Author
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Allred, Barry |
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Submitted to: Ground Water Monitoring and Remediation
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 11/12/2011 Publication Date: 12/25/2011 Citation: Allred, B.J. 2011. Laboratory evaluation of zero valent iron and sulfur modified iron filter materials for agricultural drainage water treatment. Ground Water Monitoring and Remediation. 32(2):80-95. DOI: 10.1111/j.1745-6592.2011.01379.x. Interpretive Summary: Where agricultural subsurface drainage practices are employed, fertilizer nutrients and pesticides that are applied near the ground surface will commonly leach downwards through the soil profile to be intercepted by the buried drainage pipes and then discharged into streams and lakes, oftentimes producing adverse environmental impacts on downstream surface water bodies. On-site drainage water filter treatment systems can potentially be employed to prevent the release of agricultural nutrients/pesticides into adjacent waterways. Zero valent iron and sulfur modified iron are two types of promising filter materials that could be used within these agricultural water treatment systems. Therefore, drainage water treatment capabilities of three zero valent iron and three sulfur modified iron filter materials were evaluated in the laboratory. Results from these tests document the drainage water treatment ability of both zero valent iron and sulfur modified iron to remove the phosphate, the ability of sulfur modified iron to remove nitrate, and the ability of select zero valent iron materials to remove atrazine. Consequently, these laboratory findings support the use of zero valent iron and sulfur modified iron filter materials, alone or combined, within on-site agricultural drainage water filter treatment systems. This information will be beneficial to farmers, state and local agency personnel, and environmental engineers/designers. Technical Abstract: On site filter treatment systems have the potential to remove nutrients and pesticides from agricultural subsurface drainage waters. The effectiveness and efficiency of this type of drainage water treatment will depend on the actual filter materials utilized. Two promising filter materials that could be employed for this purpose are zero valent iron (ZVI) and sulfur modified iron (SMI); however, additional investigation was needed to determine whether ZVI and/or SMI were in fact feasible for drainage water treatment of nitrate, phosphate, and pesticides, such as atrazine. Therefore, drainage water treatment capabilities of three ZVI filter materials and three SMI filter materials were evaluated in the laboratory. Laboratory evaluation included saturated falling-head hydraulic conductivity tests, contaminant (nutrient/pesticide) removal batch tests, and saturated solute transport column experiments. The major findings of this laboratory study are listed as follows. 1) The saturated falling-head hydraulic conductivity tests generally indicate that the ZVI and SMI filter materials have high enough hydraulic conductivities (> 0.001 cm/s) to allow sufficient water flow rates that are needed to make these filter materials hydraulically practical for use in drainage water filter treatment systems. 2) Batch test results, which provide a preliminary assessment of contaminant removal potential, showed a phosphate decrease of at least 94% for all tests conducted with the ZVI and SMI filter materials. Furthermore, the three SMI filter materials removed at least 86% of the nitrate originally present, while batch tests for one of the ZVI materials exhibited an 88% decrease in the pesticide, atrazine. 3) Saturated solute transport column tests further evaluated the effectiveness and efficiency for drainage water treatment of one ZVI filter material separately, one SMI filter material separately, along with these particular ZVI and SMI filter materials together in series. Column test results with the SMI filter material only show that this specific SMI is capable of removing substantial amounts of nitrate and phosphate from drainage waters under conditions where initial levels of nitrate and phosphate are moderate (nitrate-nitrogen at 10 mg/L and phosphate-phosphorous at 0.1 mg/L), where initial levels of nitrate and phosphate are extremely high (nitrate-nitrogen at 100 mg/L and phosphate-phosphorous at 1.0 mg/L), over extended periods, and in cases that the SMI filter material to drainage water exposure time is relatively short (about 9 min.). Results of a column test with the ZVI material only confirmed that this specific ZVI is capable of removing substantial amounts of phosphate and atrazine from drainage waters. A column test with both of these filter materials in series (with the SMI filter material comprising the first stage and the ZVI comprising the second stage) indicates that putting ZVI and SMI together in a filter treatment system may be a good approach to combined removal nitrate, phosphate, and pesticides, such as atrazine. Consequently, this laboratory research supports the feasibility if using ZVI and/or SMI for treatment of agricultural subsurface drainage waters. Both ZVI and SMI would appear to be especially good at reducing phosphate levels in drainage waters. However, before widespread adoption of ZVI and/or SMI drainage water filter treatment systems can even be considered, both small scale and large scale field pilot tests need to be conducted over long periods of time. |
