EVALUATION OF STABILIZED COAL-FIRED POWER-STATION WASTE FOR ARTIFICIAL REEF CONSTRUCTION

An experimental artificial reef was installed in Poole Bay in June 198 9 to test the feasibility of using U.K. coal-fired power station waste products to produce a structure with fishery enhancement potential. T hree different mixtures of the materials used, pulverized fuel ash (PF A), flue gas desulfurization (FGD) gypsum and FGD slurry, were stabili zed with cement. Fifty tons of 40 X 20 X 20 cm blocks were formed into eight conical reef units, 1 m high, replicating three different PFA/g ypsum mixtures and concrete controls. A concern arising from the use o f such materials is that the heavy metals concentrated by the combusti on of coal, and remaining in the ash, may leach out. The heavy metal c ontent (Cd, Cr, Cu, Pb, Mn, Ni, Zn) of the blocks has been monitored f rom both surface samples and sectioned cores to determine leaching rat es. There have been no significant changes in heavy metal concentratio ns to date, any temporal or spatial variation being within limits attr ibutable to material heterogeneity. However there is some indication o f a trend in block depth profiles suggesting either internal redistrib ution or surface loss of cadmium (less than 5% total) and surface enri chment by manganese and chromium. Replacement of calcium by magnesium is evident in the surface 2-4 cm of the blocks. No evidence for furthe r change was seen between block sections taken after 18 and 27 months immersion suggesting that surface diffusion changes reduce with time a nd indicating long term stability. A rich epifauna and flora quickly d eveloped on the reef blocks. The heavy metal content of epibiota on th e ash blocks has been compared to that on the concrete, surrounding se abed and local natural reefs. The organisms analyzed included: red alg ae, Calliblepharis; hydroids, Halecium halecinum; bryozoans, Bugula sp p.; sponges, Scypha ciliata; ascidians, Ascidia mentula. Molluscs, Ost rea edulis, and their predator the gastropod, Ocenebra erinacea, were also examined. No evidence of excess bioaccumulation of cadmium, chrom ium and manganese has been detected. Increasing metal concentrations i n ascidians related to elevated water column concentrations are shown by comparison of the Poole Bay natural and artificial reef samples wit h those taken from nearby Poole Harbour, which is partially urbanized.