Since the corn-derived ethanol industry began producing dried distillers grains with solubles (DDGS), the nutritional profile of the co-product has evolved depending on which fractions are recovered by the ethanol plant for other revenue streams.
While most of the modified DDGS products vary in oil content, which alters the energy and protein profiles of the product, a new process being developed at the University of Illinois is looking to remove excess phosphorus from DDGS.
DDGS often contains more phosphorus than the animals need, an announcement said, and the excess phosphorus is excreted in manure. Removing the excess phosphorus from DDGS before it becomes a feed ingredient could alleviate the problem, the University of Illinois said, noting that the recovered phosphorus could be used as crop fertilizer.
"A lot of phosphorus is in the corn itself. When corn is processed, you get different products. Some of it is fed in animal diets, which already contain plenty of phosphorus. So, the additional phosphorus comes out in the manure and leaches into the groundwater," said study co-author Vijay Singh, University of Illinois professor of agricultural and biological engineering and director of the Integrated Bioprocessing Research Laboratory. "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."
The research is part of a multipronged project spanning several departments in the University of Illinois College of Agricultural, Consumer & Environmental Sciences. The project is funded by a National Science Foundation grant under the Innovations at the Nexus of Food, Energy & Water Systems (INFEWS) umbrella.
Study lead author Ankita Juneja, a postdoctoral research associate in the department of agricultural and biological engineering, explained that the researchers first looked at how phosphorus flows through an ethanol 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 said.
The researchers were able to recover 80-90% of the phosphorus through a simple process of increasing the alkalinity of thin stillage and adding calcium chloride, followed by stirring the product for five minutes in a continuous stir reactor.
The goal was not to remove all phosphorus, because some is needed as a nutrient in DDGS, Juneja explained, adding, "The animal food requirement of phosphorus in DDGS is 3-4 mg/g of DDGS. Previously, the DDGS had about 9-10 mg/g. So, the rest was all excess, which would get into the manure. We were able to reduce it down to 3.25 mg/g, which is in the range of what the animals actually need."
Removing phosphorus also drains protein from the DDGS, but Juneja said the study's recovery process was optimized to ensure that the amounts of protein and phosphorus left in DDGS were calibrated to meet -- but not exceed -- requirements for inclusion in animal feed.
The phosphorus product that is recovered through this procedure is in the form of a solid precipitate or paste, which contains about 60-70% water. It can be dried and eventually used as fertilizer, though the study does not address that process. Singh said that is currently being tested by scientists in the University of Illinois 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 noted.
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 phosphorus fertilizer for corn and soybeans.
"We did the economic analysis of how much it would cost to add the recovery section in an existing dry-grind plant: how much it would cost in terms of fixed cost, how much it would cost in terms of operating costs every year and how much extra revenue could be generated by producing this extra co-product, which can be used as fertilizer or other applications," Juneja explained.
"We found that the additional investment was $5.7 million in an existing dry-grind plant that produces 40 million gal. of ethanol a year. The amount of added revenue is a little less than a million dollars each year," she added.
Plants are not currently implementing these practices, but processors are very interested in learning about the study's findings, Singh noted.
"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 ... is also of value to them," he added.
Singh said this is the second of three studies he and Juneja are conducting on phosphorus recovery as part of the INFEWS project.
"We are looking at three different refineries within the Upper Sangamon Watershed," he said. "In this watershed, there are many different processing plants, because Illinois has lot of bean and corn processing."
The first study looked at corn wet milling plants, where corn is converted to starch for making high-fructose corn syrup, and the third study will focus on soybean processing plants.
The article, "Recovering the Phosphorus as a Coproduct from Corn Dry Grind Plants: A Techno-economic Evaluation," was published in Cereal Chemistry.