Characterization, biomethane potential, and optimization strategies of polymer industry sludge

This study explores the feasibility of anaerobic digestion (AD) as a method for valorizing sludge from a polymer industry. This polymer industry sludge, which is mainly composed of polyvinyl acetate (PVAc), is currently landfilled, raising significant economic and environmental concerns. This research looks at the potential of AD to solve these problems and provide practical recommendations. Sludge sampling, characterization, biomethane potential (BMP) tests, and different pretreatment strategies, such as solid-liquid separation, thermal, ultrasonic, acid, and alkaline hydrolysis with sodium hydroxide (NaOH) and a mixture of NaOH and methanol (MeOH+NaOH), were performed. Among these pre-treatments, alkaline hydrolysis using NaOH provided significantly higher BMP values, i.e., an average of about 163 ± 26 mL CH 4 /g VS (with MeOH at 50 ∞C) or 151 ± 61 mL (without MeOH at 70 ∞C) as compared to 21 ± 54 mL CH 4 /g VS for raw sludge. Moreover, the BMP value of the solid fraction following centrifugation reached similar high values, i.e. 144 ± 24 mL CH 4 /g VS, confirming the presence of inhibiting compounds in the liquid fraction. The thermal, ultrasonic, and acid pretreatments were found to be ineffective, as their BMP values were lower than those of the raw sludge. As a recommendation, semi-continuous AD tests are required to evaluate methane production over time, considering the variable nature of industrial sludge, as well as to evaluate the digestate characteristics.