Effect of Bellamya-quadrata-Shells-and-Fish-Bones Mixture Removing Phosphate in Water

An experiment was conducted to study effects of Bellamya quadrata shells, fish bones and mixture of Bellamya quadrata shells and fish bones removing phosphate in water. Results show that in water, 20 mg•L^-1 in initial phosphate concentration, 7 in pH and 303K in T, and the phosphate removal rate by Bellamya quadrata shells (4 g•L^-1) reached as high as 86% after 36 hours of exposure; the phosphate removal rate by fish bones(2 g•L^-1)was comparatively low in the absence of Ca²⁺, reaching 36% or so after 5 hours of exposure; and the phosphate removal rate of by the mixture of Bellamya quadrata shells and fish bones (6 g•L^-1)was significantly higher than Bellamya quadrata shells or fish bones, reaching as high as 96% after 12 hours of exposure. Besides, pH and the existence of Cl^-, SO₄^2-, Na⁺, K⁺, or Mg²⁺ in the water did not show much effect on phosphate removal rate of the mixture, while the existence of HCO₃^- inhibited the removal, and the existence of Ca²⁺ promoted the removal. The chief mechanisms of the mixture removing phosphate include surface adsorption of phosphate on Bellamya quadrata shells and fish bones, and precipitation of calcium phosphate. Fish bones act as cores for heterogeneous nucleation, promoting calcium phosphate precipitation, while Bellamya quadrata shells and fish bones do as Ca source, releasing Ca²⁺ to form calcium phosphate that precipitates.