Comparison of alternative treatments for 4-chlorophenol removal from aqueous solutions: use of free and immobilized soybean peroxidase and KrCl excilamp

Enhanced Bioremediation of 4-Chlorophenol by Electrically Neutral Reactive Species Generated from Nonthermal Atmospheric-Pressure Plasma

4-Chlorophenol (4-CP) is a chlorinated aromatic compound with broad industrial applications. It is released into the environment as an industrial byproduct and is highly resistant to biodegradation. Pseudomonas sp. in the environment and activated sludge are used for 4-CP bioremediation; however, the degradation of 4-CP takes a long time. Consequently, the toxicity of 4-CP is a major barrier to its bioremediation. In this study, we investigated the synergistic effect of electrically neutral reactive species on the bacterial bioremediation of 4-CP. Our results showed that the concentration of 4-CP decreased from 2.0 to 0.137 mM and that it was converted to 4-chlorocatechol (4-CC; 0.257 mM), 4-chlororesorcinol (0.157 mM), hydroquinone (0.155 mM), and trihydroxy chlorobenzene and their respective ring-cleaved products following irradiation of neutral reactive species. These compounds were less toxic than 4-CP, except for 4-CC, which reduced the toxicity of 4-CP to Pseudomonas putida. When the neutral reactive species-treated 4-CP fraction was added to P. putida cultured in a synthetic sewage medium for 48 h, the 4-CP concentration was reduced to 0.017 mM, whereas nontreated 4-CP (2.0 mM) was hardly degraded by P. putida. These results suggest that the biodegradation of 4-CP can be efficiently improved by combining irradiation of neutral reactive species with microbial treatment. The irradiation of neutral reactive species of environmental pollutants may additionally lead to further improvements in bioremediation processes.

Immobilization of Peroxidase on Functionalized MWCNTs-Buckypaper/Polyvinyl alcohol Nanocomposite Membrane

Surface modified Multi-walled carbon nanotubes (MWCNTs) Buckypaper/Polyvinyl Alcohol (BP/PVA) composite membrane was synthesized and utilized as support material for immobilization of Jicama peroxidase (JP). JP was successfully immobilized on the BP/PVA membrane via covalent bonding by using glutaraldehyde. The immobilization efficiency was optimized using response surface methodology (RSM) with the face-centered central composite design (FCCCD) model. The optimum enzyme immobilization efficiency was achieved at pH 6, with initial enzyme loading of 0.13 U/mL and immobilization time of 130 min. The results of BP/PVA membrane showed excellent performance in immobilization of JP with high enzyme loading of 217 mg/g and immobilization efficiency of 81.74%. The immobilized system exhibited significantly improved operational stability under various parameters, such as pH, temperature, thermal and storage stabilities when compared with free enzyme. The effective binding of peroxidase on the surface of the BP/PVA membrane was evaluated and confirmed by Field emission scanning electron microscopy (FESEM) coupled with Energy Dispersive X-Ray Spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric Analysis (TGA). This work reports the characterization results and performances of the surface modified BP/PVA membrane for peroxidase immobilization. The superior properties of JP-immobilized BP/PVA membrane make it promising new-generation nanomaterials for industrial applications.

Oxidative biodegradation of 4-chlorophenol by using recombinant monooxygenase cloned and overexpressed from Arthrobacter chlorophenolicus A6

In this study, cphC-I and cphB, encoding a putative two-component flavin-diffusible monooxygenase (TC-FDM) complex, were cloned from Arthrobacter chlorophenolicus A6. The corresponding enzymes were overexpressed to assess the feasibility of their utilization for the oxidative decomposition of 4-chlorophenol (4-CP). Soluble CphC-I was produced at a high level (∼50%), and subsequently purified. Since CphB was expressed in an insoluble form, a flavin reductase, Fre, cloned from Escherichia coli was used as an alternative reductase. CphC-I utilized cofactor FADH₂, which was reduced by Fre for the hydroxylation of 4-CP. This recombinant enzyme complex exhibited a higher specific activity for the oxidation of 4-CP (45.34U/mg-protein) than that exhibited by CphC-I contained in cells (0.18U/mg-protein). The Michaelis-Menten kinetic parameters were determined as: v_max=223.3μM·min^-1, K_M=249.4μM, and k_cat/K_M=0.052min^-1·μM^-1. These results could be useful for the development of a new biochemical remediation technique based on enzymatic agents catalyzing the degradation of phenolic contaminants.

Chlorinated phenol treatment and in situ hydrogen peroxide production in a sulfate-reducing bacteria enriched bioelectrochemical system

Wastewaters are increasingly being considered as renewable resources for the sustainable production of electricity, fuels, and chemicals. In recent years, bioelectrochemical treatment has come to light as a prospective technology for the production of energy from wastewaters. In this study, a bioelectrochemical system (BES) enriched with sulfate-reducing bacteria (SRB) in the anodic chamber was proposed and evaluated for the biodegradation of recalcitrant chlorinated phenol, electricity generation (in the microbial fuel cell (MFC)), and production of hydrogen peroxide (H₂O₂) (in the microbial electrolysis cell (MEC)), which is a very strong oxidizing agent and often used for the degradation of complex organics. Maximum power generation of 253.5 mW/m², corresponding to a current density of 712.0 mA/m², was achieved in the presence of a chlorinated phenol pollutant (4-chlorophenol (4-CP) at 100 mg/L (0.78 mM)) and lactate (COD of 500 mg/L). In the anodic chamber, biodegradation of 4-CP was not limited to dechlorination, and further degradation of one of its metabolic products (phenol) was observed. In MEC operation mode, external voltage (0.2, 0.4, or 0.6 V) was added via a power supply, with 0.4 V producing the highest concentration of H₂O₂ (13.3 g/L-m² or 974 μM) in the cathodic chamber after 6 h of operation. Consequently, SRB-based bioelectrochemical technology can be applied for chlorinated pollutant biodegradation in the anodic chamber and either net current or H₂O₂ production in the cathodic chamber by applying an optimum external voltage.

Removal of phenol in phenolic resin wastewater by a novel biomaterial: the Phanerochaete chrysosporium pellet containing chlamydospore-like cells

A novel biomaterial, the Phanerochaete chrysosporium pellet (CP) composed of chlamydospore-like cells (CLCs), was prepared and its potential in treating phenolic resin wastewater was evaluated. CP possesses higher phenol removal ability in contrast with mycelial pellets of P. chrysosporium, and CLC can be seen as the naturally immobilized enzymes. At shake-flask level, the ideal pH value, temperature, and inoculation quantity of CP for treatment of 1430 mg/l phenol wastewater were pH 4-6, 30 °C, and 5.0 g/l, respectively, and the maximum specific removal rate, 41.1 mg phenol/g CP/h, was obtained in fixed bed reactor (FBR) when the flow rate of wastewater was 3.4 l/h. During the treatment, FBR harbored amounts of bacteria (135 genera) and eukaryotes, as analyzed by metagenomic sequencing. Bacterial pollution not only decreased reactor performance but also had a negative impact on reusability of CP. Hot water treatment (80-85 °C) is effective to inhibit bacterial pollution, and heat resistance of CLC makes the repeated regrowing of CP be feasible. This work presents an innovative and low-cost biomaterial for phenol removal and will be helpful for the practical application of P. chrysosporium in wastewater treatment.

Investigation of photo-assisted and crude peroxidase mediated transformations of chlorinated phenols (CPs) from spiked and industrial wastewaters: identification of reaction products

This work focused on photo-assisted crude peroxidase mediated transformations of chlorinated phenols (CPs) from spiked and industrial wastewaters and the identification of reaction products formed. Garden radish Raphanus sativus was the source of crude peroxidase. No chlorine bearing compounds were detected by gas chromatography-high resolution mass spectrometry analysis. Under identical test conditions, the concentrations of 4-chlorophenol and 2,4-dichlorophenol were demoted to zero from 514 mg/L, 652 mg/L and that of 2,4,6-trichlorophenol and pentachlorophenol were reduced to 18 mg/L and 37 mg/L from 790 mg/L and 1066 mg/L, respectively (high-pressure liquid chromatography analysis). Chloride ion release profiles also showed a progressively increasing trend. A neat chemical oxygen demand removal to the extent of 63-79% was achieved in the case of spiked wastewater sample and to the extent of 77% for industrial wastewaters. A hypothesis reaction scheme was also suggested to comprehend the mechanism of degradation reactions.

Photocatalytic degradation of p-chlorophenol by hybrid H₂O₂ and TiO₂ in aqueous suspensions under UV irradiation

In this study, TiO2 particles were used as photocatalysts for the degradation of aqueous p-chlorophenol (p-CP) under UV irradiation. The effect of TiO2 dose (0-3 g/L), initial p-CP concentration, H2O2 concentration (2-45 mM), solution pH (4.6-9.5), and UV light intensity on the degradation of p-CP were examined. Four oxidative degradation processes, which utilized UV alone (direct photolysis), H2O2/UV, TiO2/UV, and H2O2/TiO2/UV, were compared in a batch photoreactor with a 100-W high-pressure mercury lamp. The photodegradation of p-CP could be described by the pseudo-first-order kinetics according to the Langmuir-Hinshelwood model. Moreover, the apparent degradation rate constants increased considerably from 3.5 × 10(-)(3) min(-)(1) (direct photolysis) to 19.9 × 10(-)(3) min(-)(1) (H2O2/TiO2/UV system).

Soybean hull peroxidase immobilization on macroporous glycidyl methacrylates with different surface characteristics

Soybean hull peroxidase (SHP, E.C. 1.11.1.7) was immobilized by a glutaraldehyde and periodate method onto series of macroporous copolymers of glycidyl methacrylate (GMA) and ethylene glycol dimethacrylate (EGDMA), poly(GMA-co-EGDMA) with various surface characteristics and pore size diameters ranging from 44 to 200 nm. Glutaraldehyde immobilization method and poly(GMA-co-EGDMA) named SGE 20/12 with pore sizes of 120 nm gave immobilized enzyme with highest specific activity of 25 U/g. Deactivation studies showed that immobilization increased stability of SHP and that surface characteristics of the used copolymer had a major influence on a stability of immobilized enzyme at high temperatures and in an organic solvent. The highest thermostability was obtained using the copolymer SGE 20/12 with pore size of 120 nm, while the highest stability in dioxane had SHP immobilized onto copolymer SGE 10/4 with pore size of 44 nm. Immobilized SHP showed a wider pH optimum as compared to the native enzyme especially at alkaline pH values and 3.2 times increased K m value for pyrogallol. After 6 cycles of repeated use in batch reactor, immobilized SHP retained 25 % of its original activity. Macroporous copolymers with different surface characteristics can be used for fine tuning of activity and stability of immobilized SHP to obtain a biocatalyst suitable for phenol oxidation or polymer synthesis in organic solvents.

The suitability of Ce3+-modified ZnO photocatalyst for the mineralization of monochlorophenol isomers in sunlight exposure

The photocatalytic activity of Ce³⁺-modified hexagonal ZnO for the degradation/mineralization of monochlorophenol isomers (2-chlorophenol, 3-chlorophenol and 4-chlorophenol), in natural sunlight exposure, is reported.

Oxidation products and degradation pathways of 4-chlorophenol by catalytic ozonation with MnOx/γ-Al2O3/TiO2 as catalyst in aqueous solution

To identify the intermediates of 4-chlorophenol (4-CP) and bring forward the degradation pathways in the process of catalytic ozonation of 4-CP, 4-CP was ozonated with MnOx/γ-Al2O3/TiO2 (MAT) catalyst, and 4-CP was almost decomposed within 30 min, the mineralization reaching above 94.1% at 100 min. The evident reduction of the degradation with the addition of the radical scavenger tert-butanol (TBA) and the stronger spin-adduct signals of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) indicated that 4-CP was oxidized primarily by hydroxyl radical (·OH). Analysis of GC-MS, HPLC and IC confirmed that aromatic compounds and carboxylic acids were predominant oxidative organic intermediates of 4-CP in catalytic ozonation.The main degradation steps were hydroxylation of 4-CP and the formation of hydroquinone, 4-chlororesorcinol and 4-chlorocatechol. The low molecular weight (LMW) acids, such as malic, malonic, oxalic, acetic, and formic acid, were formed from the further oxidation of the intermediates.

Photocatalytic degradation of 4-chlorophenol by UV/H2O2/NiO process in aqueous solution

The removal of 4-chlorophenol from aqueous phase continues to be an important environmental issue. In this work, the photochemical oxidation of 4-chlorophenol in aqueous solutions in a batch reactor using ultraviolet irradiation, hydrogen peroxide and nickel oxide was studied. The efficiency of the system was evaluated with respect to reaction time, pH, feed concentration of reactants, catalyst load, light intensity, and the reaction rate constant. The concentrations of 4-chlorophenol and chloride ions were determined by high performance liquid chromatography and ion chromatography, respectively. Pure nanosized nickel oxide was characterized by X-ray diffraction and scanning electron microscopy. The results showed that the optimum conditions (the complete 4-chlorophenol removal (100%) at 60 min) were obtained at a neutral pH, with 0.2 mol/L H₂O₂, and 0.05 g/L of nickel oxide. However, no pH effects were observed in the range of 4–10. Analytical profiles on 4-chlorophenol transformation were consistent with the best line fit of the first-order kinetics. Moreover, the degradation rate constant increased with both UV light intensity and decreasing initial concentration of 4-chlorophenol. Finally, the results of mineralization and chloride ions studies indicated that dechlorination was better accomplished but more time was required to completely mineralize 4-chlorophenol into water and carbon dioxide.

Recent progress on application of UV excilamps for degradation of organic pollutants and microbial inactivation

Excilamps as modern mercury-free sources of narrow-band UV radiation represent an attractive alternative in environmental applications. This review focuses on recent studies on the water and surface decontamination with excilamps by means of direct photolysis and advanced oxidation processes. To date, direct photolysis and advanced oxidation processes (AOPs) such as UV/H(2)O(2), UV/Fenton and UV/O(3) have been applied for degradation of organic compounds (mainly, phenols, dyes and herbicides) in model aqueous solutions. Special emphasis is placed on studies combining UV irradiation (as a pre-treatment or post-treatment step) with biological treatment. In this review, the efficiencies of direct UV, UV/H(2)O(2) and UV/TiO(2) processes for inactivation of a variety of pathogenic microorganisms in water and on surfaces are discussed. The analysis of the literature shows that more works need to be done on scaling up the processes, degradation/mineralization of target pollutant(s) in real effluents and evaluation of energy requirements.

Enhanced phenol degradation in coking wastewater by immobilized laccase on magnetic mesoporous silica nanoparticles in a magnetically stabilized fluidized bed

The immobilized laccase on magnetic mesoporous silica nanoparticles has been developed for efficient phenol degradation. The degradation rate of phenol by the immobilized laccase was 2-fold higher than that of the free laccase, and the immobilized laccase retained 71.3% of its initial degradation ability after 10 successive batch treatments of coking wastewater. The phenol degradation in the coking wastewater was enhanced in a continuous treatment process by the immobilized laccase in a magnetically stabilized fluidized bed (MSFB) because of good mixing and mass transfer. The degradation rate of phenol maintained more than 99% at a flow rate of less than 450mLh(-1) and decreased slowly to 91.5% after 40h of the continuous operation in the MSFB. The present work indicated that the immobilized laccase on magnetic mesoporous supports together with the MSFB provided a promising avenue for the continuous enzymatic degradation of phenolic compounds in industrial wastewater.

Removal efficiency and toxicity reduction of 4-chlorophenol with physical, chemical and biochemical methods

Chlorophenols are well-known priority pollutants and many different treatments have been assessed to facilitate their removal from industrial wastewater. However, an absolute and optimum solution still has to be practically implemented in an industrial setting. In this work, a series ofphysical, chemical and biochemical treatments have been systematically tested for the removal of 4-chlorophenol, and their results have been compared in order to determine the most effective treatment based on removal efficiency and residual by-product formation. Chemical treatments based on advanced oxidation processes (AOP) produced the best results on rate and extent of pollutant removal. The non-chemical technologies showed advantages in terms of complete (in the case of adsorption) or easy (enzymatic treatments) removal of toxic treatment by-products. The AOP methods led to the production of different photoproducts depending on the chosen treatment. Toxic products remained in most cases following treatment, though the toxicity level is significantly reduced with combination treatments. Among the treatments, a photochemical method combining UV, produced with a KrCl excilamp, and hydrogen peroxide achieved total removal of chlorophenol and all by-products and is considered the best treatment for chlorophenol removal.

Comparison of UV and UV/H2O2 treatments using excilamps for removal of monochlorophenols in the molecular and anionic form

The efficiency of UV/H(2)O(2) treatment using KrCl (222 nm) and XeBr (282 nm) excilamps was examined for removal of 2-chlorophenol (2-CP) and 4-chlorophenol (4-CP) from aqueous solution in the molecular form (pH 2 and un-adjusted pH) and anionic form (at pH 11). UV/H(2)O(2) treatment of 2- or 4-CP was initially carried out at un-adjusted pH with varying molar ratios of chlorophenol and H(2)O(2). The para-chlorobenzoic acid was used as a hydroxyl radical (•OH) probe compound. UV/H(2)O(2) treatment of 2- and 4-CP with a molar ratio of 1:25 at ambient pH and a fluence of 4.1 J/cm(2) provided a significant decrease in chemical oxygen demand (COD). Under these conditions, the •OH exposure was found to increase from 0.5 × 10(-11) and 0.4 × 10(-11) to 1.8 × 10(-11) and 1.3 × 10(-11) M min for KrCl and XeBr excilamp, respectively. Compared with direct UV photolysis, the pseudo-first-order fluence-based rate constants of 2- and 4-CP degradation in UV/H(2)O(2) process at a molar ratio of 1:25 were significantly higher for molecular 2-CP and 4-CP in the anionic form using both excilamps. Detailed information on UV fluence and/or the exposure to •OH radicals is proposed to accurately compare studies reporting the effectiveness of AOPs based on excilamps.