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

Sustainable chrome-free leather manufacturing through the aldehyde-vegetable combination tanning method based on biomass-derived dialdehyde carboxymethyl cellulose and mimosa tannin

The potential of dialdehyde polysaccharides as chrome-free tanning agents can be enhanced through the use of aldehyde-vegetable combination tanning technology. In this study, dialdehyde carboxymethyl cellulose was synthesized by oxidizing carboxymethyl cellulose with sodium periodate. Fourier transform infrared spectroscopy revealed two characteristic bands at 1738 cm-1 and 886 cm-1. Leather tanned solely with dialdehyde carboxymethyl cellulose exhibited a shrinkage temperature of 78 °C. To enhance the properties, mimosa tannin was combined with dialdehyde carboxymethyl cellulose. The combination of dialdehyde and mimosa tannin showed enhanced mechanical properties, including a tensile strength of 245.71 kg/cm2, tear strength of 44.63 kg/cm, and elongation at break of 45.23 %. Additionally, scanning electron microscopy revealed a well-dispersed arrangement of collagen fibers. The combination tanning resulted in a synergistic effect, increasing the shrinkage temperature to 85 °C due to additional hydrogen bonding. Furthermore, the excellent organoleptic properties, including fullness and softness were observed for combined-tanned leather resulting from the synergistic effect of dialdehyde carboxymethyl cellulose and mimosa tannin. Further studies showed that the wastewater generated by the aldehyde-vegetable combination tanning method is easily biodegradable. Based on the results, the combination tanning technology offers a green, chrome-free, and metal-free approach for the sustainable development of the leather industry.

Unravelling the fouling behavior of cation exchange membrane (CEM) by waste salt containing decyltrimethylammonium chloride during membrane electrolysis

With the implementation of the zero liquid discharge (ZLD) process for industrial wastewater treatment, the generation of large quantities of industrial waste salts has become a growing concern. The presence of organic contaminants, however, limits the reuse of NaCl waste salts for ion exchange membrane electrolysis, and the fouling behavior during the electrolysis process needs to be investigated. In this study, decyltrimethylammonium chloride (DTAC)-containing salt was employed as a model industrial waste salt to evaluate the fouling of cation exchange membrane (CEM) during ion exchange membrane electrolysis involving waste salt reuse. Additionally, this study examined the effect of membrane cleaning on the properties of fouled CEMs. Results indicated that higher DTAC concentrations in the feed solution significantly exacerbated CEM fouling, forming a dense DTAC fouling layer on the membrane surface. This layer led to a marked increase in cell voltage and resistance. Electrochemical impedance spectroscopy (EIS) analysis further revealed that the DTAC fouling layer could hinder or completely obstruct the transmembrane migration of ions, particularly at elevated DTAC concentrations. Moreover, membrane cleaning proved effective in mitigating contamination during the electrolysis process. Notably, NaOH cleaning demonstrated superior performance compared to water cleaning, effectively removing most DTAC from fouled CEMs. This study provides valuable insights into organic fouling mechanisms and membrane cleaning strategies for the reuse of NaCl waste salts in ion exchange membrane electrolysis.

A systematic review of innovations in tannery solid waste treatment: A viable solution for the circular economy

Amidst growing global demand for leather goods, the efficient conversion of rawhide and skins into durable leather is crucial, yet approximately 80 % of these materials become solid and liquid waste during tannery operations. Improper management of tannery solid waste poses significant environmental risks, contaminating soil, groundwater, and surface water. This review explores thermochemical, biological, and phytoremediation methods for treating tannery solid waste, emphasizing their role in resource recovery and environmental sustainability. Thermochemical techniques like pyrolysis and gasification convert tannery solid waste into biochar, bio-oil, and syngas, which serve as soil amendments, renewable energy sources, or industrial feedstocks. Biological methods such as composting and anaerobic digestion decompose organic tannery solid waste components into nutrient-rich compost and biogas. Phytoremediation uses plants to remediate contaminants, including heavy metals, from tannery solid waste. These methods mitigate environmental pollution and support the leather industry's transition to sustainable practices, crucial for compliance with global regulations. Moreover, the review offers insights into current efforts and perspectives aimed at achieving a zero-waste policy, emphasizing the importance of a circular economy to alleviate the environmental burden associated with tannery operations and ensure their continued sustainability. Finally, a detailed discussion on the current challenges in terms of technology accessibility and economic feasibility was also discussed.

Keratin hydrolysate as a chrome exhaust aid and keratin filler in leather processing: A cleaner technology approach for tannery solid waste management and leather manufacturing

Hair burning unhairing and dampening of tannery wastes during the hair-saving unhairing process are becoming significant problems in the tanning industry. Therefore, this research article focuses on the extraction of keratin hydrolysate (KH) and its application as a chrome exhaust aid and keratin filler in leather manufacturing process. The structure, morphology and functional groups of the extract were examined using X-Ray Diffractometer (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectrometer (FTIR), respectively. To study and contrast the degree of improvement in chromium uptake, the KH solution was applied both before tanning on the pickled pelt and after tanning during basification. The thermal stability, physical strength characteristics and organoleptic properties of the leathers obtained were characterized. Furthermore, the environmental impact of the tanning system was assessed through a comparative analysis of the spent liquors. Finally, experimental retanning process was conducted to replace the commercial protein filler (Celatan F: 50, 75, and 100 %) with KH solution, with concurrent processing of control leather using conventional chrome tanning agent at 6 % dosage of chromium. The FTIR analysis of the extract confirmed the presence of alkyl side chains of amino acids as well as carboxylic, amide, carboxyl group and aldehyde functional groups at 1400-1700 cm-1,3,303.46 cm-1,3270 cm-1 and 2752 cm-1, respectively. XRD spectrum showed two diffraction peaks at 2 theta values of 9.36° and 21.16°, respectively. Leathers with improved mechanical strength, organoleptic properties and thermal stability were obtained with 100 % substitution of Celatan F at pH 6 and 10 % chromium dosage. It was also discovered that the shrinkage temperature of the experimental leather was enhanced to more than 105 °C. Environmental impact evaluation on the spent liquor showed that the complete replacement of Celatan F with KH solution brought about a notable decrease in COD and TDS in the spent liquor. The extraction and application of tannery hair waste-based keratin hydrolysate as an efficient, environmentally friendly chrome exhaust aid and keratin filler has been attempted and established in this research article.

A novel complex coupling agent for enhancing the compatibility between collagen fiber and natural rubber: A utilization strategy for leather wastes

Leather shavings are generated as solid waste in the leather industry and may cause environmental pollution if not disposed judiciously. These solid wastes, primarily composed of collagen fibers (CFs), can be recycled as biomass composites. However, CFs are incompatible with natural rubber (NR) due to its hydrophilicity. Conventionally, the compatibility has been improved by utilizing silane coupling agents (SCAs) along with a large number of organic solvents, which further contribute to environmental pollution. In this study, we developed a novel complex coupling agent (CCA) to enhance the compatibility between CF and NR. The CCA was synthesized through a coordination reaction between Cr(III) and α-methacrylic acid (MAA). Cr(III) in the coupling agent coordinates with the active groups in CFs, while the unsaturated double bonds in MAA facilitate covalent crosslinking between the CCA and NR, improving compatibility. The coordination bonding between CF and NR exhibits strong interfacial interaction, endowing the composites with desirable mechanical properties. Moreover, the proposed method is an economical and green approach that can be used to synthesize CF-based composites without requiring organic solvents. Herein, a strategy promoted sustainable development in the leather industry has been established.

Utilization of battery waste derived ZnO in the removal of dye from aqueous solution: A waste to wealth approach

Every year a huge amount of zinc carbon batteries is discarded as waste and the management of such waste has become a growing concern all over the world. However, from these waste carbon batteries different kinds of valuable materials could be recovered. On the other hand, different industries discharged large volumes of dye wastewater into the environment which has a profound impact on environment and as well as human health. In this study, ZnO was recovered from the waste carbon batteries through pyrometallurgy process and utilized it for the treatment of methylene blue and methyl orange dye water. The batch adsorption process was carried out to observe the effect of adsorbent dosage, pH, contact time, stirring speed and temperature. Under the obtained optimal conditions adsorption kinetics (Pseudo-first order and pseudo-second order) and adsorption isotherms (Langmuir, Freundlich and Temkin) were analyzed. The results disclosed that 0.5 g and 0.6 g of ZnO showed maximum removal efficiency for MB and MO dye solution (50 ppm) whereas pH 13 and 6 were the optimal for MB and MO respectively. Kinetic studies indicate that both the adsorption processes were pseudo-second order. It was also revealed that based on regression coefficient R2 value the adsorption of MB and MO on ZnO is followed Langmuir model. Furthermore, the findings revealed that the MO adsorption on ZnO is a chemical adsorption process and MB adsorption is a physical adsorption process.

Investigating recycling decisions of internet recyclers: A step towards zero waste economy

Online recycling has been recognized as an efficient method for waste recycling. This paper focuses on the information asymmetry between an internet recycler and consumers in the online transaction of used products. This paper is to find an optimal strategy for the internet recycler when the consumers would make an adverse selection in submitting the classification results (the used products would be classified into two kinds according to the quality: High quality and Low quality) of used products in online orders to avoid the loss because of internet recycler's moral hazard, which might bring the extra cost for internet recycler. Therefore, this study used game theory to establish a Stackelberg game model for analyzing an internet recycler and consumers' decision-making in the online transaction of used products. Based on the analysis of consumers' behaviors in an online transaction, internet recycler's strategies are divided into two kinds: A, high moral hazard strategy, and B, low moral hazard strategy. It is found that the strategy of low moral hazard is optimal for the internet recycler compared to the strategy of high moral hazard. Further, though strategy B is optimal, the internet recyclers is suggested to increase their moral hazard probability when the H used products are increasing (High-quality ones). Besides, for strategy B, the correction cost for wrong H orders and correction benefit from correction of wrong L orders would decrease the optimal moral hazard probability, and the impact of the correction benefit from correction of wrong L orders on the decision of moral hazard probability is more obvious.

Consumer willingness to pay more for pro-environmental packages: The moderating role of familiarity

Institutional regulations and market trends are spurring companies to invest more in pro-environmental and sustainable products. Within the pro-environmental offer, there are several packaging alternatives, from sustainably packaged to unpackaged products - so-called bulk - and/or labels, compelling companies into making a complex investment choice. Further, the required higher investments do not always find consumers' approval. Consumers often consider pro-environmental packaging as excessively expensive. Within this context, this study seeks to understand how to exploit the consumers' greater attention to sustainability and well-being to boost consumers' willingness to pay more for pro-environmental products. In doing so, the study compares two packaging options (i.e., sustainably packaged products and bulk products). Additionally, the study assesses differences between highly and slightly familiar consumers, evidencing how to properly encounter the expectations of the two segments. The findings, derived by a multigroup structural equation model conducted on 278 structured questionnaires, reveal that health concern impact is more relevant to highly familiar consumers while environmental concern is for slightly familiar consumers. For the latter, label influence plays a primary role in enhancing their willingness to pay more for pro-environmental products. Overall, sustainably packaged products are preferred to unpackaged products.

A cleaner leather chemical from feather waste for reducing ammonia-nitrogen pollution and improving biological treatment efficiency of tannery wastewater

Feather waste is produced in millions of tons globally every year, resulting in a waste of biomass resources and even environmental pollution. A sustainable strategy for utilizing feather waste was proposed by preparing a clean deliming agent for ammonia-nitrogen (NH₃-N) reduction in leather manufacture and biological treatment efficiency improvement of tannery wastewater. Briefly, chicken feather wastes were deeply hydrolyzed with sulfuric acid, and the optimized keratin hydrolysate (KH_opt) that contained 53.6% crude protein and 41.2% amino acids, such as glutamic acid, serine, proline, leucine, phenylalanine, glycine, valine, and arginine, was obtained and used to delime limed cattle hides. The appropriate ratio of amino acids in KH_opt gave KH_opt a great pH-buffering capacity and maintained a stable float pH of approximately 9 throughout the deliming process. The isoelectric points of KH_opt (3.8) and the limed hide (6.3) were both lower than the float pH, thereby bringing about an electrostatic repulsion between the KH_opt and the hide surface, which is helpful for KH_opt to penetrate and deswell the limed hide rapidly. Moreover, the KH_opt deliming effectively removed calcium from the limed hide and achieved leather comparable to conventional leather for commercial applications. KH_opt reduced the NH₃-N concentrations of deliming effluent and tannery wastewater by 91.1% and 80.6%, respectively, compared with the conventional deliming agent (ammonium sulfate), and dramatically increased the biological treatment efficiency of tannery wastewater. The results showed that efficient and high-value use of feather waste was made by preparing KH_opt for sustainable leather manufacturing.