Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes, Ministry of Education, College of Environment, Hohai University, No. 1 Xikang Road, Nanjing, 210098, China,
Environ Sci Pollut Res Int. 2015 Jul;22(14):11148-61. doi: 10.1007/s11356-015-4412-z. Epub 2015 May 5.
This study aimed to investigate the performance of chitosan-modified nano-sized montmorillonite (CTS/NMMT) during the flocculation of Microcystis aeruginosa (MA). The release of intracellular microcystins (MCs) caused by the damage of intact MA cells during the flocculation and floc storage processes was also comprehensively evaluated through scanning electron microscopy (SEM) and measurement of K(+) and Mg(2+) release. With the application of the Box-Behnken experimental design combined with response surface methodology, the quadratic statistical model was established to predict and optimize the interactive effects of content of CTS/NMMT, weight ratio of NMMT to CTS, and agitation time on the removal efficiency of MA cells. A maximum removal of 94.7 % MA cells was observed with content of CTS/NMMT 300-320 mg L(-1), weight ratio of NMMT to CTS 14-16, and agitation time 16-50 min. During the flocculation process, CTS/NMMT aggregated MA cells as flocs and served as a protection shield for cells. The extracellular and intracellular microcystin-leucine-arginine (MC-LR) decreased remarkably and the yield of intracellular MC-LR showed a decreasing trend during the flocculation. The cell integrity was slightly damaged by the mechanical actions rather than by the flocculant. During the floc storage process, cell lysis and membrane damage were remarkably aggravated. The noticeable increase of K(+) and Mg(2+) release indicated that CTS/NMMT damaged the integrity of most MA cells in the flocs and liberated the intracellular MC-LR. Meanwhile, NMMT and CTS polymers assisted the adsorptive removal of extracellular MC-LR released to water. The flocs should be timely treated within 12 h to prevent the leakage of MCs.
本研究旨在探究壳聚糖改性纳米蒙脱石（CTS/NMMT）在铜绿微囊藻（MA）絮凝过程中的性能。通过扫描电子显微镜（SEM）和 K+、Mg2+释放量的测定，全面评估了完整 MA 细胞在絮凝和絮体储存过程中受到破坏时细胞内微囊藻毒素（MCs）的释放情况。采用 Box-Behnken 实验设计结合响应面法，建立了二次统计模型，以预测和优化 CTS/NMMT 含量、NMMT 与 CTS 质量比和搅拌时间对 MA 细胞去除效率的交互作用。结果表明，当 CTS/NMMT 含量为 300-320mg/L、NMMT 与 CTS 质量比为 14-16、搅拌时间为 16-50min 时，MA 细胞的去除率最高可达 94.7%。在絮凝过程中，CTS/NMMT 聚集 MA 细胞形成絮体，并为细胞提供保护。细胞外和细胞内的微囊藻氨酸-亮氨酸-精氨酸（MC-LR）含量显著降低，细胞内 MC-LR 的产率呈下降趋势。絮体的机械作用对细胞完整性造成轻微损伤，而不是由絮凝剂造成的。在絮体储存过程中，细胞裂解和膜损伤明显加剧。K+和 Mg2+释放量的显著增加表明，CTS/NMMT 破坏了絮体中大多数 MA 细胞的完整性，并释放了细胞内的 MC-LR。同时，NMMT 和 CTS 聚合物有助于吸附去除释放到水中的细胞外 MC-LR。因此，应在 12 小时内及时处理絮体，以防止 MCs 的泄漏。
