Enhancement of anaerobic digestion of waste materials generated by a cosmetics industry by means of physic-chemical pretreatments

Anaerobic digestion (AD) implemented in an industrial context may be a key opportunity for a firm to fulfill the zero-waste concept and to enhance the sustainability of the overall productive process. This research is aimed at the investigation of the technical feasibility of AD of different wastes coming out from a plant of L’Oréal Group located in Turin area. The four wastes considered in this research (sludge from the wastewater treatment plant - WWTP, residues of shampoo and conditioner, sludge from mascara production and food waste from the canteen) were equal to about 300 t/y in 2015, with a 44% wt destined to incineration. AD tests were performed at a laboratory scale in 0.5 L batch reactors at 35°C fed with 5% wt TS on unaltered single wastes and on a mixture of them. Methanation grade value was equal to 0.11 for shampoo/conditioner residues and 0.09 for mascara sludge, witnessing a scarce biodegradability of the substrates and the consequent need for pre-treatments. WWTP sludge showed a peculiar behaviour that needs further analyses. Several options were investigated, considering alkali (0.8% wt NaOH) and acid (0.5% wt HCl), thermal at low (50- 90°C) and high (120°C) temperature, sonication and hybrid pre-treatments. Their performances were evaluated in terms of disintegration rate (DR). The most promising were for all wastes the hybrid treatments (in particular thermo-alkaline, thermo-acid and thermoalkali- sonication), with DR over 74% for shampoo/conditioner residues, at least of 50% for sludge from WWTP, around 22% for mascara sludge and over 64% for the mixture of the 4 wastes.