Simazine degradation by mixed microbial cultures was carried out in biological reactors with tepojal and sepiolite beads. The inoculum used is derived from a biotechnological product applied to plant roots, which contains mixed microbial cultures. This inoculum presented a stable adherence to the microorganism support throughout the experiment. In this research, the supports were evaluated in relation to both biofilm formation and simazine removal. For this study, hydraulic and mass starting-up parameters were established for simazine degradation and for the use of these reactors in the two types of supports. Tepojal had never been used before as a microbial support in any previous research paper. Tepojal demonstrated to be more efficient than sepiolite. Statistical analysis was done for the relationship among the parameters of chemical oxygen demand, colony formation units, total suspended solids, and volatile suspended solids. Water Environ. Res., 83, 274 (2011).