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Journal of Environmental Quality Abstract - Special Section: Moving Denitrifying Bioreactors Beyond Proof of Concept

Optimizing Hydraulic Retention Times in Denitrifying Woodchip Bioreactors Treating Recirculating Aquaculture System Wastewater


This article in JEQ

  1. Vol. 45 No. 3, p. 813-821
    unlockOPEN ACCESS
    Received: May 27, 2015
    Accepted: Sept 04, 2015
    Published: February 19, 2016November 12, 2015

    * Corresponding author(s): c.lepine@freshwaterinstitute.org
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  1. Christine Lepine *a,
  2. Laura Christiansona,
  3. Kata Sharrera and
  4. Steven Summerfelta
  1. a The Conservation Fund Freshwater Institute, 1098 Turner Rd., Shepherdstown, WV 25443
Core Ideas:
  • Woodchip bioreactor design parameters for aquaculture wastewater were developed.
  • This application resulted in the highest N removal rates reported (39 g N m−3 d−1).
  • Retention times differ for optimized removal efficiency versus removal rate.
  • Sulfate reduction intensified under prolonged N-limited environments.


The performance of wood-based denitrifying bioreactors to treat high-nitrate wastewaters from aquaculture systems has not previously been demonstrated. Four pilot-scale woodchip bioreactors (approximately 1:10 scale) were constructed and operated for 268 d to determine the optimal range of design hydraulic retention times (HRTs) for nitrate removal. The bioreactors were operated under HRTs ranging from 6.6 to 55 h with influent nitrate concentrations generally between 20 and 80 mg NO3–N L−1. These combinations resulted in N removal rates >39 g N m−3 d−1, which is greater than previously reported. These high removal rates were due in large part to the relatively high chemical oxygen demand and warm temperature (∼19°C) of the wastewater. An optimized design HRT may not be the same based on metrics of N removal rate versus N removal efficiency; longer HRTs demonstrated higher removal efficiencies, and shorter HRTs had higher removal rates. When nitrate influent concentrations were approximately 75 mg NO3–N L−1 (n = 6 sample events), the shortest HRT (12 h) had the lowest removal efficiency (45%) but a significantly greater removal rate than the two longest HRTs (42 and 55 h), which were N limited. Sulfate reduction was also observed under highly reduced conditions and was exacerbated under prolonged N-limited environments. Balancing the removal rate and removal efficiency for this water chemistry with a design HRT of approximately 24 h would result in a 65% removal efficiency and removal rates of at least 18 g N m−3 d−1.

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