Characteristics of contaminant release from lake sediment under different salinity and redox conditions

A laboratory-scale reactor containing the lake sediment obtained from two regional sites, mainly affected by live-stock wastewater and industrial wastewater, respectively, was tested for the amount of contaminants (i.e., organics, nutrients, and heavy metals) released from the sediment, under different salinity (freshwater vs. seawater) and redox (oxic vs. anoxic) conditions. Results showed that the amounts of released contaminants in freshwater were higher (e.g., up to 11.6-fold for Cd) than those in seawater, resulting from the increased saturation concentration toward the overlying water due to the relatively lower ionic strength in freshwater. On the other hand, the released amounts under the anoxic condition were higher (e.g., up to 2.9-fold for NH4+−N in livestock wastewater affecting regions) than those under the oxic condition, due to the increased amount resulted from the formation of reduced environment in overlying water under the anoxic condition. A the contaminant release proceeds through pore water in sediment under this reduced condition, the sediment it self can act as an area pollution source, resulting in a gradual deterioration of water quality pollution in lower water layers. In general, the release rates of organics and nutrients were higher than those of heavy metals. In addition, the livestock waste-water affecting regions showed high amounts of organics and nutrients released, whereas the industrial wastewater affecting regions showed high amounts of heavy metals released, due to the regional characteristics such as high content of specific components within pore water. In case of heavy metals, the release rates were in the order of Mn>Zn>Cu>Pb>Cd. Among all the conditions tested, the anoxic/freshwater condition showed the highest release of contaminants, whereas the anoxic/seawater condition showed the lowest release.