Advanced oxidation of alkylphenol ethoxylates in aqueous systems

Effect of chloride ions on persulfate/UV-C advanced oxidation of an alcohol ethoxylate (Brij 30)

In the present study, the effect of chloride ions on the oxidative degradation of an alcohol ethoxylate (Brij 30) by persulfate (PS)/UV-C was experimentally explored using Brij 30 aqueous solution (BAS) and a domestic wastewater treatment plant effluent spiked with Brij 30. Brij 30 degradation occurred rapidly during the early stages of oxidation without affecting the water/wastewater matrix. Mineralization of intermediates of Brij 30 degradation markedly influenced by presence of chloride ions. Chloride ions at concentrations up to 50 mg/L accelerated the mineralization through reactions involving reactive chlorine species, which reduced the sink of SO4·- by Cl- scavenging at both initial pH of 6.0 and 3.0 in the case of BAS. The fastest mineralization was achieved under acidic conditions. The WWTP effluent matrix significantly influenced mineralization efficacy of the intermediates. Co-existence of HCO 3 - and Cl- anions accelerated the mineralization of degradation products. Organic matter originating from the WWTP effluent itself had an adverse effect on the mineralization rate. The positive effects of organic and inorganic components present in the WWTP effluent were ranked in the following order of increasing influence: (Organic matter originating from the effluent + Cl- + HCO 3 - ) < (Cl-) < (Cl- + HCO 3 - ).

Kinetic study on degradation of micro-organics by different UV-based advanced oxidation processes in EfOM matrix

Effluent organic matter (EfOM) contains a large number of substances that are harmful to both the environment and human health. To avoid the negative effects of organic matter in EfOM, advanced treatment of organic matter is an urgent task. Four typical oxidants (H₂O₂, PS, PMS, NaClO) and UV-combined treatments were used to treat micro-contaminants in the presence or absence of EfOM, because the active radical species produced in these UV-AOPs are highly reactive with organic contaminants. However, the removal efficiency of trace contaminants was greatly affected by the presence of EfOM. The degradation kinetics of two representative micro-contaminants (benzoic acid (BA) and para chlorobenzoic acid (pCBA)) was significantly reduced in the presence of EfOM, compared to the degradation kinetics in its absence. Using the method of competitive kinetics, with BA, pCBA, and 1,4-dimethoxybenzene (DMOB) as probes, the radicals (HO^·, SO₄^-·, ClO^·) proved to be the key to reaction species in advanced oxidation processes. UV irradiation on EfOM was not primarily responsible for the degradation of micro-contaminants. The second-order rate constants of the EfOM with radicals were determined to be (5.027 ± 0.643) × 10² (SO₄^-·), (3.192 ± 0.153) × 10⁴ (HO^·), and 1.35 × 10⁶ (ClO^·) (mg C/L)^-1 s^-1. In addition, this study evaluated the production of three radicals based on the concept of R_ct, which can better analyze its reaction mechanism.

A comparison of endocrine disruption potential of nonylphenol ethoxylate, vanillin ethoxylate, 4-n-nonylphenol and vanillin in vitro

The widely used surfactant nonylphenol ethoxylate (NPEO) and its raw material 4-n-nonylphenol (4-n-NP), as well as its degradation products, are recognized as endocrine disrupting chemicals. The USA Environmental Protection Agency (EPA) released an assessment that looked for safe alternatives to NPEO. Vanillin ethoxylate (VAEO) is a novel substitute for NPEO and is quite similar to NPEO in structure; there is a risk that it has similar endocrine disrupting effects to NPEO. However, their effects on various nuclear hormone receptors have not been thoroughly examined. In this study, the effects of NPEO, VAEO, 4-n-NP and Vanillin on the estrogen receptor α (ERα), androgen receptor (AR), thyroid hormone receptor (TR), retinoic X receptor β (RXRβ) and estrogen-related receptor γ (ERRγ) were determined and compared using a battery of recombined yeast strains expressing β-galactosidase. The results showed that NPEO and 4-n-NP acted as significant antagonists of ER, AR, TR and ERRγ. In addition, 4-n-NP also had antagonistic activity toward RXRβ. Moreover, VAEO was shown to be a very weak antagonist of TR and ERRγ, and Vanillin had no interaction with any nuclear receptors. For the first time, it was found that NPEO had AR, TR and ERRγ antagonistic effects and that 4-n-NP was an antagonist of RXRβ. The in vitro data indicated that NPEO, 4-n-NP and VAEO have the potential to act as endocrine disruptors involving more than one nuclear hormone receptor, but VAEO has much lower endocrine disrupting potential than NPEO. Thus, it is critical to find safe substitutes for NPEO and a substitute of NPEO with structural analogues should be carried out with caution. Furthermore, to look for preferable alternatives for NPEO, more in vivo and in vitro studies of the alternatives concerning endocrine disruption are needed, especially in vitro studies need to involve various target points, not only focus on their effects on ER but also take other nuclear hormone receptor pathways into consideration.

Carbon nanotube modified glassy carbon electrode for electrochemical oxidation of alkylphenol ethoxylate

Electrochemical oxidation of an emerging pollutant, 2-(4-methylphenoxy)ethanol (MPET), from water has been studied by cyclic voltammetry (CV). Multiwall carbon nanotubes glassy carbon electrodes (MWCNT-GCE) were used as working electrode due to their extraordinary properties. The oxidation process is irreversible, since no reduction peaks were observed in the reverse scan. The electrocatalytic effect of MWCNT was confirmed as the oxidation peak intensity increases in comparison to bare-GCE. The effect of functional groups on MWCNT was also studied by MWCNT functionalized with NH₂ (MWCNT-NH₂) and COOH (MWCNT-COOH) groups. The oxidation peak current decreases in the following order: MWCNT > MWCNT-NH₂ > MWCNT-COOH. Taking into account the normalized peak current, MWCNT-NH₂ exhibits the best results due to its strong interaction with MPET. Under optimal conditions (pH = 5.0 and volume of MWCNT = 10 μL), degradation was studied for MWCNT-GCE and MWCNT-NH₂-GCE. A complete MPET removal was observed using MWCNT-GCE after four CV cycles, for a volume/area (V/A) ratio equal to 19. In the case of MWCNT-NH₂-GCE, the maximum MPET removal was close to 90% for V/A = 37, higher than that obtained for MWCNT-GCE at the same conditions (≈80%). In both cases, no organic by-products were detected.

UV/H2O2 process stability and pilot-scale validation for trace organic chemical removal from wastewater treatment plant effluents

This study investigated the removal of 15 trace organic chemicals (TOrCs) occurring at ambient concentrations from municipal wastewater treatment plant effluent by advanced oxidation using UV/H₂O₂ at pilot-scale. Pseudo first-order rate constants (k_obs) for photolytic as well as combined oxidative and photolytic degradation observed at pilot-scale were validated with results from a bench-scale collimated beam device. No significant difference was determined between pilot- and lab-scale performance. During continuous pilot-scale operation at constant UV fluence of 800 mJ/cm² and H₂O₂ dosage of 10 mg/L, the removal of various TOrCs was investigated. The average observed removal for photo-susceptible (k_UV>10^-3 cm²/mJ; like diclofenac, iopromide and sulfamethoxazole), moderately photo-susceptible (10^-4<k_UV<10^-3 cm²/mJ; like climbazole, tramadol, sotalol, citalopram, benzotriazole, venlafaxine and metoprolol), and most photo-resistant (k_UV<10^-4 cm²/mJ; like primidone, carbamazepine and gabapentin) compounds was 90%, 49% and 37% including outliers, respectively. The poorly reactive compound TCEP was not significantly eliminated during pilot-scale experiments. Additionally, based on removal kinetics of photo-resistant TOrCs, continuous pilot-scale operation revealed high variations of OH-radical exposure determined from removal kinetics of photo-resistant TOrCs, primarily due to nitrite concentration fluctuations in the feed water. Furthermore, a correlation between OH-radical exposure and scavenging capacity could be determined and verified by mechanistic modeling using UV fluence, H₂O₂ dosage, and standard water quality parameters (i.e., DOC, NO₃^-, NO₂^- and HCO₃^-) as model input data. This correlation revealed the possibility of OH-radical exposure prediction by water matrix parameters and proved its applicability for pilot-scale operations.

Modeling the oxidation of phenolic compounds by hydrogen peroxide photolysis

Hydrogen peroxide UV photolysis is among the most widely used advanced oxidation processes (AOPs) for the destruction of trace organics in waters destined for reuse. Previous kinetic models of hydrogen peroxide photolysis focus on the dynamics of hydroxyl radical production and consumption, as well as the reaction of the target organic with hydroxyl radicals. However, the rate of target destruction may also be affected by radical scavenging by reaction products. In this work, we build a predictive kinetic model for the destruction of p-cresol by hydrogen peroxide photolysis based on a complete reaction mechanism that includes reactions of intermediates with hydroxyl radicals. The results show that development of a predictive kinetic model to evaluate process performance requires consideration of the complete reaction mechanism, including reactions of intermediates with hydroxyl radicals.

TiO₂-Mediated Photocatalytic Mineralization of a Non-Ionic Detergent: Comparison and Combination with Other Advanced Oxidation Procedures

Triton X-100 is one of the most widely-applied man-made non-ionic surfactants. This detergent can hardly be degraded by biological treatment. Hence, a more efficient degradation method is indispensable for the total mineralization of this pollutant. Application of heterogeneous photocatalysis based on a TiO₂ suspension is a possible solution. Its efficiency may be improved by the addition of various reagents. We have thoroughly examined the photocatalytic degradation of Triton X-100 under various circumstances. For comparison, the efficiencies of ozonation and treatment with peroxydisulfate were also determined under the same conditions. Besides, the combination of these advanced oxidation procedures (AOPs) were also studied. The mineralization of this surfactant was monitored by following the TOC and pH values, as well as the absorption and emission spectra of the reaction mixture. An ultra-high-performance liquid chromatography (UHPLC) method was developed and optimized for monitoring the degradation of Triton X-100. Intermediates were also detected by GC-MS analysis and followed during the photocatalysis, contributing to the elucidation of the degradation mechanism. This non-ionic surfactant could be efficiently degraded by TiO₂-mediated heterogeneous photocatalysis. However, surprisingly, its combination with the AOPs applied in this study did not enhance the rate of the mineralization. Moreover, the presence of persulfate hindered the photocatalytic degradation.

Electrochemical sensors of octylphenol based on molecularly imprinted poly(3,4-ethylenedioxythiophene) and poly(3,4-ethylenedioxythiophene–gold nanoparticles)

Two molecularly imprinted electrochemical sensors are fabricated by using EDOT and EDOT–AuNPs as monomers, respectively. The sensors show good analytical performance for OP sensing. Note: graphene nanoribbons (GNRs), 3,4-ethylenedioxythiophene (EDOT), 4-tert-octyl-phenol (OP).

Oil removal from produced water by conjugation of flotation and photo-Fenton processes

The present work investigates the conjugation of flotation and photo-Fenton techniques on oil removal performance from oilfield produced water. The experiments were conducted in a column flotation and annular lamp reactor for induced air flotation and photodegradation steps, respectively. A nonionic surfactant was used as a flotation agent. The flotation experimental data were analyzed in terms of a first-order kinetic rate model. Two experimental designs were employed to evaluate the oil removal efficiency: fractional experimental design and central composite rotational design (CCRD). Overall oil removal of 99% was reached in the optimum experimental condition after 10 min of flotation followed by 45 min of photo-Fenton. The results of the conjugation of induced air flotation and photo-Fenton processes allowed meeting the wastewater limits established by the legislations for disposal.

Photodegradation of non-ionic surfactant with different ethoxy groups in aqueous effluents by the photo-Fenton process

The photo-Fenton process was applied to degrade non-ionic surfactants with different numbers of ethoxy groups, seven (E7), ten (E10) and twenty-three (E23). The effects of H2O2 concentration, Fe(II) concentration and number of ethoxy groups on the mineralization of surfactants were investigated. The response surface methodology (RSM) was applied to determine optimal concentrations of Fenton's reagents for each surfactant. The efficiency of the photo-Fenton process reached 95% for all surfactants studied at 45 min in optimal conditions determined in this work. The analysis of results showed that the efficiency depends upon the number of ethoxy groups in the surfactant. The increase in ethoxy groups favoured the mineralization of surfactants. The analysis of variance (ANOVA) was applied, and according to the F-test the models for the mineralization of surfactants were considered significant and predictable. The photo-Fenton process has proven to be feasible for the degradation of ethoxylated surfactants in aqueous solution.

Fenton Oxidation Kinetics and Intermediates of Nonylphenol Ethoxylates

Removal of nonylphenol ethoxylates (NPEOs) in aqueous solution by Fenton oxidation process was studied in a laboratory-scale batch reactor. Operating parameters, including initial pH temperature, hydrogen peroxide, and ferrous ion dosage, were thoroughly investigated. Maximum NPEOs reduction of 84% was achieved within 6 min, under an initial pH of 3.0, 25°C, an H₂O₂ dosage of 9.74×10^-3 M, and a molar ratio of [H₂O₂]/[Fe²⁺] of 3. A modified pseudo-first-order kinetic model was found to well represent experimental results. Correlations of reaction rate constants and operational parameters were established based on experimental data. Results indicated that the Fenton oxidation rate and removal efficiency were more dependent on the dosage of H₂O₂ than Fe²⁺, and the apparent activation energy (ΔE) was 17.5 kJ/mol. High-performance liquid chromatography and gas chromatograph mass spectrometer analytical results indicated degradation of NPEOs obtained within the first 2 min stepwise occurred by ethoxyl (EO) unit shortening. Long-chain NPEOs mixture demonstrated a higher degradation rate than shorter-chain ones. Nonylphenol (NP), short-chain NPEOs, and NP carboxyethoxylates were identified as the primary intermediates, which were mostly further degraded.

Degradation of chlorophenols and alkylphenol ethoxylates, two representative textile chemicals, in water by advanced oxidation processes: the state of the art on transformation products and toxicity

Advanced oxidation processes based on the generation of reactive species including hydroxyl radicals are viable options in eliminating a wide array of refractory organic contaminants in industrial effluents. The assessment of transformation products and toxicity should be, however, the critical point that would allow the overall efficiency of advanced oxidation processes to be better understood and evaluated since some transformation products could have an inhibitory effect on certain organisms. This article reviews the most recent studies on transformation products and toxicity for evaluating advanced oxidation processes in eliminating classes of compounds described as "textile chemicals" from aqueous matrices and poses questions in need of further investigation. The scope of this paper is limited to the scientific studies with two classes of textile chemicals, namely chlorophenols and alkylphenol ethoxylates, whose use in textile industry is a matter of debate due to health risks to humans and harm to the environment. The article also raises the critical question: What is the state of the art knowledge on relationships between transformation products and toxicity?

Identifying the factors that influence the reactivity of effluent organic matter with hydroxyl radicals

Advanced oxidation processes (AOPs) are an effective treatment technology for the removal of a variety of organic pollutants in both water and wastewater treatment. However, many background constituents in water are highly reactive towards hydroxyl radicals (HO) and decrease the efficiency of the process towards contaminant oxidation. Up to 95% of the HO scavenging can come from dissolved organic matter (OM). In this study, 28 wastewater effluent samples were analyzed to find correlations between the reactivity of HO with wastewater-derived OM (known as effluent organic matter, EfOM), water quality parameters, treatment train characteristics, and fluorescence-derived data. Rate constants for the reaction between HO and EfOM (kEfOM-HO) were measured using a bench scale UV-based AOP system with methylene blue as an HO probe and confirmed using an electron pulse radiolysis method for a subset of the samples. The EfOM was characterized using a series of physicochemical parameters, including polarity, average molecular size and fluorescence. The kinetic data were analyzed with principal component analysis and Akaike Information Criterion. Four predictors were identified as dominant: chemical oxygen demand, retention onto NH2 extraction medium, fluorescence index, and total organic carbon. These four variables accounted for approximately 62% of the variability in the value of kEfOM-HO The average kEfOM-HO value for EfOM in this study was 2.5 × 10(8) MC(-1) s(-1), which is about 31% lower than the 3.6 × 10(8) MC(-1) s(-1) value determined for natural organic matter isolates and commonly used in AOP modeling.

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.

Evaluation of Efficacy of Anionic Surfactant Degradation in the Presence of Concomitant Impurities of Natural Waters

The efficacy of anionic surfactant—sodium alkylbenzene sulfonate (ABS) degradation in the river waters and model solutions containing humic acid by various oxidation processes has been compared. The most effective method is photocatalytic ozonation (O3/TiO2/UV) which ensures maximum reduction of ABS concentration (94%-95% over 20–30 min) from ~5 mg/dm3to values not exceeding the MPC (<0.5 mg/dm3) and the highest degree of total organic carbon (TOC) removal (up to 74%) at the lowest values of specific ozone consumption per 1 mg/dm3of TOC compared to ozonation and O3/UV. Photocatalytic oxidation with air oxygen (O2/TiO2/UV) and O3/UV treatment provides a smaller decrease in ABS concentrations (86%–93% and 71%–87% within 20–30 min, resp.) and significantly lowers TOC removal (up to 57% and 47%, resp.). Ozonation and UV irradiation, used separately, are inefficient methods for ABS degradation (<40%), and for TOC removal (<15%).

Incorporating biodegradation and advanced oxidation processes in the treatment of spent metalworking fluids

The treatment of spent metalworking fluids (MWFs) is difficult due to their complex and variable composition. Small businesses often struggle to meet increasingly stringent legislation and rising costs as they need to treat this wastewater on site annually over a short period. Larger businesses that treat their wastewater continuously can benefit from the use of biological processes, although new MWFs designed to resist biological activity represent a challenge. A three-stage treatment is generally applied, with the oil phase being removed first, followed by a reduction in COD loading and then polishing of the effluent's quality in the final stage. The performance of advanced oxidation processes (AOPs), which could be of benefit to both types of businesses was studied. After assessing the biodegradability of spent MFW, different AOPs were used (UV/H2O2, photo-Fenton and UV/TiO2) to establish the treatability of this wastewater by hydroxyl radicals (*OH). The interactions of both the chemical and biological treatments were also investigated. The wastewater was found to be readily biodegradable in the Zahn-Wellens test with 69% COD and 74% DOC removal. The UV/TiO2 reactor was found to be the cheapest option achieving a very good COD removal (82% at 20 min retention time and 10 L min(-1) aeration rate). The photo-Fenton process was found to be efficient in terms of degradation rate, achieving 84% COD removal (1 M Fe2+, 40 M H2O2, 20.7 J cm(-2), pH 3) and also improving the wastewater's biodegradability. The UV/H202 process was the most effective in removing recalcitrant COD in the post-biological treatment stage.

Review of photochemical reaction constants of organic micropollutants required for UV advanced oxidation processes in water

Emerging organic contaminants (pharmaceutical compounds, personal care products, pesticides, hormones, surfactants, fire retardants, fuel additives etc.) are increasingly found in water sources and therefore need to be controlled by water treatment technology. UV advanced oxidation technologies are often used as an effective barrier against organic contaminants. The combined operation of direct photolysis and reaction with hydroxyl radicals ensures good results for a wide range of contaminants. In this review, an overview is provided of the photochemical reaction parameters (quantum yield, molar absorption, OH radical reaction rate constant) of more than 100 organic micropollutants. These parameters allow for a prediction of organic contaminant removal by UV advanced oxidation systems. An example of contaminant degradation is elaborated for a simplified UV/H(2)O(2) system.