Treatment of industrial contaminants with zero-valent iron- and zero-valent aluminium-activated persulfate: a case study with 3,5-dichlorophenol and 2,4-dichloroaniline.

Zero-valent iron (ZVI)- and zero-valent aluminium (ZVA)-activated persulfate (PS) oxidation procedure was applied to remove the industrial pollutants 3,5-dichlorophenol (3,5-DCP; 12.27 µM) and 2,4-dichloroaniline (2,4-DCA; 12.34 µM) from aqueous solutions. The effects of PS concentration and pH were investigated to optimize heterogeneous treatment systems. Negligible removals were obtained for both pollutants by individual applications of nanoparticles (1 g/L) and PS (1.00 mM). PS activation with ZVI resulted in 59% (1.00 mM PS; 1 g/L ZVI; pH 5.0; 120 min) and 100% (0.75 mM PS; 1 g/L ZVI; pH 5.0; 80 min) 3,5-DCP and 2,4-DCA removals, respectively. The ZVA/PS treatment system gave rise to only 31% 3,5-DCP (1.00 mM PS; 1 g/L ZVA; pH 3.0; 120 min) and 47% 2,4-DCA (0.25 mM PS; 1 g/L ZVA; pH 3.0; 120 min) removals. The pH decreases from 5.0 to 3.0 and from 3.0 to 1.5 enhanced contaminant removals for ZVI/PS and ZVA/PS treatments, respectively. Pollutant removal rates were in correlation with the consumption rates of the oxidants. Metal ion (Al, Fe) release increased in the presence of PS and with decreasing pH.

Toxicity of Zn-Fe Layered Double Hydroxide to Different Organisms in the Aquatic Environment.

The application of layered double hydroxide (LDH) nanomaterials as catalysts has attracted great interest due to their unique structural features. It also triggered the need to study their fate and behavior in the aquatic environment. In the present study, Zn-Fe nanolayered double hydroxides (Zn-Fe LDHs) were synthesized using a co-precipitation method and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and nitrogen adsorption-desorption analyses. The toxicity of the home-made Zn-Fe LDHs catalyst was examined by employing a variety of aquatic organisms from different trophic levels, namely the marine photobacterium Vibrio fischeri, the freshwater microalga Pseudokirchneriella subcapitata, the freshwater crustacean Daphnia magna, and the duckweed Spirodela polyrhiza. From the experimental results, it was evident that the acute toxicity of the catalyst depended on the exposure time and type of selected test organism. Zn-Fe LDHs toxicity was also affected by its physical state in suspension, chemical composition, as well as interaction with the bioassay test medium.

Degradation of 3,5-dichlorophenol by UV-C photolysis and UV-C-activated persulfate oxidation process in pure water and simulated tertiary treated urban wastewater.

UV-C and UV-C/peroxydisulfate (PS) treatments of 3,5-dichlorophenol (3,5-DCP), a model industrial pollutant, were comparatively investigated in two different water matrices namely distilled water (DW) and simulated treated urban wastewater (SWW). The treatment performance of the selected treatment processes was comprehensively examined by following changes in 3,5-DCP, dissolved organic carbon (DOC), PS consumption, Cl- release, aromatic/aliphatic degradation products and acute toxicities towards the marine photobacterium Vibrio fischeri and freshwater microalga Pseudokirchneriella subcapitata. The treatability of 2 mg/L (12.3 µM) 3,5-DCP in DW was investigated under different operating conditions such as initial PS concentrations (0.00-1.00 mM) and pH values (3-11) at a fixed light intensity (0.5 W/L). Increasing the pH and PS concentration exhibited positive effects on 3,5-DCP degradation. Even 10 mg/L 3,5-DCP was completely degraded with UV-C/PS treatment in 40 min in the presence of 0.03 mM PS at pH 6.3 accompanied with 95% DOC removal that was achieved after 120 min treatment. The second-order rate constant of 3,5-DCP (10 mg/L) with SO4⋅- was determined as 1.77×109 M-1s-1 using competition kinetics. Cl- release and formation of hydroquinone were evidences of 3,5-DCP degradation involving SO4⋅-. 3,5-DCP (2 mg/L) was also subjected to UV-C and UV-C/PS treatments in SWW. 3,5-DCP (100% after 60 min) and in particular DOC (26% after 120 min treatment) removal efficiencies observed in DW decreased dramatically in SWW. The original and UV-C/PS-treated samples were non-toxic towards Vibrio fischeri; however, Pseudokirchneriella subcapitata toxicity increased from 20% to 47% through 80 min UV-C/PS treatment of 3,5-DCP.

Toxicity evaluation of bulk and nanosheet MoS2 catalysts using battery bioassays.

Herein, the main aim is to study the influence of the materials' structural properties on their ecotoxicological properties. The acute toxicity of the bulk (molybdenum disulfide) MoS2 and 2D nanosheet MoS2 was investigated using organisms of four different taxonomic groups. Ultrasound-assisted liquid-phase exfoliation method was used for preparing 2D nanosheets from bulk MoS2. Bulk and nanosheet MoS2 were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) analyses. The acute toxicity of the bulk and nanosheet MoS2 catalysts was evaluated with four different bioassays using the test organisms Vibrio fischeri (a marine photobacterium), Pseudokirchnerialla subcapitata (a freshwater microalga), Daphnia magna (a freshwater crustacean) and the freshwater duckweed Spirodela polyrhiza. The toxic effect of the materials depended on their structural/size features and the type/sensitivity of the test organism. Generally speaking, bulk MoS2 was more toxic than its nanosheet form. The freshwater crustacean Daphnia magna appeared to be the most suitable, easy-to-handle, and at the same time sensitive test organism for bulk and nanosheet MoS2 among the tested organisms.

Effects of treatment on the characterization of organic matter in wastewater: a review on size distribution and structural fractionation.

Since it is difficult to analyze the components of organic matter in complex effluent matrices individually, the use of more collective, but at the same time, specific wastewater characterization methods would be more appropriate to evaluate changes in effluent characteristics during wastewater treatment. For this purpose, size distribution and structural (resin) fractionation tools have recently been proposed to categorize wastewater. There are several case studies available in the scientific literature being devoted to the application of these fractionation methods. This paper aimed to review the most relevant studies dealing with the evaluation of changes in wastewater characteristics using size distribution and structural (resin) fractionation tools. According to these studies, sequential filtration-ultrafiltration procedures, as well as XAD resins, are frequently employed for size and structural fractionations, respectively. This review focuses on the most relevant publications including biological treatment processes, as well as chemical treatment methods such as coagulation-flocculation, electrocoagulation, the Fenton's reagent and ozonation. This study aims at providing an insight into the possible treatment mechanisms and details the understanding what structural features of wastewater components enabled or prevented efficient treatment (removal) or targeted pollutants.

UV-C-activated persulfate oxidation of a commercially important fungicide: case study with iprodione in pure water and simulated tertiary treated urban wastewater.

Recently, the European Food Safety Authority (EFSA) has banned the use of iprodione (IPR), a common hydantoin fungicide and nematicide that was frequently used for the protective treatment of crops and vegetables. In the present study, the treatment of 2 mg/L (6.06 µM) aqueous IPR solution through ultraviolet-C (UV-C)-activated persulfate (PS) advanced oxidation process (UV-C/PS) was investigated. Baseline experiments conducted in distilled water (DW) indicated that complete IPR removal was achieved in 20 min with UV-C/PS treatment at an initial PS concentration of 0.03 mM at pH = 6.2. IPR degradation was accompanied with rapid dechlorination (followed as Cl- release) and PS consumption. UV-C/PS treatment was also effective in IPR mineralization; 78% dissolved organic carbon (DOC) was removed after 120-min UV-C/PS treatment (PS = 0.30 mM) compared with UV-C at 0.5 W/L photolysis where no DOC removal occurred. LC analysis confirmed the formation of dichloroaniline, hydroquinone, and acetic and formic acids as the major aromatic and aliphatic degradation products of IPR during UV-C/PS treatment whereas only dichloroaniline was observed for UV-C photolysis under the same reaction conditions. IPR was also subjected to UV-C/PS treatment in simulated tertiary treated urban wastewater (SWW) to examine its oxidation performance and ecotoxicological behavior in a more complex aquatic environment. In SWW, IPR and DOC removal rates were inhibited and PS consumption rates decreased. The originally low acute toxicity (9% relative inhibition towards the photobacterium Vibrio fischeri) decreased to practically non-detectable levels (4%) during UV-C/PS treatment of IPR in SWW.

Oxidative degradation of Bisphenol A by carbocatalytic activation of persulfate and peroxymonosulfate with reduced graphene oxide.

In the present study, novel metal-free activation of persulfate (PS) and peroxymonosulfate with reduced graphene oxide (rGO) was investigated to degrade Bisphenol A (BPA), one of the most important endocrine disrupting compounds, from different aqueous matrices, namely distilled water (DW) and municipal wastewater treatment plant effluent (TWW). The home-made rGO was characterize and the effect of oxidant (PS and PMS) and catalyst (rGO) concentrations on BPA degradation rates in DW and TWW samples was examined. Complete BPA degradation occurred in DW and TWW with the PS/rGO treatment system after 10 min and 30 min, respectively, whereas 94% (DW) and 83% (TWW) BPA removals were obtained with PMS/rGO for the same treatment period (BPA = 2 mg/L; rGO = 0.02 g/L; PS = 0.25 mM; PMS = 0.5 mM). The radical quenching experiments demonstrated that the SO4- predominated in the activation of PS and PMS with rGO for BPA removal, however, HO contributed to the catalytic oxidation process but to a lower extend. The reusability test results, where the catalyst was deactivated seriously just after second cycle, highlighted the need for further studies to enhance the stability of rGO. This study represented an environmentally benign and efficient oxidative treatment of BPA along with insights into the rGO activated PS or PMS processes.

Effect of inorganic and organic solutes on zero-valent aluminum-activated hydrogen peroxide and persulfate oxidation of bisphenol A.

The effect of varying inorganic (chloride, nitrate, sulfate, and phosphate) and organic (represented by humic acid) solutes on the removal of aqueous micropollutant bisphenol A (BPA; 8.8 µM; 2 mg/L) with the oxidizing agents hydrogen peroxide (HP; 0.25 mM) and persulfate (PS; 0.25 mM) activated using zero-valent aluminum (ZVA) nanoparticles (1 g/L) was investigated at a pH of 3. In the absence of the solutes, the PS/ZVA treatment system was superior to the HP/ZVA system in terms of BPA removal rates and kinetics. Further, the HP/ZVA process was not affected by nitrate (50 mg/L) addition, whereas chloride (250 mg/L) exhibited no effect on the PS/ZVA process. The negative effect of inorganic anions on BPA removal generally speaking increased with increasing charge in the following order: NO3- (no inhibition) < Cl- (250 mg/L) = SO42- < PO43- for HP/ZVA and Cl- (250 mg/L; no inhibition) < NO3- < SO42- < PO43- for PS/ZVA. Upon addition of 20 mg/L humic acid representing natural organic matter, BPA removals decreased from 72 and 100% in the absence of solutes to 24 and 57% for HP/ZVA and PS/ZVA treatments, respectively. The solute mixture containing all inorganic and organic solutes together partly suppressed the inhibitory effects of phosphate and humic acid on BPA removals decreasing to 46 and 43% after HP/ZVA and PS/ZVA treatments, respectively. Dissolved organic carbon removals were obtained in the range of 30 and 47% (the HP/ZVA process), as well as 47 and 57% (the PS/ZVA process) for the experiments in the presence of 20 mg/L humic acid and solute mixture, respectively. The relative Vibrio fischeri photoluminescence inhibition decreased particularly for the PS/ZVA treatment system, which exhibited a higher treatment performance than the HP/ZVA treatment system.

Zero-valent iron-activated persulfate oxidation of a commercial alkyl phenol polyethoxylate.

Aqueous Triton X-45 (TX-45; 20 mg/L; original total organic carbon (TOC) = 14 mg/L), a representative, commercially important alkylphenol polyethoxylate, was subjected to persulfate (PS) oxidation activated with zero-valent iron (ZVI) nanoparticles. After optimization of the ZVI/PS treatment combination (1 g/L ZVI; 2.5 mM PS at pH5) in terms of pH (3-9), ZVI (0.5-5 g/L) and PS (0.5-5.0 mM) concentrations, TX-45 could be efficiently (>90%) degraded within short treatment periods (<60 min) accompanied with significant (>40%) TOC removals. The degree of PS consumption and Fe release was also followed during the experiments and a positive correlation existed between enhanced TX-45 removals and ZVI-activated PS consumption rates accompanied with a parallel Fe release. Acute toxicity tests were conducted using two different bioassays to examine the toxicological safety of the ZVI/PS oxidation system. Acute toxicity profiles significantly decreased from an original value of 66% relative inhibition to 21% and from 16% relative inhibition to non-toxic values according to Vibrio fischeri and Pseudokirchneriella subcapitata bioassays, respectively. The photobacterium V. fischeri appeared to be more sensitive to TX-45 and its degradation products than the microalgae P. subcapitata.

S2O8(2-)/UV-C and H2O2/UV-C treatment of Bisphenol A: assessment of toxicity, estrogenic activity, degradation products and results in real water.

The performance of S2O8(2-)/UV-C and H2O2/UV-C treatments was investigated for the degradation and detoxification of Bisphenol A (BPA). The acute toxicity of BPA and its degradation products was examined with the Vibrio fischeri bioassay, whereas changes in estrogenic activity were followed with the Yeast Estrogen Screen (YES) assay. LC and LC-MS/MS analyses were conducted to determine degradation products evolving during photochemical treatment. In addition, BPA-spiked real freshwater samples were also subjected to S2O8(2-)/UV-C and H2O2/UV-C treatment to study the effect of a real water matrix on BPA removal and detoxification rates. BPA removal in pure water was very fast (⩽7 min) and complete via both H2O2/UV-C and S2O8(2-)/UV-C treatment, accompanied with rapid and significant mineralization rates ranging between 70% and 85%. V.fischeri bioassay results indicated that degradation products being more toxic than BPA were formed at the initial stages of H2O2/UV-C whereas a rapid and steady reduction in toxicity was observed during S2O8(2-)/UV-C treatment in pure water. UV-C treatment products exhibited a higher estrogenic activity than the original BPA solution while the estrogenicity of BPA was completely removed during H2O2/UV-C and S2O8(2-)/UV-C treatments parallel to its degradation. 3-methylbenzoic and 4-sulfobenzoic acids, as well as the ring opening products fumaric, succinic and oxalic acids could be identified as degradation products. BPA degradation required extended treatment periods (>20 min) and TOC removals were considerably retarded (by 40%) in the raw freshwater matrix most probably due to its natural organic matter content (TOC=5.1 mg L(-1)). H2O2/UV-C and S2O8(2-)/UV-C treatment in raw freshwater did not result in toxic degradation products.

Photo-Fenton-like treatment of K-acid: assessment of treatability, toxicity and oxidation products.

Photo-Fenton-like treatment of the commercially important naphthalene sulphonate K-acid (2-naphthylamine-3,6,8-trisulphonic acid) was investigated using UV-C, UV-A and visible light irradiation. Changes in toxicity patterns were followed by the Vibrio fischeri bioassay. Rapid and complete degradation of K-acid accompanied with nearly complete oxidation and mineralization rates (>90%) were achieved for all studied irradiation types. On the other hand, detoxification was rather limited and did not change significantly during photo-Fenton-like treatment. Several oxidation products could be identified via liquid chromatograph-mass spectrometer analyses, such as desulphonated and hydroxylated naphthalene derivatives, quinones, and ring-opening as well as dimerization products. Photo-Fenton-like treatment of K-acid with UV-C, UV-A and visible light irradiation occurred through a series of hydroxylation and desulphonation reactions, followed by ring cleavage. A common degradation pathway for photo-Fenton-like treatment of K-acid using different irradiation types was proposed.

Investigation of the toxicity of common oxidants used in advanced oxidation processes and their quenching agents.

The inhibitory effect of commonly known oxidants and their quenching agents was investigated by employing a battery of toxicity tests. Hydrogen peroxide toxicity could be effectively eliminated by the enzyme catalase, whereas sodium thiosulfate and ascorbic acid were recommended as suitable quenching agents for the removal of the oxidants persulfate and peroxymonosulfate in the Vibrio fischeri bioassays. None of the studied quenching agents was found to be suitable for persulfate and peroxymonosulfate in the Daphnia magna bioassays since high inhibitory effects were obtained for both oxidants. In the case of Pseudokirchneriella subcapitata, manganese dioxide powder should be used as an alternative quenching agent to catalase, since this enzyme exhibited a highly toxic effect towards these microalgae. Sodium sulfite, which is extensively used as a quenching agent, was not appropriate for quenching peroxymonosulfate in all studied bioassays.

Treatment of olive mill wastewater by chemical processes: effect of acid cracking pretreatment.

The effect of acid cracking (pH 2.0; T 70 °C) and filtration as a pretreatment step on the chemical treatability of olive mill wastewater (chemical oxygen demand (COD) 150,000 m/L; total organic carbon (TOC) 36,000 mg/L; oil-grease 8,200 mg/L; total phenols 3,800 mg/L) was investigated. FeCl3 coagulation, Ca(OH)2 precipitation, electrocoagulation using stainless steel electrodes and the Fenton's reagent were applied as chemical treatment methods. Removal performances were examined in terms of COD, TOC, oil-grease, total phenols, colour, suspended solids and acute toxicity with the photobacterium Vibrio fischeri. Significant oil-grease (95%) and suspended solids (96%) accompanied with 58% COD, 43% TOC, 39% total phenols and 80% colour removals were obtained by acid cracking-filtration pretreatment. Among the investigated chemical treatment processes, electrocoagulation and the Fenton's reagent were found more effective after pretreatment, especially in terms of total phenols removal. Total phenols removal increased from 39 to 72% when pretreatment was applied, while no significant additional (≈10-15%) COD and TOC removals were obtained when acid cracking was coupled with chemical treatment. The acute toxicity of the original olive mill wastewater sample increased considerably after pretreatment from 75 to 89% (measured for the 10-fold diluted wastewater sample). An operating cost analysis was also performed for the selected chemical treatment processes.

Effect of Fenton treatment on the aquatic toxicity of bisphenol A in different water matrices.

Battery tests serve as integral tools to decide whether a treatment process is ecotoxicologically safe or not. In the present study, a battery of toxicity tests was employed to elucidate the toxicity of the potential endocrine-disrupting pollutant bisphenol A (BPA) and its advanced oxidation products. For this purpose, BPA was subjected to Fenton treatment in the growth medium of the test organisms employed as well as in real lake water. Treatment results indicated that BPA removals were fast and complete within less than a minute, whereas total organic carbon (TOC) removals were rather incomplete, speaking for the accumulation of refractory degradation products. The presence of chloride and/or natural organic matter influenced H2O2 consumption rates and the treatment performance of the Fenton's reagent as well. The sensitivity of the selected test organisms for BPA and its Fenton treatment products in different water matrices was found in the following decreasing order: the freshwater microalgae (Pseudokirchneriella subcapitata) > the freshwater cladoceran (Daphnia magna) > marine photobacteria (Vibrio fischeri).

Oxidation of nonylphenol ethoxylates in aqueous solution by UV-C photolysis, H2O2/UV-C, Fenton and photo-Fenton processes: are these processes toxicologically safe?

UV-C, H2O2/UV-C, Fenton and photo-Fenton treatment of a nonylphenol polyethoxylate (NP-10) were comparatively studied, primarily focusing on the acute toxicity of degradation products. Formic, acetic and oxalic acids were all identified as the degradation products of NP-10; however, the sole common carboxylic acid was found to be formic acid for the studied treatment processes. The percent relative inhibition towards Vibrio fischeri increased from 9% to 33% and 24% after 120 min-UV-C and H2O2/UV-C treatment, respectively. Complete NP-10 and 70% of its total organic carbon (TOC) content was removed by the photo-Fenton process, which ensured the fastest removal rates and lowest inhibitory effect (8% after 120 min treatment). The acute toxicity pattern being observed during H2O2/UV-C and photo-Fenton treatment positively correlated with temporal evolution of the identified carboxylic acids, whereas unidentified oxidation products were the most likely origin of the acute toxicity in UV-C photolysis.

Photo-Fenton-like treatment of BPA: effect of UV light source and water matrix on toxicity and transformation products.

UV-A (near-UV), UV-C (short-UV) and visible-light assisted Fenton-like treatment of Bisphenol A (BPA) was investigated in pure water and raw freshwater samples spiked with BPA. Treatment performances were evaluated in terms of BPA degradation, dissolved organic carbon (DOC) removal and H2O2 consumption rates. Complete BPA degradation accompanied with significant DOC removal was achieved for all studied processes. Increasing the initial solution pH only exhibited a negative effect on treatment efficiencies when bicarbonate alkalinity was used for pH adjustment, whereas the raw freshwater matrix and irradiation type also influenced oxidation rates appreciably. Acute toxicity analysis employing Vibrio fischeri revealed that the inhibitory effect of BPA decreased significantly during the course of Photo-Fenton-like treatment. Several transformation products could be identified via HPLC and GC-MS analyses including hydroxylated phenolic compounds (hydroquinone; 2-methoxy, 1-4-benzenediol; 4-isopropenylphenol; 4'-hydroxy-acetophenone; 1-(4-cyclohexylphenyl) ethanone; 4-isopropylenecatechol; 4-4'-dihydroxybenzophenone; 4-ethyl,1,3-benzenediol), as well as the ring opening products hexanoic acid methyl ester, fumaric, succinic and oxalic acids. A reaction pathway featuring hydroxylation, dimerization and ring opening steps is proposed.

Advanced oxidation of a commercially important nonionic surfactant: investigation of degradation products and toxicity.

The evolution of degradation products and changes in acute toxicity during advanced oxidation of the nonionic surfactant nonylphenol decaethoxylate (NP-10) with the H2O2/UV-C and photo-Fenton processes were investigated. H2O2/UV-C and photo-Fenton processes ensured complete removal of NP-10, which was accompanied by the generation of polyethylene glycols with 3-8 ethoxy units. Formation of aldehydes and low carbon carboxylic acids was evidenced. According to the acute toxicity tests carried out with Vibrio fischeri, degradation products being more inhibitory than the original NP-10 solution were formed after the H2O2/UV-C process, whereas the photo-Fenton process appeared to be toxicologically safer since acute toxicity did not increase relative to the original NP-10 solution after treatment. Temporal evolution of the acute toxicity was strongly correlated with the identified carboxylic acids being formed during the application of H2O2/UV-C and photo-Fenton processes.

Bisphenol A treatment by the hot persulfate process: oxidation products and acute toxicity.

In this study, a thermally activated persulfate oxidation process was investigated to treat aqueous Bisphenol A (BPA) solution. The effect of temperature (40-50-60-70°C), initial pH (pH=3.0, 6.5, 9.0 and 11.0) and persulfate concentration (0-20mM) on bisphenol A (BPA) and TOC removals was examined. The activation energy for hot persulfate oxidation of BPA was calculated as 184 ± 12 kJ/mol. Acidic and neutral pH values were more favorable for BPA oxidation than basic pH values. TOC removals did not exhibit a specific pattern with varying initial pHs. Gas chromatography/mass spectrometry was employed to identify oxidation products. Several aromatic and a few aliphatic compounds could be detected including benzaldehyde, p-isopropenyl phenol, 2,3-dimethyl benzoic acid, 3-hydroxy-4-methyl-benzoic acid, ethylene glycol monoformate and succinic acid. Acute toxicity tests conducted with Vibrio fischeri indicated that the inhibitory effect of 88 µM BPA solution originally being 58%, increased to 84% after 30 min and decreased to 22% after 90 min hot persulfate treatment that could be attributed to the formation and subsequent disappearance of oxidation products.

Advanced oxidation of the commercial nonionic surfactant octylphenol polyethoxylate Triton™ X-45 by the persulfate/UV-C process: effect of operating parameters and kinetic evaluation.

This study explored the potential use of a sulfate radical (SO(·-) 4)-based photochemical oxidation process to treat the commercial nonionic surfactant octylphenol polyethoxylate (OPPE) Triton™ X-45. For this purpose, the effect of initial S2O(2-) 8 (0-5.0 mM) and OPPE (10-100 mg/L) concentrations on OPPE and its organic carbon content (TOC) removal were investigated at an initial reaction pH of 6.5. Results indicated that very fast OPPE degradation (100%) accompanied with high TOC abatement rates (90%) could be achieved for 10 and 20 mg/L aqueous OPPE at elevated S2O(2-) 8 concentrations (≥2.5 mM). S2O(2-) 8/UV-C treatment was still capable of complete OPPE removal up to an initial concentration of 40 mg/L in the presence of 2.5 mM S2O(2-) 8. On the other hand, TOC removal efficiencies dropped down to only 40% under the same reaction conditions. S2O(2-) 8/UV-C oxidation of OPPE was also compared with the relatively well-known and established H2O2/UV-C oxidation process. Treatment results showed that the performance of S2O(2-) 8/UV-C was comparable to that of H2O2/UV-C oxidation for the degradation and mineralization of OPPE. In order to elucidate the relative reactivity and selectivity of SO(·-) 4 and HO(·), bimolecular reaction rate coefficients of OPPE with SO(·-) 4 and HO(·) were determined by employing competition kinetics with aqueous phenol (47 µM) selected as the reference compound. The pseudo-first-order abatement rate coefficient obtained for OPPE during S2O(2-) 8/UV-C oxidation (0.044 min(-1)) was found to be significantly lower than that calculated for phenol (0.397 min(-1)). In the case of H2O2/UV-C oxidation however, similar pseudo-first-order abatement rate coefficients were obtained for both OPPE (0.087 min(-1)) and phenol (0.140 min(-1)). From the kinetic study, second-order reaction rate coefficients for OPPE with SO(·-) 4 and HO(·) were determined as 9.8 × 10(8) M(-1) s(-1) and 4.1 × 10(9) M(-1) s(-1), respectively. The kinetic study also revealed that the selectivity of SO(·-) 4 was found to be significantly higher than that of HO(·).

H2O2/UV-C treatment of textile preparation wastewater: kinetic investigation on alternative combinations of commercial textile preparation auxiliaries.

Four different textile preparation effluents were simulated to examine the applicability of the hydrogen peroxide/ultraviolet-C (H2O2/UV-C) advanced oxidation process for the treatment of real textile preparation (desizing, scouring and bleaching) wastewater bearing the non-ionic surfactant nonyl phenol decaethoxylate (NP-10). In the absence of any textile preparation chemical, NP-10 degradation was complete in 15 min (rate coefficient: 0.22 min(-1)) accompanied by 78% chemical oxygen demand (COD) (rate coefficient: 0.026 min(-1)) and 57% total organic carbon (TOC) (rate coefficient: 0.014 min(-1)) removals achieved after 60 min photochemical treatment. H2O2 consumption rates were not significantly affected by the introduction of carbonate and chloride ions (average rate coefficient: 0.032 min(-1)) at pH values <11.5, above which H2O2 dissociation to its conjugate base HO2(-) became pronounced. The organic, phosphonate-based sequestering agents competed with NP-10 for UV-C light absorption and HO* radicals. H2O2/UV-C oxidation of the simulated textile preparation effluent containing 3.0 g L(-1) Cl(-), 1.5 g L(-1) NaOH and 1.0 g L(-1) diethylenetriamine pentamethylene phosphonic acid (DTPMP) resulted in the worst treatment performance due to its high pH and organic carbon content. For this textile preparation effluent, NP-10 abatement was complete in 100min (rate coefficient: 0.018 min(-1)), while COD and TOC removals dropped down to only 16% and 8%, respectively, achieved after 60 min treatment. The highest H2O2/UV-C oxidation efficiency resulting in 34% COD and 28% TOC removals was obtained for the simulated textile preparation effluent comprising of 3.0 g L(-1) Cl(-), 1.5 g L(-1) NaOH and 1.0 g L(-1) 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP). For this textile preparation effluent, NP-10 degradation was complete after 50 min (rate coefficient: 0.061 min(-1)) exposure to H2O2/UV-C treatment.