Abstract: The fate of organic substances in soil strongly depends on biological processes. These biological processes are shaped by microorganisms, which occur in soil pores, either in suspension or as biofilms inside and outside soil aggregates. Biofilms alter the pore geometry while growing which directly influences the soil water flow field and hence the convective transport of organic substances. In this paper we present a model of the bioreactor soil at the pore scale under saturated conditions comprising coupled fluid flow, transport, reaction, sorption, and biofilm dynamics. The spatio-temporal development of the biofilm is altering properties such as viscosity, diffusion coefficient and degradation rates. The degradation potential of organic substances was analyzed by considering the influence of microbes on their breakthrough behavior. The model results underline that biological processes exert a major influence on the fate of organic substances in soil
