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Optimizing Hydraulic Retention Times in Denitrifying Woodchip Bioreactors Treating Recirculating Aquaculture System Wastewater
Author(s) -
Lepine Christine,
Christianson Laura,
Sharrer Kata,
Summerfelt Steven
Publication year - 2016
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/jeq2015.05.0242
Subject(s) - denitrifying bacteria , hydraulic retention time , bioreactor , environmental science , wastewater , recirculating aquaculture system , denitrification , aquaculture , environmental engineering , sewage treatment , waste management , pulp and paper industry , chemistry , nitrogen , fishery , fish <actinopterygii> , engineering , biology , organic chemistry
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 NO 3 − –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 NO 3 –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 . 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.