Increasing the energy yield from the integrations of anaerobic digestion and pyrolysis
EPSRC SUPERGEN Bioenergy Challenge Project EP/K036793/1
Objectives
To improve the energy yield obtained from processing the residual organic fractions of municipal solid waste (MSW), through a combination of biological (anaerobic digestion (AD)) and thermal (pyrolysis) processes.
Background
The residual organic fractions of MSW are typically disposed of via landfill, which is becoming an increasing environmental and economic concern to the government. The MSW material is not suitable for direct AD as the bacteria involved are not capable of breaking down the more complex components. Pyrolysis however can breakdown these more complex components into smaller components which can then be used by the bacteria in AD. Pyrolysis produces four by-products from the MSW: char, oil, water and gases. These by-products can be introduced into AD for further processing, to produce methane gas which can then be converted into electricity. By combining these two processes, the energy yield from MSW can be increased, enhancing renewable energy supply to consumers.
Method
The research will include a wide range of AD and pyrolysis experiments, covering primarily intermediate pyrolysis with a comparison made with fast pyrolysis. The intermediate pyrolysis experiments will optimise the process for treating MSW and the by-products produced will be introduced into AD. AD experiments will further optimise energy recovery from these by-products with the production of methane gas.
To ensure overall efficiency of the combined processes, mass and energy balances will be calculated of each of the different processing conditions for each by-product. In addition to a techno-economic study, a broader assessment from science and technology perspectives (through a literature survey, interviews and workshops) will provide a deeper understanding of stakeholder perceptions about potential synergies between AD and pyrolysis.
Key components of the work programme include; substrate targeted design and synthesis of novel catalysts, which will be screened for maximum liberation of fermentable sugars, screening of microbes for maximum production of bioethanol, design, fabrication, testing and optimisation of the parallel bench scale reactor. A key features of the reactor is the use of selective membranes to separate the liberated sugars from the catalyst. Under typical conditions the photocatalytic reaction would completely degrade compounds in contact with the catalyst hence liberated sugars will pass through the membrane where they will be available for microbial degradation. This novel reactor will be simple and scale-able facilitating implementation at local or municipal scale. For maximum versatility, the reactor will be optimised to produce bioethanol from an array of waste feed stocks from agriculture and industry.