Performance and energy aspects of single and two phase thermophilic anaerobic digestion of waste activated sludge. (February 2016) - Leite, Wanderli Rogério Moreira
Abstract: The study reported in this paper considered the results of pilot-scale experiments on single and 2-phase anaerobic digestion of waste activated sludge at high rate. Both single and 2-phase digesters were conducted at the same conditions of organic loading and retention time. The 2-phase anaerobic system showed clear increases in terms of organic matter removal and biogas production compared to the single stage system. Particularly, the volatile solids removal rose from 34% in the single stage system to 38% in the 2-phase system. Hence, the global specific biogas production increased 32%, moving from 0.21 to 0.31 m 3 /kgTVS·d respectively for the single and 2-phase systems. The 2-phase system produced 15% more energy than the single stage system. Furthermore, the heat produced in a CHP unit satisfied all heat requirements insuring more than the complete energetic sustainability of the process. Finally, both single and 2-phase digestates showed to meet requirements established for sludge reuse in agriculture regarding pathogens, metals and organic contaminants. A preliminary economic analysis showed the possibility to pay back the investment for the implementation of a second anaerobic reactor in 3 years because of both the increased biogas production and reduced quantity of excess sludge to be disposed of. Highlights: Single and 2-phase anaerobic digestion of waste activated sludge were performed. The 2-phase system showed higher organic matter removal and biogas production. The 2-phase system produced 15% more total energy than the single stage system. Heat requirements were satisfied insuring a complete energetic sustainability. Both single and 2-phase digestates met well EU requirements for agricultural use.