Pre-treatment of secondary sludge for enhanced biogas production: a process integration approach
Turning waste into energy is often presented as a key solution for sustainability. However, in wastewater treatment, managing sludge -the main by-product- remains energy-intensive, costly, and a significant source of emissions.
In his thesis, Sergio Rossano Becerril investigates how thermal hydrolysis pre-treatment (THP) can improve sludge-to-energy systems when evaluated from a whole-system perspective. THP uses heat and pressure to break down sludge before anaerobic digestion, increasing biodegradability. While it is typically studied in terms of biogas production alone, this work examines how its effects propagate across the entire treatment chain.
Experimental results showed that THP significantly alters sludge structure and flow behaviour, improving biodegradability and facilitating pumping, mixing, and dewatering. Rossano Becerril integrated these changes into mass and energy balances, life cycle assessment, and economic analysis to evaluate system-wide performance.
The findings reveal both benefits and trade-offs. THP increased net energy recovery by up to 43% and reduced operational energy requirements across multiple stages, contributing to lower operational costs and higher revenues from energy recovery. It also led to substantial improvements in several environmental impact categories, including fossil resource use, air pollution, and freshwater eutrophication. However, higher heat demand and methane losses limited climate benefits, showing that increased energy production does not necessarily lead to lower greenhouse gas emissions.
By linking experimental data with system-level modelling, this thesis clarifies the role of sludge-to-energy systems in the energy transition and identifies key levers, particularly methane emissions and heat integration, to inform design, operation, and policy decisions.