Improvement in benthic habitat environment via granulated coal ash in a water body exposed to wastewater discharge

The discharge of untreated wastewater into a water body strongly deteriorates the benthic habitat environment of bottom sediment. In this study, field experiments were conducted in the Fukuyama inner harbor (Hiroshima, Japan), which is exposed to large amounts of untreated domestic wastewater discharge. The water quality in this harbor is seriously deteriorated during the summer season, resulting in an aggravation of the marine biological environment. This study examines the improvement in benthic habitat environment at the bottom of the harbor via the use of granulated coal ash (GCA, a by-product of coal-fired electric power plants). In the field experiments, the pore water quality and benthic habitat quality (i.e., the abundance and species richness) in GCA, gravel, and sediment layers were observed over time. The experiment results suggest that both GCA and gravel provide a better habitat environment for benthos compared to the sediment. In addition, the species richness in GCA was higher than that in gravel, suggesting that benthos can more easily survive in GCA than in gravels. It appears that the absorptive ability of GCA can remove the reductants released from the anaerobic digestion of organic matter and that the dissolution of the chemical components of GCA is significant factors in creating the higher species richness in the GCA layer.