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MODELING AND SIMULATION OF HEAVY METAL TRANSPORT IN RHIZOSPHERE SOIL: INFLUENCE OF ACTIVE BIOMASS

The movement of water in the soil is modeled using Richards equation. An advection-dispersion equation, with a sink term for metal uptake by biomass, is used for modeling the metal transport. The sink term is formulated based on the non-linear kinetics of metal adsorption to the biomass. Partitioning of biomass into mobile and stationary fractions is hypothesized.

Transport of the mobile fraction is modeled with an advection-dispersion equation, having a source term, that is based on Monod growth kinetics, and a linear sink term for endogenous decay. The movement of metal in suspension with mobile biomass is also included in the metal transport. Root exudates serve as carbon substrate for the biomass growth, and their transport is modeled in a similar way as that of the biomass.

A soil column with flow vertically downward, and containing metal, biomass and carbon substrate is chosen as a hypothetical system. The influences of some important variables, such as water content, growth rate of biomass, and significant parameters, such as yield of biomass on root exudates, partitioning coefficient of biomass, and rate coefficients for biosorption of metal, on fate and transport of heavy metal are demonstrated through simulations.

Key words: lea heavy metals, rhizosphere, mathematical modeling, kinetics, biomass.