Anaerobic Co-digestion of Waste Activated Sludge with Municipal Solid Waste: Methane Production, Heavy Metal Decrease, Microbial Community, and Energy Production

This study investigates the potential of anaerobic digestion (AD) as an alternative method to improve the treatment performance of wastewater treatment plants (WWTPs) in the presence of inhibitors. This work will focus on studying the effect of the presence of certain heavy metals on the structure of microbial community and biogas production pathways during anaerobic digestion between different substrates. Waste activated sludge (WAS) from both urban and industrial WWTPs was mixed with municipal solid waste (MSW) to investigate the effect on heavy metal concentrations, microbial population balance, biogas production, and energetic benefits following the stabilization of the process. The results showed that better performance was achieved with anaerobic co-digestion (AcoD) experiments. The highest biogas rates of 0.81 L/d and 0.7 L/d were obtained with AcoD of industrial sludge (IS) and urban sludge (US) with MSW, respectively. Microbial analysis using fluorescence in situ hybridization (FISH) was conducted to quantify the major Bacteria and Archaea groups. The Archaea content reached 72% and 68% for AcoD mixtures of IS/MSW and US/MSW, respectively. Therefore, the best performance was obtained with the IS/MSW mixture, which produced a net energy production of 33.4 kJ/d. Heavy metals appeared to have a stimulating effect on AcoD between WAS and MSW by enhancing microbial activity due to a larger contact area and, thus, a higher adsorption rate.