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.

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.

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.

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.

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.

Electrocoagulation of commercial naphthalene sulfonates: process optimization and assessment of implementation potential.

The commercially important naphthalene sulfonate K-acid (C(10)H(9)NO(9)S(3); 2-naphthylamine 3,6,8-tri sulfonic acid) was subjected to electrocoagulation employing stainless steel electrodes. An experimental design tool was used to mathematically describe and optimize the single and combined influences of major process variables on K-acid and its organic carbon (COD and TOC) removal efficiencies as well as electrical energy consumption. Current density, followed by treatment time were found to be the parameters affecting process responses most significantly, whereas initial K-acid concentration had the least influence on the electrocoagulation performance. Process economics including sludge generation, electrode consumption, and electrochemical efficiency, as well as organically bound adsorbable halogen formation and toxicity evolution were primarily considered to question the feasibility of K-acid electrocoagulation. Considering process economics and ecotoxicological parameters, process implementation appeared to be encouraging.

The hydroxyl radical scavenging effect of textile preparation auxiliaries on the photochemical treatment of nonylphenol ethoxylate.

The present paper deals with the effects of frequently used textile preparation chemicals and common ions on the H2O2/UV-C treatment of a commercially important and slowly biodegradable nonionic surfactant, namely a nonylphenol bearing 10 ethoxylated chains. For this purpose, the effect of soda ash carbonate (0-5.0 g L(-1)), two phosphonic acid-based organic sequestering agents (0-2.5 g L(-1)) and chloride (0-3.0 g L(-1)) at two different pH values (3.5 and 10.5) as hydroxyl radical scavengers was experimentally investigated. Among the studied textile preparation chemicals and hydroxyl radical scavengers, the decreasing order of hydroxyl radical scavenging capacity was established as diethylene triamine pentamethylene phosphonic acid > 1-hydroxy ethylidene-1,1-diphosphonic acid > soda ash carbonate at pH 10.5 > chloride at pH 3.5 > chloride at pH 10.5.

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.

Modeling partial oxidation of a commercial textile surfactant formulation with the H(2)O(2)/UV-C process.

In the present study, the reaction conditions required for the partial oxidation of a commercial nonionic textile surfactant, an alkyl polyethoxylate, with the H(2)O(2)/UV-C treatment process were optimized using central composite design and response surface methodology (CCD-RSM). CCD-RSM allowed for the development of empirical quadratic equations that satisfactorily predicted COD and TOC removal efficiencies under all studied experimental conditions. Analysis of variance revealed that the variables "H(2)O(2) concentration" and "initial surfactant COD" were found to be the process independent parameters most positively and negatively affecting the treatment performance, respectively, whereas the process variable "treatment time" had a smaller influence on COD and TOC removal efficiencies. According to the established polynomial regression models, for the degradation of the nonionic surfactant at an initial COD of 450 mg L(-1) and pH of 10.5, the optimized treatment conditions were 15 mM H(2)O(2) and a reaction time of 80 min. In order to achieve the treatment targets (complete surfactant removal accompanied by 60% COD and TOC elimination to meet the national discharge consents into receiving water bodies) either H(2)O(2) concentration or photochemical treatment time had to be increased. Activated sludge inhibition experiments conducted with nonionic surfactant solution being subjected to photochemical oxidation under optimized reaction conditions indicated that the inhibitory effect of the nonionic surfactant could be completely eliminated during H(2)O(2)/UV-C treatment and the partial degradation intermediates were more biodegradable than the original textile surfactant.

Application of the UV-C photo-assisted peroxymonosulfate oxidation for the mineralization of dimethyl phthalate in aqueous solutions.

In this study, the degradation of dimethyl phthalate (DMP), taken as model compound for phthalate esters, by the photo-assisted peroxymonosulfate (PMS) process was investigated. The high oxidation potential of hydroxyl and sulfate radicals generated by the activation of PMS under UV-C light irradiation was used to completely oxidize aqueous DMP solutions. Experiments were conducted at varying initial pH values (3.0, 6.0, and 9.0) and PMS concentrations (0-60 mM) to evaluate the effect of different reaction conditions on DMP treatment performance with the PMS/UV-C process. It was observed that lowering the initial reaction pH slightly improved the degradation rate of DMP. On the contrary, TOC abatements were slightly enhanced with increasing initial reaction pH. An adequate (optimum) PMS concentration of 40 mM resulted in the fastest and highest DMP degradation rates and efficiencies, respectively. At an initial concentration of 100 mg L(-1), more than 95% DMP removal was obtained after only 20 min under PMS/UV-C treatment conditions. For the proposed adequate PMS concentration (40 mM) the lowest electrical energy per order (EE/O) value was calculated as 2.9 kW h m(-3) order(-1).

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.

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.

Modeling and optimization of acid dye manufacturing wastewater treatment with Fenton's reagent: comparison with electrocoagulation treatment results and effects on activated sludge inhibition.

In the present study, Fenton's oxidation of a chromium complex disazo dye (Acid Blue 193) synthesis wastewater was evaluated, modeled and optimized by employing Central Composite Design. Within this context, the individual and interactive effects of critical process parameters such as Fe(2 + ), H(2)O(2) concentrations, initial chemical oxygen demand (COD) and reaction time was assessed. The process response (output) variables were chosen as percent color, COD and total organic carbon (TOC) removal efficiencies. Optimum working conditions in terms of color and organic carbon removals were established to be Fe(2 + )=3 mM; H(2)O(2)=25 mM; reaction time = 10 min at pH 3 and an initial COD content of 245 mg/L. Under these conditions, 96% color, 82% COD and 51% TOC removals were obtained. The established polynomial regression models describing color, COD and TOC removals satisfactorily fitted the experimental data and could be used to predict Fenton's treatment results at statistically significant rates. Optimized treatment results were compared with those obtained via electrocoagulation treatment under optimized conditions (applied current = 50 A/m(2); reaction time = 15 min; initial pH = 7 for an initial COD content of 245 mg/L). The relative inhibition of heterotrophic oxygen uptake rate was measured to examine the inhibitory effect of azo dye synthesis effluent before and after Fenton's oxidation and electrocoagulation with respect to synthetic domestic wastewater. Untreated azo dye production wastewater exhibited a slightly inhibitory effect that was appreciably reduced but not entirely removed after Fenton's oxidation, whereas no inhibition of mixed bioculture was observed for azo dye synthesis effluent subjected to electrocoagulation treatment.

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.

Electrocoagulation of a real reactive dyebath effluent using aluminum and stainless steel electrodes.

Treatment of real reactive dyebath effluent comprising of an exhausted reactive dyebath and its sequential rinses with electrocoagulation (EC) using aluminum (Al) and stainless steel (SS) electrodes was investigated. The experimental study focused on the effect of applied current density (22-87 mA/cm(2); at an initial, optimum pH of 5.5) on decolorization and COD removal rates using Al and SS as electrode materials. Results have indicated that the treatment efficiency was enhanced appreciably by increasing the applied current density when Al electrodes were used for EC, whereas no clear correlation existed between current density and removal rates for EC with SS electrodes the treatment efficiency could only be improved when the applied current density was in the range of 33-65 mA/cm(2). It was established that EC with SS electrodes was superior in terms of decolorization kinetics (99-100% color removal after 10-15 min EC at all studied current densities), whereas EC with Al electrodes was more beneficial for COD removal in terms of electrical energy consumption (5 kWh/m(3) wastewater for EC with Al electrodes instead of 9 kWh/m(3) wastewater for EC with SS electrodes).

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.

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.

Integrated photochemical and biological treatment of a commercial textile surfactant: process optimization, process kinetics and COD fractionation.

The biodegradability of surfactants is a frequent and complex issue arising both at domestic as well as industrial treatment facilities. In the present experimental study, the integrated photochemical (H(2)O(2)/UV-C) and biochemical (activated sludge) treatment of a commercial grade nonionic/anionic textile surfactant formulation was investigated. Photochemical baseline experiments have shown that once the initial pH and H(2)O(2) dose were optimized, practically complete COD removal (COD(o)=500+/-30mgL(-1)) could be achieved. Once the COD was elevated to values being typical for the textile fabric preparation stage, treatment efficiency was seriously retarded provided that the photochemical treatment conditions remained constant. Moreover, a definite relationship existed between H(2)O(2) consumption and COD removal for H(2)O(2)/UV-C advanced oxidation of the textile surfactant. In the second part of the study, COD abatement was modeled for the biodegradation of untreated and photochemically pretreated textile surfactant formulation according to their COD fractions. Results have indicated that the readily biodegradable and rapidly hydrolysable COD fractions of the textile surfactant solution could be appreciably increased upon exposure to an optimum H(2)O(2) concentration (60mM; i.e. 2.1g H(2)O(2) (g COD(o))(-1)) and extended UV-C irradiation times (i.e. 90 and 120min).

Effect of photochemical treatment on the biocompatibility of a commercial nonionic surfactant used in the textile industry.

The degradability of surfactants is a frequent and complex issue arising both at domestic as well as industrial treatment facilities. The present paper describes a laboratory study conducted to elucidate the photochemical and biochemical treatability of a nonionic, alkyl polyethylene ether-based surfactant formulation commonly used in the textile preparation stage. The application of H(2)O(2)/UV-C advanced photochemical oxidation appeared to be a suitable treatment alternative and 90% COD removal (COD(0) approximately 500 mg/L) could be achieved under optimized process conditions. A significant COD removal efficiency (74%) could also be reached after biodegradation (final COD=135 mg/L) of the surfactant; however, necessitated an acclimation period of at least 6 weeks for the achievement of steady-state conditions. H(2)O(2)/UV-C treatment efficiency was seriously retarded upon elevation of the initial COD to around 1000 mg/L, resulting in 46% COD and 38% TOC removal after 120 min photochemical oxidation (H(2)O(2,0)=1020 mg/L; pH(0)=9.1). The BOD(5)/COD ratio increased from 0.23 to 0.31 after the application of H(2)O(2)/UV-C revealing that photochemical pretreatment may have a positive effect on the ultimate biodegradation of the nonionic surfactant. Although the time required for activated sludge treatment to reach steady-state conditions could be reduced to 3 weeks for the photochemically pretreated surfactant formulation biochemical COD removal efficiency dramatically decreased from 74% to 39% for the nonionic surfactant being subjected to H(2)O(2)/UV-C pretreatment (ultimate COD after activated sludge treatment=265 mg/L).