Metal-Modified Mussel Shell for Efficient Binding of Phosphorus in Eutrophic Waters

As phosphorus (P) exceeds 0.1 mg P L −1 , the water is usually considered high enough to cause eutrophication. Thermally treated mussel shell (TMS), a calcium-rich (36.76%) biological material, was an environmentally friendly and low-cost adsorbent for P removal. To achieve very low concentrations of P, composite agents of PAC–TMS, Fe–TMS and La–TMS were prepared with the optimum weight ratio of 0.4, 0.2 and 0.2 (g g −1 ) [polyaluminium chloride (PAC), Fe(OH) 3 or La 2 O 3 to TMS] with the lower cost and high P adsorption efficiency, respectively, all of which had more than 80% of P removal rate after 12-h treatment of 5 mg L −1 P solution, much higher than that of TMS alone (50%). Isotherm experiment showed that these composite agents have maximum phosphate adsorption capacities of 91.74 mg P g −1 (PAC–TMS), 101.42 mg P g −1 (Fe–TMS) and 56.50 mg P g −1 (La–TMS), respectively. Additionally, the metal-modified TMS was almost independent of pH. Long-term efficient removal of P (< 0.1 mg L −1 ) was achieved during a 3-month removal trial of P-contaminated water while using these metal-modified TMS. Since metal-modified TMS both had calcium and other multivalent metal (Al, La or Fe), the modification pathway was mainly dependent on both enhance adsorption/precipitation by a simultaneous effect of the calcium and other multivalent metal.