Nations urgently need to tackle climate change in harmony with a circular economy to accomplish Sustainable Development Goals. Using sustainable biomass for sustainable industrial ethanol production seems attractive. Recently, the outstanding features of the arid plants nopales, aka prickly pear cactus, became headlines. Nopales outcompete algae and other biomasses in many aspects. Nopales are resilient, and climate change sparked their advancing invasion across European countries and other places.
A sustainable biorefinery for ethanol production from nopales could holistically support promising outlooks on energy transition, water positive activities and food security near cities. However, the environmental impact and energy efficiency of this novel biorefinery for renewable energy under realistic scenarios is unknown. Traditional chemical pretreatments are polluters that can improve through environmental assessment and bio/chemical process design.
We conducted experiments and assessments of scenarios for cleaner ethanol production from nopales in a biorefinery. Four scenarios considered two fertilisers, two pretreatments and two operational modes. We conducted life cycle assessment, energy balances and energy efficiency calculations. The most polluting scenario uses fossil fertilisers, acid hydrolysis and neutralization of nopal nutrients, and it resulted in approximately four times the global warming potential of the best scenario. Organic fertilisers and the use and reuse of ionic liquids with acetone for washing was the most ecofriendly scenario.
We propose a cleaner design showing the lowest impacts in all categories, including Global Warming, Acidification and Eutrophication Potentials and more. Besides, the design used the lowest amount of energy per unit of energy as ethanol fuel. It also has the best energy efficiency since it converted three-fold the amount of spent energy, in the worst scenario, into net energy as ethanol fuel.
Sustainable biorefineries and sustainable biomasses are opportunities in the circular economy while pursuing climate risk mitigation, carbon neutrality and green energy for sustainable development.