Performance of denitrification beds for removing nitrate from drainage water at cold temperatures

Abstract

Abstract. Transport of soluble nitrogen and phosphorus to water bodies has been a concern for many years due to human health issues and is a major contributor to the formation of oxygen deficiency in aquatic ecosystems. Agricultural subsurface drainage is one pathway for transport of excess nutrients to surface water. Compared to other BMPs, denitrification beds (woodchip bioreactors) provide a practical solution with low maintenance and comparable expenses. The objective of this research is confirm justification for enhancing denitrification bed performance at cold temperatures by supplementing readily available carbon (i.e., acetate), and adding cold-adapted and metabolically-active bacteria to bioreactors. We retrofitted an existing bioreactor into eight woodchip beds, providing a unique replicated experiment that allows flow control and microbial manipulation. Water samples were collected during May and June 2016 for each woodchip bed. Nitrate load reduction ranged from 0.4% to 8.7% at inflow temperatures ranging from 7.5°C to 9.3°C. This shows that there is a need for a strategy to boost nitrate removal from drainage water at cold temperatures. Therefore, we will enhance nitrate removal by supplementing readily available carbon (i.e., acetate) and adding cold-adapted and metabolically-active bacteria to bioreactors. The applied significance of this research is that it will optimize bioreactor performance and enhance the quality of agricultural drainage water.