KR20080071762A - Enhanced biosorption of reactive dyes by chemical modification of corynebacterium glutamicum biomass - Google Patents

Abstract

An effective method is provided to improve adsorption performance of the dyes through the chemical modification of functional groups on a surface of the biomass according to the adsorption mechanism of the biomass and dyes when using a corynebacterium glutamicum biomass as biosorbents. In a preparation method of a biosorbent that is applied to dyestuff wastewater and removes the dyes by adsorbing dyes causing color, a preparation method of a biosorbent having enhanced adsorption performance by chemical modification of functional groups on a surface of a corynebacterium glutamicum biomass comprises the steps of: treating the corynebacterium glutamicum biomass with an acid to hydrogenate the corynebacterium glutamicum biomass, washing the hydrogenated corynebacterium glutamicum biomass with distilled water, and drying the washed corynebacterium glutamicum biomass; and chemically modifying the hydrogenated biomass through an ester reaction to remove a carboxyl group, washing the chemically modified hydrogenated biomass with distilled water, and drying the washed biomass. The step of removing the carboxyl group is performed by dispersing the hydrogenated biomass into a methanol solution, adding nitric acid as an acid catalyst into the dispersion, and agitating the mixed solution to perform an ester reaction.

Description

Enhanced Biosorption of Reactive Dyes by Chemical Modification of Corynebacterium Glutamicum Biomass with Chemical Adsorption of Surface Functional Groups of Corynebacterium glutamicum Biomass

1 is a chemical structure of a reactive dye (RR 4, RB 4) used in the embodiment of the present invention.

2 is a potential difference titration curve of hydrogenated biomass and dicarboxyl biomass according to the present invention.

3 is a Fourier transform infrared adsorption spectrum of hydrogenated Corynebacterium biomass.

Figure 4 is a graph for determining the pH dependence of the hydrogenated biomass and dicarboxyl biomass according to the present invention.

5 is a graph showing the adsorption equilibrium of reactive dyes (RR 4, RB 4) according to the present invention.

The present invention relates to a method for preparing a bioadsorbent having improved adsorption performance, wherein the hydrogenated biomass prepared by acidification of Corynebacterium glutamicum by hydrogenation is chemically modified through an ester reaction to form a carboxyl group. The present invention relates to a method for preparing a biosorbent having improved adsorption performance even at a wide range of pH.

The textile industry consumes large amounts of water and chemicals in the processing of textiles. Recently, due to high quality of fibers and various demands, a large amount of dye wastewater is generated, and a considerable amount of dye is contained in these wastewater and discharged. Dyeing wastewater has a clear color even at low concentrations, making it a target for complaints. When it enters the water system, it has a high diffusivity and blocks sunlight to adversely affect plant growth. In addition, the dye in the dyeing waste water has a very complex structure and there is a great concern that the contamination of the water system with the hardly degradable contaminants. In addition, some dyes contain carcinogens and have been reported to induce mutations.

In the second quarter of 2003, the demand for reactive dyes increased by 21.6 ~ 34% compared to the same period of 1996, and continued to rise despite the continuing recession. As a large amount of dye wastewater is expected due to the increased use of reactive dyes, an appropriate treatment method should be sought.

Chemical, physicochemical and biological treatments have been proposed for removing dyes from dyeing wastewater.

Typical chemical treatment methods include chlorine-based oxidation, Fenton's reagent method, ozone method and the like. This treatment has the disadvantage of generating chemical sludge, generating harmful intermediates, and expensive operating costs.

Biological treatment method is generally used the activated sludge process to adsorb or decompose organic matter by the activated aerobic microorganisms, but this has the disadvantage that the amount of sludge generated and the solid-liquid separation in the sedimentation tank is not good. In addition, the dyes in the dyeing waste water are mostly made of a material that is difficult to biologically decompose and can produce toxic substances even if degraded, resulting in poor treatment efficiency.

Physical treatment methods include activated carbon, ion exchange resin, membrane separation, and the like. Although the ion exchange resin method has excellent dye removal ability, the ion exchange resin has a high price and has a high adsorption power only for some dyes. Membrane separation removes irrespective of the type of dye, but the processing of the concentrated residue remaining after separation is complicated. In addition, there are problems of the possibility of clogging and the need for membrane replacement.

On the other hand, the adsorption method is known to be the most feasible method compared to other methods because the efficiency of removing contaminants from the waste water and the economical treatment process have been proved to be simple and economical. However, the activated carbon generally used in the adsorption method has a disadvantage that the price is high and most of the recycling is not possible. Due to this, there is a growing interest in bioadsorption technology which can be easily used for dye adsorption at low cost. Biosorption is a technique for removing target substances by using biomass as an ion exchange resin, although many studies have been conducted because of its high potential for use. Currently used biomass includes algae, bacteria, fungi and plants.

According to such a necessity, a hydrogenated, washed and dried biosorbent was developed by acidifying Corynebacterium glutamicum biomass, which is disclosed in Korean Patent Laid-Open Publication No. 10-2006-0030380.

In the present invention to solve the problems of the prior art as described above, using a Corynebacterium glutamicum biomass as a biosorbent, the chemical modification of the surface functional group of the biomass according to the adsorption mechanism of the biomass and dye The purpose of the present invention is to propose an effective method for further improving the adsorption performance of dyes.

In addition, the present invention is a basic study of the dye removal process of the biosorbent using the fermentation waste Corynebacterium glutamicum quantitative and qualitative analysis of the surface functional group of Corynebacterium glutamicum biomass and dye adsorption according to pH The purpose of this study is to examine the adsorption mechanism between Corynebacterium glutamicum biomass and dyes and to change the surface functional group of Corynebacterium glutamicum biomass and to provide a method for improving dye removal ability. .

In addition, the present invention by removing the carboxyl group, which is an adsorption inhibiting functional group of Corynebacterium glutamicum biomass, to provide a biosorbent with good adsorption performance even at a wider pH, reducing the cost to lower the pH and dyeing wastewater It aims to prevent the environmental pollution by acidification.

In addition, an object of the present invention is to provide a method for recycling resources of fermented waste, such as ocean dumping, into biosorbents, thereby reducing marine dumping and preventing environmental pollution such as preventing marine pollution.

In order to achieve the above object, a method of preparing a biosorbent having improved adsorption performance by chemical modification of the surface functional group of Corynebacterium glutamicum biomass according to the present invention, is applied to the dyeing wastewater to induce color In the method of producing a bioadsorbent for adsorbing and removing the dye, the adsorbent is hydrogenated by acid treatment of Corynebacterium glutamicum biomass, washed with distilled water and dried and esterification of the hydrogenated biomass Chemically modified through to remove the carboxyl group, characterized in that it comprises the step of washing with distilled water and drying.

In addition, the step of removing the carboxyl group is characterized in that to disperse the hydrogenated biomass in methanol solution and to add an acid catalyst nitric acid and stirred to cause an ester reaction.

Hereinafter, a method for preparing a biosorbent having improved adsorption performance through chemical modification of Corynebacterium glutamicum biomass according to the present invention will be described in detail with reference to the accompanying drawings.

The biosorbent according to the present invention is prepared by firstly fermenting waste Corynebacterium glutamicum as a biomass and hydrogenating it, followed by drying. The biosorbent thus prepared may be used to adsorb dyes from dyeing wastewater. have. That is, by placing Corynebacterium glutamicum in a strong acid solution and stirring, various ions on the surface thereof are substituted with hydrogen ions, and hydrogenated and hydrogenated biomass is prepared by washing with water and then drying.

In addition, as a result of research and analysis of the functional group of the hydrogenated biomass, it was found that the carboxyl group is an adsorption inhibiting functional group. The process of removing the compound group is carried out. Removal of the carboxyl group may occur by ester reaction. For this purpose, the carboxyl group may be removed by dispersing the hydrogenated biomass in a methanol solution and stirring by adding an acid catalyst, nitric acid solution.

As such, the biomass from which the carboxyl group has been removed will have more improved adsorption performance.

In the present invention, fermentation waste Corynebacterium glutamicum biomass was used, and reactive red 4 (RR 4) and reactive blue 4 (RB 4) were used. Corynebacterium glutamicum occurs a lot in the fermentation process of amino acid production. The amino acid fermentation industry produces large quantities as biological solid waste consisting of Corynebacterium glutamicum biomass. Most of these fermentation wastes are still treated by ocean dumping. Therefore, it would be very useful if there is a possibility to recycle such solid wastes as biosorbents.

The present invention is intended to chemically modify the surface of the functional group of Corynebacterium glutamicum biomass such that the optimum pH range is changed from a strong acid (pH <3) to a weak acid (pH 4 ~ 5) conditions. The use of this method is expected to significantly reduce the treatment costs for strong acidic conditions.

Example

Fermentation waste Corynebacterium glutamicum biomass (C. glutamicum biomass) is obtained in the form of dried powder from the lysine fermentation process (BASF-Korea, Gunsan, Jeonbuk), hereinafter referred to as "raw material biomass".

The raw biomass was acid treated at room temperature for 24 hours with 1N HNO ₃ solution to replace various ions on the cell surface with protons. The acid treated biomass was repeated three times with washing with distilled water and dried at 60 ° C. for 72 hours, and the dried biomass was stored in a desiccator. This is hereinafter referred to as "hydrogenated biomass".

Hydrogenated biomass was chemically treated by esterification to remove carboxyl groups.

First, 3 g of hydrogenated biomass was dispersed in 300 mL of anhydrous methanol, and an acid catalyst HNO ₃ was added thereto so that the final concentration was 1M. This mixture was then stirred at 160 rpm for 6 hours with a rotary stirrer at room temperature. In this chemical treatment, the carboxyl group in the biomass causes an esterification reaction, and the reaction formula is as follows.

B-COOH + CH ₃ OH → B-COO-CH ₃

After reacting the hydrogenated biomass for 6 hours as described above, the biomass from which the carboxyl group was removed was washed several times in distilled water and dried in an oven at 60 ° C. for 24 hours. Hereinafter, the substance obtained by the above chemical reaction is called "decarboxylated biomass".

All reagents used in the experiment were used for analysis, and dyes RR 4 and RB 4 were purchased from Sigma-Aldrich, Korea Ltd. Figure 1 shows the structural formulas of the reactive dyes (RR 4 and RB 4) with several sulfone groups, which have a negative charge in aqueous solution. General characteristics of the dyes are summarized in Table 1 below.

dyes Chemical formula Molecular Weight Color index Maximum light absorption wavelength (λ _max ) Reactive Red 4 C ₃₂ H ₂₄ ClN ₈ Na ₄ O ₁₄ S ₄ 931.3 18105 517 nm Reactive Blue 4 C ₂₃ H ₁₄ Cl ₂ N ₆ O ₈ S ₂ 637.4 61205 595 nm

Dye adsorption measurement

The resolved dye concentration was analyzed using a spectrophotometer and analyzed at 517 nm and 595 nm for RR 4 and RB 4, respectively. Prior to analyzing the dye concentration, centrifugation was performed at 3000 rpm using a solid-liquid separator. The volume change (about 5% increase) due to the addition of nitric acid solution was taken into account, and the dye adsorption amount q was calculated as follows.

V ₀ , V _f represent the volume of the initial aqueous solution and the volume of the final aqueous solution, C ₀ , C _f represents the concentration of the initial dye and the final remaining dye, M is the concentration of the biomass used.

pH edge experiment

PH edge experiments were performed to determine the equilibrium relationship between dye adsorption and final pH. The experiment was carried out by adding 10 g / L of hydrogenated and decarboxylated biomass in 40 mL of 500 mg / L dye solution in several 50 mL tubes in each tube, and then using 11N NaOH or 1N HNO ₃ at Differently adjusted until. And the pH controlled tubes were stirred at 160 rpm for 24 hours at room temperature of about 25 ^° C. After reaching the adsorption equilibrium, the final pH was measured, and the concentration of the dye remaining in the liquid phase was measured using a spectrophotometer (UVmini-1240, Shimadzu, Kyoto, Japan) after centrifugation.

Isothermal Adsorption Experiment

Isothermal adsorption experiments were performed at various pHs to calculate the dye adsorption performance of the biomass. This experiment is to keep the temperature and pH constant and to measure the dye adsorption at various dye concentrations. In the experiment, 0.4 mL of biomass and 40 mL of dye solution with different initial concentration of dye from 50 mg / L to 3000 mg / L were added to several 50 mL tubes, and the pH of each tube was set to a specific value. Each tube was stirred at 160 rpm for 24 hours at room temperature of about 25 ^° C. During the adsorption experiment, the pH of the solution was constantly adjusted using 1 N NaOH or 1 N HNO ₃ tn aqueous solution while observing the pH. After the adsorption reached equilibrium, the residual concentration of the dye was analyzed. Experimental data were modeled using the Langmuir model to calculate the maximum adsorption performance and binding affinity.

Potentiometric titration

Potentiometric titration was performed to quantitatively analyze surface functional groups of Corynebacterium glutamicum. Experimental method was made of 30 40 ml of biomass suspension (10 g biomass / L) and added sequentially by varying the amount of 1N NaOH solution. Distilled water used in the experiment was injected with nitrogen gas for 6 hours to remove CO ₂ . The biomass suspension to which NaOH was added was measured at room temperature for 24 hours to measure the pH of the stirred aqueous solution.

Detailed procedures and data processing methods are already known, and the potential difference experimental data is represented by the following model.

[OH ⁻ ] _added is the concentration of hydroxide ions added (mmol / L) and K is the hydrogen dissociation constant. b is the molecular weight of the functional groups in the biomass (mmol / g), X represents the biomass concentration (g / L), subscripts i, j represent negative and positively charged functional groups, respectively.

Adsorption Analysis

Biomass titration curves vary depending on the type and amount of functional groups present in the biomass. As shown in FIG. 2, potentiometric titration of hydrogenated Corynebacterium biomass was performed twice, and the results were identical.

To quantitatively calculate the properties of the functional groups, potentiometer data was applied to Equation 2 above. As a result, one or two functional groups were not sufficient to describe the titration results, and the titration curve could be described with three or more functional groups (two negative charges and one positive charge) (FIG. 2). This means that the hydrogenated biomass has at least three functional groups and the predicted parameters are summarized in Table 2.

Functional group 1st group 2nd group 3rd group Majesty - - + pK _H [-] 3.57 (0.08) 6.90 (0.06) 9.14 (0.07) b [mmol g ^-1 ] 0.32 (0.01) 0.56 (0.02) 0.68 (0.02)

Here, the accuracy is 0.997, and the error of the predicted parameter is written in parentheses. pK _H represents the dissociation constant of the functional group, and b is the amount of functional group.

The equilibrium constant (pK _H ) for hydrogen bound to the first group was calculated to be 3.57 _W 0.08. The carboxyl group in the biopolymer has a pK _H value in the range of 3.5-5.0, thus it can be inferred that the first group is carboxyl (B-COOH). The pK _H value and the amount of functional groups in the second group were calculated to be 6.90 W0.06 and 0.56 _W 0.02 mmol / g, respectively. This phosphate (B-PO ₄ ^-) means a group. The third group is amines (B-NH ₃ ⁺ ) with pK _H values ranging between 8 and 10 for various biomaterials. Since sulfone groups in reactive dyes are easily dissociated in aqueous solution and exhibit negative charges, negatively charged carboxyl and phosphate groups cannot adsorb with dyes, and only positively charged amine groups can adsorb reactive dyes.

Infrared spectroscopy (FTIR) experiments were also performed to demonstrate the presence of amine, carboxyl and phosphate groups in Corynebacterium glutamicum biomass. As shown in FIG. 3, the FTIR spectrum shows peaks for functional groups of the biomass. Peaks around 3500-3000 and 1538 cm ⁻¹ represent amine groups and peaks near 3600-3200, 1652, 1384 cm ⁻¹ correspond to carboxyl groups. The phosphate group shows peaks at 1157 cm ⁻¹ (PO stretching) and 1078 cm ⁻¹ (P-OH stretching).

Adsorption mechanism

As mentioned above, amine groups play a very important role with respect to the adsorption of reactive dyes. Since the pK _H value of the amine group is 9.14 ± 0.07, it has a positive charge at pH 8 or less. However, as shown in FIG. 4, there was no adsorption of reactive dye by hydrogenated biomass near pH 8. In addition, in the case of hydrogenated biomass, it can be seen that the dye adsorption decreases rapidly at pH 4 or less. This is due to the repulsive force of the negatively charged sulfone group of the dye and the negatively charged carboxyl and phosphate groups of the biomass. To clearly understand this phenomenon, the hydrogenated biomass was differentiated by Equation 2 to predict the amount of functional groups and functional groups. In FIG. 4C, the carboxyl group starts to ionize at pH 3 or higher and the phosphate group is ionized at pH 7 or higher to have a negative charge. This negatively charged group of biomass inhibits adsorption with dyes by electrostatic attraction.

When the carboxyl group of the hydrogenated biomass is removed according to a chemical reaction as in Chemical Formula 1, adsorption should be performed in a wider pH range. Predicted from this assumption, as the interference of the carboxyl groups is eliminated, the carboxylated biomass should be able to adsorb RR 4 and RB 4 effectively even near pH 5. Referring to (A) and (B) of FIG. 4, the adsorption amount of the dicarboxyl biomass from which the carboxyl group was removed was larger than that of the hydrogenated biomass, and the adsorption amount rapidly decreased below pH 6. It can be seen that.

Thus, the adsorption of reactive dyes to Corynebacterium glutamicum occurs through electrostatic attraction between the sulfone group of the anion in the biomass and the amine group of the cation, and the group of anions such as carboxyl and phosphate are repulsive This interferes with the adsorption of reactive dyes. This adsorption mechanism helps to understand the adsorption of other types of reactive dyes.

Practical Application of Decarboxylated Biomass

As seen in the pH edge experiment of FIG. 4, the use of hydrogenated biomass should be operated at low pH for maximum adsorption. However, such low pH is a cost and difficulty due to the pH reduction of the waste water. The decarboxylated biomass can be effectively used for the removal of RR 4 and RB 4 because it maintains a high level of adsorption performance even at pH 5. Thus, decarboxylation of the raw biomass can reduce the cost of adsorption to control the pH of the wastewater containing the dye.

From a practical point of view, the adsorption performance of biomass can be improved by decarboxylation. As shown in the isotherm of FIG. 5 and the calculated Langmuir parameters in Table 3 (Table 3), the maximum adsorption of the decarboxylated biosorbent at pH 4 was 2.74 times for the hydrogenated biosorbent at 105.8 ± 3.4 mg / g. Leads to For RB 4, the adsorption performance of the decarboxylated biosorbent is higher than that of the hydrogenated biosorbent. In addition, the slope of the isothermal adsorption curve of the decarboxylated biosorbent is steeper than the hydrogenated biosorbent. This slope refers to the affinity between the dye and the biomass. The affinity of the decarboxylated biosorbent (1 / K) for RR 4 and RB 4 is 16.9 and 15.9 times higher than that of the hydrogenated biosorbent at 0.625 and 0.33 L / mg, respectively. This means that dyes can be effectively removed even at low concentrations.

Furthermore, the hydrogenated biomass requires lower pH than the dicarboxyl biomass to remove the same amount of dye when applied to the actual process, and it is expected that it will be expensive to lower the pH. In addition, the dicarboxyl biomass has a very high affinity, so that the dye can be effectively treated in a short time. Therefore, the functional group change of biomass through such chemical modification is expected to be a very useful technique.

According to the present invention, quantitative and qualitative analysis of surface functional groups of biomass as a dye absorbing biosorbent for dyeing wastewater using Corynebacterium glutamicum as a fermentation waste, and based on the dye adsorption capacity and adsorption mechanism according to pH Chemically modifying to remove carboxyl groups, which are inhibitors of adsorption, among the surface functional groups of Nebacterium glutamicum biomass can provide an effective method for further improving the adsorption performance of the dye.

In addition, the present invention can provide a biosorbent having a good adsorption performance even at a wider pH to reduce the cost for lowering the pH, it is possible to prevent the environmental pollution by reducing the ocean dumping of fermentation waste.

As described above, the present invention relates to a method for preparing a biosorbent having excellent adsorption performance by converting a hydrogenated biomass into a decarboxylated biomass through a chemical reaction as a biosorbent using Corynebacterium glutamicum biomass. The present invention is not limited to the above-described embodiments, and various modifications, changes, and substitutions may be made by those skilled in the art without departing from the spirit and scope of the present invention.

Claims (2)

In the manufacturing method of the bioadsorbent which is applied to the dye wastewater by absorbing and removing the dye causing the color, The adsorbent is an acid treatment of Corynebacterium glutamicum biomass, hydrogenated, washed with distilled water and dried; And Chemically modifying the hydrogenated biomass through an ester reaction to remove carboxyl groups, followed by washing with distilled water and drying to chemical modification of the surface functional groups of Corynebacterium glutamicum biomass. Method for preparing a biosorbent having an improved adsorption performance. The method of claim 1, wherein the step of removing the carboxyl group Corynebacterium glutami, characterized in that to disperse the hydrogenated biomass in a methanol solution and to add an acid catalyst nitric acid and stirred to cause an ester reaction A method for preparing a biosorbent having improved adsorption performance by chemical modification of surface functional groups of Qum biomass.

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