Bioreactors Introduction

To make farming operations productive and viable, most agricultural land located in north central Iowa is artificially drained or tiled. As a result of the tile systems, high concentrations of soluble nutrients like nitrate-nitrogen are reaching Iowa’s streams and rivers. Bioreactors are an edge-of-field treatment practice intended to reduce the amount of nitrogen being delivered to surface waters by artificial drainage.

Edge-of-field treatment systems, such as buffer strips, have been installed to reduce contaminant loads in receiving waters. However, as research is showing, outside of large rain events, most water leaving agricultural fields is through subsurface tile flow and is never comes in contact with these filter systems at the surface. Wetlands can be installed to capture and treat subsurface flow, but costs can be prohibitive, and the land required must often be taken out of production, presenting an additional barrier to the adoption of this practice. Bioreactors are a new practice gaining interest and, when combined with other practices such as nutrient management, can have a substantial effect on the amount of nitrogen reaching the stream. Denitrifying bioreactors alone have been shown to be capable of reducing the nitrogen load 40–60% from the tiles they are treating. 

Below is a view of an installed bioreactor, showing the upper control structure and warm season grasses that have re-established in soil covering the bed of wood chips in which water is treated.