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In‐Stream Bioreactor for Agricultural Nitrate Treatment
Author(s) -
Robertson W. D.,
Merkley L. C.
Publication year - 2009
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2008.0100
Subject(s) - woodchips , tile drainage , environmental science , nitrate , drainage , environmental engineering , hydrology (agriculture) , denitrification , bioreactor , nitrogen , pulp and paper industry , chemistry , soil water , soil science , geotechnical engineering , geology , ecology , engineering , organic chemistry , biology
Nitrate from agricultural activity contributes to nutrient loading in surface water bodies such as the Mississippi River. This study demonstrates a novel in‐stream bioreactor that uses carbonaceous solids (woodchips) to promote denitrification of agricultural drainage. The reactor (40 m 3 ) was trenched into the bottom of an existing agricultural drainage ditch in southern Ontario (Avon site), and flow was induced through the reactor by construction of a gravel riffle in the streambed. Over the first 1.5 yr of operation, mean influent NO 3 –N of 4.8 mg L −1 was attenuated to 1.04 mg L −1 at a mean reactor flow rate of 24 L min −1 A series of flow‐step tests, facilitated by an adjustable height outlet pipe, demonstrated that nitrate mass removal generally increased with increasing flow rate. When removal rates were not nitrate‐limited, areal mass removal ranged from 11 mg N m −2 h −1 at 3°C to 220 mg N m −2 h −1 at 14°C ( n = 27), exceeding rates reported for some surface‐flow constructed wetlands in this climatic region by a factor of about 40. Over the course of the field trial, reactor flow rates decreased as a result of silt accumulation on top of the gravel infiltration gallery. Design modifications are currently being implemented to mitigate the effects of siltation. In‐stream reactors have the potential to be scaled larger and could be more manageable than attempting to address nitrate loading from individual tile drains. They could also work well in combination with other nitrate control techniques.