| Energy and Chemical Engineering |
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| Lake sediment treatment with aluminum, iron, calcium and nitrate additives to reduce phosphorus release |
| Guang-rong LIU, Chun-song YE, Jing-hao HE, Qin QIAN, Hua JIANG |
| College of Power and Mechanical Engineering, Wuhan University, Wuhan 430072, China |
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Abstract Treatment of lake sediments with salts is a promising approach for preventing phosphorus release from sediments. Five 35-d treatments of undisturbed sediment cores in the East Lake, Wuhan, China were applied under anoxic conditions: nothing added (control), Al2(SO4)3 added, FeCl3 added, CaCl2 added, and NaNO3 added. To identify changes in the P binding sites in the sediment caused by the treatments, different P binding forms were extracted from the sediment before and after the treatments. We found that the mean P release rates for anoxic treatments with Al2(SO4)3, FeCl3, CaCl2 and NaNO3 were −0.6, 0.03, 0.6 and 2.6 mg/(m2·d), respectively, while the P release rate with no additives was 7.3 mg/(m2·d). In suboxic conditions, the concentration of total phosphorus (TPaverage 657 mg/kg) in sediment was much lower than that of untreated sediment (TPaverage 688 mg/kg) and treatments with salts (TP(Al2(SO4)3) 793 mg/kg, TP(FeCl3) 781 mg/kg, TP(NaNO3) 802 mg/kg, TP(CaCl2) 747 mg/kg). We also found that adding CaCl2 prevented P release because of apatite formation and because PCa (Ca bound P) increased at the sediment surface. Addition of Fe3+ and NO3− to the sediment increased the amounts of PFe, Mn (Redox-sensitive P, mostly Fe and Mn compounds), since iron oxide has the ability to combine P. Addition of Al2(SO4)3 increased the fraction of PAl, Fe (P bound to metal oxides (Al, Fe)) and decreased the P and Fe in the water above the anoxic sediment, showing the greater ability of Al in binding P. The results showed that Al2(SO4)3, FeCl3, CaCl2 and NaNO3 all had an effect in controlling phosphorus release. The effect was related to the forms of phosphorus existing in the sediment before treatment and the forms resulting after adding the four reagents. The combination of Al3+ or Fe3+ with NO3− promises to be a reasonable chemical treatment for increasing the P retention capacity of sediments in eutrophic lakes. If chemical treatment is combined with bioremediation, the aim of environmental repair may be achieved.
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Received: 11 January 2009
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