Effects of different pairing configurations of woodchips and steel chips in dual media treatment systems on nutrient removal and organics and iron leaching

Abstract

Nitrogen and phosphorus are two primary nutrients that can promote eutrophication in aquatic ecosystems. Recycled steel chips have been proposed to be used in conjunction with woodchips in dual-media treatment systems to remove nutrients from water, but the effects of different pairing configurations of woodchips and steel chips on nutrient removal have not been fully understood. The use of woodchips and steel chips for water treatment can result in leaching of organic carbon and iron. However, little is known about the impact of different media configurations on organics and iron leaching. In this study, laboratory column reactors using woodchips and steel chips (volumetric ratio of 11:1) were constructed based on three pairing configurations: woodchips/steel chips, steel chips/woodchips, and mixture of the two media. The column reactors were operated to evaluate nitrate and phosphate removal efficiencies and organic carbon and iron leaching from different media pairing arrangements. The results showed that the three media pairing configurations achieved similar overall nitrate and phosphate removal efficiencies but resulted in substantially different organic carbon and iron concentrations in reactor effluents. Steel chips, when placed downstream of woodchips reduced reactor organic carbon leaching, whereas woodchips, when placed downstream of steel chips reduced reactor iron leaching. The mixed media reactor was able to effectively control both organic carbon and iron leaching. The results of flow and temperature variation experiments showed that phosphate removal efficiencies by the steel chip filter were much less affected by flow and temperature changes than nitrate removal efficiencies by the woodchip bioreactor.