Biodegradation of tannery dye effluent using Fenton's reagent and bacterial consortium: A biocalorimetric investigation

Synthesis and characterization of Co(II) porphyrin complex supported on chitosan/graphene oxide nanocomposite for efficient green oxidation and removal of Acid Orange 7 dye

Catalytic degradation of Acid Orange 7 (AO7) by hydrogen peroxide in an aqueous solution has been investigated using cobalt(II) complex of 5, 10, 15, 20 Tetrakis [4-(hydroxy)phenyl] porphyrin [Co(II) TPHPP] covalently supported chitosan/Graphene Oxide nanocomposite [Co(II) TPHPP]-Cs/GO, as highly efficient and recoverable heterogeneous catalyst. The structures and properties of [Co(II) TPHPP]-Cs/GO nanocomposite were characterized by techniques such as UV-Vis, FT-IR, SEM, EDX, TEM, and XRD. The oxidation reaction was followed by recording the UV-Vis spectra of the reaction mixture with time at λmax = 485 nm. [Co(II) TPHPP]-Cs/GO nanocomposite demonstrated high catalytic activity and could decompose 94% of AO7 within 60 min. The factors that may influence the oxidation of Acid Orange 7, such as the effect of reaction temperature, pH, concentration of catalyst, Acid Orange 7, and hydrogen peroxide, have been studied. The results of total organic carbon analysis (TOC) showed 50% of dye mineralization under mild reaction conditions of AO7 (1.42 × 10-4M) with H2O2 (8 × 10-2M) in the presence of [Co(II) TPHPP]-Cs/GO nanocomposite (15 × 10-3 g/ml) and pH = 9 at 40 °C. The reuse and stability of the nanocomposite were examined and remarkably, even after six cycles of reuse, there was no significant degradation or deactivation of the recycled catalyst. Residual organic compounds in the reaction mixture were identified by using GC-MS analyses. The radical scavenging measurements and photoluminescence probing technology of disodium salt of terephthalic acid indicated the formation of the hydroxyl radical as the reactive oxygen species in the [Co(II) TPHPP]-Cs/GO nanocomposite/H2O2 system. A mechanism for the oxidation reaction has been discussed.

Zero waste discharge in tannery industries - An achievable reality? A recent review

In the recent times, more attention is on industrial waste management due to the unaffordable space for dump yards and landfills and the increased charges for waste dumping. Even though the vegan revolution and plant-based meat products are booming, the traditional slaughterhouses and the wastes produced by them continue to be a concern. Waste valorisation is an established procedure striving to create a closed chain process in industries where there is no refuse. Although a highly polluting industry, slaughterhouse industry wastes have been recycled to economically viable leather since ancient times. However, the tannery industry is causing pollution in par with or even more than the slaughterhouses. Effective management of the liquid and solid wastes from the tannery is of utmost concern because of its toxicity. The hazardous wastes generated enter the food chain, causing long term impacts in the ecosystem. Several leather waste transformation processes are widely used in the industries, and they are yielding good products of economic value. However careful exploration into the processes and products of waste valorisation are often ignored as long as the transformed waste product is of higher value than the waste. The most efficient and environmentally friendly waste management technique should convert the refuse into a value-added utilization without any toxic leftovers. Zero waste concept is an extension of the zero liquid discharge concept, where the solid waste is also treated and reused to such an extent that there is no residue to be sent to the landfill. This review initially presents the existing methods for the de-toxification of tannery wastes and examines the possibility of solid waste management within the tannery industry to attain zero waste discharge.

Coagulation-adsorption-oxidation for removing dyes from tannery wastewater

Dye removal from tannery wastewater is now a great concern given the ramifications for the environment in which the effluent ends up. Recently, the application of tannery solid waste as a byproduct to remove pollutants from tannery wastewater has garnered increasing attention. This study aims to extract biochar from tannery liming sludge for the removal of dye from wastewater. The activated (600 ºC) biochar was characterized by SEM (Scanning Electron Microscope), EDS (Energy Dispersive Spectroscopy), FTIR (Fourier Transform Infrared Spectroscopy), and surface area analysis utilizing the BET (Brunauer-Emmett-Teller) method and pH_pzc (point of zero charges) analysis. The surface area and pH_pzc of the biochar were determined as 9.29 m²/g and 8.7, respectively. The batch-wise coagulation-adsorption-oxidation was investigated for its efficacy in dye removal. The optimized conditions were as follows: the efficiency of dye, BOD (Biochemical Oxygen Demand) and COD (Chemical Oxygen Demand) were attained at 94.9%, 95.7% and 93.5%, respectively. SEM, EDS, and FTIR analyses before and after adsorption revealed that the derived biochar could adsorb dye from tannery wastewater. The adsorption behavior of the biochar fitted well to the Freundlich isotherm (R² = 0.9987) and Pseudo 2^nd order (R² = 0.9996) kinetic model. This investigation provides a new dimension for state-of-the-art utilization of tannery solid waste as a feasible strategy to remove dye from tannery wastewater.

Management of tannery waste effluents towards the reclamation of clean water using an integrated membrane system: A state-of-the-art review

Tanning and other leather processing methods utilize a large amount of freshwater, dyes, chemicals, and salts and produce toxic waste, raising questions regarding their environmental sensitivity and eco-friendly nature. Total suspended solids, total dissolved solids, chemical oxygen demand, and ions such as chromium, sulfate, and chloride turn tannery wastewater exceedingly toxic for any living species. Therefore, it is imperative to treat tannery effluent, and existing plants must be examined and upgraded to keep up with recent technological developments. Different conventional techniques to treat tannery wastewater have been reported based on their pollutant removal efficiencies, advantages, and disadvantages. Research on photo-assisted catalyst-enhanced deterioration has inferred that both homogeneous and heterogeneous catalysis can be established as green initiatives, the latter being more efficient at degrading organic pollutants. However, the scientific community experiences significant problems developing a feasible treatment technique owing to the long degradation times and low removal efficiency. Hence, there is a chance for an improved solution to the problem of treating tannery wastewater through the development of a hybrid technology that uses flocculation as the primary treatment, a unique integrated photo-catalyst in a precision-designed reactor as the secondary method, and finally, membrane-based tertiary treatment to recover the spent catalyst and reclaimable water. This review gives an understanding of the progressive advancement of a cutting-edge membrane-based system for the management of tanning industrial waste effluents towards the reclamation of clean water. Adaptable routes toward sludge disposal and the reviews on techno-economic assessments have been shown in detail, strengthening the scale-up confidence for implementing such innovative hybrid systems.

Grafting a Porous Metal-Organic Framework [NH2-MIL-101(Fe)] with AgCl Nanoparticles for the Efficient Removal of Congo Red

Organic dyes can produce harmful effects on the water environment, such as affecting the growth of aquatic organisms, reducing the transparency of water bodies, and causing eutrophication of water bodies, so it is necessary to mitigate the hazards of organic dyes. In this study, a metal-organic framework [NH₂-MIL-101(Fe)] was synthesized by the solvothermal method as a carrier for the in situ uniform deposition of AgCl nanoparticles on its surface, which was successfully used for both adsorption and degradation of Congo red. Adsorption results showed that the adsorption kinetics conformed to the proposed secondary adsorption kinetics equation with a maximum adsorption capacity of 248.4 mg·g^-1. Furthermore, the degradation results indicated that with the aid of sodium borohydride as a reducing agent, the degradation of Congo red followed pseudo-first-order kinetics with a degradation rate of 0.077 min^-1, and the complete degradation of Congo red was finished within 18 min. Therefore, AgCl/NH₂-MIL-101(Fe) may find a potential application in the removal of dyes from wastewater.

Mesoporous calcium hydroxide nanoparticle synthesis from waste bivalve clamshells and evaluation of its adsorptive potential for the removal of Acid Blue 113 dye

Calcium hydroxide nanoadsorbent was prepared from waste bivalve clamshells and used for the adsorptive removal of Acid Blue 113 (AB113) dye. The morphology, elemental nature, functional groups, and thermal stability of the nanoadsorbent were characterized by various methods. The nanoadsorbent had a high monolayer adsorption capacity (153.53 mg/g) for AB113 dye. Langmuir and Temkin isotherms better fitted (R² > 0.95) the experimental data. The adsorption rate followed pseudo-second-order kinetics (R² > 0.99). The thermodynamic study ascertained spontaneous and exothermic adsorption. This study confirmed the possibility of using calcium hydroxide as an adsorbent to effectively remove AB113 dye from aqueous solutions.

Water reuse in the post-tanning process: minimizing environmental impact of leather production

Post-tanning wastewater is very diversified, as the post-tanning stage should meet the desirable properties of the leather for the final product, with low standardization of the process (compared to beamhouse and tanning). This makes post-tanning effluent reuse less feasible, and reuse in the post-tanning stage still needs to be explored. This work aims to evaluate the reuse of liquid effluents in the post-tanning process. The work methodology consisted of (i) characterization of water streams (groundwater, liquid effluent after primary treatment, and liquid effluent after secondary treatment); (ii) pilot-scale post-tanning tests using groundwater, primary effluent, and secondary effluent; (iii) characterization of the residual baths from pilot-scale tests (pH, conductivity, total solids, chemical oxygen demand, biochemical oxygen demand, chloride, hardness and oil and grease); and (iv) testing the leather obtained for total sulfated ash and organoleptic properties. Results showed that the primary effluent and the secondary effluent could be reused in pilot-scale post-tanning tests. There was an increase in the conductivity of the residual baths when liquid effluents were reused, which confirms the accumulation of salts in the effluents after their reuse.

Current technologies for post-tanning wastewater treatment: A review

Leather post-tanning is responsible for producing effluents that are difficult to treat due to several recalcitrant pollutants. Dyes, tannins, and fatliquoring agents are mainly related to this characteristic. This study, as the state-of-the-art, attempts to systematically review treatment technologies applied in recent years to the post-tanning effluents. The Scopus database was used to identify articles related to post-tanning pollutants removal. Through the review, Advanced Oxidation Processes (AOPs) and adsorption proved to be good alternatives to increase the effluent biodegradability when applied before biological treatment. AOPs and adsorption were also efficient for the final polishing of the effluents, to reach the regulation standards for disposal, as well as enzymatic treatment. Furthermore, Membrane Separation Processes demonstrated good applicability when the reuse of the treated effluent is aimed.

Advanced Oxidation Processes and Biotechnological Alternatives for the Treatment of Tannery Wastewater

The tannery industry is one of the economic sectors that contributes to the development of different countries. Globally, Europe and Asia are the main producers of this industry, although Latin America and Africa have been growing considerably in recent years. With this growth, the negative environmental impacts towards different ecosystem resources as a result of the discharges of recalcitrated pollutants, have led to different investigations to generate alternative solutions. Worldwide, different technologies have been studied to address this problem, biological and physicochemical processes have been widely studied, presenting drawbacks with some recalcitrant compounds. This review provides a context on the different existing technologies for the treatment of tannery wastewater, analyzing the physicochemical composition of this liquid waste, the impact it generates on human health and ecosystems and the advances in the different existing technologies, focusing on advanced oxidation processes and the use of microalgae. The coupling of advanced oxidation processes with biological processes, mainly microalgae, is seen as a viable biotechnological strategy, not only for the removal of pollutants, but also to obtain value-added products with potential use in the biorefining of the biomass.

Recent Achievements in Dyes Removal Focused on Advanced Oxidation Processes Integrated with Biological Methods

In the last 3 years alone, over 10,000 publications have appeared on the topic of dye removal, including over 300 reviews. Thus, the topic is very relevant, although there are few articles on the practical applications on an industrial scale of the results obtained in research laboratories. Therefore, in this review, we focus on advanced oxidation methods integrated with biological methods, widely recognized as highly efficient treatments for recalcitrant wastewater, that have the best chance of industrial application. It is extremely important to know all the phenomena and mechanisms that occur during the process of removing dyestuffs and the products of their degradation from wastewater to prevent their penetration into drinking water sources. Therefore, particular attention is paid to understanding the mechanisms of both chemical and biological degradation of dyes, and the kinetics of these processes, which are important from a design point of view, as well as the performance and implementation of these operations on a larger scale.

Synthetic Organic Compounds From Paper Industry Wastes: Integrated Biotechnological Interventions

Synthetic organic compounds (SOCs) are reported as xenobiotics compounds contaminating the environment from various sources including waste from the pulp and paper industries: Since the demand and production of paper is growing increasingly, the release of paper and pulp industrial waste consisting of SOCs is also increasing the SOCs' pollution in natural reservoirs to create environmental pollution. In pulp and paper industries, the SOCs viz. phenol compounds, furans, dioxins, benzene compounds etc. are produced during bleaching phase of pulp treatment and they are principal components of industrial discharge. This review gives an overview of various biotechnological interventions for paper mill waste effluent management and elimination strategies. Further, the review also gives the insight overview of various ways to restrict SOCs release in natural reservoirs, its limitations and integrated approaches for SOCs bioremediation using engineered microbial approaches. Furthermore, it gives a brief overview of the sustainable remediation of SOCs via genetically modified biological agents, including bioengineering system innovation at industry level before waste discharge.

Yellow 2G dye degradation by electro-Fenton process using steel electrode as catalysis and its phytotoxicity effect

The heterogeneous electro-Fenton process degradation of Yellow 2G from wastewater was studied using a batch reactor. The COD of the wastewater used in treatment experiments was 163 mg O₂·L^-1 and the BOD₅ was 17 mg O₂·L^-1 (hardly biodegradable). The treatment of the wastewater at different current densities (2.5 mA·cm^{- 2}-12.5 mA·cm^{- 2}), solution pH (3 and 6.6), reaction times (5-25 min), electrolyte nature (NaCl, Na₂SO₄) and electrolyte concentrations (0.15 g·L^{- 1}-1 g·L^{- 1}) was investigated. According to the results, the heterogeneous electro-Fenton process was suitable for the decolorization of wastewater containing Yellow 2G. The optimum conditions were current density of 12.5 mA·cm^-2, initial pH of the wastewater neutral, 25 min of electrolysis treatment using an additive steel electrode as a source of catalysis and in the presence of 1 g NaCl·L^-1. We obtained easily biodegradable water with a mineralization rate equal to 85% and non-toxicity confirmed by the pea grain germination test.

The heterologous expression, characterization, and application of a novel laccase from Bacillus velezensis

Laccases have a huge potential in numerous environmental and industrial applications due to the ability to oxidized a wide range of substrates. Here, a novel laccase gene from the identified Bacillus velezensis TCCC 111904 was heterologously expressed in Escherichia coli. The optimal temperature and pH for oxidation by recombinant laccase (rLac) were 80 °C and 5.5, respectively, in the case of the substrate 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and 80 °C and 7.0, respectively, in the case of 2,6-dimethoxyphenol (2,6-DMP). rLac exhibited high thermostability and pH stability over a wide range (pH 3.0, 7.0, and 9.0). Additionally, most of the metal ions did not inhibit the activity of rLac significantly. rLac showed great tolerance against high concentration of NaCl, and 50.8% of its initial activity remained in the reaction system containing 500 mM NaCl compared to the control. Moreover, rLac showed a high efficiency in decolorizing different types of dyes including azo, anthraquinonic, and triphenylmethane dyes at a high temperature (60 °C) and over an extensive pH range (pH 5.5, 7.0, and 9.0). These unique characteristics of rLac indicated that it could be a potential candidate for applications in treatment of dye effluents and other industrial processes.

A multifunctional gelatine-quaternary ammonium copolymer: An efficient material for reducing dye emission in leather tanning process by superior anionic dye adsorption

Leather wastewater is one of the most polluting industrial emissions. The efficiency of wastewater remediation is limited by its complex composition. Herein, a novel strategy for designing modified gelatine with higher degree of quaternization (MG-2) is presented. The higher degree of quaternization allows sufficient adsorption of dyes in the tanning process. It is an in situ, environmentally friendly, and innovative strategy to limit dye emissions and can circumvent the subsequent waste management. Dyes such as Direct Purple N and Acid Black 24 could be adsorbed completely within 5 min by the MG-2 film formed from MG-2 solution. In addition, a remarkable efficiency in removing Acid Red 73, Golden Orange G, and Acid Orange II (>96.1% removal rates) was achieved within 30 min. The adsorption equilibrium data suggested that the adsorption capacity was positively correlated to the concentration of MG-2. When Acid Orange II and MG-2 were used in the industrial re-tanning process, the residual dye concentration in wastewater was only 23.1 mg L^-1, indicating that MG-2 is a promising re-tanning agent for adsorbing dyes in the leather tanning process.

Taguchi Method and Response Surface Methodology in the Treatment of Highly Contaminated Tannery Wastewater Using Commercial Potassium Ferrate

The potential implementation of Envifer^®, a commercial product containing potassium ferrate (40.1% K₂FeO₄), for the purification of highly contaminated tannery wastewater from leather dyeing processes was proposed. The employment of the Taguchi method for optimization of experiments allowed the discoloration (98.4%), chemical oxygen demand (77.2%), total organic carbon (75.7%), and suspended solids (96.9%) values to be lowered using 1.200 g/L K₂FeO₄ at pH 3 within 9 min. The application of the central composite design (CCD) and the response surface methodology (RSM) with the use of 1.400 g/L K₂FeO₄ at pH 4.5 diminished the discoloration, the chemical oxygen demand, the total organic carbon, and suspended solids within 9 min. The Taguchi method is suitable for the initial implementation, while the RSM is superior for the extended optimization of wastewater treatment processes.