The devil’s lettuce as a fuel source?

In the quest of creating carbon-neutral societies and end our dependence on oil, many countries have started to look at biofuels derived from renewable biomass as an alternative to fossil fuels. A significant source of greenhouse gas emissions stemming from human activities is the transport sector, currently accounting for approximately 25% of emissions in the European Union (Eurostat, 2020). In order to reduce this share, the EU introduced a renewable energy directive in 2009, recently revised for 2030 where a minimum of 14% of the fuel used in the transport sector must consist of renewables (European commission, 2020).

This new goal might seem ambitious, but all biofuels are not equal in terms of environmental performance. Significant portions of the biofuel share are currently made up of so-called first-generation biofuels directly made from food crops such as rapeseed, soy, sugarcane, wheat and corn. The cultivation of these edible feedstocks has sparked controversy over the years with issues such as aggressive agricultural land expansion, food security issues and higher than expected cumulative GHG emissions. The EU therefore included a provision in the energy directive where at least 3,5 % of the used biofuels must be based on non-food feedstock in 2030 (European commission, 2020a).

Replacing the first-generation biofuels will not be an easy task. Second generation biofuels mainly produced from non-edible lignocellulosic materials and miscellaneous waste is not as well established in all countries. Varying regional feedstock availability and composition further compound the issue. How can we increase the share of advanced biofuels in the immediate future and meet the rapidly approaching environmental targets? Large quantities of sustainable biofuels are going to be needed that can seamlessly be included in the existing transport infrastructure.

This is where hemp comes into the picture. Industrial hemp, a non-psychoactive variant of the Cannabis sativa plant is a fast-growing biomass that has a multitude of uses. From clothing, paper and plastics to construction materials and cosmetics, the list is nearly endless. Hemp is also one of the earliest domesticated plants, dating back more than 8000 years over multiple continents and climatic zones, so the experience in its cultivation is there.  

Where hemp cultivation is possible (Alcheikh, 2015).

Advantages of hemp as an energy crop is the low water requirements, strong weed competitiveness, high disease resilience leading to low pesticide demand and a short three-month life cycle making it suitable for crop rotations during the winter. Hemp also recirculates approximately 70% of its nutrients back into the soil, drastically reducing the amount of needed fertilizer. An added benefit of hemp cultivation is also the prevention of soil erosion due to its long and fast-growing roots (Alcheikh, 2015).

A further benefit to the soil is the plant’s ability to restore them from toxic pollution, so-called phytoremediation where contaminants are absorbed by the roots of a plant capable of accommodating toxins and heavy metals (Ahmad et al., 2016). An example of this effect is the growth of hemp surrounding the Chernobyl nuclear plant where it is used to remove radioactive elements from the soil and water (Dushenkov et al., 1998). This overall resilience combined with the low nutrient and water requirements makes it a compelling feedstock for second generation biodiesel, ethanol, methanol and biogas.

The whole plant can be used in the creation of biofuels. The seeds contain around 30% oil which can be used in transesterification processes to generate biodiesel with lower sulfur content compared to soybean and rapeseed-based biodiesel (Alcheikh, 2015 p.18). The rest of the plant can be used to produce hemp equivalents of ethanol and methanol, so called hempanol or hempoline (MHFMA, nd) or biogas through anaerobic digestion.  

There are downsides to hemp as a biomass though. The economic viability may be called into question due to the versatile nature of the plant. Many products with a higher return on investment can be produced from hemp making biofuel production less attractive to farmers. Furthermore, the issues surrounding land use are only partially addressed with hemp. Arable land will still be used for monocultures of hemp and yields will be higher on fertile soil compared to cultivation on marginal land. Legal issues also remain due to the similarities between industrial hemp and marijuana. The United States banned industrial hemp production in 1937 with the rest of the world following suit soon after. In recent years, the worldwide bans have been gradually lifted but the long hiatus has led to very low levels of current production.

Industrial hemp might not be the end-all or perfect biomass but as a transitional source of biofuel it holds a lot of promise and should be further investigated if we intend to live up to the impending environmental goals.

References

Ahmad, R., Tehsin, Z., Malik, S.T., Asad, S.A., Shahzad, M., Bilal, M., Shah, M.M. and Khan, S.A., 2016. Phytoremediation Potential of Hemp (Cannabis sativa L.): Identification and Characterization of Heavy Metals Responsive Genes: Biotechnology. CLEAN – Soil, Air, Water, 44(2), pp.195–201.

European commission, 2020. Renewable Energy Directive. Available at: https://ec.europa.eu/energy/topics/renewable-energy/renewable-energy-directive/overview_en

European commission 2020a. Renewable Energy – Recast to 2030 (RED II). Available at: https://ec.europa.eu/jrc/en/jec/renewable-energy-recast-2030-red-ii

Eurostat, 2020. Greenhouse gas emission statistics – emission inventories. Available at: https://ec.europa.eu/eurostat/statistics-explained/pdfscache/1180.pdf

Minnesota Hemp Farmers & Manufacturers Association (MHFMA) n.d. Environmental Benefits of Hemp. MHFMA. Available at: https://www.mhfma.mn/resources/environmental-benefits-of-hemp/

Slavik Dushenkov, *, Alexander Mikheev, ‡, Alexei Prokhnevsky, ‡, Michael Ruchko, ‡ and and Sorochinsky‡, B., 1998. Phytoremediation of Radiocesium-Contaminated Soil in the Vicinity of Chernobyl, Ukraine. [research-article] Available at: https://pubs.acs.org/doi/10.1021/es980788%2B