Precipitation of enzyme-catalyzed phenol oxidative coupling products: background ion and pH effects

Treatment of contaminants by a cathode/FeIII/peroxydisulfate process: Formation of suspended solid organic-polymers

Treatment of highly contaminated wastewaters containing refractory or toxic organic contaminants (e.g. industrial wastewaters) is becoming a global challenge. Most technologies focus on efficient degradation of organic contaminants. Here we improve the cathode/Fe^III/peroxydisulfate (PDS) technology by turning down the current density and develop an innovative mechanism for organic contaminants abatement, namely polymerization rather than degradation, which allows simultaneous contaminants removal and resource recovery from wastewater. This polymerization leads to organic-particles (suspended solid organic-polymers) formation in bulk solution, which is demonstrated by eight kinds of representative organic contaminants. Taking phenol as a representative, 83% of PDS is saved compared to degradation process, with 87.2% of DOC removal. The formed suspended solid organic-polymers occupy 59.2% of COD of the original organics in solution, and can be easily separated from aqueous solution by sedimentation or filtration. The separated organic-polymers are a series of polymers coupled by phenolic monomers, as confirmed by FTIR and ESI-MS analyzes. The energy contained in the recovered organic polymers (4.76 × 10^-5 kWh for 100 mL of 1 mM phenol solution in this study) can fully compensate the consumed electrical energy (2.8 × 10^-5 kWh) in the treatment process. A representative polymerization model for this process is established, in which the SO₄^•- and HO^• generated from PDS activation initiate the polymerization and improve the polymerization degree by the production of oligomer intermediates. A practical coking wastewater treatment is carried out to verify the research results and get positive feedback, with 56.0% of DOC abatement and the suspended solid organic-polymers accounts for 42.5% of the total COD in the raw wastewater. The energy consumption (47 kWh/kg COD, including electricity and PDS cost) is lower than the values in previous reports. This study provides a novel method for industrial wastewater treatment based on polymerization mechanism, which is expected to recover resources while removing pollutants with low consumption.

A multifunctional and low-energy electrochemical membrane system for chemical-free regulation of solution pH

A proper pH environment is essential for a wide variety of industries and applications especially related to water treatment. Current methods for pH adjustment including addition of acid/base and electrochemical processes demonstrate disadvantages associated with environment and energy. Here, we designed a multifunctional electrochemical membrane system (EMS) with one piece of filtration membrane inserted into an electrochemical cell. When electrical field was applied, OH^- and H⁺ ions were produced from reduction and oxidation reactions at cathode and anode, respectively. The membrane posed a resistance for the transport of OH^- and H⁺ ions and prevented their mixing in the cell. The EMS can be also operated in a filtration mode, which could simultaneously regulate permeate and feed pH and accomplish water filtration. In both non-filtration and filtration modes, EMS could achieve effective control of solution pH over a wide range by exerting different voltages without dosing any chemicals. Under the voltage of 1.2 V, the solution pH could reach and be maintained at 10.7 and 3.3 in cathodic and anodic channels, respectively. Furthermore, it was experimentally demonstrated that the EMS only consumed extremely low energy. This, together with membrane filtration in an integrated manner, highlights the huge potential of the EMS for applications in various water industries.

Persistence, ecological risks, and oxidoreductases-assisted biocatalytic removal of triclosan from the aquatic environment

Triclosan (TCS) has been immensely employed in health care products and consumer items, as an active agent with fungicidal and bactericidal potentialities, such as soaps, sanitizers, tubes of toothpaste, deodorants, skin creams, and so on for over last five decades. The ultimate excretory route of TCS ends in our water matrices, thus has been frequently detected with ecological and human-health related matters and hazards. Bioactive residues of TCS reach into the key atmosphere compartment through numerous routes, such as (1) scarce or ineffective elimination or degradation throughout the treatment practices, (2) abandoned landfill leachates, (3) leakage from the discarded TCS-containing materials, and so on. Such persistence and occurrence of TCS or its degraded but bioactive residues have growing attentions. Its complete removal and/or effective prevention are still challenging tasks for safeguarding the environment. Owing to the highly effective catalytic and stability potential, enzyme-based bio-degradation approaches are considered an evocative substitute for TCS mitigation from environmental matrices. As compared to enzymes in their pristine form, immobilized enzymes, with unique catalytic, stability, selectivity, and reusability profile, are of supreme and strategic interest in environmental biotechnology. Herein, an effort has been made to signify the novel bio-catalytic and bio-degradation potentialities of various oxidoreductases, including laccases, and peroxidases including soybean peroxidase, versatile manganese peroxidase, and horseradish peroxidase with suitable examples. Following a brief introduction, the focus is given to the presence of TCS in the key atmosphere compartments. Potential sources, acquaintance, and hazardous influence of TCS are also discussed with recent and relevant examples. The second half shows the TCS removal/degradation potentialities of soluble enzyme-based catalytic systems and immobilized-enzyme-based catalytic systems. Finally, the concluding remarks, along with possible future directions are given in this significant research arena.

Mechanistic insights into the reactivity of Ferrate(VI) with phenolic compounds and the formation of coupling products

In this paper, the removal of 2-benzylphenol (2-BP), phenol (Ph), chlorophene (CP), and 4-chlorophenol (4-CP) by Fe(VI) have been examined at pH 8.0. The second-order rate constant (k) for substrates degradation at a Fe(VI) concentration of 0.2 mM was in the order of k_CP (353 M^-1 s^-1) > k_4-CP (131 M^-1 s^-1) > k_2-BP (102 M^-1 s^-1) > k_Ph (40 M^-1 s^-1), indicating that the presence of chlorine and benzyl groups in benzene ring can enhance the reactivity of the phenolic compounds with Fe(VI). Reaction products were identified by a liquid chromatography-quadrupole-time-of-flight-mass spectrometry (LC-Q-TOF-MS), and four reaction mechanisms, including hydroxylation of benzene ring, cleavage of C-C bridge bond, substitution of chlorine atom by hydroxyl group, and the single-electron coupling mechanism were proposed for phenols degradation by Fe(VI). The extracted peak areas of the degradation products showed that the single-electron coupling reaction is the main degradation mechanism in Fe(VI) oxidation processes. In addition to direct attack by Fe(VI), hydroxyl radical, as detected by electron paramagnetic resonance (EPR) spectra, also plays a role in phenols degradation. The •OH initiated reactions and single-electron coupling reactions were further explored by total charges distribution, transition state calculations and potential energy profiles. In addition, Fe(VI) could also work as a highly effective oxidant for substrates removal from real waters.

4-Chlorophenol biodegradation facilitator composed of recombinant multi-biocatalysts immobilized onto montmorillonite

A biodegradation facilitator which catalyzes the initial steps of 4-chlorophenol (4-CP) oxidation was prepared by immobilizing multiple enzymes (monooxygenase, CphC-I and dioxygenase, CphA-I) onto a natural inorganic support. The enzymes were obtained via overexpression and purification after cloning the corresponding genes (cphC-I and cphA-I) from Arthrobacter chlorophenolicus A6. Then, the recombinant CphC-I was immobilized onto fulvic acid-activated montmorillonite. The immobilization yield was 60%, and the high enzyme activity (82.6%) was retained after immobilization. Kinetic analysis indicated that the Michaelis-Menten model parameters for the immobilized CphC-I were similar to those for the free enzyme. The enzyme stability was markedly enhanced after immobilization. The immobilized enzyme exhibited a high level of activity even after repetitive use (84.7%) and powdering (65.8%). 4-CP was sequentially oxidized by a multiple enzyme complex, comprising the immobilized CphC-I and CphA-I, via the hydroquinone pathway: oxidative transformation of 4-CP to hydroxyquinol followed by ring fission of hydroxyquinol.

Comprehensive investigation of the enzymatic oligomerization of esculin by laccase in ethanol : water mixtures

The oligomerization of esculin by laccase in aqueous medium resulted in a precipitate fraction with excellent antioxidant properties.

Removal of triclosan via peroxidases-mediated reactions in water: Reaction kinetics, products and detoxification

This study investigated and compared reaction kinetics, product characterization, and toxicity variation of triclosan (TCS) removal mediated by soybean peroxidase (SBP), a recognized potential peroxidase for removing phenolic pollutants, and the commonly used horseradish peroxidase (HRP) with the goal of assessing the technical feasibility of SBP-catalyzed removal of TCS. Reaction conditions such as pH, H2O2 concentration and enzyme dosage were found to have a strong influence on the removal efficiency of TCS. SBP can retain its catalytic ability to remove TCS over broad ranges of pH and H2O2 concentration, while the optimal pH and H2O2 concentration were 7.0 and 8μM, respectively. 98% TCS was removed with only 0.1UmL(-1) SBP in 30min reaction time, while an HRP dose of 0.3UmL(-1) was required to achieve the similar conversion. The catalytic performance of SBP towards TCS was more efficient than that of HRP, which can be explained by catalytic rate constant (KCAT) and catalytic efficiency (KCAT/KM) for the two enzymes. MS analysis in combination with quantum chemistry computation showed that the polymerization products were generated via CC and CO coupling pathways. The polymers were proved to be nontoxic through growth inhibition of green alga (Scenedesmus obliquus). Taking into consideration of the enzymatic treatment cost, SBP may be a better alternative to HRP upon the removal and detoxification of TCS in water/wastewater treatment.

Immobilization of horseradish peroxidase enzymes on hydrous-titanium and application for phenol removal

Hydrous-titanium was utilized to immobilize HRP in order to improve its stability and adaptability under different water qualities by the biomimetic titanification process. The effects of the reaction conditions on phenol removal were studied.

Magnetic combined cross-linked enzyme aggregates of horseradish peroxidase and glucose oxidase: an efficient biocatalyst for dye decolourization

In this study, the magnetic combined cross-linked enzyme aggregates (combi-CLEAs) of glucose oxidase (GOD) and horseradish peroxidase (HRP) were designed and prepared successfully.

Effect of common metal ions on the rate of degradation of 4-nitrophenol by a laccase-Cu2+ synergistic system

Various metal ions are present in industrial wastewater. In this study, the role of Cu(2+) in pollutant degradation by laccase and the effect of common metal ions such as Na(+), K(+), Ca(2+), Mg(2+), Zn(2+), Hg(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Fe(3+), and Al(3+) on the degradation velocity of the laccase-Cu(2+) synergistic system using 4-nitrophenol as the target pollutant were investigated. The results show that the laccase-Cu(2+) system achieved a higher degradation velocity than the system without Cu(2+). The activity of the laccase-Cu(2+) synergistic system was inhibited when a monovalent metal ion (Na(+) or K(+)) was added into the system regardless of the concentration. The addition of relatively low concentrations of any divalent metal ions also resulted in inhibition of the activity. However, increasing concentrations of Ca(2+) or Fe(2+) increased the rate of degradation of 4-nitrophenol by the laccase-Cu(2+) system, whereas increasing concentrations of other divalent metal ions suppressed the system. The inhibition effect of the added trivalent metal ions (Al(3+) or Fe(3+)) was significant during the entire process, indicating that these trivalent metal ions can be a serious obstacle to the activity of the laccase-Cu(2+) synergistic system.

Removal of nitrate and ammonium ions from livestock wastewater by hybrid systems composed of zero-valent iron and adsorbents

The feasibility of hybrid systems for simultaneous removal of nitrate (NO3-) and ammonium ions (NH4+) from livestock wastewater was examined in batch experiments. As a part of efforts to remove nitrate and ammonium simultaneously, Fe0 and adsorbents including coconut-based granular activated carbon (GAC), sepiolite and filtralite were used. Various parameters such as adsorbent dosages and temperature were studied. Removal of NO3- increased with increase in temperature. Maximum NO3- removal (85.3%) was observed for the Fe0-filtralite hybrid system at 45 degrees C for a 24 h reaction time. Increase in GAC and sepiolite dosages had significant (P < 0.01) effect on the NH4+ removal efficiency, which was primarily due to the net negative surface charge of the adsorbents. The efficiency of hybrid systems for the removal of NO3- was in the order of filtralite > sepiolite > GAC, and the order of the removal of NH4+ was GAC > sepiolite > filtralite. The results of the present study suggest that the use of hybrid systems could be a promising innovative technology for achieving simultaneous removal of NO3- and NH4 from livestock wastewater.

Degradation of nitrobenzene in simulated wastewater by iron-carbon micro-electrolysis packing

The reductive degradation of nitrobenzene (NB) by iron-carbon micro-electrolysis packing was investigated. The influence of initial NB concentration, pH value and packing amount on the removal rate of NB were studied. The results showed that the reaction with packing followed the pseudo-first-order reaction. The optimum pH was 3.0 for the degradation of NB in the tested pH ranges of 3-9 and the optimum packing amount was 40 g/200 ml. The flow-through column packed with packing was designed to remove NB from simulated wastewater for approximately 68 days. The removal rate was over 90% within initial periods. It could be seen that after running for 68 days, the packing still had good performance after the long-term column experiment. In addition, the changes of the packing surfaces morphologies and matters before, during and after the column experiment were analysed by scanning electron microscopy in conjunction with energy-dispersion spectroscopy (EDS).

Laccase-catalyzed oxidation of oxybenzone in municipal wastewater primary effluent

Pharmaceuticals and personal care products (PPCPs) are now routinely detected in raw and treated municipal wastewater. Since conventional wastewater treatment processes are not particularly effective for PPCP removal, treated wastewater discharges are the main entry points for PPCPs into the environment, and eventually into our drinking water. This study investigates the use of laccase-catalyzed oxidation for removing low concentrations of PPCPs from municipal wastewater primary effluent. Oxybenzone was selected as a representative PPCP. Like many other PPCPs, it is not recognized directly by the laccase enzyme. Therefore, mediators were used to expand the oxidative range of laccase, and the efficacy of this laccase-mediator system in primary effluent was evaluated. Eight potential mediators were investigated, and 2,2'-Azino-bis(3-ethylbenzthiazoline-6sulphonic acid) diammonium salt (ABTS), a synthetic mediator, and acetosyringone (ACE), a natural mediator, provided the greatest oxybenzone removal efficiencies. An environmentally relevant concentration of oxybenzone (43.8 nM, 10 μg/L) in primary effluent was completely removed (below the detection limit) after two hours of treatment with ABTS, and 95% was removed after two hours of treatment with ACE. Several mediator/oxybenzone molar ratios were investigated at two different initial oxybenzone concentrations. Higher mediator/oxybenzone molar ratios were required at the lower (environmentally relevant) oxybenzone concentration, and ACE required higher molar ratios than ABTS to achieve comparable oxybenzone removal. Oxybenzone oxidation byproducts generated by the laccase-mediator system were characterized and compared to those generated during ozonation. Enzymatic treatment generated byproducts with higher mass to charge (m/z) ratios, likely due to oxidative coupling reactions. The results of this study suggest that, with further development, the laccase-mediator system has the potential to extend the treatment range of laccase to PPCPs not directly recognized by the enzyme, even in a primary effluent matrix.

Corrosion control in water supply systems: effect of pH, alkalinity, and orthophosphate on lead and copper leaching from brass plumbing

This study explored the potential of lead and copper leaching from brass plumbing in the Auckland region of New Zealand. A five-month field investigation, at six representative locations, indicated that Auckland's water can be characterized as soft and potentially corrosive, having low alkalinity and hardness levels and a moderately alkaline pH. More than 90% of the unflushed samples contained lead above the maximum acceptable value (MAV) of 10 microg/L (New Zealand Standards). In contrast, the copper level of unflushed samples remained consistently below the corresponding MAV of 2 mg/L. Flushing however reduced sharply metal concentrations, with lead values well below the MAV limit. Generally, metal leaching patterns showed a limited degree of correlation with the variations in temperature, dissolved oxygen and free chlorine residual at all sampling locations. Furthermore, a series of bench-scale experiments was conducted to evaluate the effectiveness of pH and alkalinity adjustment, as well as orthophosphate addition as corrosion control tools regarding lead and copper dissolution. Results demonstrated that lead and copper leaching was predominant during the first 24 hr of stagnation, but reached an equilibrium state afterwards. Since the soluble fraction of both metals was small (12% for lead, 29% for copper), it is apparent that the non-soluble compounds play a predominant role in the dissolution process. The degree of leaching however was largely affected by the variations in pH and alkalinity. At pH around neutrality, an increase in alkalinity promoted metal dissolution, while at pH 9.0 the effect of alkalinity on leaching was marginal. Lastly, addition of orthophosphate as a corrosion inhibitor was more effective at pH 7.5 or higher, resulting in approximately 70% reduction in both lead and copper concentrations.

Removal of acetaminophen using enzyme-mediated oxidative coupling processes: I. Reaction rates and pathways

We found that acetaminophen could be effectively transformed and removed from water by laccase-mediated oxidative coupling processes. The removal of acetaminophen followed second-order kinetics with first-order to the concentrations of both the substrate and the enzyme. Mass spectrum analysis demonstrated that polymerization through radical-radical coupling mechanism was the pathway leading to acetaminophen transformation. Coupling products thus formed are believed to be biologically inactive and more readily removable from water. Secondary mass spectra of the dimers in combination with molecular modeling analysis further elucidated that the coupling proceeded via covalent bonding between two molecules at their unsubstituted carbons in benzene rings. These findings demonstrated that laccase-mediated oxidative coupling can potentially serve as an alternative strategy to control certain micropollutants in water/wastewater treatment and reuse.

A critical review on the process of contaminant removal in Fe0-H2O systems

A central aspect of the contaminant removal by elemental iron materials (Fe0 or Fe0 materials) is that reduction reactions are mediated by the iron surface (direct reduction). This premise was introduced by the pioneers of the reactive wall technology and is widely accepted by the scientific community. In the meantime enough evidence has been provided to suggest that contaminant reduction through primary corrosion products (secondary reductants) does indeed occur (indirect reduction). It was shown for decades that iron corrosion in the pH range of natural waters (4-9) inevitably yields an obstructive oxide film of corrosion products at the metal surface (oxide film). Therefore, contaminant adsorption on to corrosion products and contaminant co-precipitation with corrosion products inevitably occurs. For adsorbed and coprecipitated contaminants to be directly reduced the oxide film should be electronic conductive. This study argues through a literature review a series of points which ultimately lead to the conclusion that, if any quantitative contaminant reduction occurs in the presence of Fe0 materials, it takes place within the matrix of corrosion products and is not necessarily a direct reduction. It is concluded that Fe0 materials act both as source of corrosion products for contaminant adsorption/coprecipitation and as a generator of FeII and H2 (H) for possible catalytic contaminant reduction.

Application of Brassica napus hairy root cultures for phenol removal from aqueous solutions

Phenolic compounds present in the drainage from several industries are harmful pollutants and represent a potential danger to human health. In this work we have studied the removal of phenol from water using Brassica napus hairy roots as a source of enzymes, such as peroxidases, which were able to oxidise phenol. These hairy roots were investigated for their tolerance to highly toxic concentrations of phenol and for the involvement of their peroxidase isoenzymes in the removal of phenol. Roots grew normally in medium containing phenol in concentrations not exceeding 100 mg l(-1), without the addition of H(2)O(2). However, roots were able to remove phenol concentrations up to 500 mg l(-1), in the presence of H(2)O(2), reaching high removal efficiency, within 1h of treatment and over a wide range of pH (4-9). Hairy roots could be re-used, at least, for three to four consecutive cycles. Peroxidase activity gradually decreased to approximately 20% of the control, at the fifth cycle. Basic and near neutral isoenzymes (BNP) decreased along time of recycling while acidic isoenzymes (AP) remained without changes. Although both group of isoenzymes would be involved in phenol removal, AP showed higher affinity and catalytic efficiency for phenol as substrate than BNP. In addition, AP retained more activity than BNP after phenol treatment. Thus, AP appears to be a promising isoenzyme for phenol removal and for application in continuous treatments. Furthermore, enzyme isolation might not be necessary and the entire hairy roots, might constitute less expensive enzymatic systems for decontamination processes.

Removal of estrogenic activity of natural and synthetic hormones from a municipal wastewater: efficiency of horseradish peroxidase and laccase from Trametes versicolor

Some researches studied the removal of steroid estrogens by enzymatic treatment, however none verified the residual estrogenicity after the enzymatic treatment at environmental conditions. In this study, the residual estrogenic activities of the key natural and synthetic steroid estrogens were investigated following enzymatic treatment with horseradish peroxidase (HRP) and laccase from Trametes versicolor. Synthetic water and municipal wastewater containing environmental concentrations of estrone, 17beta-estradiol, estriol, and 17alpha-ethinylestradiol were treated. Liquid chromatography-mass spectrometry analysis demonstrated that the studied steroid estrogens were completely oxidized in the wastewater reaction mixture after a 1-h treatment with either HRP (8-10 U ml(-1)) or laccase (20 U ml(-1)). Using the recombinant yeast assay, it was also confirmed that both enzymatic treatments were very efficient in removing the estrogenic activity of the studied steroid estrogens. The laccase-catalyzed process seemed to present great advantages over the HRP-catalyzed system for up-scale applications for the treatment of municipal wastewater.

Optimization of peroxidase-catalyzed oxidative coupling process for phenol removal from wastewater using response surface methodology

Hydroxylated aromatic compounds (HACs) are considered to be primary pollutants in a wide variety of industrial wastewaters. Horseradish peroxidase (HRP) is suitable for the removal of these toxic substances. However, development of a mathematical model and optimization of the HRP-based treatment considering the economical issues by novel methods is a necessity. In the present study, optimization of phenol removal from wastewater by horseradish peroxidase (HRP) was carried out using response surface methodology (RSM) and central composite design (CCD). As the initial experimental design, 2(4-1) half-fraction factorial design (H-FFD) is accomplished in triplicate at two levels to select the most significant factors and interactions in the phenol removal procedure. Temperature (degrees C), pH, concentration of enzyme (unit mL(-1)), and H202 (mM) were determined as the most effective independent variables. Finally, a fourfactor-five coded level CCD, 30 runs, was performed in order to fit a second-order polynomial function to the results and calculate the economically optimum conditions of the reaction. The goodness of the model was checked by different criteria including the coefficient of determination (R2 = 0.93), the corresponding analysis of variance ((Pmodel > F) < 0.0001) and parity plot (r = 0.96). These analyses indicated that the fitted model is appropriate for this enzymatic system. With the assumption that the minimum enzyme concentration was 0.26 unit mL(-1), the analysis of the response surface contour and surface plots defined the optimum conditions as follows: pH = 7.12, hydrogen peroxide concentration 1.72 mM, and 10 degrees C. This work improves phenol removal operation economically by applying minimum enzyme concentration and highest removal in comparison with previous studies.