Phosphate Removal from Agricultural Drainage Water Using an Iron Oxyhydroxide Filter Material

Abstract

Phosphate discharged in 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 (α-FeOOH) filter material for phosphate treatment. Original iron oxyhydroxide filter material (SG-IOH-O) and the same filter material regenerated with sodium hydroxide (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 with an additional 1 or 10 ppm phosphate-P (PO₄-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 PO₄-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.

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