Search Results (119)

Microbial proteases are fundamental towards the eco-sustainability of proteolysis at the industrial scale. A proteolytic broth was obtained from a bioreactor fermentation of a proteolytic Bacillus strain isolated from an industrial alkaline bath. Broth proteolytic activity was applied to leather tanning and to the removal of protein stains. The hide tanned with the microbial proteolytic fermentation broth showed better physical properties than the one tanned with commercial pancreatic proteases of the same activity (780 LVU). Proteinaceous stains on cotton fabric were removed more efficiently using the Bacillus proteolytic broth than water or a commercial detergent. Blood and egg yolk disappeared in less than 30 min. The removal of soya and English sauce stains was even faster. Broth proteolytic activity was characterised by caseinolytic (5200 LVU), collagenolytic (10.0 U mg⁻¹), elastolytic (3.7 U mg⁻¹), and keratinolytic (0.7 U mg⁻¹) activities, which were compared with those of a commonly used commercial protease. Alkaline protease activity in the broth was demonstrated by a 20% increase in caseinolytic activity from pH 5 to 8. Besides the demonstrated applications in the leather and detergent industries, the produced alkaline microbial proteases can also be used in the treatment of proteinaceous wastes and effluents, offering potential environmental benefits reinforcing and impacting the bioeconomy. Full article

Collagenases can specifically degrade collagen, showing a wide application prospect in food, leather, waste utilization, biotechnology, and other industries. Currently, Hathewaya histolytica is commonly used in industry to produce collagenases, but its application is greatly limited by its pathogenicity. This study first identified five potential Pseudomonas-derived collagenases by sequence alignment. Bioinformatics tools were used to analyze their structures and functions. Heterologous expression of two P. chlororaphis-derived collagenases was achieved in E. coli, and their enzymatic properties were characterized. Bioinformatics analysis shows that the Pseudomonas-derived collagenases had low molecular weights (22.1~50.5 kDa) and good thermal stability (aliphatic index 73.73~88.81). Deletion of P. chlororaphis GP72ANO strain colP1 and colP2 genes had no significant effect on cell growth. The yields of collagenase ColP1 and ColP2 obtained from E. coli BL21(DE3) cultivation broth were 148 mg/L and 322 mg/L, respectively. The optimum temperature of each collagenase was 28 °C, and the soluble collagen activities of ColP1 and ColP2 were up to 42.64 U/mg and 21.21 U/mg, respectively. Collagenase ColP1 had the highest enzyme activity at pH 8, while collagenase ColP2 had the highest enzyme activity at pH 4. Metal ions such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Ni²⁺, and Mn²⁺ inhibited the activity of collagenases to different degrees. This study successfully achieved recombinant expression and preliminary purification of Pseudomonas-derived collagenases in E. coli and explored their function and physicochemical properties. Full article

The valorization of wet blue leather waste represents an important strategy for both environmental management and the development of sustainable adsorbent materials. In this study, activated carbons were produced from wet blue leather residue and characterized in terms of surface area and chromium content. Pyrolysis at 700 °C yielded activated carbons with surface areas exceeding 500 m²·g⁻¹, directly associated with the chromium content of the material. The results indicate that chromium embedded in the leather matrix acts as an effective chemical activator, enhancing the porous structure. Adsorption experiments demonstrated that both pH and methylene blue concentration positively influenced adsorption capacity, whereas temperature exhibited a negative effect. The maximum adsorption capacity reached 20.2 mg g⁻¹. These results show the potential of wet blue leather waste-derived activated carbon as a low-cost and efficient adsorbent for dye removal from aqueous systems. Full article

A comparative study on the adsorption of ciprofloxacin (CIP) and sulfamethoxazole (SMX) onto CO₂-activated biochars derived from leather tannery waste (ABT) and Sargassum brown macroalgae (ABS) is presented. N₂ physisorption revealed that ABS possesses a higher Langmuir surface area (1305 m²/g) and a hierarchical micro–mesoporous structure, whereas ABT exhibits a lower surface area (412 m²/g) and a predominantly microporous texture. CHNS and FTIR analyses confirmed the presence of N-, O-, and S-containing heteroatoms and functional groups on both adsorbents, enhancing surface reactivity. Adsorption isotherms fitted well to the Langmuir model, with ABS showing superior maximum capacities of 256.41 mg/g (CIP) and 256.46 mg/g (SMX) compared to ABT (210.13 and 213.00 mg/g, respectively). Kinetic data followed a pseudo-second-order model (R² > 0.998), with ABS exhibiting faster uptake due to its mesoporosity. Over eight reuse cycles, ABS retained >75% removal efficiency for both antibiotics, while ABT declined to 60–70%. pH-dependent adsorption behavior was governed by the point of zero charge (pH_PZC≈ 9.0 for ABT; ≈7.2 for ABS), influencing electrostatic and non-electrostatic interactions. These findings demonstrate that ABS is a highly effective, sustainable adsorbent for antibiotic removal in water treatment applications. Full article

Inefficient chromium (III)–collagen cross-linking during leather tanning generates solid waste and effluents containing residual chromium, raising environmental and health concerns. Biological strategies are increasingly popular for tannery waste treatment, but the microbial communities involved in leather degradation remain poorly understood. This study did not seek to evaluate leather disintegration according to standardised compostability criteria, but to establish a thermophilic composting system suitable for characterising leather-associated microbial communities, biofilm formation on leather and isolating cultivable strains. Composting assays were carried out at two scales, in which wet blue leather was mixed with organic compost under self-heating thermophilic conditions. Temperature was monitored, and mass loss and changes in leather structure were determined by gravimetry and scanning electron microscopy. Bacterial and fungal communities in compost with and without leather were analysed using high-throughput amplicon sequencing. Thermophilic consortia dominated by Firmicutes, Actinobacteria and Ascomycota were established, and several bacterial isolates and a filamentous fungus were recovered. Together, these results provide a first basis for understanding the communities and strains associated with chromium-tanned leather during thermophilic composting, supporting future searches for microorganisms and enzymes of interest for biological strategies to manage chromium-tanned leather waste. Full article

The possibility of anaerobic digestion of leather shavings regardless of tanning agent (chrome, vegetable, synthetic) were was investigated. The fermentation batch test (38 °C) was conducted in 2 L reactors according to modified German norm DIN 38314 S8 and standardized biogas guidance issued by the Association of German Engineers in Dresden, VDI 4630. Chemical pretreatment, using organic compounds for solubilization and organic salts for chrome leaching, was applied. Evaluation encompassed the dynamics of the process, final biogas/methane efficiency, as well as the influence of tanning agent type and pretreatment on fermentation. Results showed varying effects of pretreatment methods on methane production and biogas yields. Depending on the tanning of the agent, biogas yield increased by 37–3002%, 590–3198%, and 403–694%, for chrome, synthetic, and olive-tanned shavings, respectively, compared to the control sample (raw substrate). Findings underscore the need for further mechanistic understanding and optimization of pretreatment methods to maximize biogas production from leather wastes. Full article

The leather industry generates large amounts of solid waste, creating environmental concerns for the presence of hazardous compounds such as chromium. In fact, conventional disposal practices, including landfill and incineration, promote the formation of hexavalent chromium (Cr⁶⁺) and polluting emissions. This work reviews biochemical and thermochemical processes for the energetic valorization of different leather solid wastes, namely untanned, tanned with chromium or vegetable tanning agents, and post-consumer leather. Thermochemical routes, i.e., pyrolysis, gasification, and hydrothermal treatment (HT), can convert leather waste into energy carriers including bio-oil, syngas, and char, while anaerobic digestion (AD) is a biochemical method used to produce biogas. Particularly, pyrolysis is promising for fuel precursors and chromium stabilization, HT suits wet, raw waste, while gasification enables syngas recovery. In AD, microbial chromium inhibition is mitigated through the co-digestion of degradable substrates. This review takes a waste-type-driven rather than process-driven approach to provide new insights into the conversion of leather solid waste into value-added products, showing that the optimal recycling route depends on the waste characteristics. Moreover, these methods have not yet been directly compared in terms of their energy production performance with regard to leather waste. Future work should improve process conditions, evaluate chromium and finishing additive impacts, and assess scalability. Full article

With 23.4 billion pairs made and 22 billion discarded in 2023, post-consumer footwear waste is a major environmental challenge, demanding a shift toward circular economy practices. In this work, post-consumer footwear waste is repurposed into thermal/acoustic insulation materials for building construction, producing four needle-punched nonwovens (two of them compressed) composed of a post-consumer leather (30%) and footwear waste mixture (40%) with recycled polyester fibers. Nonwovens exhibited higher strain values (95.9 and 77.1% for leather residue and footwear mixture residue, respectively) but lower tensile strength (1694 and 104.9 kPa) and Young’s modulus (1767.8 and 136.10 kPa). The compressed nonwovens demonstrated higher tensile strength (7360 and 3559 kPa) and Young’s modulus values (12992 and 4020.4 kPa) and reduced strain (56.6 and 96.9%). The thermal conductivity results revealed that the nonwovens exhibited lower values (0.040 and 0.046 W/(m·K)), indicating better insulation performance when compared with their compressed counterparts (0.060 and 0.058 W/(m·K)). The nonwovens demonstrated high sound absorption at higher frequencies, reaching peak absorption coefficients of 0.917 and 0.995, ideal for acoustic insulation. The compressed nonwovens exhibited improved absorption at lower and mid-frequencies, with maximum values of 0.510 and 0.519. Given the current lack of applications for recycled materials derived from post-consumer footwear, the findings offer a novel approach to address their recycling. Full article

Keratinous biomass, such as feathers, wool, and hair, poses environmental challenges due to its insoluble and recalcitrant nature. In this study, we identified, purified and comprehensively characterized a previously uncharacterized extracellular alkaline keratinase, KerFJ, secreted by Bacillus sp. FJ-3-16, with broad industrial application potential. KerFJ was produced at high yield (1800 U/mL) in an optimized cost-effective medium and purified to homogeneity using ion-exchange chromatography. The enzyme exhibited optimal activity at pH 9.5 and 55 °C, with remarkable alkaline and thermal stability, and high tolerance to surfactants, oxidants, and metal ions. Sequence analysis revealed that KerFJ is a member of the serine peptidase S8 family, with a molecular weight of ~27.5 kDa. It efficiently degraded native keratin substrates, achieving 70.3 ± 2.1% feather, 39.7 ± 1.8% wool, and 15.4 ± 1.2% hair degradation, and the resulting feather hydrolysates exhibited strong antioxidant activities. KerFJ also demonstrated excellent compatibility with commercial detergents and enabled effective stain removal from fabrics without damage. Moreover, both laboratory- and pilot-scale trials showed that KerFJ facilitated non-destructive dehairing of sheep, donkey, and pig skins while preserving collagen integrity. These results highlight KerFJ as a robust and multifunctional biocatalyst suitable for keratin waste valorization, eco-friendly leather processing, and detergent formulations. Full article

Keratinous wastes, generated from various industries such as poultry processing, slaughterhouses, and salons, accumulate in the environment due to their slow degradation caused by high disulfide cysteine bonds. Traditional methods of managing these wastes, including incineration, composting, open-air burning, and landfilling, have several disadvantages, such as environmental pollution, release of toxic compounds, and breeding of pathogenic and multidrug-resistant microorganisms. Microbial keratinases, produced by bacteria, fungi, and actinomycetes, offer an eco-friendly alternative for valorizing keratinous waste into valuable peptides and amino acids. The biodegradation of keratinous biomass involves four sequential steps: adhesion, colonization, production of keratinolytic enzymes, and breakdown of the keratin substrate. Optimization of culture conditions, such as pH, temperature, substrate concentration, and metal ions, can enhance keratinase production for industrial applications. Keratinases have multifaceted applications in various sectors, including cosmetics, organic fertilizers, leather treatment, animal feed, detergents, and pharmaceuticals. This review highlights the need to explore keratinolytic strains further and improve keratinase yields to develop sustainable solutions for keratinous waste management and generate value-added products, promoting a circular economy. The techno-economic considerations and current limitations in industrial-scale keratinase production are also discussed, emphasizing the importance of future research in this field. Full article

Urban industrialization is a major driver of water pollution, particularly through emerging contaminants that pose significant health risks for humans and ecosystems. This critical review focuses on Bangladesh’s Buriganga and Dhaleshwari rivers, which pass through highly industrialized and urban areas, analyzing contaminant types, sources, pathways, and impacts. By synthesizing data from studies published between 2005 and 2024, the paper examines pollutants such as heavy metals (e.g., Cr, Cd, Pb, Ni, Zn, Hg, As, Mn, Cu, Fe) and microplastics in water, sediments, and biota. The Buriganga River shows extreme heavy metal contamination, with surface water Cr concentrations reaching up to 167,160 μg/L, Pb up to 3830 μg/L, and Fe up to 30,000 μg/L, and sediment Cr up to 4249 μg/g, Pb up to 3312 μg/g, and Fe up to 15,435 μg/g. In contrast, the Dhaleshwari River exhibits elevated but comparatively lower heavy metal concentrations in surface water (e.g., Cr up to 3350 μg/L; Cd up to 1890 μg/L; Pb up to 1320 μg/L; Ni up to 1732 μg/L; Fe up to 6040 μg/L) and sediments (Cr up to 282 μg/g; Fe up to 14,375 μg/g). Microplastic contamination in Buriganga is widespread across water, sediments, and biota and dominated by polymers such as polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET). Industrial discharges, particularly from the textile, leather, and metal processing industries, are identified as primary sources for heavy metals and microplastics. Additional inputs from domestic waste, agricultural runoff, and municipal sewage intensify pollution, with Cr, Cd, and Pb notably frequently exceeding safety thresholds. Microplastics, originating from municipal waste and atmospheric deposition, persist in these rivers, posing ecological and public health risks. The persistence and bioaccumulation of heavy metals and microplastics threaten aquatic biodiversity by disrupting food chains and pose significant risks to local communities that depend on these rivers for agriculture, fishing, and daily water use. This review highlights the urgent need for comprehensive bioaccumulation studies, long-term monitoring, and enhanced detection techniques to better assess contamination levels. Strengthening environmental regulations, improving waste management, and adopting sustainable industrial practices are critical to mitigating emerging contaminant impacts and safeguarding these vital river ecosystems and public health. Full article

Leather tanning generates substantial amounts of solid waste and effluents, posing significant environmental challenges due to the presence of hazardous chromium compounds. The aim of this study was to develop and optimize a method for recycling chromium-tanned leather waste by utilizing it as a raw material in the retanning process. Collagen hydrolysate was extracted from chrome-tanned leather shavings through acid hydrolysis and subsequently incorporated, together with melamine, into novel retanning compositions. The experimental design, based on the Kleeman method, involved varying the hydrolysate content (25%, 30%, 35%) and melamine concentration (2.5%, 3.0%, 3.5%, 4.0%) to assess their impact on the physicochemical properties of retanned wet-blue leathers. An innovative aspect of the study was the integration of the Kateskór computer program, employing the Kleeman experimental planning method, to optimize the formulation of retanning compositions. This computational approach enabled the precise determination of hydrolysate and melamine quantities required to achieve leather properties that meet both producer and consumer expectations. The optimized formulation identified the hydrolysate content in the range of 28.78–29.63% and melamine in the range of 3.61–3.68% as optimal for obtaining leathers with the desired mechanical strength, shrinkage temperature, and water vapor permeability. The study presents a practical model of a circular economy within the leather industry, aligning with the European Green Deal Strategy by promoting resource efficiency and minimizing hazardous waste. The proposed methodology provides a viable pathway for sustainable leather production through waste valorization and process optimization. Full article

The leather industry produces a substantial amount of solid waste, which is frequently disposed of via incineration or landfilling. While hydrolysis offers a valuable and sustainable method to chemically recycle leather waste, both acidic and alkaline processes present challenges due to the salts produced during neutralization. This study aims to upcycle leather scraps through hydrolysis, producing a powdered filler for versatile composites suitable for both LCD vat photopolymerization and Direct Ink Writing 3D printing technologies. A zero-waste hydrolysis process was adopted using sulfuric acid neutralized with calcium hydroxide, achieving a yield of 91.3%. The composites featured a matrix composed of polyethylene-glycol-diacrylate and glycerol dimethacrylate, with embedded leather hydrolysate powder at concentrations up to 20% w/w_matrix. Tensile tests conducted on neat resin and composites demonstrated the strengthening effect of leather hydrolysate filler. Additionally, rheological tests displayed a viscoelastic behavior suitable for the adopted 3D printing technologies. The composites were successfully 3D-printed using both Direct Ink Writing and vat photopolymerization techniques, showing promising printing accuracy. This work demonstrates the potential of valorizing leather waste, upcycled via a hydrolysis method, to produce composites suitable for additive manufacturing to advance the sustainability and the circularity of the fashion sector. Full article

The large amounts of chrome-tanned leather waste (CLTW) produced annually can be valorized by applying circular economy principles in various fields due to the valuable substances contained (mainly collagen). The main problem for the direct valorization of these wastes is the presence in their composition of dangerous substances, such as chromium. Thus, before being used as raw material in new processes, chrome-tanned leather waste must be subjected to a preliminary stage of chromium removal. In this article, we propose to identify the optimal working conditions for the extraction of chromium ions from chrome-tanned hides in the presence of oxalic acid with various concentrations, at various temperatures and contact times, so that the degree of collagen hydrolysis is minimal. In this sense, the response surface methodology (RSM) method was used to optimize the working conditions, to maximize the efficiency of chrome extraction from the leather, and to minimize the efficiency of collagen hydrolysis: An undesirable process. To optimize both the extraction yield (%) and the degree of hydrolysis (%), the key operational variables, namely oxalic acid concentration (%), contact time (%), and temperature (°C), were systematically adjusted using the Box–Behnken design within the response surface methodology (RSM). The most favorable extraction conditions were identified at an oxalic acid concentration of approximately 7%, a contact time close to 120 min, and a temperature near 49 °C. Under these optimized parameters, the hydrolysis degree remained very low, around 0.38%, indicating minimal degradation during the process. Full article

Leather biodegradation is a complex microbial process with increasing relevance for sustainable waste management. In this study, we investigated bacterial communities responsible for the degradation of leather treated with different tanning agents (chrome, Zeolite, Biole^®) using high-throughput 16S rRNA gene sequencing and metatranscriptomic analysis. Proteobacteria, Bacteroidetes, and Patescibacteria emerged as the dominant phyla, while genera such as Acinetobacter, Pseudomonas, and Sphingopyxis were identified as key contributors to enzymatic activity and potential metal resistance. A total of 1302 enzymes were expressed across all the conditions, including 46 proteases, with endopeptidase La, endopeptidase Clp, and methionyl aminopeptidase being the most abundant. Collagen samples exhibited the highest functional diversity and total enzyme expression, whereas chrome-treated samples showed elevated protease activity, indicating selective pressure from heavy metals. Differential enzyme expression patterns were linked to both the microbial identity and tanning chemistry, revealing genus- and treatment-specific enzymatic signatures. These findings deepen our understanding of how tanning agents modulate the microbial structure and function and identify proteases with potential applications in the bioremediation and eco-innovation of leather waste processing. Full article