EXPERIMENTS ON SELF-PURIFICATION OF HEAVY METALPOLLUTANTS IN NATURAL RIVERS

1.INTRODUCTIONThemovementofwater,sedimentandpollutantsandtheinteractionamongtheminnaturalriversareverycomplicated.Movementofwater,sedimentandPOllutantsarerandom.ButfromastatisticalviewPOint,theirmovementfollowssomerules.Twokindsoftypicalcases,thatis,atributarywithheavymetalpollutantsjoiningamainstream,andanunPOllutedtributarywithmuchsedimententeringamainstreamcontaminatedbyheavymetals,arestudiedinthispaper.Besides,flowscenesinnaturalriversaredifferentindifferentseasons.InthenabPeriod,g…

EXPERIMENTS ON SELF-PURIFICATION OF HEAVY METAL POLLUTANTS IN NATURAL RIVERS

This paper is concerned with the experiments of simulating self-purification of heavy metal pollutants in natural rivers, such as tributaries polluted by heavy metal polutants joining a main stream, or an uncontaminated tributary with much sediment entering a main stream polluted by heavy metal pollutants, and the experiments on the effect of sediment movement on the adsorption of heavy metal pollutants. Further-more, the effect of turbulence, sediment supply conditions and sediment motion patterns on the adsorption of heavy metal pollutants are studied in a device, in which turbulence is generated by a harmonically vibrating set of grids. The results indicate that sediment motion pattern has no effect on the characteristic parameters in the adsorption isotherm, such as the saturated adsorption content by unit weight of seidment and the constant of adsorption-desorption rate in the Langmuir adsorption isotherm, but it has significant effect on the coefficient of adsorption rate (or the coefficient of desorption rate). When the turbulent intensity of flow is low and all sediment exists as bottom mud, the coefficient of adsorption rate of sediment (or the coefficient of desorption rate of sediment) is very small, thus descending rate of concentration of dissolved heavy metal pollutant concentration is small, and when the turbulent intensity of flow is high, sediment supply condition, that is, whether sediment exists on the bed or not, influences greatly the variation of dissolved heavy metal pollutant concentration. When the sediment on the bed could be lifted up, descending rate of dissolved heavy metal pollutant concentration is large. In other wards, the coefficient of adsorption rate (or the coefficient of desorption rate) by unit weight of suspended sediment is much larger than that by unit weight of bottom mud.