Han Xu, Wong Yuk Shan, Wong Ming Hung, Tam Nora Fung Yee
Department of Biology and Chemistry, City University of Hong Kong, Kowloon, Hong Kong, China.
J Hazard Mater. 2008 Oct 30;158(2-3):615-20. doi: 10.1016/j.jhazmat.2008.02.024. Epub 2008 Feb 16.
The presence of nitrate, chloride and sulfate anions on the removal of Cr(VI) by Chlorella miniata was investigated. Results of kinetic studies indicated that the equilibrium time in each anion system increased with increases of the initial salt concentration, and the inhibitory order was NO(3)(-)>Cl(-)>SO(4)(2-) for Cr(VI) removal and was SO(4)(2-)>Cl(-) approximately NO(3)(-) for the biosorption of the bioreduced Cr(III). The inhibitory effect caused by different anions was attributed to biosorption mechanism and metal speciation. Since both biosorption and bioreduction were involved in Cr(VI) removal, the presence of anions could compete with Cr(VI) for the adsorption sites, and the affinity of anions to the algal biomass followed the order of NO(3)(-)>Cl(-)>SO(4)(2-), which was consistent with their inhibitory order on Cr(VI) removal. Speciation results also indicated that the formation of CrO(3)SO(4)(2-) in the sulfate system made it easier to be adsorbed on the biomass than HCrO(4)(-). The biosorption-bioreduction model further suggested that the bioreduction rate constant k decreased with increases of anion concentrations ranging from 0 to 0.5M, and followed the order of SO(4)(2-)>Cl(-)>NO(3)(-). The biosorption constant b also decreased with anion concentrations in the range of 0-0.2M, suggesting that this parameter was more sensitive to anion effects than the k values. The higher b values in the sulfate than in the nitrate and chloride systems indicated that Cr(VI) in the sulfate system was more easily adsorbed on the algal biomass. These findings demonstrated that the presence of anions significantly affected the removal of Cr(VI) by C. miniata. Since chloride, nitrate and sulfate ions are commonly found in industrial wastewater, it may be necessary to eliminate these ions prior to chromium removal.
研究了小球藻去除六价铬过程中硝酸根、氯离子和硫酸根阴离子的存在情况。动力学研究结果表明，在每个阴离子体系中，平衡时间随初始盐浓度的增加而延长，对于六价铬去除，抑制顺序为NO(3)(-)>Cl(-)>SO(4)(2-)，对于生物还原的三价铬的生物吸附，抑制顺序为SO(4)(2-)>Cl(-)≈NO(3)(-)。不同阴离子引起的抑制作用归因于生物吸附机制和金属形态。由于六价铬的去除涉及生物吸附和生物还原，阴离子的存在会与六价铬竞争吸附位点，阴离子对藻类生物质的亲和力顺序为NO(3)(-)>Cl(-)>SO(4)(2-)，这与其对六价铬去除的抑制顺序一致。形态分析结果还表明，硫酸根体系中CrO(3)SO(4)(2-)的形成使其比HCrO(4)(-)更易吸附在生物质上。生物吸附-生物还原模型进一步表明，生物还原速率常数k随阴离子浓度从0到0.5M的增加而降低，顺序为SO(4)(2-)>Cl(-)>NO(3)(-)。生物吸附常数b在0-0.2M范围内也随阴离子浓度降低，表明该参数比k值对阴离子效应更敏感。硫酸根体系中b值高于硝酸根和氯离子体系，表明硫酸根体系中的六价铬更易吸附在藻类生物质上。这些发现表明阴离子的存在显著影响小球藻对六价铬的去除。由于氯离子、硝酸根和硫酸根离子常见于工业废水中，在去除铬之前可能有必要去除这些离子。
