Spring 2003
An infiltration and wetland system to treat beef feedlot runoff
by Jeffery Lorimor, Department of Agricultural and Biosystems Engineering
Beef and dairy producers are interested in systems to remove contaminants from open feedlot runoff before it is released into the environment. Feedlots larger than 1,000 animal units (one animal unit equals a 1,000-pound beef animal) must capture the runoff and store it in a sealed containment basin until they can irrigate it onto agricultural land. They cannot release it. Smaller lots, however, do not legally have to capture the runoff, but cannot release it directly to a waterway. They should improve the quality of the runoff to remove most of the pollutants (solids, nutrients, and microorganisms) before releasing it.
Solids settling basin at the ISU Beef Nutrition Farm.
Feedlot runoff cleanup starts with settling solids. Every feedlot should have a solids settling area below it. A properly designed settling area effectively removes most of the solids, is inexpensive, and is easily managed. Once the runoff leaves the settling area, three basic treatment technologies are of interest to producers: vegetative filter strips, wetlands, and infiltration areas.
Iowa State University has been investigating a treatment system at its Beef Nutrition Farm to improve the quality of the feedlot runoff before it reaches nearby Onion Creek. The system consists of solids settling, followed by infiltration into the soil and then wetland treatment. The system was designed for the 380+ head lot when the farm was improved in 1998. Figure 1 shows the layout of the overall system.
The infiltration area is 20 percent as large as the drainage area above it. It is designed to hold the 25-year, 24-hour storm (5.2 inches) without overtopping (it has overtopped briefly on several occasions during the 5 years of monitoring due to large storms or combinations of storms). The berm holds the runoff from the feedlot and forces it to infiltrate into the soil. The infiltrated water is collected by three tiles lines approximately 5 feet in depth. As the runoff infiltrates, the aerobic soil mass and its microbiological population change ammonia in the runoff into nitrate and organic nitrogen within the soil mass. The soil also traps and removes most of the phosphorus. The tile lines transport the infiltrated liquid to the wetland. The small wetland serves as a “polishing” treatment to further reduce nitrogen and phosphorus.
Water quality has been monitored for the past 5 years at four locations between the feedlot and the creek, and the creek was monitored. Feedlot effluent (called infiltration inflow) was sampled and measured. Infiltrated liquid as it entered the wetland via the tile lines (called wetland inflow), and wetland outflow were sampled. From the wetland, the effluent flows through a long grassed waterway and flat vegetated area between the wetland and the creek. The liquid was sampled as it left the vegetated area at the edge of the creek. Finally, the creek was sampled upstream. Table 1 shows sampling results.
Most of the cleanup occurs in the infiltration area where 80 percent of the total Kjeldahl nitrogen and ammonia are removed, as is 77 percent of the phosphorus. Nitrate almost doubled in the infiltration area. The removal rates in the wetland are lower with the incoming Kjeldahl nitrogen and ammonia reduced 22 and 6 percent, respectively. Phosphorus out of the wetland was 22 percent less than the inflow.
A significant additional cleanup results as the wetland outflow travels through the vegetated area toward the creek. TKN is reduced 68 percent; ammonia, 81percent, and phosphorus, 34 percent. The overall reduction through the system is 95, 97, and 88 percent for TKN, ammonia, and phosphorus, respectively. Nitrate increased from 0.9 to 9.2 ppm overall, but is still below the Public Health limit of 10 ppm.
Infiltration/wetland systems will not work everywhere, but where the soils are right … where they can be tile drained, and the feedlot is situated correctly, this system provides the potential for effective cleanup of feedlot runoff. Additional advantages include potential low cost to construct and that the system is passive, requiring little input by the producer after construction. Clearly, the effluent from the infiltration/wetland system is much higher quality than the raw feedlot runoff.
Alternative treatment systems such as this infiltration and wetland system may be allowed for facilities with more than 1,000 animal units if they can be shown to provide water quality protection equal to, or better than, conventional containment/irrigation systems. Whether allowed for large lots or not, they have potential to help small feedlot operators improve their environmental stewardship.
