Leather waste--potential threat to human health, and a new technology of its treatment

Effects of temperature on the migration behaviour of arsenic and chromium in tannery sludge under CO2 gasification

To reduce heavy metals (HMs) contamination from tannery sludge, this study investigated the migration behaviour of arsenic (As) and chromium (Cr) at 700-900 °C using CO2 gasification. The HMs enrichment results showed that As contents of ash decreased (6.42→1.87 mg/kg) while Cr contents increased (41.40→78.24 mg/kg) over 700-900 °C. More Si-O bonds and fewer Ca-O bonds with increasing temperature in ash primarily determined this migration behaviour of HMs. Meanwhile, the proportions of toxic As(III) and Cr(VI) declined from 96.02% and 64.26-76.96% and 21.24%, forming As(0) and Cr(III) with less toxicity. This reduction was conducted via two pathways: (i) carbon reduced As(III)/Cr(VI) and (ii) carbon reduced Fe(II)/Fe(III) to Fe(0), then Fe(0) reduced As(III)/Cr(VI) assisted with carbon via Fe(0)→Fe(II)→Fe(III). However, free calcium ions oxidized As(0)/Cr(III) to As(III)/Cr(VI) at 700 ○C. At higher temperatures, silicate glass conversion of ash immobilized free calcium ions and barely oxidized HMs. Furthermore, this study identified the positive effect of increasing temperature on enhancing the stability of HMs in ash by transforming bioavailable HMs into non-bioavailable HMs, which decreased the leaching toxicity and environmental risk. Regarding HMs emissions control and cold gas efficiency, CO2 gasification treatment of tannery sludge is most effective at 800 °C.

Stabilizing Cr(Ⅲ) deriving from tannery sludge with kaolin and organic matter

Stabilizing Cr(III) in tannery sludge (TS) via harmless method has always been the goal of environmental pollution treatment. In this study, a simple method to stabilize Cr(III) in TS is proposed via adding kaolin, based on the fact a large amount of organic matter contained in TS. Comprehensive characterizations confirm that kaolin can stabilize Cr(Ⅲ) via its abundant -OH and lamellar structure. Moreover, there are hydrogen bond interactions and ligand exchange-surface complexation between organic matter and kaolin, which is more conducive to form a stable ternary complex with Cr(III), in a state of organic matter-Cr(III)-kaolin. Simultaneously, the BCR sequential extraction experiment shows that the unstable water and acid soluble state of Cr(III) are reduced (from 0.61% to 0.35%), which further indicates that the stabilization of Cr(III) is successful.

Biological Solubilisation of Leather Industry Waste in Anaerobic Conditions: Effect of Chromium (III) Presence, Pre-Treatments and Temperature Strategies

Collagen-based polymers and their blends have attracted considerable interest for new materials development due to their unique combination of biocompatibility, physical and mechanical properties and durability. Leather, a modified natural biopolymer made from animal rawhide and the first synthetic collagen-based polymer known since the dawn of civilization, combines all these features. Rawhide is transformed into leather by tanning, a process in which the collagen is cross-linked with different agents to make it stronger and more durable and to prevent its decay. Research on the development of environmentally friendly procedures and sustainable materials with higher efficiency and lower costs is a rapidly growing field, and leather industry is not an exemption. Chrome-tanned and vegetable-tanned (chromium-free) shavings from the leather industry present a high content of organic matter, yet they are considered recalcitrant waste to be degraded by microbiological processes like anaerobic digestion (AD), a solid technology to treat organic waste in a circular economy framework. In this technology however, the solubilisation of organic solid substrates is a significant challenge to improving the efficiency of the process. In this context, we have investigated the process of microbial decomposition of leather wastes from the tannery industry to search for the conditions that produce optimal solubilisation of organic matter. Chrome-tanned and chromium-free leather shavings were pre-treated and anaerobically digested under different temperature ranges (thermophilic–55 °C-, intermediate–42 °C- and mesophilic–35 °C) to evaluate the effect on the solubilisation of the organic matter of the wastes. The results showed that the presence of chromium significantly inhibited the solubilization (up to 60%) in the mesophilic and intermediate ranges; this is the fastest and most efficient solubilization reached under thermophilic conditions using the chromium-free leather shaving as substrates. The most suitable temperature for the solubilization was the thermophilic regime (55 °C) for both chromium-free and chrome-tanned shavings. No significant differences were observed in the thermophilic anaerobic digestion of chromium-free shavings when a pre-treatment was applied, since the solubilisation was already high without pre-treatment. However, the pre-treatments significantly improved the solubilisation in the mesophilic and intermediate configurations; the former pre-treatment was better suited in terms of performance and cost-effectiveness compared to the thermophilic range. Thus, the solubilisation of chromium-free tannery solid wastes can be significantly improved by applying appropriate pre-treatments at lower temperature ranges; this is of utter importance when optimizing anaerobic processes of recalcitrant organic wastes, with the added benefit of substantial energy savings in the scaling up of the process in an optimised circular economy scenario.

Heterogeneous Photodegradation for the Abatement of Recalcitrant COD in Synthetic Tanning Wastewater

Tannery wastewater is considered one of the most contaminated and problematic wastes since it consists of considerable amounts of organic and inorganic compounds. These contaminants result in high chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total suspended solids (TSS). In this work, the heterogeneous photodegradation of recalcitrant COD in wastewater from the tanning industry was investigated, in particular the recalcitrant COD due to the presence of vegetable tannins extracted from mimosa and chestnut and from synthetic tannins based on 4,4′ dihydroxy phenyl sulfone. TiO2 Aeroxide P-25 was employed to study the photodegradation of model molecules in batch conditions under different parameters, namely initial concentration of COD, temperature, and catalyst dose. The maximum COD abatement reached was 60%. Additionally, preliminary kinetic investigation was conducted to derive the main kinetic parameters that can be useful for process scale-up. It was found to be independent of the temperature value but linearly dependent on both catalyst loading and the initial COD value.

Synergistic immobilization of chromium in tannery sludge by ZnO and TiO2 and the oxidation mechanism of Cr(III) under alkaline in high temperature

The disposal of the Cr containing tannery sludge has become a serious environmental problem in China, which has attracted increasing attention. However, experimental and theoretical research is still needed. We developed a feasible route to synergistic immobilization the Cr in tannery sludge into the spinel-based phases by addition of ZnO and TiO₂. ZnO and Cr³⁺ can form stable spinel-based phase, and TiO₂ can suppress the formation of Cr⁶⁺. The significantly synergistic effect between ZnO and TiO₂ promoted the immobilization of Cr in tannery sludge and reduce the leaching of the chromium in the annealed sludge. The oxidation of Cr³⁺ to Cr⁶⁺ in the presence of alkaline substances has been elucidated by density functional theory, and it is revealed that the electrons from the Cr-d orbit jump to the Ca-d and directly transform into the O₂.

Prevalence and Risk Factor of Occupational Skin Complaints among Male Tannery Workers of Kanpur, India

Background

Occupational skin illnesses are the second most common occupational health hazard following musculoskeletal disorders. Tannery workers have frequent and prolonged exposure to skin irritants and allergens and may have a higher risk of developing occupational dermatitis.

Aims and Objectives

The aim of this study is to examine the extent of skin problems and their determinants among male tannery workers.

Materials and Methods

The data for the present research was drawn from a cross-sectional household study of tannery and nontannery workers in the Jajmau area of Kanpur, Uttar Pradesh. A total of 284 tannery and 289 nontannery workers were interviewed using purposive sampling technique. Descriptive statistics and multivariate techniques have been used.

Results

Tannery workers experienced itching hands or fingers with fissures (21%), scaling of hands or fingers with fissures (18%), red and swollen hands or fingers (11%), and vesicles on the hands or between the fingers (11%). The workers who had moderate/high dermal exposure to chemicals were 35(P < 0.001), and they were 31 (P < 0.001) times more likely to experience vesicles on scaling hands or fingers with fissures, and itching hands or fingers with fissures. The tannery workers engaged in wet finishing work were significantly 3.9 (P < 0.1) times more likely to experienced scaling on hands or fingers with fissures.

Conclusion

The study acclaims the mechanization of tannery activities at workplaces, so that risk of skin complaints can be minimized among tannery workers. As the risk of skin complaints is very high with the dermal exposure to chemicals, personal protective equipment must be provided and their use should be included in the curriculum of the ternary workers.

Investigating the chromium status, heavy metal contamination, and ecological risk assessment via tannery waste disposal in sub-Saharan Africa (Kenya and South Africa)

To mitigate the negative environmental and public health concerns associated with increased industrial discharges amid the rapid industrial growth, sub-Saharan African countries have instituted several environmental regulations and policies. However, a paradox of good environmental policies but inadequate enforcement exists in most of these countries, with information on the pollution level unknown due to poor monitoring resources. In this study, potentially toxic heavy metal contamination and physicochemical characteristics in effluents and dumpsite soils of two tanneries in Kenya (DB) and South Africa (BO) were evaluated during the dry and rainy season of 2018. Pollution levels and ecological risk in the dumpsite soils were assessed by adopting geoaccumulation index (I_geo), contamination factor (CF), pollution load index (PLI), and ecological risk index (PRI). The results showed that the mean final effluent concentration for total dissolved solids (TDS), chemical oxygen demand (COD), and Cr, Cu, Fe, Ni, Zn, and Cd for BO (2127, 890, 1.82, 1.38, 1.96, 0.60, 1.21, and 1.16, respectively) and DB tanneries (8157, 1369, 7.90, 0.69, 1.05, 0.60, 1.72 mg/L, respectively) were above the limits of emission guidelines. The mean Cr and Cr(VI) concentrations in tannery dumpsite soils (204.9 ± 29.1 and 0.31 ± 0.01 and 943 ± 29.8 and 0.4 ± 0.07 mg/kg for BO and DB, respectively) and Fe (2498 ± 62 mg/kg in DB) exceeded acceptable thresholds of the World Health Organization (WHO), Food and Agriculture Organization (FAO), and local background levels. A positive strong correlation was observed between Cr and organic matter, OM (r > 0.7, p < 0.001), electrical conductivity, EC (r = 0.99, p < 0.05), and As (r = 0.62; p < 0.05), suggesting a common anthropogenic point source. The mean PLI values of 5.3 and 1.6 for DB and BO dumpsites indicated significant pollution of the soils with heavy metals, specifically Cr (I_geo = 18 and 2.4 for DB and BO, respectively). Similarly, PRI values of 174.8 and 57.4 indicated a moderate and low potential ecological risk for DB and BO tannery dumpsite, respectively, with several plants sampled within the two sites exhibiting elevated levels of Cr contamination. In summary, these results provide scientific insights on the need for both improved effluent management and treatment technologies of tannery wastes, coupled with the strengthening of continuous monitoring and enforcement for compliance of industrial discharges in sub-Saharan countries.

Transforming wet blue leather and potato peel into an eco-friendly bio-organic NPK fertilizer for intensifying crop productivity and retrieving value-added recyclable chromium salts

An attempt has been made to address two important issues, the solid waste management of leather industry and soil fertility. The SEM images revealed altered surface-morphology.The EDS elemental analysis exhibited presence of about 13.2% nitrogen (N), 50.56% carbon (C), 2.69% phosphorus (P) in the collagenous material of wet blue leather (WBL) after chromium removal. In potato peel biochar (PPB) prepared the EDS analysis corroborated the presence of N P K in 5%, 1.4% and 21.64% respectively. In the formulated bio-organic NPK fertilizer, using chromium free WBL and PPB, the percentage of N, P, K, was in 13.10, 2.41, 20.20% respectively which was authenticated by EDS. Its effect on okra (Abelmoschus esculentus) plant showed higher growth (1.11 fold fruit size) and total chlorophyll content (1.61 fold) than in untreated soil (control) but displayed similar result as in presence of chemical fertilizer. The released free ammonia in soil with bio-organic NPK was more (37.02%) than with chemical fertilizer (6.10%). DNA intercalation study showed the non-hazardous impact on soil. The FTIR, XRD, SEM-EDS, AAS further specified the conversion of the WBL extracted acidic chromium-rich solution by MgO into crystalline chromium for commercial use.

Chromium containing leather trimmings valorization: Sustainable sound absorber from collagen hydrolysate intercalated electrospun nanofibers

Developing value-added material from industrial waste is one of the sustainable ways of recycling solid waste produced from the leather industry. Noise which makes a considerable negative impact in the day to day life of people needs immediate attention where the sound absorbers play a vital role. Nanofibers can be used as sound absorbers due to their properties like porosity and high surface area. In this study, collagen hydrolysate extracted from waste leather trimmings was utilized to produce multilayer hybrid sound-absorbing material. Collagen hydrolysate was electrospun along with polyvinyl alcohol (PVA) and the layer was sandwiched between polyacrylonitrile (PAN) nanofibrous layers. The hierarchical structure of the composite is more porous on outer layers than medium porous inner collagen hydrolysate- PVA layer. The hybrid material was characterized using various experimental techniques and the sound absorption was measured using two-microphone impedance tube method. From acoustic measurements, it was revealed that the composite showed improved sound absorption in the frequency range of 800-2500 Hz due to its varying pore size. Hence, the leather trimmings as a component of sound-absorbing material creates an innovative solution for discarded leather waste and they can be used in practical applications like room acoustics.

Recycling of Chrome-Tanned Leather and Its Utilization as Polymeric Materials and in Polymer-Based Composites: A Review

Tanneries generate large amounts of solid and liquid wastes, which contain harmful chemical compounds in the environment, such as chromium, that is used in the tanning process. Until now, they have been almost completely dumped in landfills. Thus, finding eco-sustainable and innovative alternatives for the management and disposal of these wastes is becoming a huge challenge for tanneries and researchers around the world. In particular, the scientific and industrial communities have started using wastes to produce new materials exploiting the characteristics of leather, which are strongly connected with the macromolecular structure of its main component, collagen. None of the reviews on leather waste management actually present in the scientific literature report in detail the use of leather to make composite materials and the mechanical properties of the materials obtained, which are of fundamental importance for an effective industrial exploitation of leather scraps. This comprehensive review reports for the first time the state of the art of the strategies related to the recovery and valorization of both hydrolyzed collagen and leather waste for the realization of composite materials, reporting in detail the properties and the industrial applications of the materials obtained. In the conclusion section, the authors provide practical implications for industry in relation to sustainability and identify research gaps that can guide future authors and industries in their work.

Utilization of Leather Waste Fibers in Polymer Matrix Composites Based on Acrylonitrile-Butadiene Rubber

In this study, we present the fabrication of nitrile butadiene rubber/waste leather fiber (NBR/WLF) composites with different weight percentages of WLF and NBR (0/100, 20/80, 30/70, 40/60, 50/50, 60/40 wt/wt). WLF was prepared by cutting the scrap leathers from the waste product of the Vietnamese leather industry. Subsequently, in order to make the short fibers, it was mixed by a hammer mill. The characteristics of WLF/NBR composites such as mechanical properties (tensile strength, tear strength, hardness), dynamic mechanical properties, toluene absorption, and morphology were carefully evaluated. As a result, the tensile strength and tear strength become larger with increasing WLF content from 0 to 50 wt% and they decrease when further increasing WLF content. The highest tensile strength of 12.5 MPa and tear strength of 72.47 N/mm were achieved with the WLF/NBR ratio of 50/50 wt%. Both hardness and resistance of the developed materials with toluene increased with increasing WLF content. The SEM results showed a good adhesion of NBR matrix and the WLF. The increasing of storage modulus (E’) in comparison with raw NBR showed good compatibility between WLF and NBR matrix. This research showed that the recycled material from waste leather and NBR was successfully prepared and has great potential for manufacturing products such as floor covering courts and playgrounds, etc.

Factors Associated With Health Complaints Among Leather Tannery Workers in Bangladesh

Background: Few studies have reported associations between occupational exposure to tannery chemicals with breathing difficulty and skin diseases and none have been conducted in Bangladesh. The aim of this study was to investigate the associations of health complaints with types of work and length of employment among tannery workers in Bangladesh, where occupational health and safety regulations are less restricted compared with the developed world. Methods: One hundred sixty-seven (n = 167) workers from 10 tanneries were interviewed using a questionnaire adapted from the European Community Respiratory Health Survey (ECRHS) and the Tasmanian Longitudinal Health Study (TAHS) to collect information on occupational exposures and health outcomes. Workers' length of employment was examined, as well as their areas of work including beamhouse, wet finishing, dry finishing, and miscellaneous. Univariate and multivariate logistic regressions were performed to investigate potential associations while controlling for confounders. Results: Length of employment was positively associated with breathing difficulty (odds ratio [OR]: 1.32, 95% confidence interval [CI]:1.07-1.64). Workers involved in the wet finishing (OR: 11.75, 95% CI: 2.12-65.10) and dry finishing (OR: 13.38, 95% CI: 1.00-181.70) had higher odds of breathing difficulty; while, working in the beamhouse was associated with an increased risk of developing skin diseases (OR: 4.36, 95% CI: 1.10-17.32). Conclusion/Application to Practice: Length of employment and types of work were associated with increased risk of health complaints, including breathing difficulty and skin disease among tannery workers. Stronger regulations with regular enforcement, regular health surveillance, and worker and employer education are necessary for reducing these exposures and improving the health outcomes of the tannery workers.

Steam Explosion in alkaline medium for gelatine extraction from chromium-tanned leather wastes: time reduction and process optimization

Alkaline hydrolysis of chromium-tanned leather wastes (CTLW) is a well-known process that allows the extraction of its most valuable portion: the protein. However, alkaline hydrolysis is time-consuming. It usually takes from 2 to 10 h to be completed. In this work, alkaline hydrolysis was performed in a steam explosion reactor, using CaO as the alkalinizing agent and aiming at a short-time process. Three different temperatures and residence times were tested: 130, 140, and 150°C; 5, 10, and 15 min. When performed at 140°C for 10 min, the steam explosion in alkaline medium resulted in the optimum combination of protein extraction yield (30%) and gelatine quality (viscosity of 2.4 cP at 25°C in a 24.6 g/L protein solution - 39 kDa of molecular mass [Formula: see text]w). Not only a high extraction yield was achieved, but when compared to traditional methods, steam explosion in alkaline medium reduced the process time by a factor that varied from 12 to 36 times. It also reduced chromium content in the gelatine by a factor that varied from 16 to 96 times. Finally, to produce a high quality product, the ash content of the gelatine was reduced from 11.8% (dry basis) to 1.2% (dry basis) through diafiltration. This purification allows the application of the gelatine, for example, in the production of polymeric films.

Life cycle and End-of-Life management options in the footwear industry: A review

It is well recognized globally that the footwear industry contributes to a large waste stream throughout its life cycle. This article reviews the literature pertaining to the life cycle of footwear products and their End-of-Life (EoL) management strategies. The review discusses critical aspects of the footwear industry, commencing with a background on the growth and consumption of footwear products across the globe. The review provides an overview of the environmental impacts of different footwear materials across their life cycles. In this regard, leather materials are given intense focus due to their poor environmental performance. The review further examines proactive and reactive approaches to footwear waste management, whilst additionally exploring the challenges facing EoL footwear recovery. Finally, pyrolysis is examined as a thermochemical treatment process with value due to its potential to recover materials from post-consumer footwear. The significant findings in this review paper are as follows: (a) leather footwear materials have the most detrimental environmental impacts across their life cycle; (b) there is limited scientific literature on thermochemical processes (particularly pyrolysis) as waste recovery options for post-consumer footwear; and (c) several challenges face the recovery of post-consumer footwear products, including inefficient reverse logistics, mixed product recycling and difficulties establishing a value recovery chain. This review paper recommends further research on pyrolysis as a potential post-consumer footwear recovery option. Exploring the viability of new avenues for footwear waste recovery is significant due to its potential to divert this waste stream from landfills and allow a progression toward a more circular economy.

Assessing chromium pollution and natural stabilization processes in agricultural soils by bulk and micro X-ray analyses

A combined approach based on multiple X-ray analytical techniques and conventional methods was adopted to investigate the distribution and speciation of Cr in a polluted agricultural soil, from the bulk-scale down to the (sub)micro-level. Soil samples were collected from two different points, together with a control sample taken from a nearby unpolluted site. The bulk characterization revealed that the polluted soils contained much higher concentrations of organic matter (OM) and potentially toxic elements (PTE) than the control. Chromium was the most abundant PTE (up to 5160 g kg^-1), and was present only as Cr(III), as its oxidation to Cr(VI) was hindered by the high OM content. According to sequential extractions, Cr was mainly associated to the soil oxidisable fraction (74%) and to the residual fraction (25%). The amount of Cr potentially bioavailable for plant uptake (DTPA-extractable) was negligible. Characterization of soil thin sections by micro X-ray fluorescence (μXRF) and field emission scanning electron microscopy coupled with microanalysis (FEGSEM-EDX) showed that Cr was mainly distributed in aggregates ranging from tens micrometres to few millimetres in size. These aggregates were coated with an aluminosilicate layer and contained, in the inner part, Cr, Ca, Zn, P, S and Fe. Hyperspectral elaboration of μXRF data revealed that polluted soils were characterised by an exogenous organic-rich fraction containing Cr (not present in the control), and an endogenous aluminosilicate fraction (present also in the control), coating the Cr-containing aggregates. Analyses by high-resolution micro X-ray computed tomography (μCT) revealed a different morphology of the soil aggregates in polluted soils compared with the control. The finding of microscopic leather residues, combined with the results of bulk- and micro-characterizations, suggested that Cr pollution was likely ascribable to soil amendment with tannery waste-derived matrices. However, over the years, a natural process of Cr stabilization occurred in the soil thus reducing the environmental risks.

Chromium Concentrate Recovery From Solid Tannery Waste in a Thermal Process

Leather processing requires substantial inputs of energy, water and chemicals. Additionally, it generates significant amounts of liquid and solid waste, severely impacting the environment. Processing 1 Mg of raw hides yields up to 600-700 kg of waste, considerable amounts of which are solid tannery waste. Such waste contains chromium (Cr) compounds, which are commonly used as tanning agents. This paper reviews solid tannery waste treatment technologies, with emphasis on waste incineration in a specially designed experimental tunnel incinerator. Three different types of tannery waste were subjected to tests: trimmings, shavings and buffing dust. As the research revealed, the process can be applied to all types of solid tannery waste. Moreover, it enables the reuse of the heat of the process and results in a Cr concentrate in the process residues. The conducted analyses (carbon, hydrogen and nitrogen elemental analysis; inductively coupled plasma optical emission spectroscopy; powder X‑ray diffraction) proved that there is no or little organic content in the obtained residual ash, which contains up to 53.1%(w/w) Cr in the form of Cr (III) oxide. Such material may be used as a Cr ore substitute in the chemical or metallurgical industries.

A novel substitution-based method for effective leaching of chromium (III) from chromium-tanned leather waste: The thermodynamics, kinetics and mechanism studies

A substitution-based method for chromium (III) leaching from chromium-tanned leather waste (CTLW) without destroying the collagen matrix was proposed. The leaching efficiency of Cr (III) from CTLW using different organic salts was investigated and sodium oxalate (OA-2Na) was considered to be the best Cr leaching agent. The effects of leaching time, temperature, pH, concentration, shaking speed and leather thickness on Cr leaching rate were investigated and a Cr leaching rate of 98% was obtained. Thermodynamic parameters (ΔG⁰ < 0, ΔH⁰ > 0 and ΔS⁰ > 0) were obtained in this study. The kinetic data fitted well with the first-order kinetic equation. The apparent activation energy (Ea = 82.9563 kJ/mol) and the frequency factor (A = 2.96 × 10¹¹) were obtained. The collagen matrix remained intact after Cr leaching by the characterization of SEM and FTIR. A substitution mechanism was proposed that Cr (III) in CTLW was complexed with oxalate and dissociated from the collagen matrix.

Tannery wastewater treatment by cavitation combined with advanced oxidation process (AOP)

Studies on the degradation of organic pollutants (phenolic, tannins etc.,) present in the wastewater released from tannery industry have been carried out in this work. The combined effect of cavitation and magnetic stirring with the advanced oxidation processes (AOPs) has been compared. The different parameters that affect the chemical oxidation process of the tannery wastewater, like pH, ultrasound irradiation time and dosage of hydrogen peroxide (H₂O₂) were studied. The samples were treated by two different approaches by varying these parameters. In the first approach, wastewater was treated in the presence of cavitation using ultrasound probe sonicator and in the second approach in the presence of magnetic stirring using magnetic stirrer was used. In both the cases, the suspended total organic carbon (TOC) was measured before and after varying the parameters to ensure the destruction of organic pollutants present in the wastewater sample. The optimum conditions obtained with ultrasonic cavitation was further used in hydrodynamic cavitation set-up in order to increase the efficiency. The experimental results show that the combination of cavitation and H₂O₂gives a higher reduction in suspended TOC values of tannery wastewater than with addition of only hydrogen peroxide (H₂O₂).

Utilization of Waste Leather Powders for Highly Effective Removal of Dyes from Water

As a natural polymer, leather and its associated industries are known to be the leading economic sector in many countries. However, the huge amounts of leather waste generated from the leather industry causes severe environmental pollution. Herein, cow leather (CL) powders were prepared using a homemade machine and used as a low-cost adsorbent for the effective removal of reactive dyes from wastewater. The as-prepared CL powders exhibited dot-like, rod-like, and fiber-like morphologies. A Fourier transform infrared analysis and an x-ray diffraction analysis demonstrated that the CL powders retained the main structure of the protein contained in it. In addition, an improvement in thermal stability was also observed for the CL powders. Dye adsorption experiments indicate that the CL powders showed the highly effective removal of C.I. Reactive Red 120 (RR120), C.I. Reactive Yellow 127 (RY127), and C.I. Reactive Blue 222 (RB222) with the adsorption capacity of 167.0, 178.9, and 129.6 mg·g⁻¹, respectively. The Langmuir, pseudo-second order, and intraparticle diffusion models could well depict the adsorption equilibrium and kinetics of CL powders toward the investigated reactive dyes. The as-prepared CL powders can be used as a potential adsorbent in the treatment of dye contaminated wastewater. Future studies will mainly focus on the application of the adsorbed CL powders for the pigment printing of textile materials.

Heavy metal toxicity from the leather industry in Bangladesh: a case study of human exposure in Dhaka industrial area

Activities in the Bangladeshi leather industries have the potential to cause chemical pollutions thereby deteriorating the working environments, the surrounding residential areas, or even foodstuffs. Therefore, it is important to determine the chemical exposures among the industry workers and residents of the surrounding areas who may be directly or indirectly impacted by the contaminated environment. This study focused on evaluating the hazard arising from exposure to metals due to industrial contamination. Tissue samples of hair and nails were collected from both the leather industry workers and residents in the vicinity of the industries. Using chromium as an indicator of contamination/exposure from the leather industry, it was the most significant metal contaminant for industry workers ranging from 21.85 to 483 mg/kg and for industry-neighboring residents at 6.01 to 296.16 mg/kg. Both the workers and neighboring residents were found to be excessively exposed (P < 0.05) to chromium compared with the investigated control group of people living in a distant village area which had no industrial establishments.

Stabilization and cyclic utilization of chrome leather shavings

For the sake of the safe and efficient cyclic utilization of chrome leather shavings (CLS), the temporary stabilization of CLS during the storage and transport processes was optimized. Afterwards, the large-scale stabilized CLS degradation and collagen degradation product (CDP) extraction were completed. In this research, hydroxyapatite (HAP) and calcium hydroxide (Ca(OH)₂) were for the first time used as stabilizers in the stabilization of CLS. The results showed that both Ca(OH)₂ and HAP displayed resistance to chrome leaching, but HAP provided better stabilization effect than Ca(OH)₂. The optimized stabilization conditions giving lower chromium leaching concentration were selected: 2% HAP, temperature 300 °C, reaction time 60 min, and initially added water contents of 50%. The reason for HAP and Ca(OH)₂ stabilization was proved by energy dispersive X-ray spectroscopy (EDS). Subsequently, the exploitation value of the stabilized CLS was described by large-scale experiment. The hydrolysis of stabilized CLS could obtain the collagen degradation product (CDP), which had 3.52% of free amino content and a molecular weight of 3.4~30 kDa. The filter residue was treated by 5% sulfuric acid solution extraction and pressure filtration again. The extraction solution and final filter residue were dried separately to obtain chromium-containing organic compounds (COP) and industrial gypsum. The COP, used as a filling for tannery, contains 9.37% Cr₂O₃ content and 90.6% organic content. The industrial gypsum contains 68.37% CaSO₄, 0.13% Cr₂O₃, and 31.5% residual organic or inorganic compounds, which can be used in building materials. No waste water or solid waste was discharged in this experiment process.

Occupational exposure and consequent health impairments due to potential incidental nanoparticles in leather tanneries: An evidential appraisal of south Asian developing countries

The incidental nanoparticles' (INPs) emission at work and the consequent health impairments is a burning issue of occupational toxicology. The present study is a thorough review of available literature marking an assortment of indicators on INPs generation at leather tanneries and measurable occupational ailments. The literature reported evidences unleash a similarity between the mechanisms of leather tannery induced health damages and toxico-kinetics of incidental nanoparticles in human body. The data on physico-chemical characterization of leather tannery surface dust presents presence of stressors like heavy metals, microbes, animal fur and fibers along with organic and inorganic chemicals. Bearing same characteristics, the mechanism of INPs' induced toxicity (inflammation, increased reactive oxygen species and permeability of blood brain barrier), major target organs (lung, heart, brain, skin and liver) and health damages (cancer, DNA damage, blood coagulation, cardiac arrest, platelet alteration) are quite similar to those found among tannery workers. This review also presents the identification of the different types of potential INPs production and process sources in leather tanneries. There is no data found on Particulate size variation and consequent disparity of these characterizations has been established. However, the reported literature furnishes evidences which support the premise that there is a dire need of size based incidental particulates investigation with a special emphasis on nanoparticles.

Sustainability strategies in the Indian leather industry: an empirical analysis

Purpose

Burgeoning challenges of climate change and poverty alleviation across many parts of the world have enforced the policy makers and researchers to develop an alternate system for performance assessment of an individual, a country, and a corporate. The purpose of this paper is to analyze the sustainability strategies of three leading states in the Indian leather industry – Tamil Nadu (TN), West Bengal (WB) and Uttar Pradesh (UP) – to gain insights into their efforts and progress in generating economic, social, and environmental values.

Design/methodology/approach

This study used case study approach for investigative analysis, and triangulation method – interviews and field visits, for data verification. The study examines the various sustainability strategies by applying economic value creation (evaluation of growth in total turnover, evaluation of the growth in profitability, evaluation of leverage), social value creation (evaluation of the growth in wages, evaluation of the growth in employee welfare expenses), and environmental value creation (conservation in raw material consumption, conservation in energy consumption, evaluation of waste management practices).

Findings

The findings reveal that the three states differ significantly from each other both in terms of efforts made and progress achieved during the period of study, 1998-2013. UP seems to be making the most consistent progress in achieving economic value, while WB shows the most progress in creating social value, and TN leads the pack in terms of creating environmental value. Thus, the three leading states in the Indian leather industry have been allowing trade-offs to get competitive advantage over others.

Research limitations/implications

The opaqueness with which the Indian leather Industry conducts social and environmental practices clearly limits the sources of accurate and reliable data, and the ability of researchers to precisely identify the problems and suggest solutions.

Practical implications

The opaqueness with which the Indian leather Industry conducts social and environmental practices clearly impacts the policy makers, practitioners, and researchers to continue such initiatives and improve the lives of people in India for whom continuing this profession is a big challenge and a hurdle to accomplish their livelihood.

Originality/value

The paper gives a theoretical explanation of the sustainability in the leather industry with respect to its strategies in terms of economic value, social value, and environmental value.

Total control of chromium in tanneries - thermal decomposition of filtration cake from enzymatic hydrolysis of chrome shavings

This paper deals with the problem of chromium recovery from chrome-tanned waste and thus with reducing the environmental impact of the leather industry. Chrome-tanned waste was transformed by alkaline enzymatic hydrolysis promoted by magnesium oxide into practically chromium-free, commercially applicable collagen hydrolysate and filtration cake containing a high portion of chromium. The crude and magnesium-deprived chromium cakes were subjected to a process of thermal decomposition at 650°C under oxygen-free conditions to reduce the amount of this waste and to study the effect of magnesium removal on the resulting products. Oxygen-free conditions were applied in order to prevent the oxidation of trivalent chromium into the hazardous hexavalent form. Thermal decomposition products from both crude and magnesium-deprived chrome cakes were characterized by high chromium content over 50%, which occurred as eskolaite (Cr₂O₃) and magnesiochromite (MgCr₂O₄) crystal phases, respectively. Thermal decomposition decreased the amount of chrome cake dry feed by 90%. Based on the performed experiments, a scheme for the total control of chromium in the leather industry was designed.

A low-cost and water resistant biomass adhesive derived from the hydrolysate of leather waste

A low-cost and water resistant biomass adhesive was prepared by using collagen hydrolysate extracted from leather wastes as the starting material and silane coupling agent as the crosslinking agent.

B. amyloliquefaciens TCCC 11319, a new Cr(iii)-tolerant bacterium for chromium-tanned leather shaving disposal

A strain of B. amyloliquefaciens, TCCC11319, was isolated from tannery soil and identified by 16S rRNA gene sequencing.

The status and developments of leather solid waste treatment: A mini-review

Leather making is one of the most widespread industries in the world. The production of leather goods generates different types of solid wastes and wastewater. These wastes will pollute the environment and threat the health of human beings if they are not well treated. Consequently, the treatment of pollution caused by the wastes from leather tanning is really important. In comparison with the disposal of leather wastewater, the treatment of leather solid wastes is more intractable. Hence, the treatment of leather solid wastes needs more innovations. To keep up with the rapid development of the modern leather industry, various innovative techniques have been newly developed. In this mini-review article, the major achievements in the treatment of leather solid wastes are highlighted. Emphasis will be placed on the treatment of chromium-tanned solid wastes; some new approaches are also discussed. We hope that this mini-review can provide some valuable information to promote the broad understanding and effective treatment of leather solid wastes in the leather industry.

Kinetic model of the thermal pyrolysis of chrome tanned leather treated with NaOH under different conditions using thermogravimetric analysis

The thermal decomposition of chrome tanned leather before and after a soaking treatment with NaOH was studied using thermogravimetric analysis (TGA). The effect of the solution concentration (0.2M and 0.5M) and the soaking time (5min and 15min) was evaluated. TGA experiments at four heating rates (5, 10, 15 and 20°Cmin(-1)) were run in a nitrogen atmosphere for every treatment condition. A kinetic model was developed considering the effect of the three variables studied, i.e.: the NaOH solution concentration, the soaking time and the heating rate. The proposed model for chrome tanned leather pyrolysis involves a set of four reactions, i.e.: three independent nth order reactions, yielding the corresponding products and one of them undergoing a successive cero order reaction. The model was successfully applied simultaneously to all the experimental data obtained. The evaluation of the kinetic parameters obtained (activation energy, pre-exponential factor and reaction order) allowed a better understanding of the effect of the alkali treatment on these wastes.

A review on management of chrome-tanned leather shavings: a holistic paradigm to combat the environmental issues

Raw hide/skins come to the tanners as a by-product of meat industry which is converted into value-added leather as product for fashion market. Leather manufacturing is a chemical process of natural biological matrix. It employs a huge quantity of water and inorganic and organic chemicals for processing and thereby discharges solid and liquid wastes into the environment. One of the potential solid wastes generated from leather industry is chrome-tanned leather shavings (CTLSs), and its disposal is increasingly becoming a huge challenge on disposal to tanners due to presence of heavy metal chromium. Hence, finding a sustainable solution to the CTLS disposal problem is a prime challenge for global tanners and researchers. This paper aims to the deeper review of various disposal methods on CTLS such as protein, chromium, and energy recovery processes and its utilization methodologies. Sustainable technologies have been developed to overcome CTLS solid wastes emanating from leather processing operations. Further, this review paper brings a broader classification of developed methodologies for treatment of CTLSs.

Impact of aerobic stabilization on the characteristics of treatment sludge in the leather tanning industry

The efficiency of aerobic stabilization on the treatment sludge generated from the leather industry was investigated to meet the expected characteristics and conditions of sludge prior to landfill. The sludge types subjected to aerobic stabilization were chemical treatment sludge, biological excess sludge, and the mixture of both chemical and biological sludges. At the end of 23 days of stabilization, suspended solids, volatile suspended solids and total organic carbon removal efficiencies were determined as 17%, 19% and 23% for biological sludge 31%, 35% and 54% for chemical sludge, and 32%, 34% and 63% for the mixture of both chemical and biological sludges, respectively. Model simulations of the respirometric oxygen uptake rate measurements showed that the ratio of active biomass remained the same at the end of the stabilization for all the sludge samples. Although mixing the chemical and biological sludges resulted in a relatively effective organic carbon and solids removal, the level of stabilization achieved remained clearly below the required level of organic carbon content for landfill. These findings indicate the potential risk of setting numerical restrictions without referring to proper scientific support.

Use of Ethylenediaminetetraacetic Acid as a Scavenger for Chromium from “Wet Blue” Leather Waste: Thermodynamic and Kinetics Parameters

One serious consequence of the current consumer society is the transformation of the environment into a waste receptacle arising from human activities. Because of the potential toxic effects of chromium solid waste containing this metal there are grounds for serious concern for the tanning and leather processing industry. The application of tannery waste as organic fertilizer has led to extensive contamination by chromium in agricultural areas and may cause the accumulation of this metal in soils and plants. This work evaluated the extraction of Cr+3and Cr+6contained in solid waste from the leather industry through density functional theory (DFT) calculations. The Gibbs free energy calculations reveal that the chelator ethylenediaminetetraacetic acid (EDTA) forms more stable complexes with metal ions of chromium compared with the structures of the complexes [Cr(NTA)(H2O)2] and [Cr-collagen], the latter used to simulate the protein bound chrome leather.

Chemical and microbial remediation of hexavalent chromium from contaminated soil and mining/metallurgical solid waste: a review

Chromium is a highly toxic non-essential metal for microorganisms and plants, and its occurrence is rare in nature. Lower to higher chromium containing effluents and solid wastes released by activities such as mining, metal plating, wood preservation, ink manufacture, dyes, pigments, glass and ceramics, tanning and textile industries, and corrosion inhibitors in cooling water, induce pollution and may cause major health hazards. Besides, natural processes (weathering and biochemical) also contribute to the mobility of chromium which enters in to the soil affecting the plant growth and metabolic functions of the living species. Generally, chemical processes are used for Cr- remediation. However, with the inference derived from the diverse Cr-resistance mechanism displayed by microorganisms and the plants including biosorption, diminished accumulation, precipitation, reduction of Cr(VI) to Cr(III), and chromate efflux, bioremediation is emerging as a potential tool to address the problem of Cr(VI) pollution. This review focuses on the chemistry of chromium, its use, and toxicity and mobility in soil, while assessing its concentration in effluents/wastes which becomes the source of pollution. In order to conserve the environment and resources, the chemical/biological remediation processes for Cr(VI) and their efficiency have been summarised in some detail. The interaction of chromium with various microbial/bacterial strains isolated and their reduction capacity towards Cr(VI) are also discussed.

Green chemistry approaches to leather tanning process for making chrome-free leather by unnatural amino acids

In the present study, green and sustainable method or eco-friendly approaches to tanning process based on unnatural D-amino acids (D-AA)-aldehyde (Ald) as a substitute for chrome-free tanning has been attempted. The distribution of optically active D-AA in tanned leather, the hydrothermal stability, the mechanical properties and resistance to collagenolytic activity of tanned leather, the evaluation of eco-friendly characteristics were investigated. Scanning electron microscopic (SEM) and Atomic force microscopic (AFM) analyses indicate the surface morphology and roughness, respectively, of the tanned leather collagen matrix. Shrinkage and Differential scanning calorimetric (DSC) analyses shows that the shrinkage temperature (T(s)) and denaturation temperature (T(d)) of tanned leather are related to the content of D-AA+Ald present in the leather matrix. It has been found that the T(s) of D-AA tanned leather is more than that of Ald tanned leather and also more or less equal to chrome tanned leather. Environmental impact assessment (EIA) shows that the developed process results in significant reduction in total solids content (TSC) and improves better biodegradability of organic compound present in the effluent compared to chrome tanning.