Novel concept to develop fertilizer uses only air and water as raw materials

A group of Purdue researchers, including AAE professor Sergey Macheret, could help save Africans from famine — by using plasma.

A group of Purdue researchers could help save Africans from famine — by using plasma.

Sergey Macheret, a professor in the School of Aeronautics and Astronautics, is part of a team of researchers that has designed a plasma device that produces nitrogen oxides from the air then dilutes them in water to make a liquid nitrate fertilizer.

Macheret

That fertilizer could be a cost effective, more efficient way to address food security and plant nutrition in Sub-Saharan Africa, where corn is a major piece of the diet. Fertilizer currently is too expensive for African farmers and is not applied to about 70 percent of the corn grown in Eastern and Southern Africa.

But Purdue researchers’ novel concept would eliminate the need for massive centralized production of nitrate fertilizers and instead produce nitrates “on the spot” from air and irrigation or rain water. Unlike current fertilizer options, Macheret’s process would not use added chemicals nor would it produce side products, such as carbon dioxide and carbon monoxide.

The key technology for the concept is based on low-temperature plasma (LTP). Because plasma is made using electric power, the fertilizer production could be powered by renewable energy sources, eliminating the need for commercial fertilizers and associated pollution.

“What if we use ‘free’ electricity, which is wind or solar? So, then, after an initial investment in the plasma facility, we would not have to spend anything running the system and making fertilizer,” Macheret said. “What are the raw materials we use? Air and water and nothing else. So we use solar power, air and water and what do we make? A fertilizer to grow plants. That is an overall vision.”

The team — that also includes Tony Vyn, a professor in agronomy, and Andrei Khomenko, a postdoctoral researcher, as well as graduate students from AAE and a research associate in agronomy — tested the concept last summer, using seed money from the Strengthening Interdisciplinary Collaborations Between the Colleges of Agriculture and Engineering competition. The team was limited in how much liquid nitrate fertilizer it could produce based on laboratory-size equipment, but it produced enough liquid fertilizer for the agronomy partners to test on plots of corn during growing season.

The test included three plots: one control plot without fertilizer, one using plasma-produced fertilizer, and one using commercial fertilizer.

“The key results that are already there are encouraging,” Macheret said. “We proved that the plasma fertilizer clearly acts as well as the commercial fertilizer if the same number of kilograms of nitrogen per hectare is applied. Regardless of whether or not you use the commercial fertilizer or you use the liquid plasma-produced fertilizer, the corn growth is the same. That’s the key result.”

The plasma-produced fertilizer helped corn plants achieve the same final plant height and ear weight as the conventional fertilizer did. Purdue’s product also enabled corn leaves to maintain intermediate leaf chlorophyll contents, which improved potential photosynthesis, in June and July that were consistently above the controlled plots. The field tests also showed that plasma-produced fertilizer was effective even though about half of it was applied after the flowering has occurred.

“There are some other interesting results that we’re still trying to make sense of, but all of them are good. There is not a single bad result,” Macheret said. “So that’s an interesting proof of principle that, indeed, it works and this can be used as a fertilizer, and it’s definitely at least as good — and in some respects maybe even better — than at a commercial fertilizer you can buy. So that is an important aspect of developing the concept.”

Purdue’s team still needs to improve the energy efficiency and to better organize the process. It’d also like to scale up the operation. Currently, it used a kilowatt scale system, and farms would realistically be 2.5 acres or so. For that, Purdue would need more along the 100s of kilowatts or megawatt power.

Even at the current process efficiency, the concept is promising.

“To supply all the needs of a corn-growing farm in Kenya, for instance, in nitrogen, we would only need to cover 1.5 percent of the area of this farm with solar panels. That is a very encouraging projection,” Macheret said.

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