical and electrochemical, the degradation ratio of GSM (2-MIB) increase to 96% (95%) in 25 min. The removal ratio and rate depended on reaction time, electrolyte concentration, current density, and water quality parameters (e.g. pH, HCO₃^-, natural organic matter, and tap water). Among these parameters, a high concentration of electrolyte and acidic solutions could accelerate the rate and increase the ratio, while alkaline conditions and the impurity content had negative effects. Furthermore, the significant role of various reactive species (e.g. HO∙, Cl, ClO, etc) were highlighted by scavenging experiments. Complex free radicals exist was further verified by electron paramagnetic resonance spectroscopy (EPR) experiments. The intermediates were identified and the possible degradation pathways during the UV-assisted photoelectrochemical reactions of both compounds were proposed. Overall, the UV-assisted photoelectrochemical is beneficial to the removal of GSM and 2-MIB in water.

Moderate pre-ozonation coupled with a post-peroxone process remove filamentous cyanobacteria and 2-MIB efficiently: From bench to pilot-scale study

The increasing frequency and intensity of taste- and odour-producing cyanobacteria in water sources is a growing global issue. Odour events caused by 2-methylisoborneol (2-MIB) mainly arising from filamentous cyanobacteria have been a very common problem in water supply. Removal rates of filamentous cyanobacteria and 2-MIB by conventional water treatment, such as coagulation, and disinfection treatment processes is low. Hence, a moderate pre-ozonation of cyanobacteria (with little cell damage) was proposed in this study as an enhanced coagulation step to remove filamentous cyanobacteria and intracellular 2-MIB effectively, while avoiding the release of intracellular 2-MIB. A post-peroxone (O₃/H₂O₂) process was applied after sand filtration to degrade the residual dissolved 2-MIB. Results show that moderate pre-ozonation (0.2 mg/L O₃ oxidation for 20 min) can substantially enhance the coagulation efficiency for algae, with low cell lysis and high cell viability. Furthermore, 2.0 mg/L O₃ combined with 2.0 mg/L H₂O₂ can degrade the residual dissolved 2-MIB nearly 100% after 20 min reaction. Based on the optimal dosages, a 0.6 m³/h pilot system, including pre-ozonation, coagulation and sedimentation, sand filtration, and post-peroxone processes, was continuously run for 14 days, and it was found that the proposed process can effectively and stably remove filamentous cyanobacteria and 2-MIB.

Microbial Degradation of 2-Methylisoborneol in Forest Soil

Microorganisms use a complex array of chemical compounds to interact with their surroundings. They produce and process different molecules in response to changes in the environment or in their metabolism. One of the most well-known volatile organic compounds produced by microorganisms is the C11-terpenoid 2-methylisoborneol (2-MIB), which has received attention because of the off-flavor it confers to fresh and reservoir water as well as to cultured fish. Cleaning water supplies of the off-flavor 2-MIB has been of interest for the scientific community for years, with the use of techniques that are either expensive, e. g., activated carbon, or create toxic byproducts, e. g., ozonation. In the present study, soil samples from nature were collected from a forest and the volatile organic compounds produced by microbes were extracted and analyzed with focus on non-canonical terpenoid structures. HS-SPME-GC/MS analysis of soil samples revealed 1-methylcamphene (1-MC), 2-methylenebornane (2-MB) and 2-MIB as C11-terpenoids. Due to the high 1-MC/2-MIB ratio compared to previous reports, it was hypothesized that microbial degradation of 2-MIB was in place. Addition of synthetic 2-MIB to biologically active soil revealed complete degradation of the pollutant to 2-MB, 1-MC and 2-methyl-2-bornene (2-M2B). The results suggest the potential of using respective natural microorganisms for biodegradation of 2-MIB, with applications in water treatment, fishery and soil ecology.

Data Analytics Determines Co-occurrence of Odorants in Raw Water and Evaluates Drinking Water Treatment Removal Strategies

A complex dataset with 140 sampling events was generated using triple quadrupole gas chromatography-mass spectrometer to track the occurrence of 95 odorants in raw and finished water from 98 drinking water treatment plants in 31 cities across China. Data analysis identified more than 70 odorants with concentrations ranging from not detected to thousands of ng/L. In raw water, Pearson correlation analysis determined that thioethers, non-oxygen benzene-containing compounds, and pyrazines were classes of chemicals that co-occurred, and geosmin and p(m)-cresol, as well as cyclohexanone and benzaldehyde, also co-occurred, indicating similar natural or industrial sources. Based on classification and regression tree analysis, total dissolved organic carbon and geographical location were identified as major factors affecting the occurrence of thioethers. Indoles, phenols, and thioethers were well-removed through conventional and advanced treatment processes, while some aldehydes could be generated. For other odorants, higher removal was achieved by ozonation-biological activated carbon (39.3%) compared to the conventional treatment process (14.5%). To our knowledge, this is the first study to systematically identify the major odorants in raw water and determine suitable treatment strategies to control their occurrence by applying data analytics and statistical methods to the complex dataset. These provide informative reference for odor control and water quality management in drinking water industry.

The formation, analysis, and control of chlor(am)ination-derived odor problems: A review

Odors and tastes have become universal problems related to drinking water quality. In addition to the typical odor problems caused by algae or microorganisms, the occurrence of odors derived from drinking water disinfection have attracted attention. The chlor(am)ination-derived odor substances have certain toxicity and odor-causing characteristics, and would enter the tap water through water distribution systems, directly affecting drinking water safety and customer experience. This study provided a comprehensive overview of the occurrence, detection, and control of odor substances derived from drinking water chlor(am)ination disinfection. The occurrence and formation mechanisms of several typical types of disinfection derived odor substances were summarized, including haloanisoles, N-chloroaldimines, iodotrihalomethanes, and halophenoles. They are mainly derived from specific precursors such as halophenols, anisoles, and amino acids species during the disinfection or distribution networks. In addition, the change of disinfectant during chlor(am)ination was also one of the causes of disinfection odors. Due to the extremely low odor threshold concentrations (OTCs) of these odor substances, the effective sample pre-enrichment for instrument identification and quantification are essential. The control strategies of odor problems mainly include adsorption, chemical oxidation, and combined processes such as ozonation and biological activated carbon processes (O₃/BAC) and ultraviolet-based advanced oxidation processes (UV-AOPs). Finally, the challenges and possible future research directions in this research field were discussed and proposed.

Comparative evaluation of 2-isopropyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, and 2,4,6-trichloroanisole degradation by ultraviolet/chlorine and ultraviolet/hydrogen peroxide processes

2-Isopropyl-3-methoxypyrazine (IPMP), 2-Isobutyl-3-methoxypyrazine (IBMP), and 2,4,6-Trichloroanisole (TCA) are the primary emerging taste and odor (T&O) compounds in water systems with low thresholds (ng L^-1). The selected T&O compounds are known to be difficult to remove using conventional water treatment processes. In this study, we compared the removal characteristics of the three T&O compounds using UV/Cl₂ and UV/H₂O₂. The removal rates of the three compounds by direct photolysis at 254 nm were less than 10%, even at a high UV dose (approximately 1000 mJ cm^-2). Under conditions of an oxidant injection volume of 5 mg L^-1 and UV dose of 1000 mJ cm^-2, the degradation rate of the target compounds in the UV/H₂O₂ process exceeded that of the UV/Cl₂ process. Moreover, the results revealed that pH has a significant impact on the removal of the T&O compounds during the UV/Cl₂ process. The IPMP, IBMP, and TCA were found to be more reactive with hydroxyl radicals than reactive chlorine species (RCS). A predictive tool was developed to determine the optimal operating condition using the generalized reduced gradient (GRG) nonlinear solver. In the UV/H₂O₂ process, the EED value for 90% removing rate was 0.156 kWh m^-3 for the IPMP, 0.135 kWh m^-3 for the IBMP, and 0.154 kWh m^-3 for the TCA, respectively. In case of the UV/Cl₂, the EED value for 50% removing rate was 0.174 kWh m^-3 for the IPMP, 0.138 kWh m^-3 for the IBMP, and 0.169 kWh m^-3 for the TCA, respectively.

Optimization of ozone dosage in an ozone contact tank using a numerical model

Ozone has been widely applied in drinking water and wastewater treatment plants, and it is essential to determine the ozone dosage and its ratio in ozone contact tank to increase the ozone absorption and utilization rates. Batch experiments were performed to determine the first-order reaction rate coefficient of ozone (k₁) in different raw water qualities. Results showed that k₁ had an exponential decaying relationship with the ozone consumption amount (ΔO₃). Based on the ozone mass transfer and decomposition kinetics, a numerical model was developed to optimize the total ozone dosage and its ratio in three aeration parts by calculating the ozone absorption and utilization rates in an ozone contact tank. The ozone absorption rate was little affected by the water quality, and an even distribution of ozone could greatly increase the ozone absorption rate. However, the ozone utilization rate was tightly related with the water quality. For waters that consumed ozone quickly, ozone should be dosed equally in three aeration parts to increase the ozone utilization rate up to 94.3%. Otherwise, more ozone should be dosed in the first aeration part. An increase in ozone utilization rate would induce an increase in the degree of water purification. This model could give theoretical support for the determination of ozone dosage and its ratio in water treatment plants rather than experience.

Disinfection byproduct formation from algal organic matters after ozonation or ozone combined with activated carbon treatment with subsequent chlorination

Algal organic matter (AOM), including extracellular organic matter (EOM) and intracellular organic matter (IOM) from algal blooms, is widely accepted as essential precursors of disinfection byproducts (DBPs). This study evaluated the effect of ozonation or ozone combined with activated carbon (O₃-AC) treatment on characteristic alternation and DBP formation with subsequent chlorination of Chlorella sp.. The effects of pH and bromide concentration on DBP formation by ozonation or O₃-AC treatment were also investigated. Results showed that the potential formation of DBPs might be attributed to ozonation, but these DBP precursors could be further removed by activated carbon (AC) treatment. Moreover, the formation of target DBPs was controlled at acidic pH by alleviating the reactions between chlorine and AOM. Besides, the bromide substitution factor (BSF) value of trihalomethanes (THMs) from EOM and IOM remained constant after AC treatment. However, THM precursors could be significantly decreased by AC treatment. The above results indicated that O₃-AC was a feasible treatment method for algal-impacted water.

Development and optimization of analytical methods for the detection of 18 taste and odor compounds in drinking water utilities

Taste and odor (T&O) issues have been a major concern among drinking water utilities as source waters are becoming increasingly vulnerable to compounds released during algal blooms as well as non-algal compounds. While most of the literature focuses on the two most common T&O compounds - 2-MIB and geosmin, there are other compounds that have the potential to cause T&O events. The aim of this study was to develop an advanced analytical method using solid phase microextraction (SPME) and gas chromatography-tandem mass spectrometry (GC-MS/MS) to identify 18 T&O compounds belonging to various odor classes. The developed method was optimized for the 18 analytes and implemented to determine the holding time of the compounds in raw and treated (distribution system point-of-entry or PoE) drinking water matrices. Compounds belonging to certain classes such as pyrazines and anisoles were found to be "stable" (< 30% loss) in all tested waters for up to two weeks, while aldehydes, ketones, esters and alkyl sulfides showed > 30% loss within 96 h in raw water. Preservation of samples at low pH (< 2) using hydrochloric acid increased the holding times and reduced losses within 96 h for aldehydes, ketones and esters. The paper also discusses the occurrence of these compounds with water utilities from the Midwest and Eastern US during the summer months. The study detected eight T&O compounds - 2-MIB, geosmin, β-cyclocitral, β-ionone, hexanal, indole, dimethyl disulfide and dimethyl trisulfide. While five compounds were detected above their threshold concentrations in the raw water, two of them (2-MIB and geosmin) were detected above threshold in the PoE samples.

Simultaneous nitrification and denitrification in the bio-cathode of a multi-anode microbial fuel cell

A multi-anode microbial fuel cell (MA-MFC) was developed to investigate simultaneous nitrification and denitrification (SND) in the bio-cathode. As the chemical oxygen demand to nitrogen (COD/N) ratio of the cathode was increased from 0 to 4.5, the electricity-producing quantity ranged between 498 and 543 C and the attained total nitrogen (TN) removal rate reached 12.07 g TN·m^-3·d^-1, resulting in a TN removal efficiency of 78.8% under the target COD/N ratio of 3.5. The removal of pollutants in series and parallel, open-circuit and closed-circuit were compared, respectively. The removal rates of TN, NH4+-N, and cathode and anode COD were all higher in the parallel connection configuration than in the series configuration. In parallel connection, the TN removal rate reached 14.4 g TN·m^-3·d^-1, which was 1.9 times that in series connection. Compared with the open-circuit system, the removal rate of TN in the closed-circuit system was improved by 17.8%, which could be ascribed to electrochemical denitrification. The results of high-throughput sequencing confirmed and clarified the presence of autotrophic denitrification and heterotrophic denitrification, including aerobic denitrification, when the MA-MFC had been operated for 18 months.

Unveiling the transformation of dissolved organic matter during ozonation of municipal secondary effluent based on FT-ICR-MS and spectral analysis

Ozonation is a well-recognized process in advanced treatment of municipal secondary effluent for water reclamation. However, the transformation of dissolved effluent organic matter (dEfOM) during ozonation of real effluents, particularly at molecular level, has been scarcely reported. In this study, we performed ozonation treatments on real secondary effluents from two municipal wastewater treatment plants, and used Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and various spectroscopic techniques to probe the transformation of dEfOM at four ozone dosage levels (0.28, 0.61, 0.89, and 1.21 mg O₃/mg DOC). Most of the precursors were unsaturated and reduced compounds (positive double bond equivalent minus oxygen per carbon ((DBE-O)/C) and negative nominal oxidation state of carbon (NOSC)), whereas the products were mainly the saturated and oxidized ones (negative (DBE-O)/C and positive NOSC). As the ozone dosage increased, the relative abundance of O_8-19 species gradually increased in the ozonated samples, whereas an opposite trend was observed for O_5-7S₁ species. Further, we employed 18 types of reactions to represent the ozonation process, and found that the oxygenation reaction (+3O) possessed the largest number of possible precursor-product pairs, and CHON compounds possessed the highest reactivity. Besides the dominant oxygenation reactions, decyclopropyl (-C₃H₄) was relatively common reaction for CHON compounds, while it was oxidative desulfonation (-SH₂) for CHOS ones. In addition, the transformation of precursors to products accompanied with the drop of (DBE-O)/C, and the increase of NOSC and the O/C ratio. The precursors with aromaticity and fluorescence were mainly correlated with the compounds featuring higher (DBE-O)/C and lower NOSC values. This study is believed to help better understand and improve the application of ozonation process in advanced treatment of real wastewater.

Characteristics and Behavior of Different Catalysts Used for Water Decontamination in Photooxidation and Ozonation Processes

The objective of this study was to summarize the results obtained in a wide research project carried out for more than 15 years on the catalytic activity of different catalysts (activated carbon, metal–carbon xerogels/aerogels, iron-doped silica xerogels, ruthenium metal complexes, reduced graphene oxide-metal oxide composites, and zeolites) in the photooxidation (by using UV or solar radiation) and ozonation of water pollutants, including herbicides, naphthalenesulfonic acids, sodium para-chlorobenzoate, nitroimidazoles, tetracyclines, parabens, sulfamethazine, sodium diatrizoate, cytarabine, and surfactants. All catalysts were synthesized and then texturally, chemically, and electronically characterized using numerous experimental techniques, including N2 and CO2 adsorption, mercury porosimetry, thermogravimetric analysis, X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, diffuse reflectance UV–vis spectroscopy, photoluminescence analysis, and transmission electron microscopy. The behavior of these materials as photocatalysts and ozonation catalysts was related to their characteristics, and the catalytic mechanisms in these advanced oxidation processes were explored. Investigations were conducted into the effects on pollutant degradation, total organic carbon reduction, and water toxicity of operational variables and the presence of different chemical species in ultrapure, surface, ground, and wastewaters. Finally, a review is provided of the most recent and relevant published studies on photocatalysis and catalyzed ozonation in water treatments using similar catalysts to those examined in our project.

Ultraviolet-mediated peroxymonosulfate diminution of earthy and musty compound trichloroanisole in water

Taste and odor (T&O) problem in water is one of the main obstacles to improve the quality of drinking water, and efficient water treatment processes are urgently needed to control T&O compounds. Ultraviolet-mediated peroxymonosulfate (UV/PMS) diminution of trichloroanisole (TCA) in water was investigated in this paper. The treatment of 2,3,6-trichloroanisole (2,3,6-TCA) by three advanced oxidation processes (UV, UV/H₂O₂ and UV/PMS) was compared, and UV/PMS stood out. SO₄^•- and HO• were produced in the UV/PMS, and their specific contributions to 2,3,6-TCA oxidation were investigated. The competitive kinetic model was applied to determine the second-order reaction rate between 2,3,6-TCA and SO₄^•- or HO•. The products of 2,3,6-TCA generated in UV/PMS were analyzed with gas chromatography/high resolution-mass spectrometry (GC/HR-MS), and the degradation mechanism was proposed. The effects of water matrices (chloride, bicarbonate and humic acid) on UV/PMS performance were studied, and the decontamination of 2,3,6-TCA in real water was carried out. The disinfection byproducts (DBPs) alteration from 2,3,6-TCA by UV/PMS - chlorination treatment was explored. Overall, UV/PMS can effectively deal with the T&O pollution of TCA in water.

Hydroxyl radical scavenging factor measurement using a fluorescence excitation-emission matrix and parallel factor analysis in ultraviolet advanced oxidation processes

The performance of the UV/H₂O₂ advanced oxidation process (AOP) is dependent on water quality parameters, including the UV absorbance coefficient at 254 nm and hydroxyl radical (•OH) water background demand (scavenging factor, s^-1). The •OH scavenging factor represents the •OH scavenging rate of the background substances in the water matrix, and it is known to be one of the key parameters to predict the performance of the UV/H₂O₂ process. The •OH scavenging factor has been determined experimentally by using a probe compound such as pCBA and rhodamine B. The experimental method has been validated to accurately predict the micropollutants removal in the UV/H₂O₂ process, but there is a need for an easier and simple method of determining the OH scavenging factor. We evaluated the alternative method to analyze the •OH scavenging factor using fluorescence excitation-emission matrix and parallel factor analysis (F-EEM/PARAFAC). The correlation between •OH scavenging factor and the spectroscopic characteristics and structure of different organic matter types was evaluated. Organic matter was characterized using a fluorescence excitation-emission matrix, parallel factor analysis, and liquid chromatography-organic carbon detection. Second-order reaction rates of humic acid sodium salt, sodium alginate, Suwannee River humic acid and bovine serum albumin were calculated as 1.30 × 10⁸ M^-1 s^-1, 1.39 × 10⁸ M^-1 s^-1, 1.03 × 10⁸ M^-1 s^-1, and 3.17 × 10⁷ M^-1 s^-1, respectively. Results of PARAFAC analysis, the ratio of humic and fulvic fluorescence component 2 to terrestrial humic-like fluorescence component 1 (C2/C1), and •OH scavenging factor showed high linearity. A predictive model, which combines with the F-EEM/PARAFAC method, predicted the optimal UV and H₂O₂ dose to achieve target compound removal.

Kinetic and mechanistic investigation of water taste and odor compound 2-isopropyl-3-methoxy pyrazine degradation using UV-A/Chlorine process

The present study was launched as a continuation of global efforts to tackle problems associated with two important aesthetic characteristics, taste and odor (T&O), of drinking water. The UV-A/Chlorine process, a promising advanced oxidation process (AOP), was evaluated for the first time for the removal of 2-isopropyl-3-methoxy pyrazine (IPMP), a widely reported compound in the literature that causes unpleasant taste and odor when present in water at or below the ng L^-1 level. It was found that the studied process was efficient for the removal of IPMP in both ultrapure and drinking water. The initial chlorine dosage influenced significantly the degradation efficiency under initial neutral pH values. Degradation efficiency of IPMP was slightly inhibited by using drinking water as matrix. Scavenging experiments highlighted the significant role of various reactive species (e.g. HO, ClO, Cl, Cl₂^-) generated during the process that have not been studied comprehensively until now. In addition, the significant role of HO was further verified by Electron paramagnetic resonance spectroscopy (EPR) experiments. Overall, the formation of diverse radicals during the UV-A/Chlorine treatment enhanced the degradation of IPMP, promoting mainly the formation of hydroxy, hydroperoxy and dealkylated derivatives. In contrast, chlorinated by-products were only identified in traces.

Microbubble ozonation of the antioxidant butylated hydroxytoluene: Degradation kinetics and toxicity reduction

Butylated hydroxytoluene (BHT) is recognized as a crucial pollutant in aquatic environments, but efforts to achieve its complete removal are without success. The aim of this study was to investigate the degradation efficiency of BHT in water using ozone microbubbles (OMB), coupled with toxicity change assessment at sub-lethal BHT concentrations (0.34, 0.45 and 0.90 μM) based on oxidative stress biomarkers in Daphnia magna. The efficiency of OMB on ozone gas mass transfer was assessed and the contribution of hydroxyl radicals (·OH) in the degradation of BHT was determined using p-chlorobenzoic acid (pCBA) probe compound and a ·OH radical scavenger (sodium carbonate, Na₂CO₃). The ozone gas mass transfer coefficient (k_La = 1.02 × 10^-2 s^-1) was much larger than the ozone self-decomposition rate (k_d = 8 × 10^-4 s^-1) implying little influence of self-decomposing ozone in the volumetric ozone transfer during OMB generation. Generally, OMB improved ozone gas mass transfer (1.3-19-fold) relative to conventional ozone techniques, while indirect reaction of BHT with ·OH was dominant (82%) over the direct reaction with molecular ozone. Addition of 15, 25 and 35 mM Na₂CO₃ reduced BHT degradation by 30, 50 and 65%, respectively, indicating the significance of ·OH in the degradation of BHT. Increase in initial BHT concentration correspondingly reduced its removal rate by OMB possibly due to increase in metabolites produced during ozonation. Post BHT treatment exposure tests recorded significant (p < 0.05) reductions in oxidative stress (according to enzyme activities changes) in D. magna compared to pretreatment tests, demonstrating the effectiveness of OMB in detoxification of BHT. Overall, the results of the study indicate that OMB is extremely efficient in complete degradation of BHT in water and, consequently, significantly (p < 0.05) reducing its toxicity.

A comparative study of UV/H2O2 and UV/PDS for the degradation of micro-pollutants: kinetics and effect of water matrix

Organic micro-pollutants such as pesticides and endocrine disruptors cause serious harm to human health and aquatic ecosystem. In this study, the potential degradation of atrazine (ATZ), triclosan (TCS), and 2,4,6-trichloroanisole (TCA) by UV-activated peroxydisulfate (UV/PDS) and UV-activated H₂O₂ (UV/H₂O₂) processes were evaluated under different conditions. Results showed that UV/PDS process was more effective than UV/H₂O₂ under the same conditions. Increasing oxidant dosage or decreasing the initial ATZ, TCS, and TCA concentrations promoted the degradation rates of these three compounds. The presence of natural organic matter (NOM) could effectively scavenge sulfate radical (SO₄•^-) and hydroxyl radical (HO•) and reduced the removal rates of target compounds. Degradation rates of ATZ and TCA decreased with pH increasing from 5.0 to 9.0 in UV/PDS process, while in UV/H₂O₂ process, the increase of solution pH had little effect on ATZ and TCA degradation. In the UV/PDS and UV/H₂O₂ oxidation process, when the solution pH increased from 5 to 8, the removal rates of TCS decreased by 19% and 1%, while when the solution pH increased to 9, the degradation rates of TCS increased by 23% and 17%. CO₃^2-/HCO₃^- had a small inhibitory effect on ATZ and TCA degradation by UV/H₂O₂ and UV/PDS processes but promoted the degradation of TCS significantly (> 2 mM). Cl^- had little effect on the degradation of ATZ, TCA, and TCS in UV/H₂O₂ process. Cl^- significant inhibited on the degradation of ATZ and TCS, but the influence of Cl^- on the degradation of TCA was weak in UV/PDS process. Based on these experimental results, the various contributions of those secondary radicals (i.e., carbonate radical, chlorine radical) were discussed. This study can contribute to better understand the reactivities when UV/PDS and UV/H₂O₂ are applied for the treatment of micro-pollutant-containing waters.

Occurrence and removal of 10 odorous compounds in drinking water by different treatment processes

This study investigated the prevalence of ten odorous compounds (2-methylisoborneol, trans-1,10-dimethyl-trans-9-decalol, isophorone, 2,4,6-trichloroanisole, 2,3,6-trichloroanisole, 2,3,4-trichloroanisole, β-cyclocitral, β-ionone, 2-isobutyl-3-methyoxypyrazine, and 2-isopropyl-3-methoxypyrazine) in raw drinking water, as well as their removal by traditional processes, advanced oxidation processes, ultrafiltration, and nanofiltration processes, with the use of an ultrahigh-resolution Orbitrap. The most abundant odorous compounds referred to 2-methylisoborneol and trans-1,10-dimethyl-trans-9-decalol with maximal concentrations of 1.6 ng/L and 0.09 ng/L after treatment by traditional processes respectively, and their maximal concentration was 2.05 ng/L and lower than the detection limit after treatment by advanced oxidation processes, while the raw drinking water of the mentioned two processes was different. The high concentration of isophorone in water treated by traditional process, advanced oxidation process, and membrane process was also ascertained. On the whole, the removal rate of membrane process is the maximal for all odorous compounds except for 2,3,6-trichloroanisole, followed by the advanced oxidation process as well as the traditional process. Eight odorous compounds identified in raw water were preserved after traditional treatment, while five compounds were preserved after the advanced oxidation treatment. The combined ultrafiltration and nanofiltration with pre-flocculation was more effective than either the advanced oxidation process or the traditional treating process in removing odorous compounds, and over 90% of all the odorous compounds were removed. Further investigation is required to facilitate the removal of odorous compounds from drinking water by the incorporation of ultrafiltration and nanofiltration units based on current drinking water treatments.

Projecting competition between 2-methylisoborneol and natural organic matter in adsorption onto activated carbon from ozonated source waters

Though the ozone-activated carbon process has been widely applied for drinking water purification, little is known about how ozone-modified natural organic matter (NOM) competes with micropollutants in activated carbon adsorption. In this study, three natural waters and one synthetic water (standard humics solution) with highly heterogeneous NOM compositions were employed to investigate the interference of ozonated NOM with the adsorption of 2-methylisoborneol (MIB). Analysis using liquid chromatography with online carbon and UV₂₅₄ detection (LC-OCD-UVD) revealed that ozonation led to various disintegration patterns of macromolecules in NOM, and UV absorbance was reduced markedly for nearly all NOM fractions. Powdered activated carbon (PAC) adsorption experiments showed that increasing ozone consumption coincided with reducing NOM competition against MIB in the three natural waters, as expressed by the fitted initial concentrations of the equivalent background compound (c_0,EBC). In the synthetic water, in contrast, competition increased under low/moderate specific ozone consumptions and then decreased with further elevation of ozone consumptions. Regarding the significance on affecting ozonated NOM interference, aromaticity reduction outweighed formation of low molecular weight (LMW) organics in most cases, enhancing MIB adsorption capacity. However, disintegration of the humics fraction with larger molecular weight (1,103 g/mol, as compared to 546-697 g/mol in three natural waters) into smaller, more competitive fractions caused the observed initial deteriorated MIB adsorption in synthetic water. A superior correlation between c_0,EBC and the UV absorbance of LMW organics (R² = 0.93) over concentrations of LMW organics underlined the importance of the aromatic properties in competitive adsorption projection for ozone pretreated natural waters. Furthermore, the change of relative concentration of UV absorbing compounds during ozonation could help estimate the decrease of c_0,EBC, which could be a promising tool for waterworks to adjust PAC doses for MIB removal in ozonated waters.

OH degraded 2-Methylisoborneol during the removal of algae-laden water in a drinking water treatment system: Comparison with ClO2

The growth of algae in water and the taste and odour compounds produced by algal metabolism present a threat to water quality, public health and aquatic ecosystems and cannot be effectively removed by conventional water treatment processes. In this paper, a hydroxyl radical (OH)-based drinking water treatment system (DWTS) with a capacity of 480 m³ per day was built in the Xinglin water plant, Xiamen, China. With pretreatment at 0.88 mg L^-1, sand filtration, and disinfection at 0.31 mg L^-1 during the conveyance of algae-laden water within only 9.8 s, OH removed all five kinds of algae, with a total content of 35,180 cells mL^-1, while ClO₂ treatment left live and dead algae at 7150 cells mL^-1, which would be transported into the pipe networks for the drinking water supply. Meanwhile, OH degraded 2-Methylisoborneol (2-MIB) from 175 to 4.4 ng L^-1, which was below the Chinese standard of 10 ng L^-1, while ClO₂ degraded 2-MIB only to 155 ng L^-1. Based on analyses of the mass spectra database, OH could mineralize 2-MIB by opening the ring structures of 2,2-dimethyl-1,3-cyclopentanedione and 2-methyl-cyclohexenecarboxaldehyde to produce small-molecule compounds. After OH pretreatment and OH disinfection, all water quality and disinfection by-product indexes met the Chinese Sanitary Standards for Drinking Water. Therefore, OH advanced oxidation produced using strong ionization discharge could be practically applied for the degradation of 2-MIB during the treatment of algae-laden water in the OH DWTS.

Elimination of trichloroanisoles by UV/H2O2: Kinetics, degradation mechanism, water matrix effects and toxicity assessment

The elimination of 2,3,6-trichloroanisole (2,3,6-TCA), which produces a musty-earthy off-odor in water, by an ultraviolet (UV)/H₂O₂ process was assessed. The removal of 88.1% of 2,3,6-TCA in ultrapure water (UPW) was achieved using an initial 2,3,6-TCA concentration of 1 μg L^-1 (4.73 nM), a H₂O₂ concentration of 20 mg L^-1 (0.588 mM), a UV intensity of 1.44 mW cm^-2 and a pH of 8.2. The reaction was found to be pseudo first order with a rate constant (k_obs) of 0.0340 min^-1. Both the removal efficiency and k_obs increased significantly upon increasing the H₂O₂ concentration from 10 to 50 mg L^-1. The second order rate constant (k_{HO·,2,3,6-TCA}) in competition kinetic trials was determined to be 8.17 × 10⁷ M^-1s^-1. Degradation products generated during both the UV photolysis and UV/H₂O₂ treatment of 2,3,6-TCA solutions were analyzed using ultrahigh resolution gas chromatography/mass spectrometry, and the degradation mechanism was proposed. The toxicities of water solutions during both processes were assessed via a luminescence method in conjunction with Vibrio fischeri. The pH and Cl^-, HCO₃^- and natural organic matter concentrations of the aqueous medium were all found to significantly affect the removal of 2,3,6-TCA. The degradation rates of trichloroanisoles (TCAs) in real-world water samples demonstrated that UV/H₂O₂ has significant potential with regard to controlling TCAs as pollutants in water.

Ozonolysis of β-Caryophyllonic and Limononic Acids in the Aqueous Phase: Kinetics, Product Yield, and Mechanism

Ozonolysis of β-caryophyllonic (BCA) and limononic (LA) acids in the aqueous-phase was investigated. The rate coefficients (k_ozone) measured for the BCA + ozone (O₃) reaction at 295 ± 2 K were 4.8 ± 0.6 × 10⁵ M^-1 s^-1 at pH = 2 and 6.0 ± 0.3 × 10⁵ M^-1 s^-1 at pH = 8. The UV-vis absorption cross sections (σ, cm² molecule^-1) for BCA and LA in water were also measured. Atmospheric lifetimes of BCA and LA due to reactions with O₃, hydroxyl radicals (OH), and due to photolysis were calculated. Lifetime estimates indicate that the aqueous-phase processing of both terpenoic acids studied in this work would be relevant in the atmosphere. In cloudwater, BCA is more likely to react with O₃ with some possible contribution from the oxidation by OH, whereas the opposite is true for LA. Products of BCA and LA ozonolysis were quantified with LC-MS as well as with the UV-vis assays for quantification of formaldehyde and hydroperoxides. Oxygenated derivatives of BCA and LA that were produced following aqueous ozonolysis were identified as keto-BCA and keto-LA, respectively. Additionally, large quantities of intramolecular secondary ozonides and α-acyloxyhydroperoxy aldehydes were tentatively identified as products of aqueous ozonolysis of the two unsaturated terpenoic acids investigated.

Treatment performance comparison between regular O3-BAC and O3-BAC with rear sand filtration: verification in a full-scale study

BACKGROUND

To improve the microbial safety of drinking water, an arrangement of O₃-BAC with rear sand filtration (O₃-BAC-sand) has been proposed. In this study, efforts were devoted to evaluate the benefits and drawbacks of O₃-BAC-sand in a full-scale water treatment plant. The performance of the two configurations was compared in terms of particles, turbidity, COD_Mn and typical odorants and pesticides.

RESULTS

The O₃-BAC-sand yielded lower turbidity but higher COD_Mn (by approximately 7%) in the finished water than regular O₃-BAC (sand-O₃-BAC). Both systems removed odors in raw water; however, sand-O₃-BAC was more effective on septic and musty odorants. The total pesticide removals by sand-O₃-BAC and O₃-BAC-sand were 78% and 72%, respectively; though the latter had shorter activated carbon durable years.

CONCLUSION

The re-location of the sand filter would sacrifice the BAC efficiency in removals of organic matter and micropollutants. This tradeoff is a result of the loss of the particulate organic matter removal by sand filters, because locating the sand filter behind BAC causes particle load increase on BAC; some measures of enhanced coagulation should be suggested to improve the turbidity and particle removal. The study will be helpful for improvement of the O₃-BAC process in drinking water treatment.

Impact of UV irradiation on Chlorella sp. damage and disinfection byproducts formation during subsequent chlorination of algal organic matter

The frequent occurrence of algal blooms in surface water has attracted more and more attention, which caused many water quality problems, including disinfection byproducts (DBPs). Algal organic matter (AOM) including intracellular organic matter (IOM) and extracellular organic matter (EOM), was a well-known precursor to DBPs formation in drinking water. This study evaluated the effect of ultraviolet (UV) irradiation on the cell integrity, IOM release and DBPs formation during subsequent chlorination of Chlorella sp. Results showed the damage rates of algal cells increased to 40.1% after the high UV irradiation of 528 mJ/cm², which contributed to the release of IOM. In addition, UV irradiation was effective in reducing the formation of haloacetic acids (HAAs) both in AOM and IOM, but promoted the formation of nitrogenous DBPs (N-DBPs) from AOM in subsequent chlorination. Furthermore, neutral pH exerted a positive effect on the formation of DBPs. UV irradiation decreased the bromine substitution factor (BSF) value of AOM at a high bromide level. The BSF values increased with increasing of the concentration of bromide. Moreover, more amino acids and low molecular weight precursors were produced after UV irradiation in filtered supernatant, which contributed to the formation of N-DBPs with algal chlorination. Overall, this information demonstrated pre-oxidation of UV irradiation could be used to treat the algal-rich drinking water.

Degradation kinetics and pathways of β-cyclocitral and β-ionone during UV photolysis and UV/chlorination reactions

β-cyclocitral and β-ionone are ones of major algal odorants produced by oxidation of the β-carotene that exists in algae cells. These compounds degraded the quality of drinking water therefore it needed to be treated in drinking water treatment by advanced oxidation processes. In this study, UV photolysis and UV-chlorination reactions along with chlorination to remove these odorants in water were compared. Kinetics of three reactions were well fitted at pseudo-first order model. Among three reactions, UV-chlorination was the most effective due to generation of OH and Cl radicals. β-ionone showed faster degradation compared to β-cyclocitral due to the existence of double bond in the alkyl carbon chain. In addition, radical contributions of degradation of odorants were examined. During UV-chlorination, UV photolysis contributed around 50% of removal for two odorants. OH radical took part of 36% removal of β-ionone and 50% removal of β-cyclocitral. Unlike β-ionone, β-cyclocitral was not degraded by reactive chlorine species during UV-chlorination. Acidic pH was favorable for UV-chlorination due to different quantum yield and radical scavenging effect by chlorine species. Formation of trace amount of chloroform was observed during UV-chlorination. The methyl ketone group of β-ionone was the main site for chloroform production. Several byproducts during UV photolysis and UV-chlorination of β-ionone were identified by GC-MS, and these were degraded with further reaction by UV-induced isomerization, OH radical, and bond scission mechanisms. β-cyclocitral was formed as byproducts during UV-chlorination of β-ionone. Based on degradation byproducts, the degradation pathways of β-ionone and β-cyclocitral of UV photolysis and UV-chlorination were suggested based on the identified byproducts. This study showed UV-chlorination process can be applied for degrading odorants like β-cyclocitral and β-ionone.

The Impact of Natural Variation of OH Radical Demand of Drinking Water Sources on the Optimum Operation of the UV/H2O2 Process

Hydroxyl radical (•OH) water demand is a key parameter which impacts the design and operation of UV/H₂O₂ process for water treatment. Long-term monitoring of the •OH water demand in water sources used for drinking water production indicated significant seasonal variations of this parameter (1.59 × 10⁴ to 4.98 × 10⁴ s^-1), which coincided with the occurrence of algal blooming events. Pilot-scale tests at a drinking water treatment plant confirmed that the UV/H₂O₂ process performance for contaminant removal is predictable when the •OH water demand is accurately determined through a validated experimental method. A predictive tool was developed to identify the optimum operating conditions of the UV system with the UV/H₂O₂ process and it was used to demonstrate the significant impact of seasonal variations of •OH water demand on the operating costs.

A comparison of trichloromethane formation from two algae species during two pre-oxidation-coagulation-chlorination processes

Microcystis aeruginosa (M. aeruginosa) commonly blooms in summer while Cyclotella meneghiniana (C. meneghiniana) outbreaks in fall in water reservoirs of Southeast China. Pre-oxidation has been demonstrated to enhance the algae removal from chemical coagulation processes. However, excessive dosage of pre-oxidant can increase the disinfection by-products formation potential (DBPsFP). Additionally, the DBPs formation mechanisms from algae during the pre-oxidation-coagulation-chlorination processes have not well elucidated. In this study, the objectives were to investigate the trichloromethane (TCM) formation, the changes of water quality indexes, and the morphology changes of algal cells from M. aeruginosa or C. meneghiniana contaminated water during potassium permanganate (KMnO₄) or chlorine (Cl₂) pre-oxidation-coagulation-chlorination disinfection. The results showed that the TCM yield for two algal species decreased with the dosage increase of KMnO₄ pre-oxidation, but increased with the dosage increase of pre-chlorination. Therefore, the 2.0 mg/L KMnO₄ or 0.5 mg/L Cl₂ was proposed as the optimal dosage for preventing both M. aeruginosa blooms in summer and for C. meneghiniana outbreaks in fall. M. aeruginosa exhibited a slightly higher TCM yield than C. meneghiniana in these treatment processes. Based on the release of potassium (K) ion and SEM analysis, KMnO₄ had less damage on cell integrity than Cl₂ at the dosage ≤2.0 mg/L. In addition, C. meneghiniana was easier to be disrupted by both pre-oxidants than M. aeruginosa, combining with subsequent coagulation led to different value of dissolved organic carbon (DOC), UV-visible absorbance (UV₂₅₄) and turbidity.

Kinetics and mechanism of Pseudoanabaena cell inactivation, 2-MIB release and degradation under exposure of ozone, chlorine and permanganate

The organic pollutants produced by cyanobacteria cells, such as off-flavor compounds (e.g. 2-methylisoborneol, 2-MIB) and hazardous toxins (e.g. microcystins), are commonly detected in water sources. Although studies have shown that oxidation using potassium permanganate (KMnO₄), chlorine and ozone helps to remove cyanobacteria cells, the potential effects of these oxidants on cell viability and the release of off-flavor substances have scarcely been explored. This study investigated the impacts of three widely used oxidants on Pseudanabaena sp. (a common species of 2-MIB producing cyanobacteria) inactivation, and on the release and degradation of intracellular 2-MIB. Experiments using KMnO₄ showed that both the cell viability and 2-MIB release fit to a two-stage second-order kinetic model with a threshold of KMnO₄ exposure (ct). No significant variations in the cell viability and 2-MIB release occurred until the exposure reached ct because KMnO₄ was primarily consumed by the dissolved and cell-bound organic matters before it damaged the cell. However, chlorine permeates the cell membrane more easily, causing rapid algae inactivation and the subsequent cell lysis and 2-MIB release. Unlike permanganate and chlorine, which are unable to degrade the released 2-MIB because of their insufficient oxidation potentials, ozone is capable to inactivate the cell and degrade 2-MIB as well. When the initial O₃ concentration is above a certain level (1.0 mg ·L^-1 in this study), the released 2-MIB can be substantially oxidized. Therefore, the choice of a suitable oxidant and a proper dose is highly important in the control of off-flavor compounds during the treatment of algae-containing raw water.

Ozone/peroxide advanced oxidation in combination with biofiltration for taste and odour control and organics removal

The objective of this pilot-scale study was to investigate the effectiveness of incorporating ozone (O₃) and advanced oxidation (hydrogen peroxide/ozone: H₂O₂/O₃) in combination with biofiltration for taste and odour control, organic carbon removal, and disinfection byproduct (DBP) precursor reduction. Implementation of O₃ and H₂O₂/O₃ with and without biofiltration was investigated at pilot-scale in terms of geosmin, 2-methylisoborneol (MIB), and DBP precursor removal efficiency. Two media types (granular activated carbon and anthracite) were compared in conjunction with investigating the impact of pre-oxidation with O₃ (2 mg/L) and varying H₂O₂/O₃ mass ratios (0.1, 0.2, 0.35, and 0.5 mg/mg). When O₃ preceded biologically active carbon (BAC) or biologically active anthracite, geosmin removals of 80% and 81%, respectively, were observed at 10 °C; this increased to 89% and 90%, respectively, at 16 °C. Optimal MIB removal (67%) was achieved with 0.1 H₂O₂/O₃ (mg/mg) in combination with BAC at 16 °C. In general, geosmin proved to be more amenable to biodegradation than MIB. BAC without pre-oxidation removed 87% geosmin and 85% MIB, at 22 °C. MIB removals decreased to 60% and 46%, respectively at 16 °C and 10 °C. The application of 0.2 H₂O₂/O₃ (mg/mg) prior to BAC provided treatment which effectively removed geosmin and MIB. However, in terms of DBP precursor reduction, there was no beneficial impact of H₂O₂ addition on trihalomethane or haloacetic acid formation potentials.

Characteristics of intracellular algogenic organic matter and its reactivity with hydroxyl radicals

The aim of this study was to investigate the reactivity of intracellular algogenic organic matter (IOM) with hydroxyl radicals (·OH), a key reaction species in advanced oxidation processes. IOM was extracted from two green algae, Chlamydomonas reinhardtii and Scenedesmus sp., and two blue-green algae, Anabaena sp. and Microcystis aeruginosa using a freeze-thaw method. The second-order rate constants of the extracted IOM with ·OH were determined as 7.95 × 10⁸ M_C^-1 s^-1 (Chlamydomonas reinhardtii), 6.71 × 10⁸ M_C^-1 s^-1 (Scenedesmus sp.), 4.02 × 10⁸ M_C^-1 s^-1 (Anabaena sp.), and 4.45 × 10⁸ M_C^-1 s^-1 (Microcystis aeruginosa). These rate constants were significantly higher than values reported for dissolved organic matter in various water sources. This implies that IOM formation during algal bloom season could change the ·OH water matrix demand and adversely affect the performance of advanced oxidation processes. To investigate the physical and chemical composition characteristics of IOM and their relationship to the rate constants determined for the reaction between IOM and ·OH, liquid chromatography-organic carbon detection (LC-OCD) and fluorescence excitation-emission matrix & parallel factor analysis (FEEM-PARAFAC) were used. The IOM mainly consisted of low molecular weight (LMW) matter and protein-related compounds, as evidenced LMW neutrals (38-65%), biopolymers (7-19%), and tryptophan-like compounds (74-94%). Based on the composition characteristics of IOM, it was concluded that the molecular weight and the presence of nitrogen-containing compounds are influential parameters for determining the reactivity of IOM with ·OH.

Degradation of geosmin and 2-methylisoborneol in water with UV/chlorine: Influencing factors, reactive species, and possible pathways

Geosmin (GSM) and 2-methylisoborneol (2-MIB) are two common odor compounds in drinking water. In this paper, the performance of UV/chlorine was compared with that of chlorine and UV to degrade GSM (100 ng L^-1) and 2-MIB (100 ng L^-1) in water. UV/chlorine was further exploited, and a steady-state kinetic model was used to conduct a detailed study on efficiency, rate, reactive species and pathway. The results showed that UV/chlorine greatly could improve the removal ratio to 90% within 5 min, from approximately 20% with only UV or dark chlorine in 60 min. The removal ratio and rate depended on UV light intensity, free chlorine dosage, reaction time and water quality parameters (e.g. pH, concentrations of HCO₃^- and Cl^-). Among these factors, the first two obviously could accelerate the rate and increase the ratio. The degradation was also significantly improved in an acidic condition, while alkaline conditions and HCO₃^- had inhibitory effects, and Cl^- created no difference. Contributions of OH and Cl to the degradation of 2-MIB and GSM were further revealed, and OH was found to be the most important reactive species. In the UV/chlorine process, 6 degradation byproducts of 2-MIB, including 1 alcohol, 2 ketones, and 3 olefins, were identified, and 14 degradation byproducts of GSM, including 6 ketones, 1 aldehyde, 2 alcohols, 3 naphthenes, and 2 olefins, were found by using solid-phase microextraction coupled to gas chromatography-mass spectrometry. The possible degradation pathways of GSM and 2-MIB in UV/chlorine thus were proposed.

Factors affecting the water odor caused by chloramines during drinking water disinfection

Chloramine disinfection is one of the most common disinfection methods in drinking water treatment. In this study, the temporal variability of water odors during monochloramine auto-decomposition was investigated to elucidate the characteristics of odor problems caused by adopting chloramine disinfection in tap water. Odor intensities and dominant odorant contributions were determined using the flavor profile analysis (FPA) and odor active value (OAV), respectively. During auto-decomposition of monochloramine, Cl₂/N molar ratio, pH, temperature, and the presence of NOM all affected odor intensity and odor temporal variation in drinking water. In general, decreasing pH from 8.5 to 6.0 led to increasing perceived odor intensity due to the formation of dichloramine. The major odorants responsible for chlorinous odor under acidic and non-acidic conditions were dichloramine and monochloramine, respectively. Chloraminated water with a Cl₂/N molar ratio of 0.6 or NOM concentration <2 mg-C L^-1 inhibited odor intensity. Furthermore, the influence of rechlorination on chlorinous odor intensity for chloraminated water should not be neglected. The results of this study will be beneficial for the control of chlorinous odors caused by chloramine disinfection in drinking water.

Removal of Algae, and Taste and Odor Compounds by a Combination of Plant-Mineral Composite (PMC) Coagulant with UV-AOPs: Laboratory and Pilot Scale Studies

The seasonal occurrence of algae blooms in surface waters remains a common problem, such as taste and odor (T&Os), the risk of disinfection by-products (DBPs), and disturbance to water treatment systems. The coagulation efficiency of plant-mineral composite (PMC) coagulant followed by UV-based advanced oxidation processes (UV-AOPs; UV/H2O2 and UV/Cl2) was evaluated for removal of algae, turbidity, dissolved organic matters, and taste and odor compounds in lab-scale and pilot-scale tests. In the lab-scale test, coagulation process with 20 mg/L of PMC shows high removal efficiency of turbidity (94%) and algae (99%) and moderate removal efficiency of UV254 (51%) and geosmin (46%). The pilot test results also show good removal efficiency of turbidity (64%), chlorophyll-a (96%). After PMC coagulation process, the major water factors, which affected the performance of UV-AOPs (i.e., UV transmittance (85–94%), and scavenging factor (64,998–28,516 s−1)), were notably improved, and further degradation of geosmin and 2-methylisoborneol (2-MIB) was achieved in both lab-and pilot-scale tests of the UV-AOPs. The UV/H2O2 process shows higher removal efficiency of geosmin and 2-MIB than the UV/Cl2 process because of the pH effect. The results confirmed that the PMC-based coagulation followed by UV/H2O2 process could be an effective process for the removal of algae, geosmin, and 2-MIB.

Limononic Acid Oxidation by Hydroxyl Radicals and Ozone in the Aqueous Phase

Kinetics and mechanism of limononic acid (3-isopropenyl-6-oxoheptanoic acid, LA) oxidation by hydroxyl radicals (OH) and ozone (O₃) were studied in the aqueous phase at 298 ± 2 K. These reactions were investigated using liquid chromatography coupled to the electrospray ionization and quadrupole tandem mass spectrometry (LC-ESI/MS/MS). The rate coefficients determined for LA + OH reaction were: 1.3 ± 0.3 × 10¹⁰ M^-1 s^-1 at pH = 2 and 5.7 ± 0.6 × 10⁹ M^-1 s^-1 at pH = 10. The rate coefficient determined for LA ozonolysis was 4.2 ± 0.2 × 10⁴ M^-1 s^-1 at pH = 2. The calculated Henry's law constant (H) for LA was ca. 6.3 × 10⁶ M × atm^-1, thereby indicating that in fogs and clouds with LWC = 0.3-0.5 g × m^-3 LA will reside entirely in the aqueous phase. Calculated atmospheric lifetimes due to reaction with OH and O₃ strongly indicate that aqueous-phase oxidation can be important for LA under realistic atmospheric conditions. Under acidic conditions, the aqueous-phase oxidation of LA by OH will dominate over reaction with O₃, whereas the opposite is more likely when pH ≥ 4.5. The aqueous-phase oxidation of LA produced keto-limononic acid and a number of low-volatility products, such as hydroperoxy-LA and α-hydroxyhydroperoxides.

Effect of operational and water quality parameters on conventional ozonation and the advanced oxidation process O3/H2O2: Kinetics of micropollutant abatement, transformation product and bromate formation in a surface water

The efficiency of ozone-based processes under various conditions was studied for the treatment of a surface water (Lake Zürich water, Switzerland) spiked with 19 micropollutants (pharmaceuticals, pesticides, industrial chemical, X-ray contrast medium, sweetener) each at 1 μg L^-1. Two pilot-scale ozonation reactors (4-5 m³ h^-1), a 4-chamber reactor and a tubular reactor, were investigated by either conventional ozonation and/or the advanced oxidation process (AOP) O₃/H₂O₂. The effects of selected operational parameters, such as ozone dose (0.5-3 mg L^-1) and H₂O₂ dose (O₃:H₂O₂ = 1:3-3:1 (mass ratio)), and selected water quality parameters, such as pH (6.5-8.5) and initial bromide concentration (15-200 μg L^-1), on micropollutant abatement and bromate formation were investigated. Under the studied conditions, compounds with high second-order rate constants k_O3>10⁴ M^-1 s^-1 for their reaction with ozone were well abated (>90%) even for the lowest ozone dose of 0.5 mg L^-1. Conversely, the abatement efficiency of sucralose, which only reacts with hydroxyl radicals (OH), varied between 19 and 90%. Generally, the abatement efficiency increased with higher ozone doses and higher pH and lower bromide concentrations. H₂O₂ addition accelerated the ozone conversion to OH, which enables a faster abatement of ozone-resistant micropollutants. Interestingly, the abatement of micropollutants decreased with higher bromide concentrations during conventional ozonation due to competitive ozone-consuming reactions, except for lamotrigine, due to the suspected reaction of HOBr/OBr^- with the primary amine moieties. In addition to the abatement of micropollutants, the evolution of the two main transformation products (TPs) of hydrochlorothiazide (HCTZ) and tramadol (TRA), chlorothiazide (CTZ) and tramadol N-oxide (TRA-NOX), respectively, was assessed by chemical analysis and kinetic modeling. Both selected TPs were quickly formed initially to reach a maximum concentration followed by a decrease of their concentrations for longer contact times. For the studied conditions, the TP's concentrations at the outlet of the reactors ranged from 0 to 61% of the initial parent compound concentration, CTZ being a more persistent TP against further oxidation than TRA-NOX. Finally, it was demonstrated in both reactors that the formation of bromate (BrO₃^-), a potentially carcinogenic oxidation by-product, could be controlled by H₂O₂ addition with a general improvement on micropollutant abatement. Post-treatment by granular activated carbon (GAC) filtration enabled the reduction of micropollutants and TPs concentrations but no changes in bromate were observed. The combined algae assay showed that water quality was significantly improved after oxidation and GAC post-treatment, driven by the abatement of the spiked pesticides (diuron and atrazine).