As freshwater supplies become increasingly limited and the world's population continues to grow, Auburn University College of Agriculture researchers are working on ways to find and utilize alternative water resources for irrigating crops.

"One proven source that can meet this demand is wastewater," said Brendan Higgins, assistant professor in the Department of Biosystems Engineering. "In addition to providing water for crops, wastewater resources are rich in nutrients, specifically nitrogen and phosphorus. Combined, these nutrients can improve the growth of food crops."

Higgins is leading a research team that has received a four-year $499,577 grant from the National Institute of Food and Agriculture, or NIFA, to study the possibility of using poultry processing wastewater for irrigating in controlled-environment agriculture. He will discuss the research as part of an Auburn Talks panel during the virtual "Auburn Research: Faculty Symposium" on Jan. 29.

Other members of the research team include Daniel Wells, assistant professor in the Department of Horticulture; Dianna Bourassa, assistant professor and extension specialist in the Department of Poultry Science; and Rishi Prasad, assistant professor and extension specialist in the Department of Crop, Soil and Environmental Sciences.

The poultry industry, Higgins said, is a major generator of nutrient-rich wastewater.

"This water supply is currently being treated as a waste at a significant expense to industry and, ultimately, to consumers," he said.

In 2018, the U.S. broiler industry produced roughly 9 billion chickens, resulting in an economic impact of $31.7 billion on the U.S. economy. The processing plants that handle poultry slaughter and meatpacking also produce roughly 62 billion gallons of wastewater annually at a cost of more than $247 million to treat.

"Repurposing this water supply for use in crop production has the potential to significantly reduce treatment costs, increase food production and reduce the overall impact on the environment," Higgins said. "However, there are three main challenges that need to be addressed in order to safely and efficiently use wastewater for food production."

The first challenge, he said, is that nutrients in the wastewater should be in the appropriate form for stable crop production. Secondly, the crops irrigated with wastewater must be free of pathogens, and, lastly, the negative effects of antimicrobial chemicals in the poultry wastewater must be mitigated.

"The goal of our project is to develop engineered biological processes that overcome these three challenges," Higgins said. "Successful development of such processes will pave the way for recycling of wastewater back into safe and sustainable food production."

Researchers will meet the project's goal by engaging in four major research activities:

1. Develop an innovative wastewater treatment reactor that uses algae and bacteria deployed together to clean the water and transform existing nutrients into forms that are usable by plants.
2. Test the ability of the above reactor, along with other non-chemical treatment steps, to clean the water of pathogens so it is safe to use for crop irrigation.
3. Grow lettuce—a model crop that presents a "worst-case scenario" from a food-safety standpoint—to test the system's performance. During this step, researchers will dose in antimicrobial chemicals into the treatment system to determine how effectively it removes and mitigates their negative impact on lettuce production.
4. Develop a set of engineering models derived from the experimental data. These models will serve as the basis for scaling up the process so it can be deployed safely and effectively at commercial poultry processing plants.

The treatment system, Higgins said, will need to be located near the processing plant.

"Water can be pumped a significant distance, but of course you would need to consider the site-specific economics," he said. "Where is the supply and demand, and does it make sense for this particular location?

"One of the attractions of controlled-environment agriculture is that the footprint of the facilities is quite small, given how intensive the crop production is. You can produce a lot of lettuce on a small area of land using greenhouse technology. It is conducive to suburban and exurban areas where a lot of the poultry processors are located."

The Auburn project will be located at the College of Agriculture's Charles C. Miller Jr. Poultry Research and Education Center.

The poultry wastewater concept originated during a meeting of the "animal production" working group organized by the College of Agriculture and led by Ken Macklin, professor and extension specialist in the Department of Poultry Science.

"I've been working with poultry processing wastewater over the past few years and have been developing the idea that algae can be used to overcome the negative consequences of antimicrobial agents in the poultry processing wastewater," Higgins said. "However, it wasn't until our research team started talking that this idea of growing crops with wastewater really came to fruition."

While the research project will be focusing on growing lettuce, Higgins sees the potential for using wastewater on a variety of crops.

"Non-food crops like cotton would probably be easiest from a regulatory standpoint," he said. "However, we really wanted to grow food with the water because it is a major research challenge. There are already many options for reutilizing waste materials on non-food crops and forage."