Environmental implications of coal use for artificial reef construction

Experiments have been carried out on ash derived from coal combustion ENEL power plant as a component for artificial reef blocks. After preliminary laboratory tests in order to establish the optimum block hydrated lime-coal ash ratio and to determine their in seawater leaching capability, systematic physical, chemical and biological tests have been carried out on reef models in experimental plant. Ash and concrete cubic blocks (20x20x20 cm), the latter used as reference, have been arranged in pyramid shaped reef models inside two trial tanks supplied with flowing seawater. After two year of tests encouraging results have been obtained. No weathering, volume variation or swelling have been found; marked compressive strength and sonic velocity increases have on the contrary been recorded. In tank (water and blocks) chemical tests have shown no significant leaching phenomena for chemical elements of environmental concern while laboratory tests showed a limited blocks leaching capability (ppm) for macrocomponents such as Al, Si, Ca and to a lesser extent (ppb) for hazardous elements like As, Cr, Se, Ti. Studies on biocolonization have clearly shown that bentonic settlement on ash blocks is more evident than on concrete ones with a major number of species and biomass quantity. Chemical tests have also shown no bioaccumulation phenomena. Research goes on; in 1992 a first pilot, ash reef is in progress in the Adriatic sea to confirm the feasibility and the environmental compatibility of this kind of artificial reef. 9 refs., 3 figs., 2 tabs