Flexible Electricity Generation from Anaerobic Digestion of Sewage Sludge

The UK is a global leader in the decarbonisation of its electricity grid. However, the main renewable sources, wind and solar, are intermittent and weather dependent. Therefore, other flexible sources need to be able to rapidly increase generation when needed. Within the national system, the water industry is a large user and generator of electricity from anaerobic digestion (AD) of sewage sludge. This work aimed at investigating how the sewage sludge-to-electricity generation system can be made flexible and provide such on-demand renewable power generation.This project’s innovation lies in the fundamental concepts of how AD is designed and operated. Specific feeding regimes were designed to increase the biogas production rate at peak time and tested initially at laboratory scale (0.0009 m3 active volume), then at pilot scale (0.05 m3) to test multiple conditions under conventional and advanced configurations and finally at demonstration scale (18 m3) to confirm the scalability of the results in a relevant operational environment.The final step of the experimental research has been to put this concept in operational practice at full-scale (3,800 m3). Supported by a new dynamic kinetics AD model, appropriate feeding regimes were designed and implemented, and the biogas production rate increased at peak time as predicted. After the successful completion of the trial, this operational solution is currently implemented in business as usual.This research work proved that by implementing an appropriate control of AD, the process can produce more biogas in peak periods to generate electricity when the grid’s prices and carbon emissions peak.Economic, environmental, and societal benefits exist, making this solution more sustainable than existing practices: Flexible generation and dynamic control of AD increases financial and operational resiliency by significantly reducing operational costs and health and safety risks and contributing to the development of a fully decarbonised national power system