Abstract
Alkaline flocculation has been considered as a potential candidate to remove algae and eutrophic substances from water. A number of researches using low-cost and environmentally friendly methods have been suggested to optimize removal efficiency. In this study, a calcium-containing waste oyster shell, as an environmentally friendly substance, has been used to treat phosphorous, a eutrophic substance, and to remove algae from the fresh water simultaneously. The X-ray Fluorescence (XRF) analysis showed that CaO was a major phase in a raw oyster shell, which played an important role for flocculation of phosphorous as well as algae. In order to eliminate the algae or phosphorous effectively, oyster shell was calcined at 1000 °C and hydrated in water. The slurry of hydrated calcined oyster shell, from 5 g/L to 12.5 g/L, was utilized in this experiment, where the experimental results were compared with that of dolomite. A series of experimental investigations, such as pH and turbidity changes using the water quality analyzer and UV-Visible spectroscopy (UV-Vis), demonstrated that the algae were efficiently removed. In addition, total phosphorous (TP) and total nitrogen (TN) analyses at different amounts of slurries of the hydrated calcined oyster shell showed that almost all the phosphorous was removed at 7.5 g/L of hydrated oyster shell, but due to the high solubility of nitrogen compounds, no obvious effect for the removal of nitrogen was observed. Furthermore, powder X-ray diffractions (PXRD) showed that Ca(OH)2 compounds were transformed to the phosphate compound, suggesting that the oyster shell caused flocculation by chemically forming with phosphorous ions.
Highlights
For several decades, algal blooms by the eutrophication in a fresh water have been considered as a steadily generated worldwide issue, threatening aquatic life, human health, water quality, and fishing operation [1,2,3,4,5,6]
Our group has found that since the limestone and dolomite contained much of the Ca species, the experiments using both of them resulted in an outstanding removal efficiency of algae
To identify the chemical components in the oyster shell, a raw oyster shell was characterized by the X-ray Fluorescence (XRF), in which the result was compared with that of limestone and dolomite
Summary
Algal blooms by the eutrophication in a fresh water have been considered as a steadily generated worldwide issue, threatening aquatic life, human health, water quality, and fishing operation [1,2,3,4,5,6]. In China, main rivers and lakes, such as Yangtz River, Songhua River, Wuhan east lake, and Taihu lake, have suffered from extensive algal bloom, raising a problem for drinking water [7]. Some Asian and developing countries, including Vietnam and South Korea, have been going through severe environmental and social problems due to algal bloom [10,11,12]. Algae require diverse nutrients including nitrogen, oxygen, phosphorus, silicon, and iron, but populate with feeding mostly phosphorus (P) and nitrogen (N) as major nutrients.
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