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Valorisation of agricultural residues for bioenergy generation using a novel dry anaerobic digestion process and production of a novel fertiliser product using electrocoagulation

Primary Supervisor: Dr Marie Kirby, Animal Production, Welfare and Veterinary Sciences

Secondary supervisor: Professor Michael Theodorou

PhD project title: Valorisation of agricultural residues for bioenergy generation using a novel dry anaerobic digestion process and production of a novel fertiliser product using electrocoagulation

University of Registration: Harper Adams University

Project outline:

Developing novel pathways for the utilisation and valorisation of agricultural wastes, by-products and residues is of increasing importance. By utilising these wastes, new products could be created in the recovery of nutrients, energy and further products that replace fossil-fuel derived consumables. These new products have great potential for scalability throughout the agricultural sector and represent novel business models for bio-based manufacturing that could help to rejuvenate rural communities.

The Agricultural Centre of Sustainable Energy Systems (ACSES) based at Harper Adams University (HAU) has been investigating a range of different approaches to recover bioenergy and further products from these wastes. Midlands Integrative Biosciences Training Partnership (MIBTP) would provide an ideal opportunity to expand this research, whilst developing the required skills in future researchers to help develop these industries over the coming decade. A range of research areas have been explored by ACSES, focusing primarily on anaerobic digestion (AD) and a novel method of electrocoagulation.

Considerable growth has occurred in the UK over the last decade to develop the wet AD industry, providing renewable energy from energy crops, waste food and animal slurries. However, the wet AD industry has stagnated and further research is required to develop an alternative to wet AD. This alternative technology, dry AD, involves the digestion of waste feedstocks at an increased dry matter content (>40%), therefore increasing the bioenergy output produced per m2 of land required. Dry AD has several other advantages including lower heating input, less land and produces a solid digestate which is easier and environmentally safer to spread onto land. However, due to the drier nature of the digestion process, dry AD can have stability issues when digesting novel feedstocks. Further research is required to understand how to optimise the dry digestion process for agricultural residues to produce a reliable electrical and heat supply for decentralised use. This research would be undertaken at laboratory scale to understand the effect of manipulating various digestion factors on biogas yield. Once a greater understanding of the role agricultural residues could affect decentralised energy generation in the future, the research project will then examine the potential market opportunities for dry AD across Europe. Dry AD represents a disruptive technology for decentralised bioenergy production and utilisation of waste materials, in addition to purpose grown biomasses. Integrating this novel technology with whole-system analyses is vital to determine the preferential business models required, before the concept is introduced to industry.

ACSES research has also focused on the recovery of nutrients (N, P and K) from animal slurries and anaerobic digestates for the manufacture of replacement artificial fertilisers. The use of electrocoagulation has the ability to precipitate nutrients from animal wastes to produce cleaner process water and a more concentrated fertiliser-type products, with minimal fossil-fuel input. This is a dramatic change from current artificial fertiliser manufacture which consumers high levels of energy and requires fertiliser to be moved large distances across continents to the end user. Laboratory-scale research to date has highlighted the real-world application of this technology for producing decentralised fertiliser-type product of commercial value. Larger-scale research is now required to test this technology in real-world applications. Similarly to dry AD, if the technology is promising in the field, a whole-system analyses approach is required to identify commercial opportunities and validate earlier research. Developing electrocoagulation further with industrial partners will aid implementation of the novel technology into industry and reduce agricultural greenhouse gases from the land application of slurries and digestate.

BBSRC Strategic Research Priority: Renewable Resources and Clean Growth: Industrial biotechnology

Contact: Dr Marie Kirby, Harper Adams University