The aim of the present work was the development of a new biological method for the treatment of textile industry effluents, which is cheaper, more profitable, and eco-friendly. This method is essentially based on the synthesis of dye-fixing peptides. The use of peptides synthesized via a solid-phase synthesis to fix a reference textile dye like “Cibacron blue” (CB) and the performance analysis of binding assays were the main objectives of this study. For this reason, two peptides P1 (NH2-C-G-G-W-R-S-Q-N-Q-G-NH2) and P2 (NH2-C-G-G-R-R-Y-Q-P-D-S-NH2) binding with the CB dye were synthesized by the solid-phase peptide synthesis (SPPS) technique. The obtained results showed significant fixation yields of CB-peptides of 91.5% and 45.9%, respectively, and consequently, their interesting potential as a tool for a new biochemical method in the pollution prevention of textile wastewater.
The protection of the environment is becoming a major concern for humankind [
Expansion of the dye industry is explained by the fact that various industrial products can be colored, mainly [
The toxicity of wastewater industry is one of the most serious problems facing humanity and other life forms on our planet today. This is a very serious environmental problem [
The textile industry is one of the most polluting industries that produce large quantities of water polluted by various chemicals [
Indeed, eutrophication phosphates used as a detergent during the finishing process in textile industries [
It is worthy to note that synthetic dyes are compounds that are highly resistant to natural biological degradation [
Membrane filtration used as physical treatment of effluents, controlled by hydraulic pressure, is available in microfiltration, ultrafiltration, nanofiltration, and reverse osmosis, which is essentially done on the cutoff point of a membrane. The effluent passes through a semipermeable membrane that retains contaminants larger than the pore diameter upstream to produce a purified permeate and a concentrate that receives the organic impurities [
Adsorption is an efficient treatment for removing organic compounds, especially when the molecular weight of the effluent is high and the polarity is low. It is a process where a solid is utilized to receive the dye of water, activated carbon being the most commonly used solid. This technique is effective only on certain categories of dyes such as cationic, mordant, dispersed, vat, and reagents [
Coagulation/flocculation is the aggregation or agglomeration of colloidal particles or fine suspended solids as flocs under the action of flocculants. An additional step of settling or flotation helps to eliminate flocs. It is a method of treating textile effluents by discoloration of wastewater. This method is inexpensive and uses coagulants such as alum, ferrous sulphate, and ferrous chloride. However, it is inefficient as it eliminates only 50% of reactive, azo, acid, and basic dyes [
Since their application is easy, chemical oxidation methods are commonly used and become necessary when biological processes are ineffective. These are treatments that aim at the total mineralization of pollutants in CO2, H2O, and inorganic compounds [
Although many microorganisms are able to cleave chromophores and auxochromes of certain dyes (hence, discoloration), some can mineralize the dyes in CO2 and H2O [
Aerobic treatment is the most applied [
For a high concentration of organic pollutants, these techniques are not sufficiently effective for the treatment of textile discharges. Many classes of dyes such as azo dyes, acids (because of sulphonated groups), and reactive dyes are recalcitrant [
Sheng and Chi [
An effluent treatment technique adapted to the dyes must eliminate them completely in order to avoid the formation of more dangerous by-products than the initial compounds and more particularly to prevent the formation of carcinogenic products. Conventional methods of treatment do not meet this expectation.
The objective of this study is the development of a new biological approach which is more suitable in terms of cost-effectiveness, pollutant removal efficiency, and recyclability and inexpensive, effective, and eco-friendly (biodegradable) for the treatment of effluents of the textile industry. To our knowledge, this is the first report on the textile effluent treatments using peptides. This technology will be based on the best binding affinity of textile dyes on peptides synthesized via a solid-phase peptide synthesis (SPPS) technique.
The peptide-dye interaction is governed by low-energy type links (electrostatic, van der Walls, hydrophobic, Pi, and ionic). This mechanism is the same as the mechanism of interaction of antibodies with antigens or the interaction of a receptor with a ligand or even the interaction of a substrate with an enzyme. This interaction is very specific, that is, a peptide may interact with a dye or a dye family. The affinity between the peptide and the dye is very important, and it can approach the affinity of a substrate to an enzyme.
A manual peptide synthesis was realized. It consists in using a cylindrical glass reactor made of a container with a sintered disc and a tap that controls the filtration of the solvents. A vacuum pump was used to create vacuum to ensure better filtration of the vial and the removal of reagents in excess.
Three amino acids (C-G-G) were added in the P1: NH2- P2: NH2-
“Cibacron blue” (2-anthracenesulfonic acid, 1-amino-4-[[4-[[4-chloro-6-[(2-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-3-sulfophenyl]amino]-9,10-di/C29H20ClN7O11S3) with a molecular weight of 774.16 g/mol, a size of 25 × 10 Å, CAS-No. 84166-13-2 was provided by a textile industry “Huntsman.” The chemical structure of Cibacron blue (CB) is shown in Figure
Chemical structure of Cibacron blue [
For the achievement of the solid-phase peptide synthesis, various components were used. They are listed below.
The resin used for the synthesis gives a
Chemical structure of the rink-amide resin used in the SPPS [
The deprotection of the Fmoc protecting group is performed via the strong base, the piperidine (20%), premixed in
The elimination of the protective groups of the side chains of the amino acids as well as the solid polymer is carried out with a cocktail mixture of trifluoroacetic acid (TFA), 0.5% water, and 0.5% triisopropyl silane (TIS) as scavengers.
To get rid of excess amino acids or coupling agents, a simple washing with dichloromethane (DCM) or DMF is required.
To ensure that the amino acid coupling is done, the “Kaiser test” [ Solution A: a mixture of pyridine (49 mL) + 20 mL ethanol + 0.8 g phenol + 1 mL of KCN (1 mM) Solution B: a mixture of 1 g ninhydrin + 20 mL ethanol
Water loaded with the dye passes through the column prefilled with a solid support-bound dye-fixing peptide, the dye binds to the peptide, and the exiting water is recovered.
Loading the resin Deprotection of the resin Coupling of the unprotected cysteine because one needs the free thiol group.
The synthesis of peptides was confirmed manually by the detection of the correct mass of the two peptides in the mass spectrum (MS) analysis. Figure
Mass spectrum analysis of peptide synthesis products by liquid chromatography coupled to mass spectrometry (LCMS). (a) Synthetic peptide 1 (P1). (b) Synthetic peptide 2 (P2).
The spectrum of peptide 2 presented in Figure
A free cysteine was fixed to the resin by coupling its carboxylic group with the amine group of resin. The peptides P1 or P2 were added to this cysteyl resin in an equimolar concentration to the resin at pH = 5, which was adjusted carefully to 8.3 in order to link the peptide to the cysteyl resin.
The test is based on measuring the optical density of the dye solution before and after contact with the peptide. However, the optimal absorbance wavelength of the “Cibacron blue” is determined according to the calibration curve. By analyzing this curve, it can be concluded that the dye absorbs particularly at 616 nm.
To evaluate the amount of the dye fixed by the peptide, a range of dye “Cibacron blue” (774.16 g/mol) standards was prepared with increasing concentrations ranging from 0.5 mg·L−1 to 12 mg·L−1, and then the OD was monitored at 616 nm (Figure
Calibration curve (concentration vs. absorbance) for “Cibacron blue.”
A solution of “Cibacron blue” at a concentration of 10 mg/L was contacted with the support-bound peptides (P1 or P2) for 48 h. The absorbance of the filtrate is measured. The obtained result shows that P1 and P2 made it possible to calculate a concentration of 0.85 mg/L and 5.41 mg/L of the remaining dye after its passage through the peptide, respectively. This result shows that P1 has fixed almost all dye, and the remaining half of “Cibacron blue” is fixed by P2 (Figure
Dye-peptide binding test: Once the support is ready, a contact with the peptide in the basic medium allows their binding by means of disulfide bond formation between the cysteine of the support and the cysteine of the peptide. A solution of “Cibacron blue” at a concentration of 10 mg/L for 48 h is then contacted with the support-bound peptide, and finally, the OD of the filtrate is measured.
Dyes are an important class of synthetic organic compounds used in many industries, especially textiles. Consequently, they have become common industrial environmental pollutants during their synthesis and later during fiber dyeing. Textile industries are facing a challenge in the field of quality and productivity due to the globalization of the world market. The large-scale production and extensive application of synthetic textile dyes can cause considerable environmental pollution [
The present study aims at developing a new biological approach for the treatment of textile industry effluents. This method is essentially based on the synthesis of dye-fixing peptides. The chemical approach of this research focuses on the peptide synthesis strategy described for the first time by Merrifield [
These results are consistent with the work of Iannolo et al. [
This new biochemical method, based on the fixation of textile dyes by peptides, offers a great contribution to the industry. This method allows the reuse of the depolluted water, the dyes (after the release of the peptides), and the synthesized peptides. On the contrary, it is free from disadvantages that characterize conventional methods (physical, chemical, and biological). Such methods are not effective for certain dyes, suitable only for waters containing low concentrations of these toxic substances, and they generate degradation products that may themselves be more toxic than the starting dyes [
This new approach goes beyond these limits, and it is adaptable to large concentrations of dyes given the high affinity of peptides to them and given their high yield. It is also effective in a wide range of dyes by the use of various peptides having affinities to different dyes or peptides with high affinity to a family of dyes. Also, by the “phage display” technique, one can select more than one peptide for a single dye or one peptide is able to fix more than one dye or a family of dye, as reported by Iannolo et al. [
It should be pointed that, to better exploit this new approach, some assays are in progress for other dyestuff classes, in particular monoazo and diazo dyes, as well as for dyes used in the cooking industry.
This study allows the setting up of a new biochemical method in textile wastewater treatment. It is based on the passing of the textile wastewater through a column which contains in advance a fixing peptide of the dye or a fixing peptide of a family of dyes bound to a support. The dye binds to the peptide, and the water passing through the column will be recovered. Thanks to this eco-friendly as well as a cost-saving method, the water and the colorant can be reused. To begin this project and before embarking on the “phage display” technique to identify a whole range of dye-fixing peptides, an attempt was made to validate the methodology with peptides that bind the “Cibacron blue.”
Thanks to this new approach, significant fixation yields of CB-peptides were obtained (91.5% and 45.9%). These results reveal the effectiveness of the peptides synthesized (by SPPS or by cell expression in multimer) for the fixation of the “Cibacron blue” dye and to get rid of the depollution of textile effluents. As a perspective, it is interesting to adapt and extrapolate this simple, fast, inexpensive, and eco-friendly technique on an industrial scale.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that they have no conflicts of interest.
The authors are grateful to the ISBST, Biotechpole, Manouba University, Sidi Thabet, Tunisia, for providing infrastructural facilities and assistance.