Progress 11/15/00 to 11/14/04
Outputs Previous lysimeter and laboratory studies found a small DC electrical current could attract anions to and retain them near the anode in sandy soil even with solute flow towards the cathode. Additional laboratory experiments were conducted with sandy, loamy and clayey soils to determine if nitrate transport could similarly be controlled in the other two soils using electrokinetic (EK) technology. The tests were conducted in vertical plastic columns with anode inserted in the soil near the top of the column, cathode located close to the bottom. Nitrate solute was applied to the soil surface until liquid dripped from column bottom; then columns were left to equilibrate before initiating the electrical input. Constant electrical current was applied to the system for 9 hours and the system changes were observed for a total of 48 hours. Nitrate concentration, pH values, electrical potential and soil water content were measured for the three soils at selected times at
different distances from the anode. In sandy soils, nitrate was strongly retained near the anode against gravity with an 80 mA input. When the percentage of illite clay in the soil was increased, the EK effect on ion movement was reduced. With the loamy soil, there was a slight increase in nitrate concentration near the anode with an 60 mA electrical input, but no change in ion distribution was observed in the clayey soil column. It is concluded that EK treatment could be considered to concentrate nitrate near the anode and prevent nitrate migration in sandy soil, but additional research is required to evaluate the electrical current level and duration and electrode configuration required to move or retain nitrate in loamy and clayey soils, perhaps using a modified laboratory setup that better permits release of generated gases.
Impacts Research is determining effectiveness of controlling nitrate movement in different soils with different DC electrical inputs. Results are expected to provide guidelines for electrokinetic application to different soils and electrical inputs needed to achieve effective control. The guidelines could be used in design of electrokinetic systems to reduce nitate losses from the crop root zone and control of pollution of shallow groundwater or adjacent surface waters.
Publications
- Jia, X., DL Larson, D Slack, J Walworth. 2004. Electrokinetic control of nitrate movement in soil. Engineering Geology, In press: available online 15 September 2004.
- Jia, X., DL Larson, WS Zimmt, J Walworth. 2004. Nitrate pollution control in different soils using electrokinetic technology. Paper SW-05528, presented at the Annual Mtg of ASAE, Ottawa, Canada, Aug.
- Jia, X., DL Larson, D Slack, J Walworth. 2004. Effective nitrate control with electrokinetics in sandy soil. Proc. USDA CSREES Natl. Water Quality Conf, Clearwater, FL, Jan.
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Progress 01/01/03 to 12/31/03
Outputs Nitrate contamination of surface and ground water has been an emerging problem worldwide. Nitrate in drinking water presents a human health risk. The major source of nitrate contamination is believed to be nitrogen fertilizer from agricultural fields. Best Management Practices have been developed to guide fertilizer use and minimize losses, but do not address control of nitrate movement from the crop root zone. It is proposed that an in-situ method, electrokinetics, could be used to control nitrate movement, retaining it near the root zone. The 2003 experiments evaluated nitrate movement and pH changes in a vertical, partially saturated sandy soil column subjected to an electrical current and the identification of optimal electrokinetic parameters for future field applications. The highest measured nitrate concentration (7155 ppm) was within 5 mm of the anode, located at the top of the soil column, after application of an 80 mA current. The nitrate concentration at
the cathode at column bottom was 1/5 of the inflow solute. The pH near the cathode was 11, near the anode was 3.5, with no significant pH changes in intermediate layers. Findings with different nitrate concentrations and electrical current levels suggest an 80 mA electrical current applied for 6 hr duration might effectively control nitrate migration in sandy soil. Soil column tests are continuing with a loam and a clay soil.
Impacts Research is determining effectiveness of controlling nitrate movement in different soils with different DC electrical inputs. Results are expected to provide guidelines for electrokinetic application to different soils and electrical inputs needed to achieve effective control. The guidelines could be used in design of electrokinetic systems for use with drip irrigation.
Publications
- Jia, X., D.L. Larson, D.C. Slack, J. Walworth. 2003. Electrokinetic control of nitrate movement in soil. Proc. 4th Int. Symposium on Electroremediation. Mol, Belgium, May.
- Jia, X., D.L. Larson, D.C. Slack, J. Walworth. 2003. Electrokinetic remediation of nitrate contamination in a sandy loam soil. Proc. Annual ASAE Meeting, Las Vegas, NV, July.
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Progress 01/01/02 to 12/31/02
Outputs Laboratory box lysimeter tests found the application of dc electrical currents of 0-900 mA between the parallel, buried, horizontal anode and cathode had little effect on nitrate distribution in a saturated, clay soil, but did reduce the pH nearer the anode. Small field plot experiments, in which the cathode was placed just below the buried drip irrigation tubing and the anode intermediate between rows of lettuce planted on adjacent beds at the University of Arizona's Tucson research farm, yielded inconclusive results on the effectiveness of an electrical input on nitrate and pH distribution in the soil between the electrodes. Laboratory soil column tests are being conducted in 2003 to better control electrokinetics experiments and explain contradictory results of prior research.
Impacts Improved management of nitrate movement could yield environmental and economic benefits in production of crops produced with large fertilizer inputs. Electrokinetics might provide the means for better control of chemical migration in soils.
Publications
- Jia, X., D.Larson, D.Slack, J.Walworth. 2002. Effect of current density on nitrate migration in a clay soil. Paper 022243, presented at the ASAE Int. Mtg, Chicago, July.
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Progress 01/01/01 to 12/31/01
Outputs Three experiments evaluated the hypothesis that a small dc electrical current would attract and retain nitrates and increase soil acidity in the region near a positive electrode, thus reducing leaching losses of fertilizer and increasing nutrient availability to plants whose root zone was in the region near the electrode. The experiments involved 1) laboratory comparison of chemical movement in soils with application of different levels of electrical input, 2) small lysimeter comparison of nitrate and pH distribution from row to row and 3) field plot testing of the use of an electrical input in subsurface drip irrigated lettuce growth. Results were inconsistent, but generally showed an electrical input increased nitrate content and yielded lower pH and electrical conductivity values near the anode located in the plant root zone. Electrical input schedule and level will be further evaluated in future tests.
Impacts Improved management of nutrient availability could yield environmental and economic benefits in the production of crops, particularly those grown with large fertilizer inputs.
Publications
- No publications reported this period
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