Laboratory Evaluation of Porous Iron Composite for Agricultural Drainage Water Filter Treatment

Abstract

Agricultural subsurface drainage waters containing nutrients (nitrate/phosphate) and pesticides are discharged into neighboring streams and lakes, frequently producing adverse environmental impacts on local, regional, and national scales. On-site drainage water filter treatment systems can potentially prevent the release of agricultural contaminants into adjacent waterways. A recently developed porous iron composite (PIC) product may have promise as a filter material for drainage water treatment. Therefore, a laboratory study was initiated to evaluate the feasibility of using PIC for this purpose. Laboratory experiments included saturated falling-head hydraulic conductivity tests, contaminant (nutrient/pesticide) removal batch tests, and saturated solute transport column tests. The saturated falling-head hydraulic conductivity tests indicate that the original PIC product by itself has a high enough hydraulic conductivity (>0.001 cm s-1) to make this material hydraulically practical for filter treatment use. PIC hydraulic conductivity can be further enhanced (>0.01 cm s-1) by utilizing only the portion of this material retained on a 100 mesh sieve (particle size > 0.15 mm). Batch test results carried out with spiked drainage water and either unsieved or 100 mesh sieved PIC showed nitrate reductions of greater than 30%, and 100% removal of the pesticide atrazine. Saturated solute transport column tests with spiked drainage water provided more insight on the effectiveness and efficiency of utilizing PIC for drainage water filter treatment. These column tests confirm that PIC is capable of nearly complete removal of atrazine, and significant nitrate reduction. Additionally, once the phosphate originally present within the PIC material is leached out, the PIC then exhibited ability to remove large quantities of phosphate. Consequently, these laboratory findings support employment of PIC for use within on-site agricultural drainage water filter treatment systems.