Performance of denitrifying bioreactors in southern Alberta

Abstract

Denitrifying bioreactors are an edge-of-field passive treatment technology that can reduce nutrient export from subsurface drainage waters to aquatic ecosystems. This technology is gaining popularity in many parts of the world including eastern Canada, but has not gained widespread acceptance in the Canadian prairies. This study evaluated the performance of pilot-scale denitrifying bioreactors for removing nitrate under agricultural field conditions in southern Alberta. Local agricultural residues– barley straw and hemp straw– were tested in comparison to wood chips for nutrient removal potential under varying retention times and temperatures during the growing season. Results from this study identified that the primary factors affecting nitrate-nitrogen removal in this region were temperature, flow rate, carbon source material and the age of the materials in the bioreactor. Both agricultural residues exceeded wood chip performance in the first year of operation, but all fill materials performed similarly in the second year of operation– the percent reduction of nitrate-nitrogen dropped from 72% to 34% and 55% to 32% for barley straw and hemp straw, respectively, while increasing from 27% to 29% for wood chips. These results indicate that more research is needed on the use of barley straw and hemp straw in bioreactors after an overwinter period.

Keywords

• Bioreactor
• Nitrate-nitrogen (NO3-N)
• Wood chips
• Agricultural residues
• Canadian prairies