Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 24, 2012
Publication Date: October 1, 2012
Repository URL: http://handle.nal.usda.gov/10113/58173
Citation: Allred, B.J. 2012. Laboratory evaluation of porous iron composite for drainage water treatment. Transactions of the ASABE. 55(5):1683-1697. Interpretive Summary: Effective methods are needed to remove nutrient (nitrate/phosphate) and pesticide contaminants from agricultural drainage waters before these waters are released into local streams and lakes. One possible solution is the use of on site filter treatment systems. The critical factor with this type of water treatment system will be choosing a proper filter material that effectively removes agricultural contaminants. One promising filter material is a recently developed modified iron product. A laboratory study was initiated to directly evaluate the feasibility of employing this new modified iron product as a filter material to treat drainage waters. The test results indicate that the modified iron allows sufficient water flow rates needed to make this filter material hydraulically practical for use in drainage water filter treatment systems; that modified iron can remove significant amounts of nitrate and almost all atrazine from drainage waters; and the modified iron exhibits ability to remove large quantities of phosphate. Consequently, these laboratory findings support employment of this modified iron product for use within on-site agricultural drainage water filter treatment systems.
Technical Abstract: The removal of excess soil water with a subsurface drainage pipe system is a common agricultural practice employed to improve crop yields, especially in the Midwest U.S. However, fertilizer nutrients (nitrate and phosphate) and pesticides applied on farm fields will frequently leach downwards through the soil profile to be intercepted by the buried drainage pipes and then discharged with drainage water into neighboring streams and lakes, oftentimes producing adverse environmental impacts on local, regional, and national scales. On-site drainage water filter treatment systems can potentially be employed to prevent the release of agricultural nutrients/pesticides into adjacent waterways. A recently developed modified iron product may have promise as a filter material used within this type of drainage water treatment system. Therefore, a laboratory study was initiated to directly evaluate the feasibility of employing this new modified iron product as a filter material to treat drainage waters. Laboratory research included saturated falling-head hydraulic conductivity tests, contaminant (nutrient/pesticide) removal batch tests, and saturated solute transport column experiments. The saturated falling-head hydraulic conductivity tests indicate that the unaltered modified iron product by itself has a high enough hydraulic conductivity (> 0.001 cm/s) to normally allow sufficient water flow rates that are needed to make this material hydraulically practical for use in drainage water filter treatment systems. Modified iron hydraulic conductivity can be improved substantially (> 0.01 cm/s) by using only the portion of this material that is retained on a 100 mesh sieve (particle size > 0.15 mm). Batch test results carried out with spiked drainage water and either unaltered or 100 mesh sieved modified iron showed nitrate reductions of greater than 30% and 100% removal of the pesticide, atrazine. Saturated solute transport columns tests with spiked drainage water provided further insight on the effectiveness and efficiency of utilizing modified iron as a filter material for drainage water treatment. These column tests confirm that the modified iron is capable of nearly complete removal of atrazine, and also significant amounts of nitrate. Furthermore, once the phosphate originally present within the modified iron leaches out, the modified iron then exhibits ability to remove large quantities of phosphate. Consequently, these laboratory findings support employment of this modified iron product for use within on-site agricultural drainage water filter treatment systems; although, field pilot tests are now needed to further document this particular application for modified iron.