Efficient Algorithms for Modeling the Transport and Biodegradation of Chlorinated Ethenes in Groundwater

Predicting the fate and transport of chlorinated ethenes in groundwater requires the solution of equations that describe both the transport and the biodegradation of the contaminants. In this poster, we present a model that accounts for (1) transport of chlorinated ethenes in flowing groundwater, (2) mass transfer of contaminants between mobile groundwater and stationary biofilms, and (3) diffusion and biodegradation within the biofilms. The equations for biodegradation kinetics are based on previous work by other researchers and account for biomass growth within the biofilms, the effect of hydrogen on dechlorination, and competitive inhibition between vinyl chloride and cis-dichloroethene. Therefore, the overall model consists of coupled, non-linear, partial differential equations; solution of such a model is challenging and requires innovative numerical algorithms. We developed and tested two new numerical algorithms to solve the equations in the model; one is called system splitting with operator splitting (SSOS), and the other is called system splitting with Picard iteration (SSPI). Comparison of the two algorithms shows that the SSPI method is computationally more efficient under most conditions tested, but under some conditions the Picard iteration does not converge rapidly and the SSOS is superior. The model presented here can be used to explore phenomena that depend on the interaction between macro-scale and biofilm-scale phenomena, e.g., to identify how diffusion limitations or metabolism limitations affect macroscopic contaminant fate and transport.