Saving emissions by producing cheap fertilizers with air

Summary

For good and bad, African countries consume fertilizer at one of the lowest rates in the world. Many such nutrients both nourish crops and contribute to the climate change that's already damaging food production in Africa.

Feeding the world

Feeding the increasing African population is an enormous challenge. It is projected that by 2050, Africa’s population will be 2.5 billion, a quarter of the world’s total population. Artificial fertilizers play a key role in meeting this challenge. But while fertilizers are widely available and cheap worldwide, sub-Saharan Africa is the world’s most expensive fertilizer market.

Nitrogen, phosphorus and potassium are the most important macronutrients required by plants to grow. Of them, nitrogen is required in the largest quantity: in 2015, about one in every two humans consumed food that was cultivated with nitrogen-based fertilizers. But the manufacture of nitrogen-based fertilizers using the standard Harber-Bosch process is one of the industries that contributes most to global warming.

The Harber-Bosch process uses 3-5% of the world’s total natural gas (a fossil fuel), consumes approximately 1-2% of the world’s total energy and emits 830 million tons of carbon dioxide into the atmosphere annually. This approach is not consistent with meeting the UN Sustainable Development Goal (SDG) 13 (Climate Action.)

Fertilizer: the necessary evil

Climate change is already upon us; effects on the planet will only get worse in the coming years if current practices continue business-as-usual. But the global population continues to increase, demanding more food production. Artificial fertilizers can double or triple a farmer’s yield, spelling the difference between hunger and food security for the people fed and for the farmer. However, in addition to the environmental unsustainability of current fertilizers, they are expensive in Africa. Uganda is the world’s most expensive fertilizer market at twice the price of Europe or the U.S. For this reason, Ugandan farmers apply an average of 1.3 kg fertilizer per hectare compared to 17 kg in the rest of Sub-Saharan Africa and 135 kg globally. This cost drives food insecurity in Africa; the environmental damage caused by fertilizer makes it, for now, a “necessary evil”.

My research seeks to find and demonstrate the sustainability of alternative methods of fertilizer production. If farmers could produce their own cheap fertilizers on their own farms using state-of-the-art plasma technology, it would reduce carbon dioxide by 830 million tons compared to production by the traditional process.

Plasma is the fourth state of matter, in which negatively charged electrons are equal to positively charged ions. Lightning contains plasma, as do neon signs. In fact, plasma can be considered “lightning in a bottle”. The plasma production method used to create this fertilizer is non-thermal: while the electrons that drive the reaction of breaking nitrogen from air reach extremely high temperatures, the gas that surrounds them stays relatively cool, at about 60oC. This process makes plasma technology an attractive alternative to the traditional method, which requires both high pressure and high temperatures of up to 650,000oC. While Harber-Bosch uses 1-2% of the world’s total energy, plasma technology has a very low energy demand that it can run on solar energy. In Africa, with abundant, free air and sunshine, this approach has the potential to enable smallholder farmers to purchase cheap fertilizers or buy their own fertilizer unit, either individually or collectively as a village.

Fixing the nitrogen

Although air consists of 78% nitrogen, plants don’t simply inhale it as humans do oxygen. Nitrogen is fixed in the soil root zone into ammonia, nitrites and nitrates. Nitrates is the form of nitrogen most available to plants. But the natural process of converting nitrogen to nitrates is not sufficient to feed the world. Plasma technology can also fix nitrogen to make nitrogen-based fertilizer.

To convert nitrogen molecules from air into fertilizer, they must first be ‘activated’ by introducing an electrical charge. This ensures that the bonds that hold the nitrogen atoms together are broken, creating a plasma. In the case of our pilot machinery, the electricity for plasma generation is provided by solar energy, a cheap and sustainable source widely available in Africa. The plasma reactor converts the nitrogen (N2) from the air into NOx, which in turn reacts with oxygen and water to form nitrate (NO3-). This can then be used as an ingredient in liquid fertilizer. Our comparisons of plant response to artificial fertilizers on the market, found the nitrate level of these plasma fertilizers to be most preferred by plants than solid fertilizers ammonium nitrate, NPK (nitrogen, phosporus and potassium) and urea.

Such decentralized production of fertilizers can significantly save emissions from industry, costs and transportation and has the capability to point to new process pathways that can lead to the decarbonization of the fertilizer industry.

About Stella Kabiri

Stella Kabiri is a Ugandan Plant Scientist at the National Agricultural Research Organisation (NARO) in Uganda. Her research interests are in the development of a zero-carbon process of site-specific fertilizer production for poor farmers. She is a grantee of Climate Research for Development in Africa (CR4D), funded by the UK Foreign, Commonwealth & Development Office (FCDO, formerly DFID), the Weather and Climate Information Services for Africa (WISER) programme and the Africa Climate Policy Centre (ACPC) of the United Nations Economic Commission for Africa (UNECA) under the auspices of the Alliance for Accelerating Excellence in Science in Africa (AESA).