| Polybrominated diphenyl ethers(PBDEs), extensively used as a additive flame retardants, are a class of global persistent organic pollutants(POPs). BDE-209 is a major PBDEs congeners in china, has got international concern on its harmfulness and degradation. Because of have excellent reduction performance, zero valent iron was widely used in the dehalogenation technology, and gradually applied on PBDEs.However, the small surface area, easy to reunite and oxidize and other shortcomings,limited the conventional zero valent iron to play a better reduction performance. In order to resolve this problem, we use the liquid phase reduction method to prepare and character the montmorillonite Nano-Fe/Ni-composite materials. Influencing factors in the degradation of BDE-209 were investigated, which includes the initial p H,temperature of solution, concentration of nano-zero valent iron(n ZVI) or BDE-209,and ultrasonic. The BDE-209 degradation effects of n ZVI and modified n ZVI were compared. The reaction mechanisms were discussed and reaction kinetic equations were calculated. At the same time, in order to explore the threat of BDE-209 and its degradation products in aquatic ecosystems,choose primary producers(Microalgae)and primary consumers(Daphnia magna) as experimental subjects, analysis the toxicity of BDE-209 and its degradation products.The results indicated:(1) The prepared montmorillonite(mont)-Fe/Ni has a large specific surface area(107.7 m2/g), and the metal particles are uniformly dispersed in the surface of montmorillonite, effectively inhibit the agglomeration of metal particles, and the size is up to about 40 nm.(2) The optimum condition were p H=3, 35℃, 2.0 g/kg n ZVI, 5.0 mg/kg BDE-209. Ultrasonic played an important role in the degradation of BDE-209.BDE-209 was completed degradated within 10 minutes for the ultrasonic group with the mont-Fe/Ni, and its observed rate constant(Kobs)(0.519 min-1) was 40 times faster than the shaking group(0.013 min-1), and 130 times faster than the standing group(0.004min-1). Within 10 minutes, the BDE-209 degradation rate was followed the order0 f mont-Fe/Ag(100%)> mont-Fe/Ni(99.5%)> mont-n ZVI(85.1%)> Fe/Ni(64.8%)>n ZVI(48.1 %)> mont(4.1%)> Ni(1.1%). Within120 minutes, the Kobs was followed the order of mont-Fe/Ag(1.103 min-1)> mont-Fe/Ni(0.519 min-1)> mont-n ZVI(0.209min-1)> Fe/Ni(0.050 min-1)> n ZVI(0.024 min-1).(3) In Daphnia magna test, the propagation index is more sensitive than growth index. The toxicity of pollutants order is: intermediate products> BDE-209> final products. The48hLC50 of BDE-209, intermediate products and final products is 20.9mg/L, 0.81 mg/L and 62.5 mg/L, We can conclude that BDE-209 and final products are the low toxic pollutants, and the intermediate products is the highly toxic pollutants.(4) In toxicity test of Chlorella pyrenoidosa and Microcystis flos-aquae, the toxicity of pollutants order is: intermediate products> BDE-209> final products. under1 mg/L of BDE-209, intermediate products and final products, The inhibition rate of Chlorella pyrenoidosa is 19.1%, 28.1% and7.2%, Microcystis flos-aquae is 15.7%,93.7% and 6.6%. The sensitivity of different algae is not alike, in the test of BDE-209 and final product, Chlorella pyrenoidosa is more sensitive than Microcystis flos-aquae to BDE-209 and final product; in the test of intermediate products, Microcystis flos-aquae is more sensitive than Chlorella pyrenoidosa, because the nature and the toxic mechanism of the pollutants are not the same. In the high toxicity environment(1mg/L intermediate products), Chlorella pyrenoidosa tolerated than Microcystis flos-aquae, the inhibition rate of Chlorella pyrenoidosa in 6th day reached 71.2%,finally fall back to 28.1% at 16 th day, but Microcystis flos-aquae has been maintained at above 90% after 6th day. |
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