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Making The Case for Nutrient Recycling in Agriculture and Energy

Due to the rising cost of natural gas and increased production costs to secure essential materials, the cost of fertilizer has skyrocketed around the world, leading to higher production costs and financial headaches for farmers.

Nitrogen, phosphorous and potassium are the three critical components in fertilizers used in crop production. According to the International Food Policy Research Institute, prices for these essential materials increased 125 percent from January 2021 to January 2022. Prices jumped another 17 percent from January 1, 2022 through the end of April 2022, before falling 30 percent by the end of May 2022 due to a decline in consumer demand. These increases are the result of several factors. Including the fact that most countries source the raw materials to make fertilizer through a global network. Thus, the price is heavily influenced by global events.

For example, China, which typically provides 24 percent of the world’s phosphates, 13 percent of nitrogen and two percent of its potash, halted fertilizer exports last year.

Russia is another significant contributor of all three essential ingredients to the global fertilizer market, and its invasion of Ukraine has disrupted the global supply chain and the flow of input materials as well as food. Further, natural gas is used as both a feedstock and an energy source to produce nitrogen-based fertilizer. The price of natural gas has risen significantly worldwide over the past two years.

These market swings have significant implications for Minnesota’s producers and agribusinesses. Realizing the significance of these developments, the Agricultural Utilization Research Institute (AURI) began focusing on ways to recapture and recycle nutrients such as nitrogen, phosphorous and potassium from various processing streams. In addition, AURI has started exploring ways to develop and refine innovative approaches to recover these materials from agricultural byproducts and reuse them in future production. Shortening the supply chain and revisiting value propositions for byproduct streams can be a win-win approach by providing lower cost options for farmers while adding value to byproduct streams produced by Minnesota agribusinesses, and at the same time, providing supply chain resiliency and reducing the carbon intensity of crop production.

In May 2022, AURI hosted a webinar highlighting some of the work conducted previously in Minnesota to advance the recycling of essential nutrients in agricultural production and agri-processing streams to reuse these materials as inputs in crop production.

Reusing these materials shows positive outcomes both environmentally and economically, said Dr. Luca Zullo, AURI’s Senior Director of Science and Technology.

Nutrient recovery creates brand new value-chains for the agriculture sector. All of this is part of a larger movement to decarbonize the fertilizer production cycle and make the system more resilient to these global shocks, he said.

AURI works in both nutrient recovery and recycling, and there are many opportunities of exploration to accomplish these goals and conduct further research. AURI staff have also worked to find ways to incorporate byproducts like corn stover into soil during the next planting season. These byproducts contain nitrogen, phosphorous and potassium. Additionally, work focuses on utilizing food processing byproducts as a nutrient source for crop production. For example, in 2008, AURI conducted research utilizing ethanol solubles from ethanol production as a nutrient source for growing corn.

Ethanol production from corn is a significant industry in Minnesota. In the fermentation and distillation process, large quantities of a slurry byproduct are produced. This coproduct, referred to as ethanol solubles, is rich in nutrients, containing 70 to 80 pounds of nitrogen, 80 to 100 pounds of phosphate, 60 to 70 pounds of potash and seven to nine pounds of sulfur per 1,000 gallons. Reusing these solubles creates significant value. Most ethanol plants spray solubles onto distillers grains to add nutritive value to the dry distillers grains solubles. The resulting product is Dried Distillers Grain with Solubles (DDGS). The DDGS is used as a livestock protein, fiber and energy source, and also has potential use as a liquid feed for beef and swine.

AURI partnered with the Minnesota Corn Research and Promotion Council on this 2008 study to evaluate the performance of ethanol solubles when used as a fertilizer. The study objective was to determine how nitrogen, potassium and phosphorous applied via the liquid solubles versus a typical fertilizer application impacted corn yields. Research was conducted by the University of Minnesota Southern Research and Outreach Center in Waseca.

The results were positive, showing nitrogen availability at 21 percent in the first year with an increase in soil phosphorous and potassium as well. AURI is currently exploring methods to remove the nutrients and process them in a solid form versus liquid. Having a safe, easily transportable solid material that is rich in nutrients stimulates many new markets, said Alan Doering, AURI’s Senior Scientist, Coproducts.

“This is an incredible opportunity. Recovery and recycling of one to possibly three major nutrients has a direct impact on the fertilizer carbon cycle,” said Doering. “If we can recapture these ingredients and find efficient and safe ways to transport them locally to be used in fertilizers, it will significantly reduce the transportation costs and expand the area of distribution.”

AURI is also working on research that recovers nutrients from the waste streams generated by livestock manure application to fields. Doering said this technology can reduce runoff and save farmers money. Farmers have also learned that animals often need less phosphorus than was once industry practice and have made strides in reducing the practice of overfeeding animals this mineral. Reducing the amount of phosphorous in animal feed and even recovering it from the manure before it is field applied is another promising area of exploration.

Recovering nutrients from wastewater treatment facilities and ag processing streams through anaerobic digestion is another intriguing opportunity area.

An example of this work is in St. Cloud, Minn. The city owns and operates the St. Cloud Wastewater Treatment Facility shared with the cities of St. Augusta, St. Joseph, Sartell, Sauk Rapids and Waite Park. The facility treats an average flow of 13 million gallons per day, generated from a population of over 120,000 people.

It also recycles and reuses nutrients in the wastewater stream and turns them into a liquid nitrogen and solid phosphorus fertilizer product distributed to farmers throughout central Minnesota. On site biofuel storage helps optimize the fuel produced for the biofuel generator. The facility runs almost 100 percent on energy produced on site through renewable sources, generating revenue for St. Cloud.

Overall, the facility generates about 1,700 tons of Ostara Pearl (magnesium ammonium phosphate/struvite) per year by recovering the nutrients from wastewater. This fertilizer component is shipped and utilized in the Red River Valley. The facility also generates approximately 7 million gallons of Class A liquid biosolids fertilizer that is injected into area farmland.

In addition to the fertilizer production, the St. Cloud wastewater facility also generates energy through a biogas generator. The process of anaerobic digestion reduces the wastewater organic pollutant load and converts the waste feedstocks into renewable natural gas and ultimately to electrical energy.

“We are taking a product with enormous amounts of nutrient value and energy value and reusing it. We aren’t sending it through the [treatment system] which would be increasing our carbon footprint,” said Tracy Hodel, Public Services Director for the city of St. Cloud.

Plus, by taking materials from local industries like breweries and other manufacturers, the city is saving local businesses money. Without the St. Cloud treatment center, they would have to build their own treatment facility or pay to haul the waste to another facility and incur expensive tipping fees, Hodel said.

“A lot of people ask why we are doing this. They think that going green and green energy is expensive. But our experience to date has been that this [wastewater treatment program] has exceeded our expectations for energy efficiency and savings. We discovered that green is cheaper and that helps us stabilize our taxes and our utility rates in the city,” said Hodel. “It has also helped our local businesses reduce operation and maintenance costs and allowed those companies to expand and add jobs. We are excited to continue looking into and exploring green technologies and being a leader in this area.”