Abstract
This chapter describes how environmental pollution is the major problem associated with rapid industrialization, due to which the quantity of solid waste generated from the industries is increasing substantially. Solid wastes generated in leather industries are briefly classified into pre-tanned and post-tanned wastes. Although landfills, composting, anaerobic digestion and thermal incineration are available for disposal of these solid wastes, they do again pose severe environmental and financial burdens to the tanners. Microbe-mediated tannery solid waste management points to the recovery of value-added products from these wastes. Microbial valorization of tannery solid wastes for the production of saleable products would be a convincing, challenging and eco-friendly opening for its utilization when compared to that of chemical and thermal hydrolysis. Exploitation of traditional chemicals could be reduced and innovative products could be recovered, enabling sustainable solid waste management. This would ultimately alleviate the solid waste disposal problems and financial crisis faced by the tanners.
TopBackground
Leather industries aim at the transformation of putrescible (liable to decompose) animal raw hides and skins into a stable non-putrescible material (leather), ultimately resulting in the generation of solid as well as liquid wastes. An average of 250 kg non-tanned waste and 50,000 kg waste water is produced during one metric ton of raw hide processing (Sundar et al., 2011). Tanneries in India alone produce 150,000 tonnes of unutilized solid wastes out of the whole tanning process, which result in severe environmental threat (Rai et al., 2010). Many biological methods have been implemented to reduce environmental pollution emerging through tannery effluents (Bhaskar et al., 2007). Although numerous cleaner technologies and effluent treatment plants support in the alleviation of liquid waste generation, there remains inadequacy in the healthy disposal of solid waste among the tanners. One of the major issues faced by the leather industry lies at the improper disposal of solid waste generated during leather processing, with maximum waste emerging at the pre-tanning operations. From 1000 kg of raw hide, nearly 850 kg of solid wastes are generated which infers that only 150 kg of raw material is converted into finished leather. Tannery solid wastes consist of: fleshing waste (56-60%); skin trimmings (5-7%); chrome shaving, splits and buffing dust (35-40%) and hair (2-5%) that are generated predominantly during beam house operations (80%) followed by tanning (19%) and finishing (1%) processes (Kanagaraj et al., 2006). Briefly, tannery solid waste could be classified into tanned and untanned collagenous wastes (Figure 1).
Figure 1. Solid waste generation from leather industries
Untanned wastes consist of raw hide trimmings, green fleshings, limed fleshings, limed trimmings and hair waste.
Key Terms in this Chapter
Probiotics: Microorganisms generally considered as safe that exert beneficial effects in the host system when consumed either in viable or attenuated form.
Valorization: Transformation of any unutilized substance into a value added saleable substance.
Fleshings: Undesirable cutaneous and sub-cutaneous layers of muscles scrapped out from the animal hides during beam house operation using fleshing machine.
Lactic Acid Fermentation: Process of conversion of available substrate sugars into lactic acid by lactic acid producing bacteria through oxidation.
Proteinaceous: A substance which is highly enriched with single or a group of proteins.
Deliming: Process of removing calcium hydroxide and sodium sulfide from hides with the help of commercial ammonium salts, weak acid or alkali solutions.
Tanning: Process of conversion of animal raw hides into wet-blue uniform leather pieces using vegetable oil or chromium.
Proteases: A group of enzymes that degrade (hydrolyze) complex proteins into simpler peptide units.
Putrefaction: Stage of decomposition of any organic material due to the action of microorganisms with emission of notorious smell.
Dehairing: Process of removing hairs from raw hides and skins by lime treatment and mechanical agitation followed by gentle scrapping manually.