Biomethanisation of CO2 in Anaerobic Digestion Plants

The research aims to develop a hybrid anaerobic digestion process in which hydrogen made from renewable energy sources (e.g. wind and photovoltaics) is used to produce biomethane at more than 95% purity. The process therefore provides an efficient in situ biogas upgrading technique which will maximise the conversion of the available carbon in waste biomass into a fuel product that has a wide range of applications, including short-term storage for grid balancing and use as a vehicle fuel. The process is likely to be more environmentally friendly and sustainable than current methods for biogas upgrading as there is reduced process loss of methane. The target is to develop the system for use in the water industry where there is a large potential to integrate it into existing infrastructure and to maximise the use of process heat and other by-products. A second targeted application is at a smaller scale on farms, where there is an abundant supply of waste biomass and a lack of suitable biogas upgrading plant.
The overall aim of the project is 'to achieve biogas upgrading to 95% CH4 in an anaerobic digester by reducing biogas CO2 through H2 injection and mediated by a stable evolutionarily adapted predominantly hydrogenotrophic population'.

Aim and Objectives

The overall aim of the project is 'to achieve biogas upgrading to 95% CH4 in an anaerobic digester by reducing biogas CO2 through H2 injection and mediated by a stable evolutionarily adapted predominantly hydrogenotrophic population'. This is supported by the following objectives:

- Using biogas as a CO2 source, establish a predominantly hydrogenotrophic culture through ex situ H2 enrichment in the absence of supplementary substrates (WP1)
- Develop a biogas upgrading approach where CO2 formed in the reactor from supplementary feedstocks is reduced in an in situ digestion process (WP1)
- Determine process kinetics and the influence of reactor conditions (e.g. pH, alkalinity, H2 partial pressure) on digester performance and stability (WP1)
- Optimise digester operating conditions to achieve >95% CH4 and to minimise slippage (WP1)
- Chart H2-enriched microbial populations to identify the species required for improved biomethane yield through hydrogenotrophic metabolism (WP2)
- Identify genetic indicators of effective hydrogenotrophic community members for diagnostic (WP2)
- Identify useful process indicators among soluble metabolites (WP2)
- Develop rapid diagnostic tests from a 'long list' of target indicators for process assessment (WP2)
- Develop a kinetic model to describe fully, both in situ and ex situ, the physio- and bio-chemical stages of H2 methanisation, and perform parameter estimation and validation of the model (WP3)
- Identify and develop control strategies, based on available on-line sensors, for the H2 injection/ biogas upgrading process, and use the kinetic model to perform in silico to test them (WP3)
- Test the control system at laboratory scale in order to assess its performance and robustness, and further optimise the control algorithms with respect to rates of reaction and product quality (WP3).
- Make recommendations for control requirements for scale-up of the proposed process (WP3)
- Use the experimental data to flowchart different process configurations, and assess these under different operating scenarios on the basis of their potential for heat integration, net energy productivity and resource utilisation using process integration modelling (WP4)
- Review engineering design issues and prepare outline plans for testing at pilot scale (WP4)
- Develop a preliminary techno-economic analysis to underpin the technology development routes based on the potential renewable energy sources (e.g. PV, wind and hydro) for: (i) the water industry for grid injection, vehicle fuel use and power grid balancing applications and (ii) de-centralised smaller scale rural applications (WP4)
- Consider implications of process scale-up as a basis for refined economic analyses (WP4).