Odor and Nutrient Management Newsletter

Winter 2001

Settling basin alternative feedlot systems

by Christa Hartsook, Iowa Cattlemen’s Association

Iowa and federal laws require that all feedlots must settle the solids from feedlot runoff. Concentrated animal feeding operations (CAFOs), feeding operations with greater than 1,000 animal units (a.u.), must contain all runoff from the feedlot, including liquid in a total containment basin. However, smaller feedlots may release liquids after settling solids. Total containment is expensive and labor-intensive. The proposed Environmental Protection Agency (EPA) regulations for Iowa’s open feedlots would require total containment structures to be built in Iowa, at a high cost to cattle producers.

The Iowa Cattlemen’s Association has been working with EPA officials to allow for implementation of alternative structures, such as vegetative filter strips or a combination of an infiltration area and a constructed wetland, for feedlot operators who have less than 1,000 a.u. and who do not discharge directly to waters of the state. Both alternatives seem practical and less expensive for Iowa producers.

Iowa State University (ISU) began researching the effectiveness of a constructed wetland to remove harmful nutrients from effluent in 1997, when an infiltration area and a wetland were constructed below the ISU Beef Nutrition Farm. The nutrition farm consists of a 56- by 756-ft concrete feedlot and an additional 11- by 340-ft earthen lot. Total capacity is approximately 500 head between the two lots.

photo of settling basinResearch by Jeff Lorimor, ISU ag and biosystems engineering state specialist and cooperator with the Iowa Beef Center, suggests that wetlands can handle high nitrate levels. Lorimor and coworkers want to study how well the wetland would turn ammonia from the effluent into nitrate, and there has been considerable interest from producers of all species to study a wetland.

Initially, Lorimor constructed an infiltration area 120 by 350 ft below both feedlots. All the feedlot solids were settled and then stored in concrete bunkers. Runoff was collected and carried to this infiltration area through a 14-in. underground pipe. The infiltration area reduced the phosphorus and converted the ammonia into nitrate. Tile lines carried the infiltrated water to a 90- by 150-ft wetland, which was 18 in. in depth. The wetland further treated tile effluent before releasing it into the waterway. The outcome of 2 years of sampling on the overall nutrient reduction is shown in Table 1.

Lorimor and coworkers have been pleased with the overall results of the wetland and infiltration area. Most of the cleanup occurs in the infiltration area, but they are not satisfied with the water released - it still needs to be cleaner.

The infiltration field is sized at one-quarter the area of the feedlot and the wetland is one-fifth the area of the infiltration field. This technology is expected to remove more than 90 percent of the nutrients from the effluent. The wetland can be loaded at a rate of 3 to 10 lb of nitrogen per acre per day.

According to Lorimor, the wetland and infiltration system offers producers a lower cost-effective method to treat their runoff. It also requires less management. However, unless the regulations are changed, these alternative technologies are only available for feedlots with less than 1,000 a.u.

Vegetative filter strips offer another low-cost alternative to total containment. The vegetative filter strips are equal to the area of the feedlot and are expected to remove 80 percent of the nutrients from the effluent. The liquid is allowed to spread over the surface of the forage and soak in to the ground. It is important that the vegetative cover is thick enough to retain the liquid until it soaks into the ground and that it does not form a gully wash. Table 1. Nutrient reduction results after 2 years of sampling in a wetland.

  Runoff (mg/l) Remaining (mg/l) Reduction (%)
Nitrate N 0.9   1.4 –55.2
Ammonia N 108 14.6   86.3
Phosphorus 34   0.9   91.4

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