Utilization of by-products from the tequila industry. Part 5. Biodegradation of Fleshing materials from tanneries [Utilizaci�n de subproductos de la industria tequilera. Parte 5. Biodegradaci�n del material de descarne de la industria de curtidur�a]

Abstract

Tanneries have the non-enviable reputation of being one of the dirtiest and bad smelliest industries, and thus, the Official Mexican Norm (NOM-052-ECOL-1993) classifies tannery waste (No.RP4.2/ 01) as hazardous residues. By weight, tannery residuals come mainly from the preparation of the hide for hardening. This waste is mainly composed of hair and flesh material. Using two wooden cells, 2.5 m x 2.5 m x 1.5 m high, the discarded flesh material was subjected to a layered biodegradation process, placing a layer of agave bagasse, followed by one of "green compost" (pig intestins) and another one of discarded flesh material. This sequence was repeated until a height of 0.7 m was reached. One ton of tannery solid waste was used per cell. Temperature changes were daily monitored during the biodegradation process. Microbial and chemical analyses were performed on the compost, as well as germination studies, using root elongation and initial growth of Raphanus sativus seeds to evaluate the compost maturity index. After a 42 day curing period of the biodegradation product, there were neither germination nor radical growth problems (p > 0.05). Only the hypocotyl growth was lightly affected by the material of the pile 2. The biomass production (g of dry matter) was higher (p < 0.05) for the components of the piles 1 and 2 in comparison to the control treatment (116.5, 102.1 g vs. 88.1 g). At the end of 154 days of thermophilic degradation, the discarded flesh material was completely decomposed, obtaining a blackish product with a smell and texture similar to a gardening soil. It was determined that the total lost of dry matter was in average about 67.3 % for the two piles considering the initial and final weights of the ingredients. In both piles final product, no organisms such as Staphylococcus aureus, Salmonella sp. or fecal coliforms were detected, although the presence of Escherichia coli was found. The most probable number of fecal coliforms for piles 1 and 2 was 7 and 43 per gram of sample, respectively. From the present research work it could be concluded that the layers biodegradation process, may be come a technically and economically viable alternative for the tanneries in the management and final disposal of discarded flesh material and, at the same time, producing with this process a product with agronomic potential.