Towards resource circular biodiesel production through glycerol upcycling

Highlights: • Resource circular initiatives within biodiesel production investigated. • Anaerobic digestion decreases annual energy consumption by 44%. • Glycerol reforming with CCU decreases net GHG emissions by 51%. • Feasible thermochemical routes to glycerol upcycling plagued by high capital costs. The implications of climate change on a global scale have resulted in the shift towards resource circular platforms which encourages waste valorization and lowers environmental impact. Within the transport sector, biofuels-namely biodiesel, has emerged as a successful candidate promoting greater sustainable development. However, due to its growth and popularity, crude glycerol- a by-product of the biodiesel process, has remained as an underrated waste stream which threatens the inherent sustainability of the biodiesel process. Here, we showcase multiple decision criteria facilitated by techno-economic and environmental assessments, to support a resource circular biodiesel process through glycerol upcycling- utilizing anaerobic digestion (AD) for energy integration and glycerol reforming for circular methanol production. Our findings illustrate increased energy efficiency through AD, with reductions in electricity and fuel consumption across the biodiesel process promoting reduced annualized costs compared to capital- intensive circular methanol production. Insights into life cycle assessments and the use of planetary boundaries, reveal circular methanol production as the desired pathway for reduced GHG emissions associated with carbon capture and utilization. However, the subsequent increase in energy consumption necessary for thermochemical conversion inadvertently causes burden-shifting to other impact categories- consolidating higher environmental impacts specifically for human health and resource depletion; increasing penalties associated with environmental quality. Thus, in considering current and future operating costs coupled with monetisation, AD outperforms all other platforms as the most competitive resource circular initiative; providing greater sustainable operations within the biodiesel process.