Dried distiller’s grains with solubles (DDGS) is a co-product generally obtained during the processing of corn ethanol. This co-product is often used as feed for swine, poultry, and cattle.
But DDGS contains more quantities of phosphorus than required by the animals. This surplus phosphorus reaches manure and ends up in the watershed, thereby aiding the production of algae and ultimately contributing to massive dead zones in the Gulf of Mexico. This problem could be reduced by eliminating excess amounts of phosphorus from DDGS before it turns into feedstuff.
The University of Illinois performed new research that analyzes the best possible method to recover phosphorus as a co-product. This by-product could then be utilized as fertilizer for producing corn and soybeans.
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.
Vijay Singh, Study Co-Author and Professor of Agricultural and Biological Engineering, University of Illinois
Singh is also the Director of the Integrated Bioprocessing Research Laboratory (IBRL).
Singh added, “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 study is part of a multi-pronged project covering quite a number of departments in the College of Agricultural, Consumer and Environmental Sciences at the University of Illinois. The project is financed by a National Science Foundation grant under the innovations at the Nexus of Food, Energy and Water Systems (INFEWS) umbrella.
Ankita Juneja is the study’s lead author and a postdoctoral research associate in the department of agricultural and biological engineering. She explained that scientists initially looked at the way phosphorus flows via the production facility.
Ankita stated, “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.”
The scientists recovered 80% to 90% of the phosphorus through an easy process in which the alkalinity of thin stillage was increased, calcium chloride was added, and then the product was finally stirred in a continuous stir reactor for five minutes.
The aim of this study was not to eliminate all the phosphorus from DDGS as some of this element is required as nutrients in the feedstuff, explained Juneja.
The animal food requirement of phosphorus in DDGS is 3 to 4 milligrams per gram of DDGS. Previously, the DDGS had about 9 to 10 milligrams per gram. So the rest was all excess, which would get into the manure. We were able to reduce it down to 3.25 milligrams per gram, which is in the range of what the animals actually need.
Ankita Juneja, Study Lead Author and Postdoctoral Research Associate, Department of Agricultural and Biological Engineering, University of Illinois
Additionally, eliminating phosphorus drains proteins from DDGS but according to Juneja, the recovery process in this study was improved to make sure that the amounts of phosphorus and protein that remain in the DDGS were calibrated to fulfill the needs for animal feed but not exceed them.
The product that is retrieved via this process is in the form of solid paste or precipitate containing around 60% to 70% water. Even though the study does not deal with the following process, the resultant product can be dried and ultimately utilized as a fertilizer. According to Singh, this method is presently being tested by researchers in the Department of Crop Sciences at the University of Illinois.
“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,” noted Singh.
The scientists assessed both the economic and technical aspects of the recovery procedure. While processors need to invest in the latest equipment to carry out the separation, the recovered co-product could potentially be sold as P fertilizer for soybeans and corns.
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.
Ankita Juneja, Study Lead Author and Postdoctoral Research Associate in the Department of Agricultural and Biological Engineering, University of Illinois
She continued, “We found that the additional investment was $5.7 million in an existing dry grind plant that produces 40 million gallons of ethanol a year. The amount of added revenue is a little less than a million dollars each year.”
Singh observed that at present, plants are not adopting these practices; however, processors have shown a great deal of interest in learning about the study’s results.
“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 added.
Singh further added that this is the second of three analyses that were performed by him and Juneja on phosphorus recovery as part of the INFEWS project.
“We are looking at three different refineries within the Upper Sangamon Watershed,” he added. “In this watershed, there are many different processing plants because Illinois has lot of bean and corn processing.”
The first study of the researchers focused on the corn wet milling plants, where high fructose corn syrup is produced by converting corn to starch, while the third study will look at soybean processing plants.
The article titled, “Recovering the phosphorus as a co-product from corn dry grind plants: A techno-economic evaluation” was published in the Cereal Chemistry journal.
The study’s authors include Ankita Juneja and Vijay Singh, Department of Agricultural and Biological Sciences, and Roland Cusick, Department of Civil and Environmental Engineering, University of Illinois.
The first study titled, “Techno‐economic feasibility of phosphorus recovery as a co-product from corn wet milling plants,” was also published in the Cereal Chemistry journal.
The authors of this study include Ankita Juneja, Navneet Sharma, Roland Cusick, and Vijay Singh.
The National Science Foundation, Division of Earth Sciences, funded both studies.