Co-metabolism of nonylphenol ethoxylate in sequencing batch reactor under aerobic conditions.

The study evaluated the co-metabolism of nonylphenol polyethoxylate (NPEO) within a main substrate stream subjected to biodegradation in an activated sludge system. Peptone mixture simulating sewage was selected as the synthetic substrate. As a novel approach, the NPEO concentration was magnified to match the COD level of the peptone mixture, so that co-metabolism could be evaluated by respirometry and modeling. A sequencing batch reactor (SBR) set-up at high sludge age to also allow nitrification was operated for this purpose. A long acclimation phase was necessary to start NPEO biodegradation, which was completed with 15% residual by-products. Modeling of respirometric data could identify COD fractions of NPEO with corresponding process kinetics for the first time, where the biodegradation of by-products could be interpreted numerically as a hydrolysis mechanism. Nonylphenol diethoxylate (NP2EO) was observed as the major by-product affecting the biodegradation of NPEO, because NPEO and NP2EO accounted for 60 to 70% of the total soluble COD in the solution during the course of biological reactions. The co-metabolism characteristics basically defined NPEO as a substrate, with no appreciable inhibitory action on the microbial culture both in terms of heterotrophic and autotrophic activities.

A New Activated Sludge Model with Membrane Separation-Implications for Sewage and Textile Effluent.

A new model for the activated sludge process with membrane separation is presented, based on the effective filtration size. A new size threshold is imposed by the membrane module. The model structure requires a modified fractionation of the chemical oxygen demand and includes chemical oxygen demand fractions entrapped in the reactor or in the flocs as model components. This way, it offers an accurate mechanistic interpretation of microbial mechanisms taking place in membrane activated sludge systems. Denim processing wastewater was selected for model implementation, which emphasized the significance of entrapped fractions of soluble hydrolysable and soluble inert chemical oxygen demand responsible for better effluent quality, while underlining the shortcomings of existing activated sludge models prescribed for systems with conventional gravity settling. The model also introduced particle size distribution analysis as a new experimental instrument complementing respirometric assessments, for an accurate description of chemical oxygen demand fractions with different biodegradation characteristics in related model evaluations.

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.

Evaluation of advanced oxidation processes for the treatment of nanofiltration membrane concentrate considering toxicity and oxidation by-products.

This paper offers a feasible solution for the treatment of membrane concentrate produced from the textile industry, using the Fenton, Advanced Fenton (AF), ozonation and hydrodynamic cavitation (HC) and combination of these processes. The study investigated the optimum oxidant and catalyst concentrations, optimum operational conditions and comparison of these processes. The potential formation of chlorinated organic compounds after oxidation of membrane concentrate was also investigated by analyzing total organic halogen (TOX) and polychlorinated biphenyl (PCBs). Also, toxicity analysis was performed with Vibrio fischeri photobacteria to identify the production possibility of oxidation intermediates that are more toxic and difficult to treat than the targeted contaminants. Maximum removal efficiencies in chemical oxygen demand (COD) and color were 18.8% and 60.7% respectively using HC alone at a cavitation number (CN) of 0.1. Maximum COD, total organic carbon (TOC), and color removal efficiency at molar concentrations of 175 mM H2O2 and 35 mM Fe2+ and pH 3 after 30 min was 87.1, 80.8 and 99%. Combined HC with Fenton showed the highest removal efficiency in terms of COD, TOC, and color. It was also stated that the use of high oxidant concentrations masks the synergistic effect of HC on Fenton processes due to the scavenging effect.

Determination of the potential of pickle wastewater as feedstock for biopolymer production.

Food industry wastewater (FIWW) streams with high organic content are among the most suitable and inexpensive candidates for polyhydroxyalkanoate (PHA) biopolymer production. Due to its high organic acid content, pickle industry wastewater (PIWW), can be considered as one of the prospective alternatives to petroleum-based polymers for PHA production. In this context, this study aimed to investigate the production of PHA with enriched microbial culture using PIWW. Two laboratory scale sequencing batch reactors (SBRs) were operated under aerobic dynamic feeding conditions at a sludge retention time of 8 days, with a total cycle duration of 24 hours. SBRs were fed with peptone mixture and PIWW. In-cycle analysis and batch respirometric tests were performed to evaluate PHA storage together with biodegradation kinetics. In-cycle analysis showed that maximum PHA content was 1,820 mgCOD/L, corresponding to 44% in the biomass (ratio of chemical oxygen demand (COD) to volatile suspended solids) for PIWW. Experimental results were also confirmed with activated sludge model simulations. As for the PHA composition, hydroxybutyrate was the major fraction. Model simulations proposed a unique conversion-degradation-storage pathway for the organic acid mixture. This paper presents a novel insight for better understanding of PHA biopolymer production using high saline FIWW.

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.

A comparative study of HO•- and SO4•--based AOPs for the degradation of non-ionic surfactant Brij30.

In the present study aqueous solutions of Brij30, an alcohol ethoxylate surfactant, were photocatalytically and photochemically treated by employing the TiO2/UV-A, H2O2/UV-C and persulfate (PS)/UV-C processes. During TiO2/UV-A treatment, even in short reaction periods (10 minutes), high rates of Brij30 removals were achieved; however, longer experiment periods (240-480 minutes) were needed in order to obtain notable total organic carbon (TOC) removals. Increasing the TiO2 dosage exhibited a positive effect on treatment efficiencies. For initial pH value of 3.0, increasing the TiO2 dosage from 1.0 to 1.5 g/L resulted in an improvement in Brij30 removal from 64% to 79% after 10 minutes whereas 68 and 88% TOC removals were observed after 480 minutes, respectively. Brij30 removal was very fast and complete via both H2O2/UV-C and PS/UV-C treatments, accompanied with significant mineralization rates ranging between 74 and 80%. Toxicity assessed by Vibrio fischeri, was found to be similar to that of the original Brij30 solution during H2O2/UV-C treatment, while in the PS/UV-C process, the relative inhibition of Brij30 towards V. fischeri fluctuated throughout the treatment and eventually non-toxic products were formed by the oxidation of SO4•- radicals.

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.

Abatements of reduced sulphur compounds, colour, and organic matter from indigo dyeing effluents by electrocoagulation.

In the present study, the treatability of indigo dyeing effluents by the electrocoagulation (EC) process using stainless steel electrodes was experimentally investigated. The samples used were concentrated with main pollutant parameters of chemical oxygen demand (COD) (1000-1100 mg/L), reduced sulphur species (over 2000 mg SO2-(3)/L), and colour (0.12-0.13 1/cm). The study focused on the effect of main operation parameters on the EC process performance in terms of abatement of reduced sulphur compounds as well as decolourization and organic matter reduction. Results indicated that the performance of EC proved to be high providing total oxidation of the reduced sulphur compounds, almost complete decolourization, and COD removal up to 90%. Increasing applied current density from 22.5 to 45 mA/cm2 appreciably improved abatement of the reduced sulphur compounds for Sample I, but a further increase in the applied current density to 67.5 mA/cm2 did not accelerate the conversion rate to sulphate. The process performance was adversely affected by increasing initial concentration of the reduced sulphur compounds. Decolourization and organic matter removal efficiency enhanced with increasing applied current density. The main removal mechanism of the reduced sulphur compounds by EC was explained as conversion to sulphate via oxidation. Conversion rate to sulphate fitted pseudo-first-order kinetics very well.

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.

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(·).

Adsorption of textile reactive dyestuffs by treatment sludges of inorganic nature.

Colour removal from industrial effluents, particularly from the textile industry, has become an important requirement as the adverse effects ofdyestuffs, such as toxicity, on the environment have been proven. Adsorption is a commonly used treatment method for colour removal. Although activated carbon is very effective for this purpose, a number of natural materials and waste materials, such as waste sludges generated from treatment systems, have been tested to reduce the cost of the process. In this paper, sludges arising from the operation of an electrocoagulation process that used stainless steel or aluminium electrodes were investigated as adsorbents for decolorization of reactive dyestuffs. Electrocoagulation waste sludges produced with the use of stainless steel electrodes provided higher than 90% or complete decolorization of Crimson HEXL, Yellow HE4R and RB5 dyestuffs. The sludge produced with aluminium electrodes yielded colour adsorption between 95% and 100% at a 1 g/L dose and pH 8.5-9.1 for two of the dyestuffs; the removal of RB5 did not exceed 60% up to a 4.76 g/L dose. FeCl3 coagulation and adsorption using freshly precipitated coagulation sludge resulted in poor colour removals of 10% for all three dyestuffs. The superior colour adsorption performance of electrocoagulation waste sludges was attributed to modification of the surface properties of the sludges during the electrocoagulation operation. A batch-wise kinetic study indicated that the adsorption of RB5 on to electrocoagulation waste sludges was well fitted by the pseudo-second-order kinetic model, suggesting the intra-particle diffusion process as the rate-limiting step of the adsorption process.