Journal of Environmental Quality 32:1222-1227 (2003)
© 2003 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
TECHNICAL REPORTS
Bioremediation and Biodegradation
Use of Additives to Enhance the Removal of Phenols from Water Treated with Horseradish and Hydrogen Peroxide
Masami Tonegawa,
Jerzy Dec and
Jean-Marc Bollag*
Laboratory of Soil Biochemistry, Center for Bioremediation and Detoxification, The Pennsylvania State Univ., 129 Land and Water Building, University Park, PA 16802
* Corresponding author (jmbollag{at}psu.edu)
Received for publication April 29, 2002.
 |
ABSTRACT
|
|---|
Use of additives, such as polyethylene glycol (PEG), selected surfactants, chitosan gel, or activated carbon, has been shown to enhance enzymatic treatment of water polluted with organic compounds. In this study, additives were used to facilitate the removal of 2,4-dichlorophenol (2,4-DCP) from water using minced horseradish (Armoracia rusticana P. Gaertn. et al.) as a carrier of peroxidase activity. The specific objectives of the study were to (i) enhance the pollutant removal activity of minced horseradish by the addition of PEG and other additives (e.g., Tween 20, Triton X-100, and rhamnolipid); (ii) eliminate colored reaction products by the addition of chitosan; and (iii) eliminate color by amending treated water with activated carbon. The disappearance of 2,4-DCP in horseradish-treated water samples amended with PEG or various surfactants (75–90%) was greatly increased over that observed in nonamended samples (29%). The effect of PEG depended on its average molecular weight. As indicated by visible spectrophotometry, enclosing horseradish pieces between two sealed chitosan films completely eliminated colored reaction products; however, the decolorization was accompanied by a reduction in 2,4-DCP removal (from 95 to 60%). On the other hand, commercially available activated carbon completely removed colored reaction products from the treated water without reducing the removal efficiency. Based on the results obtained, it can be concluded that the use of additives may considerably improve the quality of wastewater treated by plant materials.
Abbreviations: 2,4-DCP, 2,4-dichlorophenol • HRP, horseradish peroxidase • PEG, polyethylene glycol
|
INTRODUCTION
|
|---|
OXIDOREDUCTIVE ENZYMES, such as peroxidase and tyrosinase, are capable of oxidizing phenols and aromatic amines to free radicals or quinones that are subject to polymerization and partial precipitation from aqueous solutions. Klibanov et al. (1983) demonstrated that horseradish peroxidase (HRP) could be exploited for the removal of aromatic compounds, particularly phenols and anilines, from industrial wastewaters. Subsequently, other oxidoreductases were successfully tested for water treatment (Maloney et al., 1986; Dec and Bollag, 1990). One of the major drawbacks of this method was the inactivation of enzymes by reaction products, resulting in excessive enzyme consumption (Wu et al., 1993). Several studies demonstrated that enzyme consumption can be largely reduced by the use of additives, such as gelatin or polyethylene glycol (PEG), to prevent adsorption of the reaction products on the active sites of enzyme molecules (Nakamoto and Machida, 1992; Wu et al., 1993). Another drawback was the formation of colored reaction products (quinone oligomers) that stayed in the aqueous solution (Edwards et al., 1999). As shown in recent studies (Sun and Payne, 1996; Edwards et al., 1999), this problem can be eliminated by enclosing enzymes between two sealed films of chitosan gel capable of adsorbing the colored products. Color removal can also be achieved by the application of coagulants after an enzymatic reaction (Wada et al., 1995; Ganjidoust et al., 1996; Tatsumi et al., 1994). Coagulants are also effective in protecting enzymes against inactivation (Tatsumi et al., 1994).
This study focused on including the use of additives in horseradish treatment known to be an efficient and inexpensive method for removing phenols and aromatic amines from wastewater (Dec and Bollag, 1994; Roper et al., 1996). Horseradish roots contain large amounts of peroxidase activity. Before application, they need only to be cut into small pieces to maximize enzyme contact with contaminants. Combining additives with minced horseradish was expected to enhance the decontamination effect and to improve the quality of treated water. The specific objectives of this study were to (i) test PEG and selected surfactants for their ability to prevent the inactivation of peroxidase present in the plant tissue, (ii) determine the removal of colored reaction products by horseradish pieces enclosed between two sealed chitosan films, and (iii) determine color removal by amending treated water with activated carbons.
|
MATERIALS AND METHODS
|
|---|
Plant Material, Chemicals, and Additives
Horseradish roots were purchased at a vegetable market, washed with water, minced into approximately 1-mm cubes in a blender, and stored in a freezer (-20°C) before use.
Model pollutants (phenol, 2,4-dichlorophenol, and 4-chlorophenol) and chitosan were purchased from Sigma Chemical Co. (St. Louis, MO). Polyethylene glycol and surfactants (Triton X-100, Tween 20, SDS, and NP-40) were purchased from Aldrich (Milwaukee, WI). Rhamnolipid was donated by Dr. Swaranjit S. Cameotra, Institute of Microbial Technology, India. Activated carbons (Filtrasorb 400, Norit 1240, and Hydrodarco 4000) were obtained from Norit (Atlanta, GA).
Preparation of Chitosan Gels and Enclosing Horseradish Pieces between Chitosan Films
The chitosan gel was prepared according to Sun and Payne (1996). Chitosan (4 g) was dissolved in 100 mL of 8% (v/v) acetic acid solution by stirring overnight at ambient temperature; the undissolved residue was removed by a 20-min centrifugation at 4080 x g. The solution was spread on a glass plate (20 x 20 cm) and covered with another plate that rested on small glass bands (0.3 x 2.0 cm) placed on each side. The height of the bands (1 mm) controlled the thickness of the final chitosan film. Gelling was initiated by immersing the whole setup in 1 M NaOH solution. After 4 h, the assembled plates were taken out and drained briefly. After removing the upper plate, the chitosan film on the bottom plate was divided into 30- x 40-mm sections using a razor blade (the average dry weight of one chitosan slice was 50 mg). All sections were carefully peeled off, and transferred to a container with deionized water. The water was exchanged several times until the pH was brought to 7. The slices were stored in water at 4°C until use. Immediately before the experiment, 0.3-g portions of minced horseradish roots were placed between two films, and the edges were sealed tight using rubber cement (Pacer Technology, Rancho Cucamonga, CA).
Decontamination Reactions
The test compounds were dissolved at various concentrations in deionized water buffered with 0.2 M NaH2PO4 and Na2HPO4 (pH 7). Triplicate samples of the pollutant solutions (5 or 10 mL) were amended with different additives and incubated with minced horseradish roots (or horseradish pieces enclosed between two sealed chitosan films) and H2O2. The incubations involving different surfactants and PEG were performed without agitating the reaction mixture. Reaction mixtures involving horseradish enclosed between chitosan films were agitated by magnetic bar stirring. Activated carbons were added and shaken (360 rpm) with the reaction mixture following the incubation. Unless otherwise stated, the incubation was performed for 3 h at 25°C. Specific reaction conditions (substrate concentration = 1–9 mM, surfactant concentration = 0.01–1 g/L, amount of horseradish = 0.02–0.15 g/5 mL, amount of activated carbon = 0.001–0.1 g/mL, H2O2 concentration = 1–18 mM) are detailed in the legends of Fig. 1 through 8
and Table 1
. Based on previous studies (Roper et al., 1996), peroxidase activity contained in 1 g of minced horseradish roots (on a wet weight basis) from different batches was expected to range from 20 to 30 purpurogallin units. In this study, absolute enzyme activity was not determined, since the effect of horseradish treatment was always compared with the effect shown by control samples.
View larger version (19K):
[in this window]
[in a new window]
|
Fig. 1. Time-course of the 2,4-DCP removal by horseradish in the presence of polyethylene glycol (PEG; molecular weight = 2000) or Tween 20. Reaction mixture volume = 5 mL; horseradish amount = 0.02 g; 2,4-dichlorophenol (2,4-DCP) concentration = 9 mM; H2O2 concentration = 9 mM; PEG and Tween 20 concentrations = 0.1 g/L; pH = 7.0; incubation temperature = 25°C.
|
|
View larger version (21K):
[in this window]
[in a new window]
|
Fig. 8. The effect of the amount of various activated carbons on color removal after horseradish treatment. Reaction mixture volume = 10 mL; horseradish amount = 5.5 g; 2,4-dichlorophenol (2,4-DCP) concentration = 1 mM; H2O2 concentration = 1 mM; pH = 7.0; incubation time = 3 h; incubation temperature = 25°C.
|
|
View larger version (20K):
[in this window]
[in a new window]
|
Fig. 2. Effect of molecular weight of polyethylene glycol (PEG) on the 2,4-dichlorophenol (2,4-DCP) removal by horseradish. Reaction mixture volume = 5 mL; horseradish amount = 0.02 g; 2,4-DCP concentration = 9 mM; H2O2 concentration = 9 mM; PEG concentration = 0.1 g/L; pH = 7.0; incubation time = 3 h; incubation temperature = 25°C.
|
|
View larger version (25K):
[in this window]
[in a new window]
|
Fig. 3. Effect of polyethylene glycol (PEG; molecular weight = 2000) on the 2,4-dichlorophenol (2,4-DCP) removal by horseradish at varying concentrations of 2,4-DCP and H2O2. Reaction mixture volume = 5 mL; horseradish amount = 0.02 g; ratio of 2,4-DCP to H2O2 concentrations (mM) = 1:1; PEG concentration = 0.1 g/L; pH = 7.0; incubation time = 3 h; incubation temperature = 25°C.
|
|
View larger version (22K):
[in this window]
[in a new window]
|
Fig. 4. The effect of polyethylene glycol (PEG; molecular weight = 2000) concentration on the removal of selected phenolic pollutants by horseradish. Reaction mixture volume = 5 mL; horseradish amount = 0.02 g; pollutant concentration = 9 mM; H2O2 concentration = 9 mM; pH = 7.0; incubation time = 3 h; incubation temperature = 25°C.
|
|
View larger version (26K):
[in this window]
[in a new window]
|
Fig. 5. The effect of chitosan gel on visible spectra of the horseradish-treated water. Reaction mixture volume = 10 mL; horseradish amount = 0.3 g enclosed between two 30- x 40-mm chitosan films of a total mass of about 100 mg (dry weight); 2,4-dichlorophenol (2,4-DCP) concentration = 9 mM; H2O2 concentration = 18 mM; pH = 7.0; incubation time = 3 h; incubation temperature = 25°C. The standard error for triplicate absorbance measurements ranged from 0.003 to 0.033.
|
|
View larger version (17K):
[in this window]
[in a new window]
|
Fig. 6. The effect of chitosan gel on the 2,4-dichlorophenol (2,4-DCP) removal by horseradish. Reaction mixture volume = 10 mL; horseradish amount = 0.3 g enclosed between two 30- x 40-mm chitosan films of a total mass of about 100 mg (dry weight); 2,4-DCP concentration = 9 mM; H2O2 concentration = 18 mM; pH = 7.0; incubation time = 3 h; incubation temperature = 25°C.
|
|
View larger version (14K):
[in this window]
[in a new window]
|
Fig. 7. The time course of color removal by activated carbon (Filtrasorb 400; 0.01 g/mL) following the horseradish treatment. Reaction mixture volume = 110 mL; horseradish amount = 5.5 g; 2,4-dichlorophenol (2,4-DCP) concentration = 1 mM; H2O2 concentration = 1 mM; pH = 7.0; incubation time = 3 h; incubation temperature = 25°C.
|
|
View this table:
[in this window]
[in a new window]
|
Table 1. The effect of polyethylene glycol (PEG) and different surfactants (0.1 g/L) on the removal of 2,4-dichlorophenol (2,4-DCP; 9 mM) after a 3-h treatment with minced horseradish roots at 25°C (0.02 g/5 mL + 9 mM H2O2).
|
|
After incubation, the reaction mixtures were centrifuged at 5500 x g for 10 min, and the supernatants were analyzed by high-performance liquid chromatography (HPLC) for the remaining phenols, and by visible spectrophotometry for color removal (experiments with chitosan and activated carbons).
High-Performance Liquid Chromatography Analysis and Visible Spectrometry
Before HPLC analysis, the supernatants (0.5 mL) were filtered through a micropore membrane (0.45 µm) into 2-mL HPLC vials. The membranes were washed with 0.5 mL water and then 0.5 mL methanol into the same vials. The same procedure (filtration and washing) was applied for calibration standards (0.1–9 mM). The injection volume for all of the filtered samples was 10 µL. The analysis was conducted on a Waters (Milford, MA) HPLC system equipped with a Model 6000A solvent delivery system, a 4.6-mm-i.d. x 25-cm-length Waters Spherisorb 5-µm ODS1 column, and a Model 440 wavelength absorbance detector at 280 nm. The mobile phase, at a flow rate of 1.0 mL/min, was composed of an aqueous component (2% acetic acid, 0.018 M ammonium acetate, pH 3.3) and an organic component (methanol) delivered isocratically at ratios of 40:60 or 50:50 aqueous to organic. Retention times for the compounds tested ranged from 4 to 9 min. Pollutant concentrations and the percentage of pollutant removal were determined based on the peak area and the slope of the calibration curve. The visible spectra were obtained with a Model 2000 spectrophotometer (Bausch & Lomb, Rochester, NY).
The standard error was calculated for each set of triplicate samples, and Student's t test at the 95% level of confidence was used to compare the individual values for the percentage of pollutant removal and for absorbance measurements.
|
RESULTS
|
|---|
Table 1 presents the effect of PEG and different surfactants on the removal of 2,4-DCP from water treated for 3 h with minced horseradish and H2O2. In the absence of additives, the removal of 2,4-DCP was 28.5%. It increased dramatically when PEG or surfactants were added (by 54% for PEG to 61% for Triton X-100). Both in the absence and presence of additives (PEG and Tween 20), horseradish removed 2,4-DCP very quickly (Fig. 1), practically within the first 15 min (20% for control as compared with 70% for each of the additives). Differences in the removal of 2,4-DCP between control and additive-amended samples were significant; however, the differences between additive-amended samples were not. Further incubation (up to 60 min) resulted in no significant increase of 2,4-DCP removal in the control sample, and in a minor increase (by 10%) of 2,4-DCP removal in the presence of additives.
The effect of PEG differed depending on the average molecular weight and the concentration of PEG. As shown in Fig. 2, 2,4-DCP removal increased with increasing molecular weight of PEG, from 42% for molecular weight = 200 (as compared with a 35% removal in the control sample) to 97% for molecular weight = 400. The removal increased to 98.5% for molecular weight = 1000 and to 99.5% for molecular weight = 2000. For molecular weight = 8000 and 10000, the removal was also 99.5% (data not shown). The increases for molecular weight = 200 to molecular weight = 2000 were significant, whereas the removals for molecular weight = 2000, 8000, and 10000 were not.
The concentration of 2,4-DCP, ranging from 1 to 9 mM, had no significant effect on the removal of 2,4-DCP (90–95%) in the presence of PEG (molecular weight = 2000; 0.1 g/L) (Fig. 3). In contrast, in the control samples containing no PEG, the removal decreased dramatically with increasing 2,4-DCP concentration (from 85 to 42% for 1 mM and 5 mM 2,4-DCP solutions, respectively). Removal remained constant (42–45%) only at higher 2,4-DCP concentrations (7 and 9 mM).
As determined for three different chemicals (phenol, 2,4-DCP, and 4-chlorophenol), the pollutant removal significantly increased (from 53 to 91% for 2,4-DCP and from 10 to 40% for the remaining two phenols) when the concentration of PEG increased from 0 to 0.1 g/L (Fig. 4). In the case of phenol and 2,4-DCP, further increasing PEG concentration did not result in a significant increase in pollutant removal. However, significant increase was observed in the removal of 4-chlorophenol (from 40–82%) when PEG concentration increased from 0.1 to 0.5 g/L.
Enclosing horseradish pieces (0.3 g) between two chitosan films before incubation with a 9 mM 2,4-DCP solution resulted in an effective color removal from the reaction mixture (Fig. 5). The light absorbance at 400 nm shown by the reaction mixture involving the gel-coated plant material was only 0.07, as compared with 0.57 for non-enclosed horseradish, and to 0.44 for horseradish that was amended with two sealed chitosan films but not enclosed between them. A visual inspection of the chitosan films confirmed the absorption of colored reaction products in the gel. However, the decolorization effect was accompanied by a significant reduction in the 2,4-DCP removal (from 95 to 60%), as shown in Fig. 6.
Following the addition of activated carbons to horseradish-treated water (1 mM 2,4-DCP) (Fig. 7 and 8), the absorbance at 400 nm decreased from 0.55 to 0.05. More than 95% of 2,4-DCP disappeared before the addition of activated carbon (data not shown). As shown in Fig. 7 for Filtrasorb 400, the adsorption of colored reaction products on activated carbon was fast; a complete color removal occurred within 2 h. The three tested activated carbons had similar decolorization effects (Fig. 8). Color removal increased with increasing amounts of activated carbon. Using 0.01 g of activated carbon per 1 mL of the reaction mixture was sufficient to reduce the absorbance (at 400 nm) from 0.52 to between 0.03 and 0.12 (i.e., to achieve a satisfactory decolorization effect). When the amount of activated carbon was increased to 0.1 g/mL, the absorbance decreased to between 0 and 0.05.
|
DISCUSSION
|
|---|
As anticipated, combining the application of additives with horseradish treatment greatly enhanced the removal of 2,4-DCP and other phenols from aqueous solutions, resulting in a significant improvement in the quality of treated water. Previous studies demonstrated that plant materials, such as horseradish roots, potato tubers, white radish roots (Dec and Bollag, 1994), raw soybean hulls (Flock et al., 1999), and parts of 50 other plant species (Flanders, 1997) are effective carriers of peroxidase activity, which is instrumental in removing phenols, anilines, and other aromatic compounds from water solutions (Klibanov et al., 1983; Dec and Bollag, 1994). Unfortunately, water treatment with plant materials had the same two drawbacks (inhibition of enzyme activity and color formation) as water treatment involving isolated enzymes (Dec and Bollag, 1994; Roper et al., 1996).
Using isolated horseradish peroxidase (HRP), Nakamoto and Machida (1992) and Wu et al. (1993) showed that PEG could suppress the adsorption of reaction products on enzyme molecules and thus reduce the inhibition. In the study of Wu et al. (1993), the removal of phenol (10 mM) by HRP was almost doubled in the presence of PEG, as compared with the removal achieved in the absence of PEG. A similar enhancement of the removal potential by PEG (by 60%) was observed in this study using minced horseradish for the treatment of water polluted with 2,4-DCP (9 mM) (Table 1, Fig. 1).
A 60% increase in the 2,4-DCP removal was also observed with the five surfactants (rhamnolipid, Triton X-100, Tween 20, SDS, and NP-40) (Table 1). The enhancement was probably due to reduced adsorption of the reaction products on peroxidase molecules present in the plant tissue (Wu et al., 1993). Except for rhamnolipid, the concentration of the surfactants (0.1 g/L) was below the respective critical micelle concentrations (CMC, given in Table 1), suggesting that micelle formation did not affect the removal of 2,4-DCP. Polyethylene glycol and the five tested surfactants vary in their chemical structures and molecular weights. They are commonly used as detergents, solubilizing agents, or lubricants. Other chemicals, such as borate, gelatin, and polyvinyl alcohol, also can suppress peroxidase inhibition by reaction products (Nakamoto and Machida, 1992). Therefore, it is not clear which chemical or physical factors may be critical for the protective effect of additives.
The effect of molecular weight of PEG on the horseradish treatment (Fig. 2) showed the pattern of increasing 2,4-DCP removal with increasing molecular weight, which was similar to that determined by Nakamoto and Machida (1992) for the HRP-mediated removal of phenol. The only difference was that in the study of Nakamoto and Machida (1992), PEG of molecular weight = 400 was ineffective in suppressing the inhibition of HRP, whereas when applied with minced horseradish, it was reasonably effective in improving the 2,4-DCP removal (Fig. 2). The difference was probably due to differences in the reaction conditions: using different pollutants (2,4-DCP vs. phenol), different pollutant concentrations (9 mM 2,4-DCP vs. 106 mM phenol), different forms of the enzyme (plant material vs. purified horseradish peroxidase), different buffers (phosphate buffer vs. GTA buffer), and different pH values of the reaction mixture (pH 7 vs. 6) (Nakamoto and Machida, 1992).
Polyethylene glycol applied at a relatively low concentration of 0.1 g/L secured high 2,4-DCP removals (90–95%) within a broad range of 2,4-DCP concentrations (1–9 mM) (Fig. 3). As in the study of Wu et al. (1993) with HRP, increasing the concentration of PEG resulted in the increased removal of phenol, 4-chlorophenol, and 2,4-DCP during incubation with horseradish (Fig. 4). However, the cost of increasing the PEG concentration above 0.1 g/L may be of little or no benefit in terms of pollutant removal, as suggested by Fig. 4, at least in the case of phenol and 2,4-DCP.
In the case of 4-chlorophenol, increasing the PEG concentration to 0.5 g/L caused a substantial increase in the pollutant removal (from 40–80%) (Fig. 4). In previous studies (Dec and Bollag, 1994), the transformation of 4-chlorophenol by HRP was inferior (20%) as compared with that of 2,4-DCP (94%). It is possible that the reaction products from 4-chlorophenol were stronger inhibitors of enzyme activity than those originating from 2,4-DCP. If this is the case, the transformation of 4-chlorophenol could be influenced to a greater degree by increasing concentration of PEG than the transformation of 2,4-DCP.
The chitosan film around horseradish pieces efficiently removed colored reaction products from the aqueous solution (Fig. 5); but at the same time, it reduced the removal of 2,4-DCP (Fig. 6). Chitosan is a natural polymer of glucosamine and is considered a good absorbent for quinones originating from tyrosinase-mediated oxidation of phenols (Tatsumi et al., 1994; Wada et al., 1995). Water-soluble quinones (monomers and oligomers) are largely responsible for color formation in the reaction mixtures involving phenols and various phenoloxidases (Edwards et al., 1999). Sun and Payne (1996) successfully used chitosan films to encapsulate tyrosinase and thus remove colored reaction products originating from the oxidation of phenol.
In the presence of HRP or horseradish, phenol is not transformed to colored reaction products (Klibanov et al., 1983), but 2,4-DCP is. Chitosan gel could be a useful component of the reaction mixture as a decolorizing agent if not for the reduced substrate transformation. The access of 2,4-DCP through the chitosan film to horseradish was probably as little restricted as that of phenol to tyrosinase in the study of Sun and Payne (1996). The major obstacle could be reduced transport of H2O2 through the chitosan film, a problem that does not pertain to the oxygen-reliant tyrosinase. In a preliminary experiment with chitosan, H2O2 concentration in the outside solution was 9 mM as in other experiments (data not shown); however, increasing H2O2 concentration to 18 mM had no effect on the removal of either 2,4-DCP or color (Fig. 6). Changes in pH, chitosan gel thickness, and the amount of gel-coated horseradish were also of little effect (data not shown). Regarding the latter, one can speculate that at increased amounts of horseradish, the local concentration of reaction products inside the chitosan capsule was greater than that outside the capsule, causing an increase in peroxidase inhibition. This possibility is partly supported by findings for tyrosinase that substrate transformation decreased with increasing enzyme to chitosan ratio (Sun and Payne, 1996).
The negligible color removal using two sealed chitosan films without enclosing horseradish pieces between them (Fig. 5) is a surprising observation, because in other studies, both with tyrosinase and horseradish peroxidase, chitosan showed encouraging effects as a color adsorbent (Wada et al., 1995; Ganjidoust et al., 1996; Sun and Payne, 1996). In this study, the light absorbance at 400 nm, which was 0.55 in the absence of chitosan, dropped to only 0.44 when chitosan was added. The poor performance of chitosan, as compared with that in previous studies, probably resulted from different origins of the adsorbent, different substrates tested, and different reaction conditions. Regarding the latter, pollutant concentration was probably the most critical factor. In this study 2,4-DCP was 9 mM, whereas in other studies the concentration of phenols ranged from 0.05 to 1 mM only (Wada et al., 1995; Ganjidoust et al., 1996; Sun and Payne, 1996). The relatively high concentration of phosphate buffer (0.2 M in this study vs. 0.01–0.05 M in other studies) might be another factor that affected the performance of chitosan as a color adsorbent.
The application of activated carbon appears to be an efficient approach to color removal from reaction mixtures involving phenols and minced horseradish. A maximum color removal (reduction of the absorbance from 0.55 to below 0.1) was achieved within a relatively short time (2 h) after carbon addition (Fig. 7). On the other hand, 2,4-DCP concentration for activated carbon (1 mM) was much lower than that for chitosan (9 mM). Activated carbons are common adsorbents widely used in a variety of industries. Because a relatively low amount is required to achieve a satisfactory color removal (0.02 g/mL; Fig. 8), activated carbons may be considered cost-effective decolorization agents.
|
CONCLUSIONS
|
|---|
Minced horseradish, H2O2, and additives proved to be a promising combination for the removal of phenols from aqueous solutions and for improving the quality of treated water at the same time. However, the choice of additives and the development of application methods for specific situations (e.g., pollutant combinations, environmental conditions, the amount of pollution, etc.) require further studies.
|
ACKNOWLEDGMENTS
|
|---|
Funding for this research was provided by the Office of Research and Development, USEPA (Grant no. R-826646).
|
REFERENCES
|
|---|
- Dec, J., and J.-M. Bollag. 1990. Detoxification of substituted phenols by oxidoreductive enzymes through polymerization reactions. Arch. Environ. Contam. Toxicol. 19:543–550.
- Dec, J., and J.-M. Bollag. 1994. Use of plant material for the decontamination of water polluted with phenols. Biotechnol. Bioeng. 44:1132–1139.
- Edwards, W., W.D. Leukes, P.D. Rose, and S.G. Burton. 1999. Immobilization of polyphenol oxidase on chitosan-coated polysulphone capillary membranes for improved phenolic effluent bioremediation. Enzyme Microb. Technol. 25:769–773.
- Flanders, C. 1997. Selecting phytoremediation based on specific plant enzymes. M.S. thesis. The Pennsylvania State Univ., University Park.
- Flock, C., A. Bassi, and M. Gijzen. 1999. Removal of aqueous phenol and 2-chlorophenol with purified soybean peroxidase and raw soybean hulls. J. Chem. Technol. Biotechnol. 74:303–309.
- Ganjidoust, H., K. Tatsumi, S. Wada, and M. Kawase. 1996. Role of peroxidase and chitosan in removing chlorophenols from aqueous solution. Water Sci. Technol. 34(10):151–159.
- Klibanov, A.M., T.-M. Tu, and K.P. Scott. 1983. Peroxidase-catalyzed removal of phenols from coal-conversion wastewaters. Science (Washington, DC) 221:259–260.[Abstract/Free Full Text]
- Lang, S., and D. Wullbrandt. 1999. Rhamnose lipids—Biosynthesis, microbial production and application potential. Appl. Microbiol. Biotechnol. 51:22–32.[ISI][Medline]
- Maloney, S.W., J. Manem, J. Mallevialle, and F. Fiessinger. 1986. Transformation of trace organic compounds in drinking water by enzymatic oxidative coupling. Environ. Sci. Technol. 20:249–253.
- Mukerjee, P., and K.J. Mysels. 1971. Critical micelle concentrations of aqueous surfactant systems. U.S. Dep. of Commerce, Washington, DC.
- Nakamoto, S., and N. Machida. 1992. Phenol removal from aqueous solutions by peroxidase-catalyzed reactions using additives. Water Res. 26:49–54.
- Roper, J.C., J. Dec, and J.-M. Bollag. 1996. Using minced horseradish roots for the treatment of polluted waters. J. Environ. Qual. 25:1242–1247.[Abstract/Free Full Text]
- Sun, W.-Q., and G.F. Payne. 1996. Tyrosinase-containing chitosan gels: A combined catalyst and sorbent for selective phenol removal. Biotechnol. Bioeng. 51:79–86.
- Tatsumi, K., H. Ichikawa, and S. Wada. 1994. Dephenolization from aqueous solution by treatment with peroxidase and a coagulant. Water Sci. Technol. 30(9):79–86.
- Wada, S., H. Ichikawa, and K. Tatsumi. 1995. Removal of phenols and aromatic amines from wastewater by a combination treatment with tyrosinase and a coagulant. Biotechnol. Bioeng. 45:304–309.
- Wu, J., K.E. Taylor, J.K. Bewtra, and N. Biswas. 1993. Optimization of the reaction conditions for enzymatic removal of phenol from wastewater in the presence of polyethylene glycol. Water Res. 27:1701–1706.
Related articles in JEQ:
- This Issue in Journal of Environmental Quality
JEQ 2003 32: 1167-1172.
[Full Text]
TOP
ABSTRACT
INTRODUCTION
