Impacts of Fly-Ash-Shell-Blocks on pH and Nutrient Environments in Seawater

Abstract

In this study, we examined the impacts of fly-ash-shell-blocks (FSBs) on the pH and nutrient environments in seawater to determine the usefulness of utilizing fly ash and scallop shell to form a marine macroalgal reef. Ordinary portland cement paste (OPC) , FSB, and FSB blended with blast furnace slag were placed in seawater at a liquid : solid ratio of 10 : 1, and the changes in pH and nutrient (SiO₂, PO₄, NH₄, NO₂, and NO₃) concentrations for 7 days were investigated. The experiments were conducted using blocks four months and one year after production. Whereas the pH of the original seawater was about 8.0, the pH after the OPC treatment increased to about 9.9 and only SiO₂ was eluted. With the FSB and blended FSB treatments, the pH increased to 8.2–8.5 and all the nutrients were eluted. The source of the nutrients in FSB and blended FSB should be the fly ash. The eluted nutrients would positively affect the growth of the attached kelp. FSB and blended FSB may be more useful for a macroalgal reef than OPC because of their smaller pH increase and greater nutrient leaching.