Transformation and fate of organic esters in layered-flow systems: the role of trace metal catalysis

Abstract

A simple mass transport model with chemical and biochemical reactions has been developed to predict the relative degree of degradation of organic esters in a layered-flow or density-stratified system. A numerical method was used to solve a system differential equations involved when metal-catalyzed hydrolysis, biodegradation, and adsorption were assumed to be major pathways for ester transformation. The relative importance of each pathway for the time-dependent concentration profiles of an organic ester was examined by use of dimensionless parameters given a known initial concentration profile across the depth of the water column for a catalyst, for a microbial population, for particles, and for a hypothetical ester. Both the ester and the catalyst were allowed to interdiffuse and to react. Results show that the characteristic times for metal-catalyzed ester hydrolyses alone are in the range of 6-700 days. These values depend strongly on initial concentration profiles, the magnitude of either the diffusion or dispersion coefficients, and the magnitude of the hydrolysis rate constant. Limitations of model applicability are discussed.