Laboratory comparison of four iron-based filter materials for drainage water phosphate treatment

Authors: Allred, Barry; RACHARAKS, RATANACHAT - The Ohio State University

Submitted to: Water Environment Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2014
Publication Date: 9/1/2014
Publication URL: http://handle.nal.usda.gov/10113/59965
Citation: Allred, B.J., Racharaks, R. 2014. Laboratory comparison of four iron-based filter materials for drainage water phosphate treatment. Water Environment Research. 86(9):852-862.

Interpretive Summary: Phosphate, if present in high amounts in agricultural drainage water, can have adverse environmental impacts on downstream water bodies by supporting harmful algal blooms. On-site filter treatment using iron-based filter materials can potentially remove phosphate from drainage water before these waters are discharged into local streams. Laboratory investigations were conducted to determine the treatment potential of four iron-based filter materials; zero valent iron (ZVI), porous iron composite (PIC), sulfur modified iron (SMI), and a synthetic iron oxide/hydroxide (IOH). IOH had the highest water flow rates, but the other three materials were also capable of allowing sufficient flow rates. IOH had the largest phosphate removal capacity, followed by SMI, with ZVI next, and then PIC. The tests showed that once phosphate is adsorbed or precipitated onto particle surfaces of the iron-based filter materials, this phosphate becomes fixed in place and does not go back into solution. The ZVI, PIC, SMI, and IOH filter materials were all capable of rapid and effective removal of drainage water phosphate. Field investigations are needed to confirm this conclusion. This result has strong implications for environmental remediation and water quality organizations and industry.

Technical Abstract: Phosphate released with agricultural subsurface drainage water can cause environmental degradation of downstream water bodies. On-site filter treatment with iron-based filter materials could potentially remove phosphate from drainage waters before these waters are discharged into local streams. Therefore, a laboratory investigation was carried out to evaluate phosphate drainage water treatment capabilities of four iron-based filter materials. The iron-based filter materials tested were zero valent iron (ZVI), porous iron composite (PIC), sulfur modified iron (SMI), and iron oxide/hydroxide (IOH). The laboratory investigation included saturated falling-head hydraulic conductivity tests, contaminant removal or desorption/dissolution batch tests, and low-to-high flow rate saturated solute transport column tests. Each of the four iron-based filter materials have sufficient water flow capacity as indicated by saturated hydraulic conductivity values that in most cases were greater than 0.01 cm/s. For the 1, 10, and 100 ppm phosphate-phosphorus contaminant removal batch tests, each of the four iron-based filter materials removed at least 95% of the phosphate originally present. However, for the 1000 ppm phosphate-phosphorus contaminant removal batch tests, IOH by far exhibited the greatest removal effectiveness (99% phosphate removal), followed by SMI (72% phosphate removal), then ZVI (62% phosphate removal), and finally PIC (15% phosphate removal). The desorption/dissolution batch test results, especially with respect to SMI and IOH, indicate that once phosphate is adsorbed/precipitated onto surfaces of iron-based filter material particles, this phosphate becomes fixed and is then not readily desorbed/dissolved back into solution. The results from the column tests showed that regardless of low or high flow rate and even with high phosphate concentrations (1 ppm or 10 ppm phosphate-phosphorus), ZVI, PIC, SMI, and IOH removed almost all of the phosphate originally present. Consequently, these laboratory results indicate that the ZVI, PIC, SMI, and IOH filter materials all exhibit substantial promise for phosphate drainage water treatment.