Biogas can accelerate the decarbonisation of the European energy sector, and is suggested to play significant roles in future transport systems. Producing biogas from algae and other renewable substrates may be effected through anaerobic digestion (AD), which converts biodegradable components into biogas (a mixture of approximately 60% CH4 and 40% CO2) through different communities of syntrophic bacteria and archaea. The upgraded “green” gas containing over 97% biomethane can be used to as an advanced transport biofuel for heavy goods vehicles and bus fleets. However, existing AD technologies can suffer from two major drawbacks: (1) Efficiency of the AD process is sensitive to many factors (such as substrate hydrolysis, pH and microbial activity), which can result in instability and inefficiency of biogas production; (2) the anaerobic digestate generated after AD still possess a significant amount of energy and may require significant land area to assimilate nutrient load. The inefficiency of AD fundamentally arises from the interspecies electron transfer between syntrophic bacteria and methanogenic archaea. Therefore, the challenges on how to improve electron transfer efficiency and overall energy recovery of AD are significant and must be overcome to enhance biogas yield and optimise the third-generation biofuel system.
The overall research objective is to propose a future AD-based circular economy system, which produces renewable gaseous transport biofuel. The research explores the mechanisms of microbial electron transfer in the presence of different conductive materials, such as highly conductive but expensive graphene and more cost effective biochar including those derived from digestate for ultimate system circularity. The biomethane production rate in the proposed system can be enhanced by between 20 and 40% as compared to existing AD technology without addition of conductive materials.
