MODELING THE PHOTOCHEMICAL DEGRADATION OF ETHYLENEDIAMINETETRAACETATEIN THE RIVER GLATT

Laboratory experiments, field measurements, and mathematical modeling were used to evaluate the processes responsible for the fate of ethyle nediaminetetraacetate (EDTA) in the River Glatt, a tributary to the Ri ver Rhine. Direct photolysis was identified as the most important proc ess for the degradation of EDTA. With respect to environmental conditi ons, direct photolysis acts only on the Fe(lll)-EDTA complex. Thus, th e extent to which EDTA is degraded in rivers is directly related to it s speciation. Approximately 50% of EDTA present in the River Glatt is discharged in the form of Fe(III)-EDTA from sewage treatment plants. A vailable Fe(III)-EDTA in the River Glatt is photolyzed within approxim ately 1 d during summer daylight conditions (global irradiation of abo ut 800 W h m(-2) at noon). The results of a spike experiment were used for the calibration of the light conditions within the water column. It showed that a great deal of sunlight was absorbed by water plants, which led to a decrease of the photolysis rate of Fe(lll)EDTA in the R iver Glatt of 85%. The predictions of the chosen model showed good gen eral agreement with data from field investigations.