Advanced oxidation of bio-treated incineration leachate by persulfate combined with heat, UV254 nm, and UV365 nm: Kinetics, mechanism, and toxicity

This study compared and evaluated the ultraviolet/persulfate (UV/PS) at 254 or 365 nm and heat/persulfate (heat/PS) systems for advanced treatment of biologically pre-treated incineration leachate. The UV365 nm/PS system with the highest removal reduced chemical oxygen demand (COD) by 81.7%, total organic carbon by 73.8%, NH3-N by 96.8%, total nitrogen by 47.3%, and color by 98.6% within 24 h, separately. Kinetics tests suggested that a highest concentrations of 4.8 × 10-10 M for [SO4·-]ss and 2.8 × 10-11 M for [·OH]ss were reported in UV365/PS and UV254/PS systems, respectively. Characterization of leachate organic matter species revealed that low molecular weight organic matter < 5 kDa was preferentially degraded in three systems. Ketones are relatively easily degraded by both heat/PS and UV/PS systems, whereas esters were the most recalcitrant. Three-dimensional fluorescence analysis revealed > 99% humic acid and fulvic acid removal in all three systems. In practical applications, it is crucial to consider the pH and toxicity of SR-AOPs in the treatment of bio-treated incineration leachate. Furthermore, the ecotoxicity of MBR effluent treated by the heat/PS system and UV365 nm/PS system increased, which was caused by the strong acidity exhibited in the systems. In addition, we found that PS could interfere with 3.3% of the COD's detection. The findings of this study suggest that secondary effects of PS on water quality at high doses should be investigated in future research.

Degradation of emerging per- and polyfluoroalkyl substances (PFAS) using an electrochemical plug flow reactor

In recent years, shorter-chain fluorinated compounds have been manufactured as alternatives to legacy per- and polyfluoroalkyl substances (PFAS) after a global ban on some long-chain PFAS. This study is the first to investigate the degradability of emerging PFAS by an electrochemical plug flow reactor (EPFR). Ten different emerging PFAS, representing classes of fluorotelomer alcohol, perfluoroalkyl ether carboxylate, polyfluoroalkyl ethersulfonic acids, perfluoroalkyl ether/polyether carboxylates, perfluoroether sulfonate, N-alkyl perfluoroalkylsulfonamido carboxylate, fluoroalkyl phosphonic acid, and perfluoro alkane sulfonamide were investigated. The process kinetics was performed. The degradation of parent compounds increased with increasing retention time (RT). At 45.2 min of RT, the degradation of parent compounds ranged between 68%-100% with a current density of 17.2 mA/cm2. A linear increase in pseudo-first order rate constants was observed for all PFAS with increasing current density from 5.7 to 28.7 mA/cm2 (R2 > 0.91). The effect of pH, natural organic matter, and bicarbonate on the degradation, defluorination, and fluorine mass balance are reported. Alkaline pH (11) caused a decrease in degradation for all PFAS. While the presence of natural organic matter (NOM) significantly decreased the degradation and defluorination processes, the presence of bicarbonate at all studied concentrations (25, 50, and 100 mg/L) did not affect the process efficiency. The defluorination reduced to 34% from 81% with 15 mg/L NOM. The unknown/undetected fluorine fraction also increased in the presence of 15 mg/L NOM indicating the formation of NOM-PFAS complexes. Additionally, C2-C8 perfluoro carboxylic acids (PFCAs), one perfluoro sulfonic acid (PFSA), two H-PFCAs, and 4:2 fluorotelomer sulfonate (FTS) were identified as degradation byproducts in suspect screening. The electrical energy per order for PFAS ranged between 1.8 and 19.4 kWh/m3. This study demonstrates that emerging types of PFAS can potentially be degraded using an EPFR with relatively low electrical energy requirements.

Augmented photocatalytic degradation of Acetaminophen using hydrothermally treated g-C3N4 and persulfate under LED irradiation

Photocatalytic degradation of organic pollutants in water using graphitic carbon nitride and persulfate under visible light (g-C₃N₄/PS system) has been studied. Here, we demonstrate augmentation of photocatalytic degradation of Acetaminophen (AAP) using hydrothermally treated g-C₃N₄ and PS under 400 nm LED irradiation (HT-g-C₃N₄/PS system). A pseudo-first-order rate constant (k_obs, 0.328 min^-1) for degradation of AAP using HT-g-C₃N₄/PS system was determined to be 15 times higher compared to g-C₃N₄/PS system (k_obs, 0.022 min^-1). HT-g-C₃N₄ showed a higher surface area (81 m²/g) than g-C₃N₄ (21 m²/g). Photocurrent response for HT-g-C₃N₄ was higher (1.5 times) than g-C₃N₄. Moreover, Nyquist plot semicircle for HT-g-C₃N₄ was smaller compared to g-C₃N₄. These results confirm effective photoelectron-hole separation and charge-transfer in HT-g-C₃N₄ compared to g-C₃N₄. AAP degradation using HT-g-C₃N₄/PS system was significantly inhibited with O2.- and h⁺ scavengers compared to ¹O_2,SO4.- and HO. scavengers. ESR results revealed O2.- formation in HT-g-C₃N₄/PS system. Moreover, photocurrent measurements reveal AAP oxidation by h⁺ of HT-g-C₃N₄ was effective than g-C₃N₄. HT-g-C₃N₄ was reused for five cycles in HT-g-C₃N₄/PS system. Augmented photocatalytic degradation of AAP by HT-g-C₃N₄/PS system compared to g-C₃N₄/PS is attributed to effective photoelectron hole separation of HT-g-C₃N₄ that generates O2.- and h⁺ for oxidation of pollutant. Importantly, electrical energy per order (E_EO) was 7.2 kWh m^-3 order^-1. k_obs for degradation of AAP in simulated groundwater and tap water were determined as 0.029 and 0.035 min^-1, respectively. Degradation intermediates of AAP were proposed. AAP ecotoxicity against marine bacteria Aliivibrio fischeri was completely removed after treatment by HT-g-C₃N₄/PS system.

Comparison of UV and UV-LED activated sodium percarbonate for the degradation of O-desmethylvenlafaxine

As an active metabolite of venlafaxine and emerging antidepressant, O-desmethylvenlafaxine (ODVEN) was widely detected in different water bodies, which caused potential harm to human health and environmental safety. In this study, the comparative work on the ODVEN degradation by UV (254 nm) and UV-LED (275 nm) activated sodium percarbonate (SPC) systems was systematically performed. The higher removal rate of ODVEN can be achieved under UV-LED direct photolysis (14.99%) than UV direct photolysis (4.57%) due to the higher values of photolysis coefficient at the wavelength 275 nm. Significant synergistic effects were observed in the UV/SPC (80.38%) and UV-LED/SPC (53.57%) systems and the former exhibited better performance for the elimination of ODVEN. The degradation of ODVEN all followed the pseudo-first-order kinetics well in these processes, and the pseudo-first-order rate constant (k_obs) increased with increasing SPC concentration. Radicals quenching experiments demonstrated that both ·OH and CO₃·^- were involved in the degradation of ODVEN and the second-order rate constant of ODVEN with CO₃·^- (1.58 × 10⁸ (mol/L)^-1 sec^-1) was reported for the first time based on competitive kinetic method. The introduction of HA, Cl^-, NO₃^- and HCO₃^- inhibited the ODVEN degradation to varying degrees in the both processes. According to quantum chemical calculation, radical addition at the ortho-position of the phenolic hydroxyl group was confirmed to be the main reaction pathways for the oxidation of ODVEN by ·OH. In addition, the oxidation of ODVEN may involve the demethylation, H-abstraction, OH-addition and C-N bond cleavage. Eventually, the UV-LED/SPC process was considered to be more cost-effective compared to the UV/SPC process, although the UV/SPC process possessed a higher removal rate of ODVEN.

Visible light-driven degradation of Acid Orange 7 by light modulation techniques

The impact of light modulation on the decolorization of Acid Orange 7 (AO7) in aqueous solution was examined in this paper. A fixed bed batch photocatalytic reactor with a flat plate geometry, irradiated by 240 white-light LEDs, was used. A successful transfer of visible active photocatalyst (N-TiO₂) in powder form on a polystyrene (PS) transparent plate was realized. The structured photocatalyst was characterized through SEM-EDX, Raman and UV-DRS analyses, evidencing the formation of a coating of N-TiO₂ in the anatase phase, with a band-gap energy of 2.5 eV, and almost uniform distribution on the PS surface. Different LED dimming techniques, with fixed and variable duty-cycle values, were tested, and four types of light modulation were compared: fixed duty cycle (constant irradiation), sinusoidal variable duty cycle (sinusoidal variable irradiation), triangular variable duty cycle (triangular variable irradiation), and square wave variable duty cycle (square wave variable irradiation). The resulting responsiveness/efficiency of the LED versus the current intensity was evaluated, and the stability of the photocatalyst activity and the influence of optimized irradiation waveforms were examined in the decolorization of 400 mL of 10 ppm AO7 solution. The sinusoidal modulation, with current between 50 and 100 mA and 10 s as the period, shows the highest value of the apparent pseudo-first-order kinetic constant, resulting equal to 0.0044 min^-1, at parity of total transmitted photons. An energy saving with the application of sinusoidal irradiation is highlighted with respect to the literature.

Synthesis of visible light responsive ZnCoFe layered double hydroxide towards enhanced photocatalytic activity in water treatment

In this study, a ternary layered double hydroxide containing Zn, Co, and Fe transition metals (ZnCoFe LDH) was developed using a co-precipitation procedure. The as-synthesized photocatalyst was evaluated for its performance in the degradation of methylene blue (MB) under visible light irradiation. The effects of various process conditions including photocatalyst dosage, pollutant concentration, pH, lamp distance, and lamp power were investigated. The ZnCoFe LDH achieved approximately 74% photodegradation efficiency owing to the narrow bandgap of 2.14 eV. The Langmuir-Hinselwood rate constants were calculated as 1.17 min^-1 and 3.55 min^-1 for photolysis by LED lamp alone and for photocatalysis by LED/ZnCoFe LDH, respectively. The photocatalytic ability of the LDH was attributed to the generation of radical species like ^•OH and O₂^•-. The photocatalytic degradation intermediates of MB were determined by GC-MS analysis. The catalyst retained its performance throughout seven reuse cycles with only a 4.17% reduction in removal efficiency. The energy per order E_EO of the ZnCoFe/LED process in 180 min treatment time was determined as 5.41 kWh.m^-3. order^-1. This study shows that ZnCoFe LDH has sufficient activity and photostability for long-term application in photocatalytic water treatment.

Impact of water matrices on oxidation effects and mechanisms of pharmaceuticals by ultraviolet-based advanced oxidation technologies: A review

The binding between water components (dissolved organic matters, anions and cations) and pharmaceuticals influences the migration and transformation of pollutants. Herein, the impact of water matrices on drug degradation, as well as the electrical energy demands during UV, UV/catalysts, UV/O₃, UV/H₂O₂-based, UV/persulfate and UV/chlorine processes were systemically evaluated. The enhancement effects of water constituents are due to the powerful reactive species formation, the recombination reduction of electrons and holes of catalyst and the catalyst regeneration; the inhibition results from the light attenuation, quenching effects of the excited states of target pollutants and reactive species, the stable complexations generation and the catalyst deactivation. The transformation pathways of the same pollutant in various AOPs have high similarities. At the same time, each oxidant also can act as a special nucleophile or electrophile, depending on the functional groups of the target compound. The electrical energy per order (EEO) of drugs degradation may follow the order of EEO_UV > EEO_UV/catalyst > EEO_UV/H2O2 > EEO_UV/PS > EEO_UV/chlorine or EEO_UV/O3. Meanwhile, it is crucial to balance the cost-benefit assessment and toxic by-products formation, and the comparison of the contaminant degradation pathways and productions in the presence of different water matrices is still lacking.

O3/H2O2 and UV-C light irradiation treatment of oil sands process water

The oil sands industry generates large volumes of oil sands process water (OSPW). There is an urgent need for OSPW treatment to reduce process water inventories and to support current reclamation approaches. This study discusses how efficient ozone (O₃)-based combined advanced oxidation processes (AOPs), including hydrogen peroxide (H₂O₂) and UV-C, are at achieving mineralization while reducing the toxicity arising from such organic components as naphthenic acids (NAs) in OSPW. The results showed that the dissolved organic carbon (DOC) removals of 45%, 84%, 84% and 98%, obtained after 90-min treatments with O₃, O₃/H₂O₂, UVC/O₃ and UVC/O₃/H₂O₂, respectively, at a production rate of 6 g/L·h O₃ were considerably higher than at lower O₃ production rates. The acute toxicity on Vibrio fischeri was significantly reduced by all the treatments, which explains the high percentages of NA removal (up to 99% as confirmed by UPLC-QTOF-HRMS.) Mineralization (expressed as DOC removal) was highest with UVC/O₃/H₂O₂ at ca. 2 mg C/L in the treated effluent, which means that it could be used as cooling/boiling process water in bitumen upgrading units. However, considering the energy demand of the treatments tested, the treatment using O₃/H₂O₂ was found to be the most realistic for large-scale applications.

Photochemical degradation of the antidepressant sertraline in aqueous solutions by UVC, UVC/H2O2, and UVC/S2O82

Antidepressants are released into the aquatic environment because of their incomplete removal from wastewater treatment plants. In the present work, we investigated the photochemical degradation of a commonly prescribed antidepressant, namely sertraline, in aqueous matrices. The molar absorption coefficient of sertraline at 254 nm and at various pH values in the range from 4.0 to 9.0 was 444±65 L•mol^-1•cm^-1, while the quantum yield of its direct photolysis under UVC radiation (λ = 254 nm) was (1.7±0.1) × 10^-2 mol∙einstein^-1 (i.e., both values were relatively low). Next, we investigated the photochemical degradation of sertraline under UVC radiation in the presence of hydrogen peroxide, H₂O₂ (i.e., UVC/H₂O₂) or persulfate ions, S₂O₈^2- (i.e., UVC/PS). Several parameters were studied, such as the initial concentrations of the oxidants, solution pH, and the composition of the aqueous matrix (experiments were carried out in aqueous phosphate buffers, in synthetic wastewater, as well as in synthetic fresh and hydrolyzed human urine). It was found that, in all aqueous matrices, the photochemical degradation of sertraline followed pseudo first-order kinetics. The values of the observed pseudo first-order rate constants in the UVC/H₂O₂ and UVC/PS processes were from one to three orders of magnitude higher than the corresponding value in the UVC process. The UVC/PS process was more efficient than the UVC/H₂O₂ process, either in aqueous phosphate buffer solutions or in synthetic wastewaters, despite the comparable reactivity of sertraline towards hydroxyl and sulfate radicals. However, both processes resulted in partial mineralization of the compound after prolonged irradiation. In the UVC/H₂O₂ process, there was an optimum H₂O₂ concentration which depended on the aqueous matrix, while in the UVC/PS process, there was an almost linear increase in treatment efficiency as a function of PS concentration, at least in the range of concentrations studied in the present work. Solution pH in the range from 6.0 to 9.0 had a relatively negligible effect on treatment performance for both processes. In synthetic urine matrices, despite the reduction in reaction rate (the observed pseudo first-order rate constants were reduced by approximately one to two orders of magnitude), the photochemical degradation of sertraline proceeded to a relatively satisfactory degree. Finally, the calculations of the electrical energy per order and the associated cost showed that the UVC/H₂O₂ and UVC/PS processes are cost-efficient and suitable for full-scale applications.

Energy efficient photocatalytic activation of peroxymonosulfate by g-C3N4 under 400 nm LED irradiation for degradation of Acid Orange 7

Photocatalytic activation of peroxymonosulfate (PMS) by graphitic carbon nitride (g-C₃N₄) is emerging as a sulfate radical anion based advanced oxidation process (S-AOP) for degradation of organic pollutants. Importantly, photocatalytic activation of PMS by g-C₃N₄ is energy intensive as light irradiation requires high electrical energy. Here, we studied activation of PMS by g-C₃N₄ under 400 nm light emitting diode (LED) irradiation (g-C₃N₄/PMS/400-LED system) for degradation of Acid Orange 7 (AO7). LED array having optical emission maximum around 400 nm (FWHM = 16 nm), with electrical input power of 1.54 W (14 V and 110 mA) was used for irradiation. Pseudo-first order rate constant (k_obs) value for degradation of AO7 by g-C₃N₄/PMS/400-LED system was determined to be 0.094 min^-1. O₂^·-, SO₄^·- were revealed by radical scavenging and ESR investigations. k_obs value in simulated ground and real tap water were determined to be 0.068 min^-1 and 0.063 min^-1, respectively. g-C₃N₄ was stable, and reused four times without any significant loss in its photocatalytic activity. Importantly, electrical energy per order (E_EO) for degradation of AO7 by g-C₃N₄/PMS/400-LED system was determined to be 24.51 kWh m^-3 order^-1. In contrast, the E_EO value for the degradation of AO7 by g-C₃N₄ activated PMS under visible light irradiation (>400 nm), using conventional xenon lamp, (g-C₃N₄/PMS/Vis-Xe system) was found to be very high as 2702 kWh m^-3 order^-1. Thus, the study highlights, LED irradiation source is promising for the development of energy efficient g-C₃N₄ photocatalytic activation of PMS for removal of organic pollutants.

Electro-oxidation to convert dissolved organic nitrogen and soluble non-reactive phosphorus to more readily removable and recoverable forms

Conventional wastewater treatment processes cannot effectively remove dissolved organic nitrogen (DON) and soluble non-reactive phosphorus (sNRP), which can pose regulatory compliance challenges for total nitrogen and total phosphorus discharges. Moreover, DON and sNRP are not easily recoverable for beneficial reuse as part of the waste to resource paradigm. Conversion of DON and sNRP to more readily removable dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (sRP), respectively, will help meet stringent nutrient limits and facilitate nutrient recovery. In this study, electro-oxidation (EO) was evaluated for conversion of four DON compounds to DIN and five sNRP compounds to sRP. EO was more efficient and provided higher extents of conversion of the recalcitrant nutrient fractions compared to a more traditional advanced oxidation process, UV/H₂O₂. Direct electron transfer was likely the dominant oxidation mechanism for EO-based DON and sNRP conversion, with DON being more recalcitrant. Among the DON compounds tested, greater availability of primary amine (C-N bonds) yielded greater conversion compared to compounds with fewer primary amine or those with secondary amine (C-N-C bond). Among the sNRP compounds tested, those with P-O-C bonds (organic sNRP) converted more readily than those with P-O-P bonds (inorganic sNRP), presumably because cleavage of the latter bond requires greater energy. Using 30 min of EO treatment, the highest DON and sNRP compound conversion was 11.7 ± 0.09% for urea and 31.1 ± 0.75% for beta-glycerol phosphate. A similar extent of EO-based conversion of DON (6.41 ± 1.5%) and sNRP (32.7 ± 3.3%) was observed in real wastewater.

Removal of micropollutants from water in a continuous-flow electrical discharge reactor

The emergence of micropollutants into our aquatic resources is regarded as an issue of increasing environmental concern. To protect the aquatic environment against further contamination with micropollutants, treatment with advanced oxidation processes (AOPs) is put forward as a promising technique. In this work, an innovative AOP based on electrical discharges in a continuous-flow pulsed dielectric barrier discharge (DBD) reactor with falling water film over activated carbon textile is examined for its potential application in water treatment. The effect of various operational parameters including feed gas type, gas flow rate, water flow rate and power on removal and energy efficiency has been studied. To this end, a synthetic micropollutant mixture containing five pesticides (atrazine, alachlor, diuron, dichlorvos and pentachlorophenol), two pharmaceuticals (carbamazepine and 1,7-α-ethinylestradiol), and 1 plasticizer (bisphenol A) is used. While working under optimal conditions, energy consumption was situated in the range 2.42-4.25 kW h/m³, which is about two times lower than the economically viable energy cost of AOPs (5 kW h/m³). Hence, the application of non-thermal plasma could be regarded as a promising alternative AOP for (industrial) wastewater remediation.

Evaluating UV-C LED disinfection performance and investigating potential dual-wavelength synergy

A dual-wavelength UV-C LED unit, emitting at peaks of 260 nm, 280 nm, and the combination of 260|280 nm together was evaluated for its inactivation efficacy and energy efficiency at disinfecting Escherichia coli, MS2 coliphage, human adenovirus type 2 (HAdV2), and Bacillus pumilus spores, compared to conventional low-pressure and medium-pressure UV mercury vapor lamps. The dual-wavelength unit was also used to measure potential synergistic effects of multiple wavelengths on bacterial and viral inactivation and DNA and RNA damage. All five UV sources demonstrated similar inactivation of E. coli. For MS2, the 260 nm LED was most effective. For HAdV2 and B. pumilus, the MP UV lamp was most effective. When measuring electrical energy per order of reduction, the LP UV lamp was most efficient for inactivating E. coli and MS2; the LP UV and MP UV mercury lamps were equally efficient for HAdV2 and B. pumilus spores. Among the UV-C LEDs, there was no statistical difference in electrical efficiency for inactivating MS2, HAdV2, and B. pumilus spores. The 260 nm and 260|280 nm LEDs had a statistical energy advantage for E. coli inactivation. For UV-C LEDs to match the electrical efficiency per order of log reduction of conventional LP UV sources, they must reach efficiencies of 25-39% or be improved on by smart reactor design. No dual wavelength synergies were detected for bacterial and viral inactivation nor for DNA and RNA damage.

Photocatalytic degradation of carbofuran by TiO2-coated activated carbon: Model for kinetic, electrical energy per order and economic analysis

The photocatalytic removal of carbofuran (CBF) from aqueous solution in the presence of granular activated carbon supported TiO2 (GAC-TiO2) catalyst was investigated under batch-mode experiments. The presence of GAC enhanced the photocatalytic efficiency of the TiO2 catalyst. Experiments were conducted at different concentrations of CBF to clarify the dependence of apparent rate constant (kapp) in the pseudo first-order kinetics on CBF photodegradation. The general relationship between the adsorption equilibrium constant (K) and reaction rate constant (kr) were explained by using the modified Langmuir-Hinshelwood (L-H) model. From the observed kinetics, it was observed that the surface reaction was the rate limiting step in the GAC-TiO2 catalyzed photodegradation of CBF. The values of K and kr for this pseudo first-order reaction were found to be 0.1942 L  mg(-1) and 1.51 mg L(-1) min(-1), respectively. In addition, the dependence of kapp on the half-life time was determined by calculating the electrical energy per order experimentally (EEO experimental) and also by modeling (EEO model). The batch-mode experimental outcomes revealed the possibility of 100% CBF removal (under optimized conditions and at an initial concentration of 50 mg L(-1) and 100 mg L(-1)) at a contact time of 90 min and 120 min, respectively. Both L-H kinetic model and EEO model fitted well with the batch-mode experimental data and also elucidated successfully the phenomena of photocatalytic degradation in the presence of GAC-TiO2 catalyst.

Removal of atrazine in water by combination of activated carbon and dielectric barrier discharge

Efficiency of modern wastewater treatment plants to remove or decompose persistent contaminants in low concentration is often insufficient to meet the demands imposed by governmental laws. Novel, efficient and cheap methods are required to address this global issue. We developed a new type of plasma reactor, in which atrazine decomposition by atmospheric dielectric barrier discharge (DBD) in dry air is combined with micropollutant adsorption on activated carbon textile and with extra bubbling of generated ozone. Investigation of reaction kinetics and by-product analysis shows that increasing input power with a factor 3.5 leads to deeper atrazine oxidation without significantly changing energy yield of atrazine removal. By-products of first and later generations are detected with HPLC-MS analysis in water and adsorbed on the activated carbon textile. Our reactor is compared in energy efficiency with reactors described in literature, showing that combination of plasma discharge with pollutant adsorption and ozone recycling is attractive for future applications of water treatment.

Degradation and mineralization of Bisphenol A (BPA) in aqueous solution using advanced oxidation processes: UV/H2O2 and UV/S2O8(2-) oxidation systems

This work reports on the removal and mineralization of an endocrine disrupting chemical, Bisphenol A (BPA) at a concentration of 0.22 mM in aqueous solution using inorganic oxidants (hydrogen peroxide, H2O2 and sodium persulfate, Na2S2O8;S2O8(2-)) under UV irradiation at a wavelength of 254 nm and 40 W power (Io = 1.26 × 10(-6) E s(-1)) at its natural pH and a temperature of 29 ± 3 °C. With an optimum persulfate concentration of 1.26 mM, the UV/S2O8(2-) process resulted in ∼95% BPA removal after 240 min of irradiation. The optimum BPA removal was found to be ∼85% with a H2O2 concentration of 11.76 mM. At higher concentrations, either of the oxidants showed an adverse effect because of the quenching of the hydroxyl or sulfate radicals in the BPA solution. The sulfate-based oxidation process could be used over a wider initial pH range of 3-12, but the hydroxyl radical-based oxidation of BPA should be carried out in the acidic pH range only. The water matrix components (bicarbonate, chloride and humic acid) showed higher scavenging effect in hydroxyl radical-based oxidation than that in the sulfate radical-based oxidation of BPA. UV/S2O8(2-) oxidation system utilized less energy (307 kWh/m(3)) EE/O in comparison to UV/H2O2 system (509 kWh/m(3)) under optimum operating conditions. The cost of UV irradiation far outweighed the cost of the oxidants in the process. However, the total cost of treatment of persulfate-based system was much lower than that of H2O2-based oxidation system.

Kinetic modeling and energy efficiency of UV/H₂O₂ treatment of iodinated trihalomethanes

Photodegradation of I-THMs including CHCl2I and CHI3 by the UV/H2O2 system was investigated in this study. CHCl2I and CHI3 react rapidly with hydroxyl radical (OH) produced by the UV/H2O2 system, with second-order rate constants of 8.0 × 10(9) and 8.9 × 10(9) M(-1) s(-1), respectively. A fraction of CHCl2I could be completely mineralized within 15 min and the remaining fraction was mainly converted to formic acid (HCO2H). Cl(-) and I(-) were identified as the predominant end-products. No ClO3(-) was observed during the photodegradation process, while IO3(-) was detected but at less than 2% of the total liberated iodine species at the end of the reaction. The effects of pH, H2O2 dose, and matrix species such as humic acid (HA), HCO3(-), SO4(2-), Cl(-), NO3(-) on the photodegradation kinetics were evaluated. The steady-state kinetic model has been proven to successfully predict the destruction of CHCl2I and CHI3 by UV/H2O2 in different water matrices. On this basis, the kinetic model combined with electrical energy per order (EE/O) concept was applied to evaluate the efficiency of the photodegradation process and to optimize the H2O2 dose for different scenarios. The optimal H2O2 doses in deionized (DI) water, model natural water, and surface water are estimated at 5, 12, and 16 mg L(-1), respectively, which correspond to the lowest total energy consumption (EE/Ototal) of 0.2, 0.31, and 0.45 kWhm(-3)order(-1).