USING DECOMPOSITION KINETICS TO MODEL THE REMOVAL OF MINE WATER POLLUTANTS IN CONSTRUCTED WETLANDS

Although numerous mathematical models have been used to describe decom position, few, if any, have been used to model the removal of pollutan ts in constructed wetlands. A steady-state model based on decompositio n kinetics and reaction stoichiometry has been developed which simulat es the removal of ferrous iron entering wetlands constructed for mine drainage treatment. Input variables for the model include organic matt er concentration, reaction rate coefficient, porosity and dry density, and hydraulic detention time. Application of the model assumes comple te anaerobic conditions within the entire substrate profile, constant temperature, no additional organic matter input, and subsurface flow o nly. For these ideal conditions, model simulations indicate that wetla nds constructed with readily decomposable substrates rich in organic c arbon are initially capable of removing far greater amounts of iron th an wetlands built with less biodegradable substrates. However, after t hree to five years of operation this difference becomes negligible. Fo r acceptable long-term treatment performance, therefore, periodic addi tions of decomposable organic matter will be required.