The potential use of a water treatment residue as a temporary growth medium over a coal combustion ash: yield response of two creeping grasses

Abstract

Recent research has indicated the potential for recovery of aluminium from alumina-rich coal-combustion ashes (CCA). However, the ash disposal sites, if not vegetated, often present environmental risks due to water and air-borne dispersal of contaminants. This study investigated the potential of a lime-softening water treatment residue (LWTR) as a temporary growth medium for grass over a CCA prior to the reprocessing of the ash dump. Cynodon dactylon and Stenotaphrum secundatum were grown in 20, 40 and 60 mm layers of LWTR over a CCA, with and without added fertiliser. Chemical and physical properties of the LWTR and CCA were determined and above and below-ground biomass for each treatment measured. Both species performed best in the 60 mm layer with fertiliser, and C. dactylon yielded higher than S. secundatum. The roots of the grass species did not readily penetrate the ash layer, this being attributed to a combination of adverse physical conditions and aluminium. Cynodon dactylon was more tolerant of the high pH, but both species have potential as cover vegetation on the ash dumps when these are capped with LWTR.