Location: Soil Drainage ResearchTitle: Phosphate removal from agricultural drainage water using an iron oxyhydroxide filter material Author
Submitted to: Water, Air, and Soil Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/23/2017
Publication Date: 6/8/2017
Citation: Allred, B.J., Martinez, L.R., Gamble, D.L. 2017. Phosphate removal from agricultural drainage water using an iron oxyhydroxide filter material. Water, Air, and Soil Pollution. https://doi.org/10.1007/s11270-017-3410-9. Interpretive Summary: Phosphate released with agricultural drainage waters can have adverse environmental impacts at local, regional, and national scales. Filter treatment with iron-based porous media has potential for removing phosphate from drainage waters. Laboratory saturated column experiments and field tests with small filter treatment systems were carried out to evaluate the effectiveness and efficiency of a synthetic goethite iron oxyhydroxide for removing phosphate from drainage water, and additionally, whether this material, once it becomes spent, can be regenerated and reused for phosphate treatment. The original synthetic goethite iron oxyhydroxide direct from the manufacturer, SG-IOH-O, proved effective and efficient for drainage water phosphate treatment. In replicated column experiments, SG-IOH-O was found to remove greater than 98% of phosphate from drainage waters that had been spiked an additional 1 or 10 ppm phosphate-P. These same column experiments also showed SG-IOH-O to be very efficient, needing only a 12 seconds contact time for near complete phosphate removal. An average of 89% phosphate removal was observed during the first 200 days in an initial small-scale filter treatment system field test with SG-IOH-O, but in the final 80 days of the test, phosphate removal averaged 40%. A second SG-IOH-O field test exhibited an average 75% phosphate removal over 193 days. Synthetic goethite iron oxyhydroxide regenerated with sodium hydroxide, designated SG-IOH-R, exhibited much greater effectiveness for drainage water phosphate treatment in the laboratory column experiments (> 98% removal) than in a field test (only 34% removal). For the SG-IOH-R field test, prior formation of calcium/magnesium-phosphate precipitates may have substantially reduced the success of the regeneration process, thereby limiting the capability of SG-IOH-R to remove phosphate. To solve this problem, the regeneration process has to be modified to include a dilute acid wash for dissolving these calcium/magnesium-phosphate precipitates. The column experiments and field tests additionally indicate that neither SG-IOH-O or SG-IOH-R have any adverse impact on water pH. The overall implication from the results of this investigation is that goethite iron oxyhydroxide filter materials have substantial promise for drainage water phosphate treatment; however, there is a need for larger-scale field investigations and further optimization of regeneration procedures.
Technical Abstract: Phosphate discharged with agricultural drainage causes water quality degradation on local, regional, and national scales. Iron oxyhydroxide filter materials can potentially remove the soluble phosphate present in drainage waters. Laboratory saturated column experiments and preliminary small-scale field tests were carried out to evaluate the effectiveness and efficiency of a synthetic goethite iron oxyhydroxide filter material for phosphate treatment. Original iron oxyhydroxide filter material (SG-IOH-O) and the same filter material regenerated with a sodium hydroxide rinse (SG-IOH-R) were assessed. Results of replicated laboratory experiments showed that columns packed with SG-IOH-O or SG-IOH-R almost totally removed phosphate (> 98%) from drainage waters spiked an additional 1 or 10 ppm phosphate-P. The column experiments with SG-IOH-O or SG-IOH-R additionally indicated that contact times of only 10 to 15 s were sufficient for near complete removal of phosphate from drainage water spiked with 1 ppm phosphate-P. In an initial small-scale filter treatment system field test with SG-IOH-O, percent phosphate removal averaged 89% in the first 200 days, which then decreased to an average 40% phosphate removal in the last 80 days. Following this initial field test, two field tests, one with SG-IOH-O and the other with SG-IOH-R, were conducted concurrently over a period of 193 days, with the SG-IOH-O system phosphate removal averaging 75%, while the SG-IOH-R system phosphate removal averaged 34%. This study's findings support possible goethite iron oxyhydroxide filter material use for drainage water phosphate treatment; however, larger-scale field investigations are needed, particularly with modified regeneration procedures.