Lab-Scale Column Study on Phosphorus Removal from Synthetic Wastewater by Filtralite P and Iron Filings

Abstract

Column study was performed in order to compare phosphate phosphorus (PO₄-P) removal capacity of iron filings and Filtralite P. The experiment with two vertical downflow columns (0.05 in diameter and with 0.9 m medium height) feeding synthetic wastewater was carried out over a period of 66 days at wastewater temperature of 17.2–21.8 ºC. The study also aimed to determine the effect of submergence of the medium on Filtralite P PO₄-P removal potential. During the experiment the submerged Filtralite P sorbed almost double amount of PO₄-P (1581 mg PO₄-P/kg filter material or 662 mg PO₄-P/m³ filter material) compared to the unsubmerged (881 mg PO₄-P/kg filter material or 369 mg PO₄-P/m³ filter material). In both cases PO₄-P removal efficiency exceeded 90 % when pH in the effluent was higher than 9.5. Through the experimental period the iron filings removed 2249 mg PO₄-P/kg filter material. When evaluating the amount of removed PO₄-P per volume of filter material, the iron filings removed 2164 mg PO₄-P/m³ filter material, i. e. 3.3 times more than the submerged Filtralite P did. In the case of iron filings the largest PO₄-P amount was removed in the top layer (0–30 cm) of the filter material. The amount of removed PO₄-P decreased and PO₄-P removal efficiency increased with depth of the medium: in the top layer (0–30 cm) PO₄-P removal efficiency was 27 %, whereas in the bottom layer (60–90 cm) it reached 44 %. The same tendency of PO₄-P removal efficiency was observed in the column with the submerged Filtralite P; however, the PO₄-P removal efficiency in all layers of this filter material was lower in comparison with the iron filings.