In India, managing solid particle wastes has grown to be a significant environmental problem. The tanning business, which produces roughly 1,50,000 tonnes of offal annually in a form of raw hide (and skin) trimmings, limed animal fleshings, split hides, and chrome shavings, are one among the most polluting and growth-oriented enterprises[1][2][3]. Another form of the solid wastes produced during the pretanning processes of producing leather is animal fleshing (ANFL). It has the largest content of protein (50–60%) and collagen fiber content (3–5%), both of which are now wasted and contributing the problem to management of solid waste in tanneries[4][5]. An unavoidable waste product of the leather-making process, ANFL pollutes the environment. If this isn't handled in some way before disposal, it will pollute the land and smell bad[6].
For the purpose of producing methane gas through the biomethanation process, ANFL was anaerobically digested[7][8]. Although biomethanation is an excellent process for producing energy, it has its own ecological disadvantages due to inadequate biogas recovery, relatively high water consumption (1 tonne of solid waste dilution required1 m3 water), and high investment costs for the entire process[9][6]. The ANFL that was removed from the leather industry has been used to make glue, enzymes, and animal feed[10].
Fleshings mainly comprises 80–90 percent moisture along with the minimum amount of collagen, fats and lipids[11]. Food industries, slaughterhouses, edible oil processing industries, dairy products industries and olive oil plants generate lipid rich wastes[12]. Nonetheless, lipids are a desirable substrate for anaerobic digestion because they produce more methane than proteins or carbohydrates[13][14]. Lipids-rich waste can be viewed as one of the big potential renewable energy sources in this aspect. Lipids are initially degraded to free fatty acids and glycerolsor otherwise non-esterified fatty acids in an anaerobic environment. Extracellular lipases, which are extracted by acidogenic bacteria, catalyse this process[11][15]. The hydrolysis products are then converted further in the bacterial cells. Acidogenesis converts glycerol to acetate, while the β-oxidation pathway converts LCFAs to acetate (or propionate in the case of odd-carbon LCFAs) and hydrogen (syntrophic acetogenesis). The free fatty acids play a crucial role in lipid degradation inhibition[16][17].
Deliming is one among the efficient unit operations in leather industry, carried out to remove the lime from pelt. During this liming process, adding of alkali compounds like lime and sodium sulphides makes the fleshings more basic in nature[18]. Hence the usage of ammonium salts will neutralize the lime content in the tannery fleshings.
Anaerobic digestion is a process of diverse variety of symbiotic microbes convert organic materials into biogas, nutrients, and new cell matter under oxygen-free conditions, leaving salts as well as stubborn organic waste behind. Methane (60%) and carbon dioxide (40%) are the most common components of raw biogas, along with water vapour and a small amounts of hydrogen sulphide[19][16]. In this study the investigation of sample analysis techniques and equipments to study the changes of structure, chemical composition, thermal decomposition and the functional groups in the organic substance were estimated using the TGA, FTIR, SEM and the EDAX[20][21].
