Suppression of nutrient release from freshwater lake sediments using granulated coal ash

Abstract In order to investigate the applicability of granulated coal ash (GCA), a by-product of coal thermal power stations, to freshwater lakes, two incubation experiments (fall and summer experiments) were conducted using large-volume vessels and sediments taken from eutrophic lakes. The phosphorus and nitrogen release fluxes in the vessels with GCA (up to 2.9 mg m−2 d−1 for total phosphorus and 23.9 mg m−2 d−1 for total nitrogen) were considerably smaller than those in the vessels without GCA (up to 8.9 mg m−2 d−1 and 56 mg m−2 d−1, respectively), except in the case of phosphorus in the fall experiment, and thus the phosphorus concentration released from the vessel without GCA under anoxic conditions in the summer experiment was extraordinarily higher (over 1.5 mg l−1) than those in the other vessels (less than 0.31 mg l−1). Supplementary experiments with smaller columns indicated that the chemical effect of GCA was on a similar level with its physical effect and that the threshold phosphorus concentration for removing it was lower in freshwater than seawater. The chromium level slightly exceeded the standard for drinking water and the development of technology to suppress its release is a future challenge.