Evaluation of Stabilized Coal-Fired Power Station Waste for Artificial Reef Construction

An experimental artificial reef was installed in Poole Bay in June 1989 to test the feasibility of using U.K. coal-fired power station waste products to produce a structure with fishery enhancement potential. Three different mixtures of the materials used, pulverized fuel ash (PFA), flue gas desulfurization (FGD) gypsum and FGD slurry, were stabilized with cement. Fifty tons of 40 × 20 × 20 cm blocks were formed into eight conical reef units, 1 m high, replicating three different PFA/gypsum mixtures and concrete controls. A concern arising from the use of such materials is that the heavy metals concentrated by the combustion of coal, and remaining in the ash, may leach out. The heavy metal content (Cd, Cr, Cu, Pb, Mn, Ni, Zn) of the blocks has been monitored from both surface samples and sectioned cores to determine leaching rates. There have been no significant changes in heavy metal concentrations to date, any temporal or spatial variation being within limits attributable to material heterogeneity. However there is some indication of a trend in block depth profiles suggesting either internal redistribution or surface loss of cadmium (less than 5% total) and surface enrichment by manganese and chromium. Replacement of calcium by magnesium is evident in the surface 2–4 cm of the blocks. No evidence for further change was seen between block sections taken after 18 and 27 months immersion suggesting that surface diffusion changes reduce with time and indicating long term stability. A rich epifauna and flora quickly developed on the reef blocks. The heavy metal content of epibiota on the ash blocks has been compared to that on the concrete, surrounding seabed and local natural reefs. The organisms analyzed included: red algae, Calliblepharis; hydroids, Halecium halecinum; bryozoans, Bugula spp.; sponges, Scypha ciliata; ascidians, Ascidia mentula. Molluscs, Ostrea edulis, and their predator the gastropod, Ocenebra erinacea, were also examined. No evidence of excess bioaccumulation of cadmium, chromium and manganese has been detected. Increasing metal concentrations in ascidians related to elevated water column concentrations are shown by comparison of the Poole Bay natural and artificial reef samples with those taken from nearby Poole Harbour, which is partially urbanized.