Optimum energy integration of thermal hydrolysis through pinch analysis

• Thermal hydrolysis is the pretreatment of choice to anaerobic digestion.
• A strategy is developed to integrate it within the wastewater treatment plant.
• Select a second-generation thermal hydrolysis technology.
• Define the optimum combined heat and power scheme.
• Find sludge concentration for self-sufficiency and minimum polyelectrolyte use.

Anaerobic digestion, a well-established technology to generate biogas from sewage sludge, is constrained by the hydrolysis (or solubilization) stage. Several pretreatments attempt to overcome this limitation, with thermal hydrolysis emerging as the technology of choice due to its techno-economic advantages. The objective of this work is to optimize the integration of this energy intensive pretreatment within the wastewater treatment plant, ensuring that the digestion performance improves in an energy-efficient way. By applying pinch analysis, a methodology to optimize energy systems, a strategy is suggested that selects a second-generation thermal hydrolysis technology designed to recover all process vapors, defines the optimum combined heat and power scheme to ensure an efficient integration and determines the minimum sludge feed concentration to guarantee energy self-sufficiency, the recovery of all waste heat and the minimization of expensive polyelectrolyte use.