Medium pressure UV combined with chlorine advanced oxidation for trichloroethylene destruction in a model water

The effectiveness of ultraviolet (UV) combined with chlorine as a novel advanced oxidation process (AOP) for drinking water treatment was evaluated in a bench scale study by comparing the rate of trichloroethylene (TCE) decay when using UV/chlorine to the rates of decay by UV alone and UV/hydrogen peroxide (H₂O₂) at various pH values. A medium pressure mercury UV lamp was used. The UV/chlorine process was more efficient than the UV/H₂O₂ process at pH 5, but in the neutral and alkaline pH range, the UV/H₂O₂ process became more efficient. The pH effect was probably controlled by the increasing concentration of OCl⁻ at higher pH values. A mechanistic kinetic model of the UV/chlorine treatment of TCE showed good agreement with the experimental data.     

Modeling the UV/hydrogen peroxide advanced oxidation process using computational fluid dynamics

The use of numerical models for the design and optimization of UV/H₂O₂ systems must incorporate both reactor design (hydrodynamics, lamp orientation) and chemical kinetics (reaction mechanisms, kinetic rate constants). This study was conducted to evaluate the performance of comprehensive CFD/UV/AOP models for the degradation of an indicator organic contaminant. The combination of turbulence sub-models, fluence rate sub-models, and kinetic rate equations resulted in a comprehensive and flexible design tool for predicting the effluent chemical composition from a UV-initiated AOP reactor. The CFD model tended to under predict the percent removal of methylene blue compared to pilot reactor trials under the same operating conditions. In addition, the percent difference between the pilot and the CFD results increased with increasing flow rates. The MSSS fluence rate sub-model predicted higher contaminant removal values than the RAD-LSI sub-model while the different two-equation turbulence sub-models did not significantly impact the predicted removal for methylene blue in the tested reactor configuration. The overall degradation of methylene blue was a strong function of the second-order kinetic rate constant describing the reaction between methylene blue and the hydroxyl radical. In addition, the removal of methylene blue was sensitive to the concentration of dissolved organic carbon in the water matrix since DOC acts as a scavenger of hydroxyl radicals.     

Degradation of azo dye by an UV/H2O2 advanced oxidation process using an amalgam lamp

The discharge of dyes into water is an ecological problem that can be alleviated by advanced oxidation processes (AOPs), such as UV/H₂O₂ treatments. Searching for more efficient light sources is a way to improve AOPs’ efficiency. This work tested the efficiency of an amalgam lamp on the degradation of an azo dye, studying the effect of dye and H₂O₂ concentrations and pH, and the influence of some salts on the decolouration rate of methyl orange. Actinometry showed that the amalgam lamp system was able to provide a high incident photon irradiance (6.30·10^?5 mol/cm² s). The amalgam lamp‐driven AOP was able to decolourize the dye at pseudo‐first‐order rates of 0.654–4.008 1/min, with increasing rates at low dye concentration and low pH and at high H₂O₂ concentrations until a maximum value is reached. The results show that the amalgam lamp can be an alternative light source for fast dye degradation by AOPs.     

Feasibility studies: UV/chlorine advanced oxidation treatment for the removal of emerging contaminants

UV/chlorine (UV/HOCl and UV/ClO₂) Advanced Oxidation Processes (AOPs) were assessed with varying process layout and compared to the state of the art UV/H₂O₂ AOP. The process comparison focused on the economical and energy saving potential of the UV/chlorine AOP. Therefore the experiments were performed at technical scale (250 L/h continuous flow reactor) and at process energies, oxidant and model contaminant concentrations expected in full scale reference plants. As model compounds the emerging contaminants (ECs): desethylatrazine, sulfamethoxazole, carbamazepine, diclofenac, benzotriazole, tolyltriazole, iopamidole and 17α-ethinylestradiol (EE2) were degraded at initial compound concentrations of 1 μg/L in tap water and matrixes with increased organic load (46 mg/L DOC).UV/chlorine AOP organic by-product forming potential was assessed for trihalomethanes (THMs) and N-Nitrosodimethylamine (NDMA). A process design was evaluated which can considerably reduce process costs, energy consumption and by-product generation from UV/HOCl AOPs.     

Comparison of UV/H(2)O(2) and UV/TiO(2) for the degradation of metaldehyde: Kinetics and the impact of background organics

The kinetics of photodegradation of the pesticide metaldehyde by UV/H₂O₂ and UV/TiO₂ in laboratory grade water and a natural surface water were studied. Experiments were carried out in a bench scale collimated beam device using UVC radiation. Metaldehyde was efficiently degraded by both processes in laboratory grade water at identical rates of degradation (0.0070 and 0.0067 cm² mJ⁻¹ for UV/TiO₂ and UV/H₂O₂ respectively) when optimised doses were used. The ratio between oxidant and metaldehyde was significantly higher for H₂O₂ due to its low photon absorption efficiency at 254 nm. However, the presence of background organic compounds in natural water severely affected the rate of degradation, and whilst the pseudo first-order rate constant of degradation by UV/H₂O₂ was slowed down (0.0020 cm² mJ⁻¹), the degradation was completely inhibited for the UV/TiO₂ process (k′ = 0.00007 cm² mJ⁻¹) due to the blockage of active sites on TiO₂ surface by the background organic material.     

Comparison of advanced oxidation processes for the removal of natural organic matter

This study examined the impact of UV, ozone (O₃), advanced oxidation processes (AOPs) including O₃/UV, H₂O₂/UV H₂O₂/O₃ in the change of molecular weight distribution (MWD) and disinfection by-product formation potential (DBPFP). Bench-scale experiments were conducted with surface river water and changes in the UV absorbance at 254 nm (UV₂₅₄), total organic carbon (TOC), trihalomethane and haloacetic acid formation potential (THMFP, HAAFP) and MWD of the raw and oxidized water were analyzed to evaluate treatment performance. Combination of O₃ and UV with H₂O₂ was found to result in more TOC and UV₂₅₄ reduction than the individual processes. The O₃/UV process was found to be the most effective AOP for NOM reduction, with TOC and UV₂₅₄ reduced by 31 and 88%, respectively. Application of O₃/UV and H₂O₂/UV treatments to the source waters organics with 190-1500 Da molecular weight resulted in the near complete alteration of the molecular weight of NOM from >900 Da to <300 Da H₂O₂/UV was found to be the most effective treatment for the reduction of THM and HAA formation under uniform formation conditions. These results could hold particular significance for drinking water utilities with low alkalinity source waters that are investigating AOPs, as there are limited published studies that have evaluated the treatment efficacy of five different oxidation processes in parallel.     

Assessment of the UV/chlorine process as an advanced oxidation process

Several organic compounds were used as radical scavengers/reagents to investigate the possibility of the UV/chlorine process being used as an advanced oxidation process (AOP) in the treatment of drinking water and wastewater. The UV/H₂O₂ process was selected as a reference, so that the results from the UV/chlorine process could be compared with those of the UV/H₂O₂ process. Methanol was added to active chlorine solutions at both pH 5 and 10 and into hydrogen peroxide samples. The photodegradation quantum yields and the OH radical production yield factors, which are significant in evaluating AOPs, were calculated for both the UV/chlorine and the UV/H₂O₂ processes. The yield factor for the UV/chlorine process at pH 5 was 0.46 ± 0.09, which is much lower than that of the UV/H₂O₂ process, which reached 0.85 ± 0.04. In addition to methanol, para-chlorobenzoic acid (pCBA) and cyclohexanoic acid (CHA) were added to active chlorine solutions and to H₂O₂ solutions, to evaluate the efficiencies of oxidizing these organic compounds. The specific first-order reaction rate constants for the oxidation of pCBA and CHA, using the UV/chlorine process, were lower than those found using the UV/H₂O₂ process.     

The effect of UV/H2O2 treatment on disinfection by-product formation potential under simulated distribution system conditions

Advanced oxidation with ultraviolet light and hydrogen peroxide (UV/H₂O₂) produces hydroxyl radicals that have the potential to degrade a wide-range of organic micro-pollutants in water. Yet, when this technology is used to reduce target contaminants, natural organic matter can be altered. This study evaluated disinfection by-product (DBP) precursor formation for UV/H₂O₂ while reducing trace organic contaminants in natural water (>90% for target pharmaceuticals, pesticides and taste and odor producing compounds and 80% atrazine degradation). A year-long UV/H₂O₂ pilot study was conducted to evaluate DBP precursor formation with varying water quality. The UV pilot reactors were operated to consistently achieve 80% atrazine degradation, allowing comparison of low pressure (LP) and medium pressure (MP) lamp technologies for DBP precursor formation. Two process waters of differing quality were used as pilot influent, i.e., before and after granular activated carbon adsorption. DBP precursors increased under most of the conditions studied. Regulated trihalomethane formation potential increased through the UV/H₂O₂ reactors from 20 to 118%, depending on temperature and water quality. When Post-GAC water served as reactor influent, less DBPs were produced in comparison to conventionally treated water. Haloacetic acid (HAA5) increased when conventionally treated water served as UV/H₂O₂ pilot influent, but only increased slightly (MP lamp) when GAC treated water served as pilot influent. No difference in 3-day simulated distribution system DBP concentration was observed between LP and MP UV reactors when 80% atrazine degradation was targeted.     

An evaluation of a pilot-scale nonthermal plasma advanced oxidation process for trace organic compound degradation

This study evaluated a pilot-scale nonthermal plasma (NTP) advanced oxidation process (AOP) for the degradation of trace organic compounds such as pharmaceuticals and potential endocrine disrupting compounds (EDCs). The degradation of seven indicator compounds was monitored in tertiary-treated wastewater and spiked surface water to evaluate the effects of differing water qualities on process efficiency. The tests were also conducted in batch and single-pass modes to examine contaminant degradation rates and the remediation capabilities of the technology, respectively. Values for electrical energy per order (EEO) of magnitude degradation ranged from <0.3 kWh/m³-log for easily degraded compounds (e.g., carbamazepine) in surface water to 14 kWh/m³-log for more recalcitrant compounds (e.g., meprobamate) in wastewater. Changes in the bulk organic matter based on UV₂₅₄ absorbance and excitation-emission matrices (EEM) were also monitored and correlated to contaminant degradation. These results indicate that NTP may be a viable alternative to more common AOPs due to its comparable energy requirements for contaminant degradation and its ability to operate without any additional feed chemicals.     

Removal of disinfection by-product precursors with ozone-UV advanced oxidation process

The efficacy of using ozone (O3), ultraviolet irradiation (UV) and the combined O3-UV advanced oxidation process (AOP) to remove 2 classes of disinfection by-product (DBP) precursors from raw surface water samples have been evaluated and compared. In particular, trihalomethane and haloacetic acids formation potentials were measured. Laboratory batch scale experiments were carried out as a function of ozone and UV dosage in order to study the removal kinetics. It is concluded that the combined O3-UV AOP is more effective than either the ozone or UV treatment alone. Ozone-UV AOP is capable of mineralizing up to 50% of the total organic carbon from the raw source water at an ozone dose of 0.62+/-0.019 mg O3/mL and a UV dose of 1.61 W s/cm2. In addition, O3-UV AOP can reduce trihalomethane formation potential by roughly 80% and haloacetic acids formation potential by roughly 70% at the same ozone and UV dosage.     

A review of novel electrode materials and techniques for electro-Fenton process applied to the degradation of phenolic compounds

A major problem coming across humanity in the early 21st century is related to environmental crises, including shortage and pollution of water sources. For this reason, extensive studies have been conducted to find effective techniques for purifying water from industrial pollutants. Advanced oxidation process (AOP) has lately caught the attention of researchers, which is an efficient, clean and contemporary method to remedy wastewater effluents. However, primitive versions of AOP methods lacked several aspects like strict pH requirements and involvement of sediments, which is why further modifications to the technique have been developed, including an electrochemical catalytic degradation approach, namely, electro-Fenton and similar processes. This study will look through a set of novel papers investigating the application of various electrodes for the electrochemical treatment of solutions contaminated with phenol and phenolic compounds, which tried to address several shortcomings of more outdated practices and optimize the method for a set of different scenarios.     

Degradation of 40 selected pharmaceuticals by UV/H2O2

The occurrence of pharmaceuticals in source waters is increasing. Although UV advanced oxidation is known to be an effective barrier against micropollutants, degradation rates are only available for limited amounts of pharmaceuticals. Therefore, the degradation of a large group of pharmaceuticals has been studied in this research for the UV/H₂O₂ process under different conditions, including pharmaceuticals of which the degradation by UV/H₂O₂ was never reported before (e.g., metformin, paroxetine, pindolol, sotalol, venlafaxine, etc.). Monochromatic low pressure (LP) and polychromatic medium pressure (MP) lamps were used for three different water matrices. In order to have well defined hydraulic conditions, all experiments were conducted in a collimated beam apparatus. Degradation rates for the pharmaceuticals were determined. For those compounds used in this research that are also reported in literature, measured degradation results are in good agreement with literature data. Pharmaceutical degradation for only photolysis with LP lamps is small, which is increased by using a MP lamp. Most of the pharmaceuticals are well removed when applying both UV (either LP or MP) and H₂O₂. However, differences in degradation rates between pharmaceuticals can be large. For example, ketoprofen, prednisolone, pindolol are very well removed by UV/H₂O₂, whereas metformin, cyclophosphamide, ifosfamide are very little removed by UV/H₂O₂.     

Mechanism of phenol photodegradation in the presence of pure and modified-TiO(2): A review

In recent years, the application of heterogeneous photocatalytic water purification processes has gained wide attention due to its effectiveness in degrading and mineralizing the recalcitrant organic compounds as well as the possibility of utilizing the solar UV and visible-light spectrum. By far, titania has played a much larger role in this scenario compared to other semiconductor photocatalysts due to its costly effectiveness, inert nature and photostability. A substantial amount of research has focused on the enhancement of TiO₂ photocatalysis by modification with metal, non-metal and ion doping.This paper aims to review and summarize the recent works on the titanium dioxide (TiO₂) photocatalytic oxidation of phenol and discusses various mechanisms of phenol photodegradation (indicating the intermediates products) and formation of OH radicals. Phenol degradation pathway in both systems, TiO₂/UV and doped-TiO₂/Vis, are described.     

Comparison of the efficiency of *OH radical formation during ozonation and the advanced oxidation processes O3/H2O2 and UV/H2O2

Comparison of advanced oxidation processes (AOPs) can be difficult due to physical and chemical differences in the fundamental processes used to produce OH radicals. This study compares the ability of several AOPs, including ozone, ozone+H2O2, low pressure UV (LP)+H2O2, and medium pressure UV (MP)+H2O2 in terms of energy required to produce OH radicals. Bench scale OH radical formation data was generated for each AOP using para-chlorobenzoic acid (pCBA) as an OH radical probe compound in three waters, Lake Greifensee water, Lake Zurich water, and a simulated groundwater. Ozone-based AOPs were found to be more energy efficient than the UV/H2O2 process at all H2O2 levels, and the addition of H2O2 in equimolar concentration resulted in 35% greater energy consumption over the ozone only process. Interestingly, the relatively high UV/AOP operational costs were due almost exclusively to the cost of hydrogen peroxide while the UV portion of the UV/AOP process typically accounted for less than 10 percent of the UV/AOP cost and was always less than the ozone energy cost. As the *OH radical exposure increased, the energy gap between UV/H2O2 AOP and ozone processes decreased, becoming negligible in some water quality scenarios.     

Comparison of UV-Cl and UV-H2O2 advanced oxidation processes in the degradation of contaminants from water and wastewater: A review

Applications of advanced oxidation processes (AOPs) in water and wastewater treatment have been the subject of growing interest throughout the last decade. Although UV/hydrogen peroxide (UV-H₂O₂) is the most established technology among the UV-AOPs, UV-chlorine (UV-Cl) is emerging as a reliable and potentially more cost-effective alternative. Recent studies have indicated that UV-Cl processes may be more efficient and economically favourable for the degradation of some chemicals of emerging concern from contaminated water. Moreover, in terms of the formation of disinfection by-products (DBPs), UV-H₂O₂ seems to have no superiority over UV-Cl. This said, more investigation in the assessment of genotoxicity and cytotoxicity of DBPs is required. Additionally, more pilot-scale and full-scale studies are required to establish UV-Cl as a reliable alternative to UV- H₂O₂. This paper compares UV-Cl and UV-H₂O₂ AOPs for the degradation of intractable chemicals from water and wastewater based on the practical considerations of efficiency, cost, DBP formation, kinetics and sensitivity to water matrix variability. Finally, various modelling approaches to UV-Cl have been reviewed. This review showed that UV-Cl is superior to UV-H₂O₂ in terms of degradation efficiency and cost effectiveness and can be a robust alternative in many UV-AOPs applications.     

The role of effluent nitrate in trace organic chemical oxidation during UV disinfection

Most conventional biological treatment wastewater treatment plants (WWTPs) contain nitrate in the effluent. Nitrate undergoes photolysis when irradiated with ultraviolet (UV) light in the 200-240 and 300-325 nm wavelength range. In the process of nitrate photolysis, nitrite and hydroxyl radicals are produced. Medium pressure mercury lamps emitting a polychromatic UV spectrum including irradiation below 240 nm are becoming more common for wastewater disinfection. Therefore, nitrified effluent irradiated with polychromatic UV could effectively become a de facto advanced oxidation (hydroxyl radical) treatment process. UV-based advanced oxidation processes commonly rely on addition of hydrogen peroxide in the presence of UV irradiation for production of hydroxyl radicals. This study compares the steady-state concentration of hydroxyl radicals produced by nitrate contained in a conventional WWTP effluent to that produced by typical concentrations of hydrogen peroxide used for advanced oxidation treatment of water. The quantum yield of hydroxyl radical production from nitrate by all pathways was calculated to be 0.24 ± 0.03, and the quantum yield of hydroxyl radicals from nitrite was calculated to be 0.65 ± 0.06. A model was developed that would estimate production of hydroxyl radicals directly from nitrate and water quality parameters. In effluents with >5 mg-N/L of nitrate, the concentration of hydroxyl radicals is comparable to that produced by addition of 10 mg/L of H₂O₂. Nitrifying wastewater treatment plants utilizing polychromatic UV systems at disinfection dose levels can be expected to achieve up to 30% degradation of some micropollutants by hydroxyl radical oxidation. Increasing UV fluence to levels used during advanced oxidation could achieve over 95% degradation of some compounds.     

Efficient removal of microcystin-LR by UV-C/H₂O₂ in synthetic and natural water samples

The destruction of the commonly found cyanobacterial toxin, microcystin-LR (MC-LR), in surface waters by UV-C/H₂O₂ advanced oxidation process (AOP) was studied. Experiments were carried out in a bench scale photochemical apparatus with low pressure mercury vapor germicidal lamps emitting at 253.7 nm. The degradation of MC-LR was a function of UV fluence. A 93.9% removal with an initial MC-LR concentration of 1 μM was achieved with a UV fluence of 80 mJ/cm² and an initial H₂O₂ concentration of 882 μM. When increasing the concentration of MC-LR only, the UV fluence-based pseudo-first order reaction rate constant generally decreased, which was probably due to the competition between by-products and MC-LR for hydroxyl radicals. An increase in H₂O₂ concentration led to higher removal efficiency; however, the effect of HO scavenging by H₂O₂ became significant for high H₂O₂ concentrations. The impact of water quality parameters, such as pH, alkalinity and the presence of natural organic matter (NOM), was also studied. Field water samples from Lake Erie, Michigan and St. Johns River, Florida were employed to evaluate the potential application of this process for the degradation of MC-LR. Results showed that the presence of both alkalinity (as 89.6-117.8 mg CaCO₃/L) and NOM (as ∼2 to ∼9.5 mg/L TOC) contributed to a significant decrease in the destruction rate of MC-LR. However, a final concentration of MC-LR bellow the guideline value of 1 μg/L was still achievable under current experimental conditions when an initial MC-LR concentration of 2.5 μg/L was spiked into those real water samples.     

The effect of UV/H2O2 treatment on biofilm formation potential

Greater Cincinnati Water Works (GCWW) evaluated the efficacy of ultraviolet light/hydrogen peroxide advanced oxidation (UV/H₂O₂) for reducing trace organic contaminants in natural water with varying water qualities. A year-long UV/H₂O₂ pilot study was conducted to examine a variety of seasonal and granular activated carbon (GAC) breakthrough conditions. The UV pilot-scale reactors were set to consistently achieve 80% atrazine degradation, allowing comparison of low pressure (LP) and medium pressure (MP) lamp technologies for by-product formation. Because hydroxyl radicals react non-selectively with organic compounds, unintended by-product formation occurred.Total assimilable organic carbon (AOC) concentration increased through the reactors from 14 to 33% on average, depending on water quality. Natural organic matter (NOM) contains the precursors for AOC production, so when post-GAC water (versus conventionally treated water) served as reactor influent, less AOC was produced. No appreciable difference in AOC concentration was observed between LP and MP UV reactors. The Spirillum strain NOX fraction of the AOC increased from 50 to 65% on average, depending on the quality of the water. The increase in this fraction of AOC occurred because oxidation of NOM yielded smaller more assimilable organic compounds such as organic acids that are necessary for NOX growth. The Pseudomonas fluorescens strain P17 AOC concentration increased only when conventionally treated plant water was used as pilot influent. This organism thrives in waters of differing organic energy sources, but does not thrive well in carboxylic acids alone. The CONV water had more overall TOC that could contribute to higher P17 AOC counts.Biofilm coupon studies indicated that biofilms with greater heterotrophic plate counts were observed in the granular activated carbon (GAC) effluent streams receiving UV/H₂O₂ pre-treatment. Biofilm coupon studies additionally indicated that the effluent stream of the GAC column proceeded by the MP reactor exhibited more viable biofilm than the other GAC effluent streams based on an ATP-bioluminescence method. The increased viability of the biofilm produced by the MP UV reactor is likely a result of the multiple UV wavelengths and higher energy input characteristic of this technology.     

UV/H2O2 treatment of drinking water increases post-chlorination DBP formation

Ultraviolet (UV) irradiation has become popular as a primary disinfectant because it is very effective against Cryptosporidium and does not directly form regulated disinfection by-products. Higher UV doses and UV advanced oxidation (UV/H₂O₂) processes are under consideration for the treatment of trace organic pollutants (e.g. pharmaceuticals, personal care products). Despite the disinfection effectiveness of UV light, a secondary disinfectant capable of maintaining a distribution system residual is required to meet current U.S. regulation. This study investigated changes in disinfection by-product (DBP) formation attributed to UV or UV/H₂O₂ followed by application of free chlorine to quench hydrogen peroxide and provide residual disinfectant. At a UV dose of 1000 mJ/cm², trihalomethane (THM) yield increased by up to 4 μg/mg-C and 13 μg/mg-C when treated with low and medium pressure UV, respectively. With the addition of hydrogen peroxide, THM yield increased by up to 25 μg/mg-C (5 mg-H₂O₂/L) and 37 μg/mg-C (10 mg-H₂O₂/L). Although no changes in DBPs are expected during UV disinfection, application of UV advanced oxidation followed by chlorine addition was assessed with regard to impacts on DBP formation.     

Evaluation of UV/H2O2 treatment for the oxidation of pharmaceuticals in wastewater

Advanced oxidation treatment using low pressure UV light coupled with hydrogen peroxide (UV/H₂O₂) was evaluated for the oxidation of six pharmaceuticals in three wastewater effluents. The removal of these six pharmaceuticals (meprobamate, carbamazepine, dilantin, atenolol, primidone and trimethoprim) varied between no observed removal and >90%. The role of the water quality (i.e., alkalinity, nitrite, and specifically effluent organic matter (EfOM)) on hydroxyl radical (OH) exposure was evaluated and used to explain the differences in pharmaceutical removal between the three wastewaters. Results indicated that the efficacy of UV/H₂O₂ treatment for the removal of pharmaceuticals from wastewater was a function of not only the concentration of EfOM but also its inherent reactivity towards OH. The removal of pharmaceuticals also correlated with reductions in ultraviolet absorbance at 254 nm (UV₂₅₄), which offers utilities a surrogate to assess pharmaceutical removal efficiency during UV/H₂O₂ treatment.