As the world becomes increasingly more urban and countries look for robust solutions to climate change, sustainable mobility has become a necessity. The U.S. Environmental Protection Agency calculated that in 2018, emissions from transportation totaled 28.2% of all U.S. greenhouse gas emissions. The transport sector plays a crucial role in our economies and societies, allowing for the mobility of people and goods, and a responsible approach to transportation requires the rapid implementation of alternative technologies. In this context, renewable fuels such as hydrogen from renewable sources, as well as biofuels, are bound to play much bigger roles in the near and distant future.

Hydrogen is already used in fuel cell buses and cars around the world. Its great advantage is that the only byproduct from its use is water, emitted in the form of vapor. Since the vast majority of hydrogen production relies on fossil feedstock—an emission-intense process in itself—researchers have spent the past few decades looking at renewable sources for its production. Despite the high cost associated with fuel cell technology, car manufacturers are still interested. In fact, Volvo and Daimler recently announced a partnership to develop fuel cell systems for heavy-duty vehicle applications.

On the other hand, biofuels represent a sustainable solution that has consistently been gaining ground over the past decades, and is already being integrated into our fuels. In fact, most of the gasoline sold in the U.S. already contains ethanol, about 10% on average. Currently, the U.S. and Brazil are the main producers of ethanol, using corn and sugarcane respectively, which together account for 85% of global production. However, these so-called first-generation biofuels raise several issues. First, corn and sugarcane are food crops, and using them as biofuel feedstock impacts food prices and availability. 

Secondly, they consume resources, specifically water and arable land. For these reasons, scientists have consistently examined alternative crops for biofuel production over the past decade. Second-generation biofuels use cellulose as feedstock, encouraging the use of non-food crops and agricultural residues, while third-generation biofuels are based on the extraction of oil from algae. But these solutions have yet to gain ground, as the underlying technologies are still being developed and tested. Thus, the quest for efficient feedstock for production of renewable fuels continues. Two recent scientific discoveries in particular highlighted new feedstocks for renewable hydrogen and bioethanol: wastewater from beer production and agave tequilana.

SwitcH2, a spin-off company from the University of New South Wales, recently presented a system to extract hydrogen from wastewater derived from beer production. The solution, created by three chemical engineering students, consists of a proprietary process that oxidizes the organic matter contained in brewery wastewater—a feedstock requiring less energy to oxidize than water. The system relies on electrolysis, a well-known technology to induce chemical reactions, to separate the hydrogen from the liquid.

Beer production requires high amounts of water; it is estimated that producing one liter of beer uses 10 liters of water, most of which will need to be disposed. The advantages of SwitcH2's solution are manifold—breweries sustain high costs to process and dispose of their wastewater, which this solution would significantly reduce. Hydrogen is a fuel, and SwitcH2 proposes ways for breweries to reuse it for heating, transportation, and electricity. And of course, repurposing waste is one of the main tenets of the circular economy, as it keeps products and materials in use, increasing their value.

Looking forward, the company could also tackle other kinds of wastewater from the food and beverage sector to scale up their business. For now, though, SwitcH2 is currently working on implementing a pilot electrolyzer in a brewery by the end of 2020. To maximize sustainability, the company is also looking into powering it systems with photovoltaic cells that breweries could install on top of their buildings.

In addition to beer, a group of scientists might make us look at another beverage in a different way: tequila. Researchers from the University of Sydney, University of Adelaide, and the University of Exeter recently conducted a study with the aim of producing “the first lifecycle assessment and economic analysis on ethanol produced by agave."

Their research, based on data from a field experiment in Queensland, Australia, has shown that agave tequilana, the blue agave variety used for tequila production, yields nearly 200% as much ethanol as that obtained from corn by using 46% less water. Compared to sugarcane, agave yields a significantly lower amount of ethanol—25% less,—yet requires 69% less water.

The main advantage of agave is its capability to grow on arid land that couldn't be used for food crops. This opens up new possibilities as the plant could be destined for cultivation in semi-desert areas, where it wouldn't compete with agricultural production. Such a scenario could be considered in the southwestern U.S. states, where soil and climatic conditions would be favorable.

In Australia, the agribusiness company, MSF Sugar, is already testing the local feasibility of large-scale cultivation of agave for bioethanol production. According to their estimates, the plant yields “around 400 tonnes of biomass per hectare—similar to the per hectare biomass produced by sugarcane but with no irrigation."

Research on feedstocks for biofuel production is rapidly evolving, proposing more efficient solutions as we learn which challenges to overcome based on current and past results. Leaving first-generation biofuels behind to protect food availability and prices is just a matter of time.

Considering the amount of replacements currently being investigated with promising results, a conclusion might also be that there simply is no silver bullet. The best solution could be a multi-pronged approach that makes use of several viable solutions depending on locally available resources, be it brewery wastewater, agave grown on arid land, or other feedstock, such as used cooking oil.