– Anaerobic Digestion at 20°C with Ozonation to Minimize Waste Biosolids and Maximize Energy Recovery from Wastewater
Biosolids disposal from wastewater treatment can account for 50% of operation budget. Anaerobic digestion of waste activated sludge (WAS) can reduce production and recover energy. However, slow hydrolysis imposes the operation of digesters at or above 35 °C to maintain residence times around 20 days, which implies significant energy expenditures. Here, we demonstrate at lab-scale (1 to 4 L) and pilot-scale (300 L) that ozonation of WAS enhances its conversion to methane at 35 °C. Furthermore, lab-scale experiments revealed the possibility to operate digesters at 20 °C while keeping a 20-day SRT and achieving higher volatile suspended solids (VSS) destruction and CH4 production than for a conventional 35°C digesters. Therefore, combining WAS ozonation/20 °C-anaerobic digestion system can improve the net energy recovery over a conventional system. Process scale-up and complete elimination of heating are the new R&D goals to improve the sustainability of biosolids management.