Water Environ Res. ;73 (2):165-72
11563376
Cit:4
Faculty of Engineering, Civil Engineering Department, Aim Shams University, Cairo, Egypt.
Phenols are present in petroleum refining wastewater. An enzymatic method for removing phenols from industrial aqueous effluent has been developed in the past several years. In this method, a peroxidase enzyme catalyzes the oxidation of phenol by hydrogen peroxide generation of phenoxyl radicals. These radicals diffuse from the active center of the enzyme into solution and react nonenzymatically to eventually form higher oligomers and polymers, which can be removed from wastewater by conventional coagulation and sedimentation or filtration. In this study, Arthromyces ramosus peroxidase (ARP) was applied to treat a petroleum refining wastewater containing 2 mM (188 mg/L) phenol in a batch and continuous-flow system. The latter consisted of a plug-flow reactor (PFR) where the reaction took place between phenol and hydrogen peroxide catalyzed by the enzyme in the presence of polyethylene glycol (PEG). A flocculation tank followed the PFR where alum and sodium hydroxide were added and then the polymers formed were settled in a sedimentation tank and removed from the system. Most (95 to 99%) of the phenol was removed by the same dose of ARP required for the treatment of synthetic wastewater containing an equal amount of phenol. Polyethylene glycol, as an additive, reduced enzyme inactivation and consequently reduced the enzyme dose and the cost of the treatment process. Step feeding of hydrogen peroxide was not effective in reducing the enzyme requirement. A significant removal of chemical oxygen demand was achieved when using PEG to reduce the enzyme dose.
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3-133 NREF Building, University of Alberta, Edmonton, Alberta, Canada T6G 2W2.
An integrated enzymatic treatment system, which includes Coprinus cinereus peroxidase (CIP) production, processing, and usage in batch or plug flow reactors, is being developed to remove phenolic compounds from the aqueous waste streams. CIP production at bench scale yielded a maximum growth medium activity of approximately 60 U CIP ml(-1). A CIP enzyme solution was prepared for use in treatment by successive filtration steps. This yielded a 4.5-fold increase in enzyme activity, with 87% enzyme activity recovery, and 83% reduction in the solution's Chemical Oxygen Demand. The purity of CIP was observed to have no effect on the ability of the enzyme to remove phenol from the aqueous solutions within the range of enzyme solution purities tested. Contrary to observations reported for phenol removal from buffered solutions, the addition of polyethylene glycol to non-buffered reaction solutions had no positive effect on the phenol removal accomplished at pH 7 in these experiments. The efficiency of enzyme use in a plug flow reactor was improved by step additions of CIP and H2O2.
Escola de Química, Universidade Federal do Rio de Janeiro, Centro de Tecnologia, Bloco E, Lab 113, Cidade Universitária, CEP 21949-900, Rio de Janeiro-RJ, Brasil.
Phenols are toxic pollutants found in industrial wastes imposing several risks to human health. Tyrosinase (EC 1.14.18.1) is an oxygenase oxyreductase found in several life forms, like the mushroom Agaricus bisporus. This enzyme is readily available from this fungal tissue leading to high activity extracts without extensive purification, thus suggesting its potential as a biocatalyst for applications involving biomodification of phenols or bioremediation of phenol-polluted waters. The purpose of this work was to employ a crude extract from the Agaricus bisporus mushroom and its biomass for the removal of phenol from polluted water. Experiments were carried out without pH control. The initial phenol concentration in all solutions was 100 mg l(-1). Four enzymatic concentrations (50, 100, 200 and 400 U ml(-1)) were tested. Reactions, with 200 U ml(-1) and 400 U ml(-1) enzymatic activity, led to 90% of phenol removal. Chitosan was used as a coagulant, but no significant improvement was observed. The in natura fungi was also able to remove 90% of phenol, demostrating its viability as a biocatalyst in bioremediation process.
Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2W2.
Non-ligninolytic fungal peroxidases produced by Coprinus cinereus UAMH 4103 and Coprinus sp. UAMH 10067 were purified, characterized and evaluated as cost-effective alternatives to horseradish peroxidase for aqueous phenol treatment. Purified Coprinus peroxidases exhibited a molecular weight of 36 kDa on matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Although the catalytic properties of the two Coprinus peroxidases were nearly identical in both crude and purified forms, the stabilities were substantially different. The peroxidase from Coprinus sp. UAMH 10067 was more stable at 50 degrees C and under basic conditions (up to pH 10) than the enzyme from C. cinereus UAMH 4103. The former enzyme also performed better at pH 9 than the latter one in aqueous phenol treatment. The phenol removal efficiency of the Coprinus peroxidase was comparable to those of previously studied plant peroxidases. The broader working pH and higher thermal and alkaline stability of the peroxidase from Coprinus sp. UAMH 10067 may be advantageous for its application to industrial wastewater treatment.
Department of Civil Engineering, University of Waterloo, Waterloo, ON, Canada, N2L 3G1.
The main objective of this work was to investigate the removal of aqueous phenol using immobilized enzymes in both bench scale and pilot scale three-phase fluidized bed reactors. The enzyme used in this application was a fungal tyrosinase [E.C. 1.14.18.1] immobilized in a system of chitosan and alginate. The immobilization matrix consisted of a chitosan matrix cross-linked with glutaraldehyde with an aliginate-filled pore space. This support matrix showed superior mechanical properties along with retaining the unique adsorptive characteristics of the chitosan. Adsorption of the o-quinone product by the chitosan reduced tyrosinase inactivation that is normally observed for this enzyme under these conditions. This approach allowed reuse of the enzyme in repeated batch applications. For the bench scale reactor (1.2-l capacity) more than 92% of the phenol could be removed from the feed water using an immobilized enzyme volume of 18.5% and a residence time of the liquid phase of 150 min. Removal rates decreased with subsequent batch runs. For the pilot scale fluidized bed (60 l), 60% phenol removal was observed with an immobilized enzyme volume of 5% and a residence time of the liquid phase of 7 h. Removal decreased to 45% with a repeat batch run with the same immobilized enzyme.
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Department of Civil & Environmental Engineering, University of Windsor, Windsor ON, N9B 3P4, Canada. sahad@uwindsor.ca
This study investigated the feasibility of a two-step process for the removal of benzene from buffered synthetic wastewater. Benzene is outside the scope of enzymatic removal. In order to remove it from wastewater using enzyme, its pretreatment by modified Fenton reaction was employed to generate the corresponding phenolic compounds. In the first phase, the optimum pH, H2O2 and Fe2+ concentrations and reaction time for the Fenton reaction were determined to maximize the conversion of benzene to phenolic compounds without causing significant mineralization. The pretreatment process was followed by oxidative polymerization of the phenolic compounds catalyzed by a laccase from Trametes villosa. Factors of interest for the three-hour enzymatic treatment were pH and laccase concentration. Under optimum Fenton reaction conditions, 80% conversion of the initial benzene concentration was achieved, giving a mixture containing oxidative dimerization product (biphenyl) and hydroxylation products (phenol, catechol, resorcinol, benzoquinone and hydroquinone). Enzymatic removal of biphenyl and benzoquinone was not possible but 2.5 U/mL laccase was successful in removal of the rest of the phenolic
Department of Civil & Environmental Engineering, University of Windsor, Ontario, Canada.
The priority pollutant lists of both the U.S. Environmental Protection Agency (U.S. EPA) and the European Union (EU) include diphenylamine (DPA), a contaminant found in wastewater of various industries. This work demonstrates the potential of using enzymatic treatment to remove DPA from buffered synthetic wastewater. This treatment method includes oxidative polymerization of DPA using laccase from Trametes villosa, followed by removal of those polymers via adsorptive micellar flocculation (AMF) using sodium lauryl sulfate (SDS) and alum. Researchers investigated the effects of pH, laccase concentration, molecular mass, and concentration of polyethylene glycol (PEG) in continuously stirred batch reactors to achieve 95% substrate conversion in three hours. Treatment of 0.19 mM DPA was best at pH 7 and an enzyme concentration from 0.0025 to 0.0075 standard activity unit/mL. Except for PEG400 optimum enzyme and PEG concentrations decreased with an increase in PEG molecular mass. Optimum AMF conditions were pH 3.0 to 6.5, 200 mg/L of SDS, and 150 mg/L of alum.
Department of Civil Engineering, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4. hijyoti_2000_2001@yahoo.com
The potential use of laccase (SP-504) in an advanced oxidation-based treatment technology to remove 2,4-dimethylphenol (DMP) from water was investigated with and without the additive, polyethylene glycol (PEG). The DMP concentration was varied between 1.0 and 5.0 mM. The optimization of pH and enzyme concentration in the presence and absence of PEG was carried out. All experiments were carried out in continuously stirred reactors for 3h at room temperature. The reaction was initiated by adding enzyme to the reaction mixture. For more than 95% removal of DMP, the presence of PEG reduced the inactivation of enzyme so that the required enzyme concentrations were reduced by about 2-fold compared to the same reactions in the absence of PEG. Finally, the PEG concentrations were optimized to obtain the minimum dose required. For higher substrate concentrations, the availability of oxygen was insufficient in achieving 95% or more removal. Therefore, the effect of increasing dissolved oxygen at higher substrate concentration was investigated. The laccase studied was capable of efficiently removing DMP at very low enzyme concentrations and hence shows great potential for cost-effective industrial applications.
University of Windsor, Ontario, Canada.
Research was conducted to evaluate the potential use of laccase and its susceptibility to inactivation in an alternative enzyme-based treatment technology to remove parent phenol from buffered distilled water. Enzymatic oxidative polymerization of phenol with laccase was carried out in continuously stirred batch reactors. The reaction products were insoluble polymers, which precipitated out of the solution once their solubility limits were exceeded. The findings demonstrated that the polymeric products had significant effects on enzyme activity consumption and subsequent phenol removal. Enzyme species present in the reaction vessel were classified into enzyme remaining in the solution (type 1) and enzyme adhering to the precipitate polymers (type 2). Type 1 enzyme was more efficient in removal of phenol from solution compared with type 2. Subsequent filtration enhanced the phenol removal by removing type 2 enzyme adhering to the polymer particles and decelerating enzyme inactivation. The study also investigated the effects of available dissolved oxygen, provided through aeration and hydrogen peroxide addition, on phenol removal. Aeration and hydrogen peroxide addition increased the dissolved oxygen concentration, but had no effect on the progress curve for phenol removal.
Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ont., Canada N9B 3P4. patapas@uwindsor.ca
A two-step process for the removal of dinitrotoluene from water is presented: zero-valent iron reduction is coupled with peroxidase-catalyzed polymerization of the resulting diaminotoluenes (DAT). The effect of pH was examined in the reduction step: at pH 6 the reaction occurred much more rapidly than at pH 8. In the second step, optimal pH and substrate ratio, minimal enzyme concentration and effect of polyethylene glycol (PEG) as an additive for greater than 95% conversion of DAT, over a 3h reaction period were determined using high performance liquid chromatography. Two enzymes were investigated and compared: Arthromyces ramosus peroxidase (ARP) and soybean peroxidase (SBP). The optimal pH values were 5.4 and 5.2 for ARP and SBP, respectively, but SBP was more resistant to mild acid whereas ARP was more stable in neutral solutions. SBP was found to have a greater hydrogen peroxide demand (optimal peroxide/DAT molar ratio for SBP: 2.0 and 3.0 for 2,4-diaminotoluene (2,4-DAT) and 2,6-diaminotoluene (2,6-DAT), respectively; for ARP: 1.5 and 2.75 for 2,4-DAT and 2,6-DAT, respectively) but required significantly less enzyme (0.01 and 0.1 U ml(-1) for 2,4-DAT and 2,6-DAT, respectively) to convert the DAT than ARP (0.4 and 1.5 U ml(-1) for 2,4-DAT and 2,6-DAT, respectively). PEG was shown to have no effect upon the degree of substrate conversion for either enzyme.
Department of Civil and Environmental Engineering, University of Windsor, Windsor, Ontario Canada N9B 3P4. modares@uwindsor.ca
The feasibility of using the enzyme laccase to treat synthetic wastewater containing bisphenol-A (BPA) was examined. Optimization of pH, laccase concentration, polyethylene glycol (PEG) as an additive for >95% conversion and precipitation of BPA over 3 h of reaction period was determined through colorimetric assay and HPLC. PEG reduced enzyme inactivation, allowing a 5.2-fold reduction in the amount of laccase required for >95% removal of BPA in the range of 0.1-1 mM over 3 h. The fate of PEG after the reaction was also monitored. Linear relationships were found between the concentration of BPA (0.1-1 mM) and the optimum concentrations of laccase and PEG. Little PEG remained in the solution when up to 75 mg/L of PEG was used to treat 0.5 mM BPA. Beyond this level, PEG concentration increased linearly in the supernatant. It is inferred that an interaction between PEG and the polymeric products resulted in the protection of laccase.
Department of Civil & Environmental Engineering, University of Windsor, Ontario, Canada.
Nitrobenzene is a major environmental pollutant, and its degradation is difficultto achieve. Hence, a chemical reduction pretreatment is sought in this research, before the resulting aniline can be treated by enzyme-mediated oxidative polymerization. Zerovalent iron (Fe0) has been successfully employed to reduce nitrobenzene to aniline in synthetic wastewater in both batch and continuous flow reactors. The concentration of nitrobenzene studied was thatwhich would be present in industrial wastewater streams (millimolar, 123 ppm), a concentration range considerably higher than those studied previously with groundwater by other researchers. Anaerobic conditions were maintained in the reactors by including Na2SO3 as an oxygen scavenger in the presence of CoCl2.6H2O, which acted as a catalyst. Batch reactors exhibited adsorption of aniline on the Fe0, which could be described by a langmuir isotherm. A 200 g Fe0 (particle size: 1-2 mm) bed completely converted 1 mM of nitrobenzene flowing upward for about 600 pore-volumes before experiencing flow reduction due to clogging due to corrosion products. Green-black precipitates (Fe0 corrosion products) were formed at the influent end of the column which were identified as maghemite.
Department of Chemistry and Biochemistry, University of Windsor, Ont., Canada.
Inactivation of horseradish peroxidase (HRP) was examined in the presence of hydrogen peroxide alone and in the presence of hydrogen peroxide plus phenol. HRP is inactivated upon exposure to hydrogen peroxide (H2O2) by the combination of two possible pathways, dependent upon hydrogen peroxide concentration. At low H2O2 concentrations (below 1.0 mM in the absence of phenol), inactivation is predominantly reversible, resulting from the formation and accumulation of catalytically inert intermediate compound III. As H2O2 concentrations increase, an irreversible mechanism-based inactivation process becomes predominant. The overall inactivation comprised of both processes exhibits a second-order inactivation rate constant (kapp) of 0.023 +/- 0.005 M-1 s-1 at pH 7.4 and 25 degrees C. In the presence of both hydrogen peroxide fixed at 0.5 mM and phenol, HRP was inactivated in an irreversible, time- and phenol concentration-dependent process, also mechanism-based, with a kapp of 0.019 +/- 0.004 M-1 s-1.
Department of Chemistry and Biochemistry, University of Windsor, Ontario, Canada.
The use of enzymes such as horseradish peroxidase (HRP) for degrading or removing toxic organics from synthetic wastewater has been demonstrated previously. Potential alternatives to HRP are other peroxidases, various ligninases, haloperoxidases and laccases. Results of this study indicate that a fungal peroxidase from Coprinus macrorhizus (CMP) has the capability to catalyze the same reactions as HRP. Similarly, in batch reactors the trend and removal efficiency of aromatic compounds by CMP from synthetic wastewater depend on the nature of the compound.
Department of Environmental Engineering, Institute of Environmental Studies and Research, Ain-Shams University, Cairo, Egypt.
Experiments were carried out to investigate the ability of water hyacinth (Eichhornia crassipes) to remove five heavy metals (cadmium, chromium, copper, nickel, and lead) commonly found in leachate. All experiments were conducted in batch reactors in a greenhouse. It was found that living biomass of water hyacinth was a good accumulator for copper, chromium, and cadmium. The plants accumulated copper, chromium, and cadmium up to 0.96, 0.83, and 0.50%, respectively, of their dry root mass. However, lead and nickel were poorly accumulated in water hyacinth. Also, nonliving biomass of water hyacinth dry roots showed ability to accumulate all metals, except Cr(VI), which was added in anionic form. The highest total metal sorption by nonliving dry water hyacinth roots was found to take place at pH 6.4. The current research demonstrates the potential of using water hyacinth for the treatment of landfill leachate containing heavy metals.
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J Environ Qual. ;38 (5):2034-40
19704146
Dep. of Agricultural & Biosystems Engineering, Iowa State Univ., Ames, IA 50011, USA. alokb@iastate.edu
Peroxidase-mediated oxidation has been proposed as a treatment method for naphthol-contaminated water. However, the impact of solution chemistry on naphthol polymerization and removal has not been documented. This research investigated the impact of pH and ionic strength on peroxidase-mediated removal of 1-naphthol in completely mixed batch reactors. The impact of hydrogen peroxide to 1-naphthol ratio and activity of horseradish peroxidase was also studied. Size exclusion chromatography was used to estimate the molecular weight distribution of oligomeric products, and liquid chromatography/mass spectrometry was used to estimate product structure. Naphthol transformation decreased with ionic strength, and substrate removal was lowest at neutral pHs. Solution pH influenced the size and the composition of the oligomeric products. An equimolar ratio of H(2)O(2):naphthol was sufficient for optimal naphthol removal. Polymerization products included naphthoquinones and oligomers derived from two, three, and four naphthol molecules. Our results illustrate the importance of water chemistry when considering a peroxidase-based approach for treatment of naphthol-contaminated waters.
J Hazard Mater. 2009 Apr 7;:
19409698
Shiva Agarwal,
Ana E Ferreira,
M Teresa A Reis,
M Rosinda C Ismael,
Licínio M Ferreira,
Remígio M Machado,
Jorge M R Carvalho
Centre for Chemical Processes, Department of Chemical and Biological Engineering, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
The removal of phenol and formaldehyde from phenolic resin plant effluents has been studied by using a combined process. In the first step, phenol was removed from effluent by solvent extraction. Special attention was paid to the effluent with a low content of phenol, which was treated by non-dispersive solvent extraction in hollow fibres. It was found that a single module of Liqui-Cel((R)) 2.5in.x8in. membrane contactor allowed processing approximately 24L/h of effluent with 0.4-0.7g/L phenol and attaining values as low as 0.5mg/L in the raffinate. Formaldehyde, which was left in phenolic resin plant effluent after the removal of phenol, has been treated with hydrogen peroxide in alkaline medium and also in acidic medium (Fenton process). In alkaline medium, formaldehyde was oxidized with hydrogen peroxide to formate ion, which was recovered by solvent extraction. The oxidation of formaldehyde with Fenton process was also studied under several operating conditions. It was found that a large amount of hydrogen peroxide (i.e. mole ratio H(2)O(2):HCHO>6) was necessary to mineralize more than 90% HCHO in 1-2h, at atmospheric pressure and 25 degrees C. The combination of pressure and high temperature strongly increased the kinetics of the process and allowed achieving a very high overall efficiency of the treatment under moderate H(2)O(2) dosage.
Performic acid (PFA): tests on an advanced primary effluent show promising disinfection performance.
Department of Civil Engineering, McGill University, Montreal, QC H3A 2K6, Canada. ronald.gehr@mcgill.ca
Performic acid, or PFA (CH(2)O(3)), is a well-known oxidizing agent and disinfectant in the medical field and food industry. It has recently become available on a commercial scale for potential use in wastewater disinfection. This study investigated its application to an advanced primary effluent which is recalcitrant to disinfection by UV and peracetic acid (PAA). Methods were developed for determining PFA concentrations in stock solutions as well as in residual concentrations in the wastewater. Batch and continuous-flow pilot studies showed a correlation between log fecal coliform removals and PFA doses. A PFA dose of approximately 3.4 mg/L and a contact time of 45 minutes could achieve 3-logs removal, and almost total disinfection could be achieved using a dose of 6 mg/L. The by-products of PFA addition are hydrogen peroxide and formic acid (CHOOH), neither of which is considered to be toxic to aquatic fauna at the doses required for disinfection.
Laboratory of Applied Biochemistry, Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
A new enzymatic method for the removal of phenols from industrial aqueous effluents has been developed. The method uses the enzyme polyphenol oxidase which oxidizes phenols to the corresponding o-quinones; the latter then undergo a nonenzymatic polymerization to form water-insoluble aggregates. Therefore, the enzyme in effect precipitates phenols from water. Polyphenol oxidase has been found to nearly completely dephenolize solutions of phenol in the concentration range from 0.01 to 1.0 g/L. The enzymatic treatment is effective over a wide range of pH and temperature; a crude preparation of polyphenol oxidase (mushroom extract) is as effective as a purified, commercially obtained version. In addition to phenol itself, polyphenol oxidase is capable of precipitating from water a number of substituted phenols (cresols, chlorophenols, naphthol, etc.). Also, even pollutants which are unreactive towards polyphenol oxidase can be enzymatically coprecipitated with phenol. The polyphenol oxidase treatment has been successfully used to dephenolize two different real industrial waste-water samples, from a plant producing triarylphosphates and from a coke plant. The advantage of the polyphenol oxidase dephenolization over the peroxidase-catalyzed one previously elaborated by the authors is that the former enzyme uses molecular oxygen instead of costly hydrogen peroxide (used by peroxidase) as an oxidant.
In this study the effectiveness and feasibility of the degradation of microcystin-LR (MC-LR) using a combined method ozone/Fenton reagent was investigated. The decomposition of the toxin was determined by the chromatographic technique. The effect of the Fenton reaction on the ozonation was observed at various concentrations of ozone at pH 3.0 and 6.8. A low concentration of ozone (0.01 mg/L) given simultaneously with Fenton reagent was more effective in MC-LR degradation than ozone or Fenton reagent treatment individually regardless of the pH. At higher concentrations of ozone the use together with Fenton reagent at pH 6.8 was less efficient in MC-LR degradation than treatment with ozone alone, whereas at pH 3.0 Fenton process turned out to be more effective. The mixture of ozone and hydrogen peroxide was more striking than using ozone with Fenton reagent regardless of the pH. The complete degradation of MC-LR was achieved using ozone alone at a concentration of 0.10 mg/L, whereas the same result using ozonation with Fenton reagent required a dose of ozone of 0.20 mg/L at pH 6.8. In acidic pH the total removal of MC-LR was achieved using ozone alone at a concentration of 0.20 mg/L and the same result was obtained for the combined method of ozone/Fenton reagent.
Nuclear Agriculture and Biotechnology Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India.
Aseptically grown Vetiveria zizanoides were evaluated for their potential for phytoremediation of phenol from Murashige and Skoog's liquid medium. Phenol was found to be completely removed from incubation medium at the end of 4 days by V. zizanoides plantlets, when medium was supplemented with 50 and 100 mg L(-1) phenol, while with 200, 500, and 1000 mg L(-1) of phenol, 89%, 76% and 70%, respectively, were removed. Phenol removal was found to be associated with inherent production of peroxidase and hydrogen peroxide. Coupled with H(2)O(2) formation, the levels of antioxidant enzymes like superoxide dismutase and peroxidase showed an enhancement when plants were exposed to phenol, whereas catalase levels initially showed a decline due to the utilization of H(2)O(2) by peroxidase for phenol oxidation. However, when peroxidase levels declined, there was an enhancement in catalase levels to minimize the presence of H(2)O(2) in the medium. Having confirmed that the removal of phenol was by V. zizanoides plantlets, in the next phase, micropropagated plantlets and well-developed plants grown in hydroponics were used under in vivo conditions to study the effect of phenol (200 mg L(-1)) on plant growth and reuse. Although plant growth was reduced in presence of phenol, the results of the reuse study indicated the possibility of plants getting adapted to phenol without any decline in potential for phenol remediation.
A novel, enzymatic approach has been developed for the removal of phenols from coal-conversion aqueous effluents. Treatment with horseradish peroxidase and hydrogen peroxide precipitates 97 to 99 percent of the phenol in a wide range of pH and phenol concentrations; both model mixtures and real industrial waste-water samples have been treated successfully. Other pollutants, such as polychlorinated biphenyls, can be enzymatically coprecipitated with the phenols.
University of Waikato, Hamilton, New Zealand, Private Bag 3105, Hamilton, New Zealand.
Up to 30% of the released colour arising from bleached kraft pulp and paper production comes from the alkaline extraction stage. This waste stream can therefore be readily targeted to remove colour at source in mills where improved colour management is required. The efficacy of five advanced oxidative treatment and physico-chemical technologies in removing colour from a typical Eop stage effluent was compared. The most effective oxidative treatment was peroxymonosulphate (79% colour removal in 15 minutes). Ozone and TAML treatments removed 74% and 58% of colour respectively within 30 minutes. In comparison, hydrogen peroxide alone was only able to remove 35% of the colour over 4 hours. Coagulation with polyaluminium chloride achieved 89% colour removal within 5 minutes. However, this treatment produced an undesirable sludge, and may cause toxicity in the treated wastewater. Overall, colour removal ability of the five technologies ranked from highest to lowest was polyaluminium chloride > peroxymonosulfate > ozone > TAML > hydrogen peroxide. Other factors, such as operating costs, feedstock modification and capital infrastructure, also need to be taken into account when selecting the most suitable colour management option.
Department of Chemistry and Biochemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ont., Canada N9B 3P4. patapas@uwindsor.ca
A two-step process for the removal of dinitrotoluene from water is presented: zero-valent iron reduction is coupled with peroxidase-catalyzed polymerization of the resulting diaminotoluenes (DAT). The effect of pH was examined in the reduction step: at pH 6 the reaction occurred much more rapidly than at pH 8. In the second step, optimal pH and substrate ratio, minimal enzyme concentration and effect of polyethylene glycol (PEG) as an additive for greater than 95% conversion of DAT, over a 3h reaction period were determined using high performance liquid chromatography. Two enzymes were investigated and compared: Arthromyces ramosus peroxidase (ARP) and soybean peroxidase (SBP). The optimal pH values were 5.4 and 5.2 for ARP and SBP, respectively, but SBP was more resistant to mild acid whereas ARP was more stable in neutral solutions. SBP was found to have a greater hydrogen peroxide demand (optimal peroxide/DAT molar ratio for SBP: 2.0 and 3.0 for 2,4-diaminotoluene (2,4-DAT) and 2,6-diaminotoluene (2,6-DAT), respectively; for ARP: 1.5 and 2.75 for 2,4-DAT and 2,6-DAT, respectively) but required significantly less enzyme (0.01 and 0.1 U ml(-1) for 2,4-DAT and 2,6-DAT, respectively) to convert the DAT than ARP (0.4 and 1.5 U ml(-1) for 2,4-DAT and 2,6-DAT, respectively). PEG was shown to have no effect upon the degree of substrate conversion for either enzyme.
Nuclear Agriculture and Biotechnology Division, Bhabha Atomic Research Centre, Trombay, Maharashtra, Mumbai 400085, India.
Removal of phenol, a major pollutant in aqueous effluents was studied using plant hairy root cultures. Among four different species of hairy roots tested, Brassica juncea showed the highest potential for phenol removal. The effect of phenol concentration and reuse in a batch system was studied using B. juncea hairy root cultures. Unlike most of the studies reported earlier, phenol removal by the hairy roots was seen to take place without the need for addition of external hydrogen peroxide (H(2)O(2)). To understand the mechanism of phenol removal, levels of peroxidase and phenol oxidase were monitored in the hairy roots. Peroxidase activity in the roots was enhanced when exposed to phenol, while phenol oxidase remained constant. Since peroxidase has a pre-requisite for H(2)O(2), the levels of H(2)O(2) were monitored for its in situ synthesis. H(2)O(2) levels were seen to increase in the presence of phenol. Thus, a mechanism wherein hairy roots also produce H(2)O(2) besides peroxidase, as a protection strategy of plant against xenobiotic stress is plausible.
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