Table 1. Diffusion coefficients in electrochemically active biofilm models.

Three diffusion coefficient assumptions are considered: 1) the diffusion coefficient is an effective value; 2) there is diffusion coefficient spatial variability; and 3) there is diffusion coefficient temporal variability. An effective diffusion coefficient (D_e) takes into account hindered diffusion caused by the porous nature of the biofilm matrix. D_e are smaller in magnitude than the free bulk liquid diffusion coefficient (D_aq). Spatial variability takes into account biofilm structural heterogeneity and allows for the diffusion coefficients to change with location in the biofilm. Temporal variability takes into account the non-steady state nature of biofilms and allows the diffusion coefficients to change with time as the biofilm grows or changes morphology. This is a non-exhaustive list curated from the Thomson Reuters Web of Knowledge^SM database, ordered by publication date. Electrochemically active biofilm (EAB) models that do not rely on diffusive mass transport in the biofilm are not included (i.e., convection-only models).

				Biofilm Diffusion Coefficients
Citation	Article	Model Description	Dimensions	Effective	Spatial Variability	Temporal Variability
57, 58	Picioreanu et al., 2007 and 2008	Biofilm-based microbial fuel cells	1D,2D,3D	Yes	None	None
59	Marcus et al., 2007	Conduction-based biofilm anode (Nernst-Monod)	1D	Yes	None	None
60	Picioreanu et al., 2010	pH and electrode geometry in microbial fuel cell	2D	No	None	None
61	Marcus et al., 2010	Electromigration impact on biofilm anode (PCBIOFILM)	1D	Yes	Yes*	None
62	Marcus et al., 2011	Biofilm-based microbial electrolysis cell (PCBIOFILM)	1D	Yes	None	None
63	Strycharz et al., 2011	Cyclic voltammetry of Geobacter biofilm	1D	No†	None	None
64	Merkey and Chopp, 2012	Anode geometry in microbial fuel cell	2D	Yes	None	None

^†This model provides qualitative analysis of EAB cyclic voltammograms and uses diffusion coefficient values several orders of magnitude larger than realistic values.

^*The consideration of migration causes an apparent change in the diffusion coefficient of charged solutes based on the electric field magnitude, which is a function of distance in this model.