Abstract
The tanning industry generates effluents with a high contaminant load represented in a considerable amount of liquid, solid, and gaseous waste. Solid waste, such as residual hair, fat, and meat, are dumped directly in landfills, triggering serious environmental problems. The objective of this research was to compost this waste, previously desulfurized, in a mixture with remnants from pruning as a bulking agent. This low-cost strategy may reduce the total amount of waste. A composting pile was created using residual hair and pruning remnants in a proportion of 3:1 (w/w) and then an inoculum was added. The waste degrading process ran for 141 days, followed by a maturation period of 64 days. Throughout the process, the temperature, moisture, pH, and electrical conductivity (EC) were monitored. The highest temperature reached was 69.7°C, which secured good disinfection. The EC was 0.27 dS/cm, having lower values than Spanish regulations, possibly due to the salt removal over the irrigation periods. The organic matter content decreased continuously, to reach an endpoint of 42%; this result agrees with the high organic matter content of the tannery waste and the pruning remnants. Germination index was 43.55%, which indicates the presence of phytotoxic substances. As compared to the initial value (10.73%) there was partial degrading of these substances. The challenge is to improve this parameter by identifying new mixtures and adding efficient microorganisms that help to degrade phytotoxic substances.
Highlights
Modern society has to address a broad suite of sustainability challenges in urban[1] and rural areas[2,3]
The quantity and type of nutrients in this compost allowed the rapid growth of microorganisms, while recording thermophilic temperatures close to 70°C, which guaranteed an adequate hygiene of the product
Based on the contents of organic matter, in accordance with the Spanish Standard Royal Decree 506/201318, it was assessed that the obtained compost belonged to Group 6
Summary
Modern society has to address a broad suite of sustainability challenges in urban[1] and rural areas[2,3]. The tanning process converts the skins of bovine animals, sheep, and pigs into leather, ready to be used for various purposes. Tannery operations are divided into four processes: riverbank, tanning, post-tanning, and finishing. From an environmental standpoint (cleaner production), the first two processes are important for the volume and pollutant load of effluents, while the last two processes account for the amount of solid wastes and solvent emissions generated in different operations that yield finished leather[4]. Of the total weight of the skins entering the tannery, 60% is eliminated[5]. In Tungurahua province, Ecuador, it is estimated that out of the 920,000 cattle headcount, 500,000 skins are treated in tanneries yearly[6]
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