Institute: South Dakota
Year Established: 2017 Start Date: 2017-03-01 End Date: 2018-02-28
Total Federal Funds: $23,062 Total Non-Federal Funds: $46,151
Principal Investigators: Guanghui Hua, Christopher Schmit
Abstract: Agricultural subsurface drainage is a widely adopted water management practice to increase crop production in the Midwestern United States and many other areas. Subsurface drainage removes excess water from the soil profile through a network of underground perforated pipes or surface ditches, which allows cultivation of agricultural fields with poor natural drainage. However, subsurface drainage systems also provide direct conduits that can transport nutrients from agricultural fields to surrounding natural water. Elevated nutrient levels in surface waters can lead to a number of negative water quality impacts including harmful algal blooms, hypoxic zones in the ocean, and contamination of drinking water supplies. Therefore, it is critical to develop effective technologies to reduce the loss of nutrients through subsurface drainage to protect natural water resources and increase the sustainability of agricultural production. Nitrate has been a major water quality concern for many subsurface drainage systems due to its high solubility and mobility in soils. Nitrate-nitrogen concentrations in subsurface drainage water often exceed the United States Environmental Protection Agency drinking water standard of 10 mg/L. Increased nitrate loading into the Mississippi River Basin from agricultural drainage in the Midwest has been identified as a major contributor to growing hypoxia in the Gulf of Mexico. Denitrification bioreactors have emerged as an important edge-of-field treatment technology to reduce nitrate loads from subsurface drainage. These bioreactors typically utilize an organic carbon medium to support the growth of denitrifying bacteria which use organic substrates as electron donors to reduce nitrate to nitrogen gas. Woodchips are by far the most widely used materials in field-scale denitrification bioreactors and have shown the ability to deliver long-term (> 10 years) nitrate removal while requiring minimum maintenance. The nitrate removal efficiency of denitrification bioreactors is dependent on the quantity of readily biodegradable carbon that can be utilized by the denitrifying bacteria. However, a major portion of organic carbon derived from wood materials is not easily biodegradable, which can limit the nitrate removal rates. Organic carbon media derived from agricultural residues such as corn cobs, corn stover and wheat straw have shown the ability to produce high quantities of easily biodegradable carbon and to support high densities of denitrifying microorganisms in bioreactors. Recent studies also showed that on-farm agricultural resides exhibit better nitrate removal performance than woodchips, especially at low temperatures. Clearly, the longevity and hydraulic properties of agricultural residue media warrant further study for field applications. The goal of this project is to develop a new bioreactor system that uses a combination of an agricultural residue and woodchips to increase the nitrate removal efficiency and reduce the cost of the bioreactors. The use of on-farm residues may also increase the acceptance of this technology for agricultural water management.