URBANA, IL —  A co-product from corn ethanol processing, dried distiller's grains with solubles (DDGS), is commonly used as feed for livestock including cattle, swine, and poultry. However, since DDGS contains more phosphorus than the animals need, the excess often ends up in manure and subsequently drains into nearby watersheds. Excessive phosphorus in surface water promotes algae overgrowths and contribute to large dead zones in the Great Lakes and the Gulf of Mexico. 

Removing excess phosphorus from DDGS before it becomes feedstuff could alleviate the problem. A new study from the University of Illinois examines the best way to recover phosphorus as a co-product, which can then potentially be used as fertilizer for corn and soybean production. The study, "Recovering phosphorus as a coproduct from corn dry grind plants: A techno‐economic evaluation," was published in Cereal Chemistry. 

Vijay Singh, co-author of the study, professor of agricultural and biological engineering, and director of the Integrated Bioprocessing Research Laboratory (IBRL) at U of I, says excess phosphorus in livestock diets comes out in manure and leaches into groundwater. 

“We asked, can we do something in the process itself to recover this phosphorus, and put it back on the land as fertilizer? It’s like a circular economy,” he adds.

The research is part of a multi-pronged project spanning several departments in the College of Agricultural, Consumer and Environmental Sciences at U of I. The project is funded by a National Science Foundation grant under the Innovations at the Nexus of Food, Energy and Water Systems (INFEWS) umbrella.

Ankita Juneja, a postdoctoral research associate in the Department of Agricultural and Biological Engineering, is the study’s lead author. She explains that researchers first looked at how phosphorus flows through the production facility.

“We started with a model and estimated the flow of phosphorous in the entire diagrammed plant. Then we determined where the maximum concentration of phosphorus occurs, which will help us recover it economically,” she says.

The researchers were able to recover 80% to 90% of the phosphorus through a simple process of increasing the alkalinity of thin stillage (an evaporation process that separates ethanol from the DDGS) and adding calcium chloride, followed by stirring the product for five minutes in a continuous stir reactor.

Juneja explains because some phosphorus is needed as nutrients in the feedstock, the goal was not to remove all the phosphorus. Previously, there were 9 to 10 milligrams of phosphorus per gram of DDGS, although the animal food requirement was only 3 to 4 milligrams per gram. Using this new process, the researchers were able to reduce the amount of phosphorus in the DDGS to 3.25 milligrams per gram.

Removing phosphorus also drains protein from the DDGS, but Juneja says the study’s recovery process was optimized to ensure that the amounts of protein and phosphorus left in the DDGS were calibrated to meet—but not exceed—requirements for animal feed.

The product that is recovered through this procedure is in the form of a solid precipitate or paste, which contains about 60 to 70% water. It can be dried and eventually used as fertilizer, though the study does not address that process. Singh says that it is currently being tested by scientists in the U of I Department of Crop Sciences.

“We have clearly shown that you can recover this phosphorus from a processing plant so that it doesn't go in different co-products such as animal feed,” he notes.

The researchers evaluated both the technical and economic aspects of the recovery process. While processors do have to invest in new equipment to perform the separation, there is the potential for selling the recovered co-product as P fertilizer for corn and soybeans.

Plants are not currently implementing these practices, but processors are very interested in learning about the study’s findings, Singh notes. 

“They want to know how to do it. Even just providing them with information on how phosphorus flows in their plant is a lot of value. And then giving them strategies to recover it; that is also of value to them,” he adds.