Exploiting Tannery Sludge as Renewable Resource for Biogas and Short-chain Fatty (SCFAs) Acids Production

The tannery industry is a very lucrative and widespread sector in Italy, and it is yet one of the most polluting, mainly due to the tannery sludge’s disposal in landfills, as it is considered a special residue by Italian legislation. An evaluation of the performance of the anaerobic fermentation process to obtain biogas and short-chain fatty acids (SCFAs) has been performed in this paper in different conditions concerning temperature, total solids content, and oxidizing and/or thermal pretreatments. The batch test trials revealed that the hydrogen peroxide pretreatment proved to be effective in increasing the biogas production, already at low doses but reaching the highest amount of 204 mL with the dose of 0.6 g H2O2/gTS. Regarding the SCFAs production, the combined microwave and hydrogen peroxide (MW-H2O2) pretreatment followed by thermophilic conditions gave the best results, with maximal SCFA concentration above 24 g CODSCFA/L. In the tests conducted without pretreatment, the mesophilic temperature seem preferable since the acidification performances were comparable to or even better than their thermophilic counterparts while being less energy intensive. The obtained results proved that tannery sludge can be employed in different ways and provide a viable alternative to landfilling, to handle this waste in a greener way, in a circular economy approach.