Preparation and application of unhairing enzyme using solid wastes from the leather industry-an attempt toward internalization of solid wastes within the leather industry

An efficient dehairing system supported by oxidative-enzymatic auxiliary towards sustainability

A method of dehairing of goat skins using oxidative chemicals and protease enzymes has been attempted. The dehairing process is one of the important and essential steps in leather making, where hair is removed by lime and sodium sulphide in the conventional process. This conventional dehairing system generates a higher amount of pollution problem as compared to the other unit operations and unit processes. In this work, dehairing of the goat skins through oxidative agents namely magnesium peroxide and protease enzyme has been attempted. For this, protease has been produced from Bacillus sp. at the laboratory level and the activity was found. The dehairing of goat skins takes place for the duration of 14-16 h. The leather produced with the experimental sample showed comparable organoleptic and strength properties with the conventional sample. This method paved the way for the reduction of pollution loads especially BOD, COD, and TDS to the level of 59, 27, and 77%, respectively, in comparison with the control sample. The reaction kinetics for the formation of the ligand-macromolecular complex is found in the isothermal titration calorimetry (ITC) experiment and a mathematical model has been formulated. The dyed crust leather showed comparable colour properties. In addition to that, there is a reduction in processing time for leather making through skipping reliming and deliming processes which are said to be another advantage of this method. The physical strength properties of the experimental leather were also comparable with conventionally produced leather.

Valorization of tannery solid wastes for sustainable enzyme induced carbonate precipitation process

Biocementation via enzyme induced carbonate precipitation (EICP) is an emerging ground improvement technique that utilizes urease for calcium carbonate precipitation. Usage of expensive laboratory grade chemicals in EICP hinders its implementation at field level applications. In this study, the feasibility of utilizing solid wastes generated from leather industry was investigated for EICP process. Initially, the proteinaceous fleshing waste was used as nitrogen source for production of an extracellular urease from Arthrobacter creatinolyticus MTCC 5604 followed by its subsequent use in EICP with suspended solids of tannery lime liquor, as alternative calcium source. The calcium ion solution was prepared by treating suspended solids of lime liquor with 1 N HCl. The EICP was optimum with 1000 U of urease, 1.0 M urea and 1.0 M CaCl₂.2H₂O for test tube experiments. Sand solidification experiments under optimal conditions with five times addition of cementation solution yielded a maximum unconfined compressive strength (UCS) of 810 kPa with laboratory grade CaCl₂.2H₂O and 780 kPa with calcium from lime liquor. The crystalline phases and morphology of the CaCO₃ precipitate were analyzed by XRD, FTIR and SEM-EDX. The results showed the formation of more stable calcite in EICP with calcium obtained from lime liquor, while calcite and vaterite polymorphs were obtained with CaCl₂.2H₂O. Utilization of fleshing waste and lime liquor in EICP could reduce the pollution load and sludge formation that are generated during the pre-tanning operations of leather manufacturing. The results indicated the viability of process to achieve cost effective and sustainable biocementation for large scale applications.

Unconventional microbial proteases as promising tools for the production of bioactive protein hydrolysates

Enzymatic hydrolysis is the most prominent strategy to release bioactive peptides from different food proteins and protein-rich by-products. Unconventional microbial proteases (UMPs) have gaining increased attention for such purposes, particularly from the 2010s. In this review, we present and discuss aspects related to UMPs production, and their use to obtain bioactive protein hydrolysates. Antioxidant and anti-hypertensive potentials, commonly evaluated through in vitro testing, are mainly reported. The in vivo bioactivities of protein hydrolysates and peptides produced through UMPs action are highlighted. In addition to bioactivities, enzymatic hydrolysis acts by modulating the functional properties of proteins for potential food uses. The compiled literature indicates that UMPs are promising biocatalysts to generate bioactive protein hydrolysates, adding up to commercially available enzymes. From the recent interest on this topic, continuous and in-depth research is needed to advance toward the applicability and commercial utility of both UMPs and obtained hydrolysates.

Current trends in solid tannery waste management

The tannery is one of the leading revenue-generating sectors in developing countries. The ever-increasing demand for leather products in the global market requires converting large amounts of rawhide/skins into resilient non-putrescible finished leather. Only 20% of the raw material is converted into a finished product; the rest 80% is discarded as solid and liquid wastes during leather processing. A heavy discharge of improperly treated solid tannery waste (STW) causes a severe impact on the surrounding environment by polluting soil, surface water, and groundwater resources, posing severe hazards to human and animal health. STW comprises proteinaceous untanned and tanned waste, which requires proper treatment for eco-friendly disposal. Several strategies have been developed over the years for the reduction and recycling of STW for producing renewable energy (biogas and biohydrogen), biofuels (biodiesel and briquettes), construction material, fertilizers, commercial products (adsorbents, animal feeds, proteins, fats, and enzymes), and biodegradable packaging and non-packaging materials. In this review, we discuss various strategies adopted for recycling, reutilization, and reduction of STW in an environment-friendly manner. Furthermore, an overview of the current perspectives toward achieving a zero-waste policy is also presented to reduce the environmental burden using green-clean technology to aid the survival of present-day tanneries.

Compact glyoxal tanning system: a chrome-free sustainable and green approach towards tanning-cum-upgradation of low-grade raw materials in leather processing

Increased concern over the use of metal salts such as chromium, zirconium, and aluminum for tanning of hides and skins has made the leather production industry to be constantly on the lookout for organic tanning agents in place of the inorganic system. Though glutaraldehyde has been looked at as a viable option, it still lags in imparting superior strength properties to the leather and also it has been reported to have inherent toxicity. With that concept in view, this research work focuses on the usage of glyoxal along with synthetic tanning agents as a replacement for glutaraldehyde and other inorganic tanning systems. The offer level and starting pH for the glyoxal tanning process was optimized as 6% (w/w) and 5.0, respectively, and the shrinkage temperature of the collagen was found to be around 80 °C. Additionally, the controlled shrunken grain effect of the aldehyde tanning system was explored by changing the pH of the process, which helped to improve the thickness of low-grade thinner raw materials by up to 40%. The mechanism for the shrunken grain effect has also been proposed in this work by studying the dimensional changes occurring in the leather matrix upon treating skin/hide with glyoxal at different pH levels. The mechanical and strength properties of the leather were found to be better than the glutaraldehyde tanning system. The BOD/COD ratio of wastewater generated from the glyoxal process was found to be greater than 0.3 making them easily treatable. Considering all these factors, compact glyoxal-based tanning along with synthetic tanning agents can be a game-changing technology for the leather processing industry.

Unhairing of bovine hide using wastewater from Merox unit of oil refinery: techno-environmental aspect

The effluent generated by Merox unit of oil refinery was used instead of freshwater for bovine hide unhairing because of its proper composition and alkalinity. The effect of temperature, treatment period, sodium sulfide (Na₂S), and calcium carbonate (CaCO₃) dosage was investigated on unhairing efficiency using lutrom (unhairing slurry) prepared from the Merox effluent (effluent-based lutrom). Under similar operating conditions and chemicals' dosage, the effluent-based lutrom resulted in a higher efficiency (98.6%) than water-based lutrom (67.3%) indicating faster unhairing kinetics for the former lutrom. Moreover, an acceptable swelling (48%) and suitable mechanical properties were also observed. The experimental strategy can save 50 to 67% toxic chemicals and 100% of water consumption in unhairing, which is equivalent to US$ 34 per ton of hide, leading to zero discharge from Merox unit. Recycling of effluent-based lutrom after 3 consecutive runs was associated with a significant reduction in COD (55.6 kg/t hide) and BOD₅ (11.6 kg/t hide) load. The effluent-based and conventional lutroms, before and after unhairing, were treated with ozone under moderate conditions. The FTIR results indicated a high-quality and low costly pelt benefits from the integration of wastewater treatment units of both industries in an environment-friendly manner.

Multilayer Structure Ammoniated Collagen Fibers for Fast Adsorption of Anionic Dyes

Dye wastewater has become one of the difficult industrial wastewaters due to its significant characteristics such as high chroma and poor biodegradability. Here, we use collagen fibers (CFs) as the matrix, glutaraldehyde as the cross-linking agent, and polyethyleneimine (PEI) as the ammoniating modifier to prepare cationic-modified collagen fibers (CF-PEI). The CF-PEI still maintained the original fibrous structure with a larger adsorption area. The content of primary amino groups on CF-PEI was significantly increased, which not only improved the hydrophilic swelling performance of CFs but also improved the adsorption capacity. The adsorption capacity of CF-PEI for soap yellow and acid red could reach 538.2 and 369.7 mg g-1, respectively. The adsorption rate was fast, and the adsorption equilibrium could be reached in about 60 min. Desorption regeneration studies have shown that 0.1 mol L-1 HCl could achieve a better desorption effect, and the CF-PEI had a good recycling performance. The ammoniated modified CF-PEI was an excellent adsorption treatment material for anionic dye wastewater. It is expected to become an effective way for high-value resource utilization of waste dander in the leather industry.

Investigation on pyrolysis and incineration of chrome-tanned solid waste from tanneries for effective treatment and disposal: an experimental study

Chrome-tanned leather solid wastes (leather finished trimmings (LFT) and chrome shavings (CS)) from tanneries were studied using pyrolysis and incineration. Detailed characterization of CS and LFT indicated higher calorific value of 15.77 MJ/kg and 19.97 MJ/kg respectively, which makes it suitable for thermal treatment. Thermal Gravimetric Analysis (TGA) of CS and LFT recorded a weight loss of 79.82% and 68.22% at 800 °C respectively. Energy-dispersive X-ray spectroscopy and scanning electron microscopy analysis for CS and LFT were also carried out. Pyrolysis of CS and LFT was carried out using a fixed bed-type pyrolysis unit at a temperature of 500 ± 10 °C for a reaction time of 30 min and three different by-products (bio-oil, biochar and pyrolytic gas) were obtained as a result of pyrolysis. From pyrolysis process, higher bio-oil yields of 52 wt.% and 49 wt.% from LFT and CS with calorific value of 28.0 and 27.8 MJ/kg respectively were obtained. The calorific values of the biochar obtained from LFT and CS were found to be 20.5 and 23.0 MJ/kg respectively. Incineration was carried out in the existing incineration facility of 150 kg/h capacity at a temperature of 1200 °C. The results of incineration process showed a higher weight reduction (93.0 wt.%) and higher concentration of gaseous emissions, revealing the need for off-gas treatment. Further, FT-IR spectra of residual ash from the incineration process revealed the occurrence of oxidation of trivalent chromium to its hexavalent form, which could be a potential raw material in the metallurgical/chemical industry for the synthesis of sodium chromate or ferrochrome alloy. Comparative experimental investigations of pyrolysis and incineration revealed that incineration could be a potential treatment and disposal option, in developing countries like India, for chrome-tanned leather solid wastes from tanneries, for producing heat energy and the residue with potential utilization viability in another industry paving a way towards circular economy.

A biological clean processing approach for the valorization of speckled shrimp Metapenaeus monoceros by-product as a source of bioactive compounds

The efficiency of the proteolytic strain Anoxybacillus kamchatkensis M1V in the fermentation of speckled shrimp by-product was investigated for the recovery of a deproteinized bioactive hydrolysate. The biological activities of the resulting hydrolysate were also examined by applying several antioxidant and enzyme inhibitory assays. The strain M1V was found to produce high level of protease activity (2000 U/mL) when grown in media containing only shrimp powder at 25 g/L. The crude protease displayed a significant deproteinization capabiliy, with the best efficiency (48%) being recorded for an enzyme to substrate (E/S) ratio of 30 U/mg. Following the deproteinization, chitin was recovered and the authenticity was confirmed by Fourier-transform infrared spectroscopy (FTIR) analysis. On the other hand, the obtained hydrolysate showed a significant enzymatic inhibitory potential against acetylcholinesterase, tyrosinase, amylase, and angiotensin I convertase, and a strong antioxidant activity. Graphical Abstract.