Modeling and Calibration of Drainage Denitrification Bioreactor Design Criteria

Abstract

Design methods for agricultural drainage denitrification bioreactors must be optimized for these novel systems to provide maximized water quality improvement. The objective of this paper was to further develop science-based bioreactor sizing guidelines by calibrating an existing design procedure with multiple years of drainage flow data collected at two sites in Iowa. The models created for the two hypothetical bioreactor sites showed the original design criteria (use of a design flow rate one-fifth of the peak flow rate) generally allowed simulated bioreactor treatment of the majority of total annual drainage volume, but treatment of this majority was not necessary to maximize nitrate removal. Larger bioreactors resulting from use of either increased design flow rate or higher design retention time increased the extent of nitrate removal, but had lower nitrate removal rates. This modeled simulation analysis informs that bioreactor design procedures considering flow rate and retention time should use design flow rates of 10 to 20% of the anticipated peak flow rate at design retention times of 6 to 8 h, thus updating and refining the original design procedure. This approach produces bioreactors of increased length to width ratios, with improved performance based on nitrate removal extent and removal rate. Further field-scale validation is suggested for this drainage bioreactor design procedure.