My research project
Dynamic control of anaerobic digestion for flexible and sustainable generation in the water industry
The transition to provision of reliable energy from renewable sources is crucial for a sustainable future. However, the renewable energy sources mostly used are intermittent and therefore are not adequate to cope with the dynamic nature of electricity demand.
In the UK, the water industry currently generates around 800 GWh pa of electricity mainly from Anaerobic Digestion (AD). AD is an established technology for the stabilisation and sterilisation of sewage sludge and the generation of renewable energy (in the form of biogas) from the organic content in human waste. The biogas is used in combined heat and power generation plants that are normally located very close to urban areas and so is an example of locally-sourcing.
A combination of technologies alongside AD constitutes the Thames Water advanced sewage sludge-to-energy generation system. It maximises material and energy recovery from the final by-product of the wastewater treatment according to agreed sustainability criteria, and produces a reliable but steady supply of electricity. Thus, the challenge of this project is to develop a system that can rapidly respond to the dynamic nature of electricity demand, and thereby potentially replace existing non-renewable flexible electricity sources.
The dynamic control of AD could constitute the basis for a modern flexible sewage sludge-to-electricity generation. This research will investigate in which conditions the bacteria in the digesters could produce biogas at varying rates and, optimise the entire sewage sludge electricity generation system in order to maximise its flexibility and ability to meet the dynamic demand.
Overall, this project aims to increase the contribution of renewably sourced electricity in the UK energy mix, by introducing an effective modern sewage sludge-to-electricity system to meet the demands of the UK electricity supply.
In the media
Mauro's research interests are in the water and energy sectors, and in particular:
- sustainable and integrated urban water management,
- sustainable urbanisation,
- water management at catchment level,
- resources and energy recovery in the urban water cycle,
- energy management.
This research project falls at the nexus of water and energy sectors, linking the chemical and biochemical engineering of energy recovery from sewage sludge to the complexity of the electricity market. The general aim of the project is to investigate the feasibility for the Water Industry, to flexibly generate electricity from sewage sludge and contribute to assuring the supply of electricity.
This research project is in collaboration with the Research, Development and Innovation department of Thames Water Utilities Ltd.
Lafratta, M., Thorpe, R.B., Ouki, S.K., Shana, A., Germain, E., Willcocks, M. and Lee, J., 2020. Dynamic biogas production from anaerobic digestion of sewage sludge for on-demand electricity generation. Bioresource Technology. https://doi.org/10.1016/j.biortech.2020.123415
The aim of this work was to study the potentials and benefits of dynamic biogas production from Anaerobic Digestion (AD) of sewage sludge. The biogas production rate was aimed to match the flexible demand for electricity generation and so appropriate feeding regimes were calculated and tested in both pilot and demonstration scale. The results demonstrate that flexibilization capability exists for both conventional AD and advanced AD using Thermal Hydrolysis Process (THP) as pre-treatment. Whilst the former provides lower capability, flexible biogas production was achieved by the latter, as it provides a quick response. In all scenarios, the value of the biogas converted into electricity is higher than with a steady operational regime, increasing by 3.6% on average (up to 5.0%) in conventional and by 4.8% on average (up to 7.1%) with THP. The process has proven scalable up to 18m3 digester capacity in operational conditions like those in full scale.
The power system needs flexible electricity generators. Whilst electricity generation from anaerobic digestion (AD) of sewage sludge has traditionally been baseload, transforming the generation capacity into a modern flexible operator is an opportunity to further valorise the resource. This work aims to demonstrate that AD of sewage sludge can support flexible generation and be operated dynamically in a relevant operational environment, to promote full scale implementation. A demonstration scale plant (20 m3 conventional AD reactors) was used to test several feeding regimes designed to return a biogas production rate that matches the demand. Two demand profiles are defined, either by common corporate power purchase agreements or by the main balancing mechanism used by the grid operator in UK. Demand-driven biogas production is demonstrated in this relevant operational environment, and the flexibilisation performance is positive in all scenarios. The value of the biogas increases by up to 2%, which outperforms the results obtained at pilot scale. Additionally, an increase in biogas yield is observed. Whilst transitional imbalances are recorded, they last for few hours and the overall stability is not affected. In conclusion, these trials demonstrate demand-driven biogas production is a feasible operational solution and full-scale implementation is possible.