Abstract
Abstract Woodchip bioreactors are capable of removing nitrate from agricultural runoff and subsurface tile drain water, alleviating human health hazards and harmful discharge to the environment. Water pumped from agricultural tile drain sumps to nearby ditches or channels could be cost-effectively diverted through a woodchip bioreactor to remove nitrate prior to discharge into local waterways. Sizing the bioreactor to achieve targeted outlet concentrations within a minimum footprint is important to minimizing cost. Determining the necessary bioreactor size should involve a hydrological component as well as reaction type and rates. We measured inflow and outflow nitrate concentrations in a pumped open-channel woodchip bioreactor over a 13-month period and used a tanks-in-series approach to model hydrology and estimate parameter values for reaction kinetics. Both zero-order and first-order reaction kinetics incorporating the Arrhenius equation for temperature dependence were modeled. The zero-order model fit the data better. The rate coefficients (k = 17.5 g N m−3 day−1 and theta = 1.12 against Tref = 20 °C) can be used for estimating the size of a woodchip bioreactor to treat nitrate in agricultural runoff from farm blocks on California's central coast. We present an Excel model for our tanks-in-series hydrology to aid in estimating bioreactor size.
Highlights
Nitrate contamination of surface and groundwater is a pervasive issue in areas where intensive agriculture uses fertilizer to increase crop yields (Wang & Li 2019)
This study corroborates the findings and assumptions of other woodchip bioreactors (WBR) research that denitrification is explained by zero-order kinetics over the range of inlet concentrations that is of concern in agricultural runoff
We developed an Excel version of a TIS model that can be used to estimate WBR sizing where local decay rate parameters can be inputted along with field conditions for flow rate, water temperature and nitrate concentration
Summary
Nitrate contamination of surface and groundwater is a pervasive issue in areas where intensive agriculture uses fertilizer to increase crop yields (Wang & Li 2019). Management practices that match fertilizer and water applications to meet crop needs will help reduce the infiltration of nitrate to groundwater and runoff to surface water; 100% efficiency of nutrient uptake is not possible and about 80% recovery of nitrate by the crop is the practical upper limit (Harter et al 2012). California’s Environmental Protection Agency sets limits for contaminants based on assessments of beneficial uses of a waterbody. These beneficial uses include drinking water, recreation, wildlife habitat, fisheries and other uses, with allowable limits for nitrate concentration varying between 1 and 10 mg N LÀ1 on California’s central coast (CCRWQCB 2017). Regional Water Quality Control Boards are implementing a phased and progressive approach to agricultural compliance with achievement of water quality objectives (WQOs) at the
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
