The success of in situ biological contaminant destruction depends on the distribution of microorganisms through a flow field. Using numerical tools, a strategy is developed which causes the biomass to grow in a more uniform fashion throughout the flow field. The results obtained using this strategy are compared with a conventional strategy. Here, we demonstrate that by properly alternating the direction of flow through a flow field and by internally recycling the nutrients and contaminants, the biomass can be distributed more uniformly and significantly more contaminant destruction can be attained than would be possible if a unidirectional strategy were employed.