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

A laboratory investigation evaluated phosphate (PO43-) 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 3 10(-2) cm/s. For the 1, 10, and 100 ppm PO43--P contaminant removal batch tests, each of the four iron-based filter materials removed at least 95% of the PO43--P originally present. However, for the 1000 ppm PO43--P contaminant removal batch tests, IOH by far exhibited the greatest removal effectiveness (99% PO43--P removal), followed by SMI (72% PO43--P removal), then ZVI (62% PO43--P removal), and finally PIC (15% PO43--P removal). The desorption/dissolution batch test results, especially with respect to SMI and IOH, indicate that once PO43- is adsorbed/precipitated onto surfaces of iron-based filter material particles, this PO43- 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 PO43- concentration (1 ppm or 10 ppm PO43--P), PIC, SMI, and IOH reduced PO43--P concentrations to below detection limits, while ZVI removed at least 90% of the influent PO43--P. Consequently, these laboratory results indicate that the ZVI, PIC, SMI, and IOH filter materials all exhibit promise for phosphate drainage water treatment.