Importance of natural sedimentation in the fate of microcystins

Sedimentation processes of microcystins (MCs), cyanobacterial toxins, were studied in three reservoirs located in Central Spain in which the cyanobacterial community was dominated by the genus Microcystis. MCs were detected in the sediment traps deployed in all reservoirs. In Santillana reservoir, MCs were identified in sediment traps even though they could not be found in the pelagial samples. In the other reservoirs studied, sedimentation rates for MC-containing particles during the bloom period ranged from 0.43 to 2.53 mg m⁻² d⁻¹. Interestingly, this very high sedimentation of toxic biomass is not exclusively related to decaying blooms or autumnal sedimentation due to a drop in water temperature. Instead, it seems that MC-containing colonies may be settling constantly during the bloom period and we were able to estimate that during such a Microcystis dominated bloom, around 4.5% of pelagial MCs may be involved in sedimentation. Further, these settling colonies seem to maintain good cell integrity and MCs seem not to be excreted massively. A certain loss of toxin content along the vertical settling may be attributed to minor losses due to cell lysis or to variations in MC cell quota explained by reduced production or internal consumption. Our results for the first time establish specific settling rates for MC-containing particles in freshwaters and definitely identify sedimentation as a major destination for these toxins. These data may contribute to improve managing strategies concerning risks associated with MCs.     

氰化电镀废水中含氰络合离子的去除

氰化电镀废水中含氰离子的去除主幂分为简单氰离子（CN^-）和古氰络合离子（如[Fe（CN）6]^4-等）的去除。虽然针对前者已有较成熟的氯氧化法和电解氧化法，然而对后者即大量的含氰络合离子的去除方法研究，目前国内正处于对其探索与完善阶段。本文以广东省某五金电镀厂废水处理为研究实例，探讨了以沉淀法去除含氰络合离子的可行性，阐明了其主要工艺过程并进行工艺分析。论述了该方法取得较理想的处理效率时的工艺参数。