Laboratory Comparison of Four Iron‐Based Filter Materials for Drainage Water Phosphate Treatment

A laboratory investigation evaluated phosphate (PO4(3-)) 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). Only filter material retained on a 60-mesh sieve (> 0.25 mm) was used for evaluation. 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 1 x 10(-2) cm/s. For the 1, 10, and 100 ppm PO4(3-)-P contaminant removal batch tests, each of the four iron-based filter materials removed at least 95% of the PO4(3-)-P originally present. However, for the 1000 ppm PO4(3-)-P contaminant removal batch tests, IOH by far exhibited the greatest removal effectiveness (99% PO4(3-)-P removal), followed by SMI (72% PO4(3-)-P removal), then ZVI (62% PO4(3-)-P removal), and finally PIC (15% PO4(3-)-P removal). The desorption/dissolution batch test results, especially with respect to SMI and IOH, indicate that once PO4(3-) is adsorbed/precipitated onto surfaces of iron-based filter material particles, this PO4(3-) 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 (contact time ranged from a few hours to a few minutes) and PO4(3-) concentration (1 ppm or 10 ppm PO4(3-)-P), PIC, SMI, and IOH reduced PO4(3-)-P concentrations to below detection limits, while ZVI removed at least 90% of the influent PO4(3-)-P. Consequently, these laboratory results indicate that the ZVI, PIC, SMI, and IOH filter materials all exhibit promise for phosphate drainage water treatment.