Denitrifying woodchip bioreactors for aquaculture manifold design and potential water reuse
One of the fastest-growing global food production sectors is aquaculture, the farming of aquatic plants and animals. Land-based aquatic production in recirculating aquaculture systems (RAS) offers an alternative to unsustainable conventional aquaculture methods. However, RAS production currently lacks an affordable nitrate reduction technology. Early studies on denitrifying woodchip bioreactors, a biological nitrate-remediation system, have demonstrated their potential for RAS wastewater treatment. Bioreactors are highly effective at nitrate removal via the process of denitrification but have also demonstrated a propensity for premature system failure as characteristics unique to wastewater may clog a bioreactor’s inlet. Another challenge for this application is that bioreactor outflows are discharged from the facility which is conceptually inconsistent with water-saving RAS design that favors in-process water recycling. The objectives of this research were to i) characterize woodchip outflows beyond nitrate removal, assessing outflow reuse potential for RAS applications and ii) evaluate longer-term bioreactor performance under various temperature regimes and wastewater characteristics given inflow manifold engineering design. Column experiments with two common hardwood species were used to demonstrate that potentially harmful contaminants such as aluminum, copper, iron, and zinc were flushed generally within 21 pore volumes (21 d). Toxicity testing with the indicator species Ceriodaphnia dubia showed no acute toxicity after five cumulative pore volumes were eluted, but chronic toxicity was observed after restarting bioreactors following a 72-h dry period. Optimal water quality concentrations for salmonid production were sustained, provided bioreactors were operated under recommended conditions. A two-year, pilot-scale bioreactor experiment was used to compare a conventional straight tee inflow manifold design with an experimental multiple inflow header. Manifold design did not significantly impact bioreactor performance under “normal” wastewater conditions, but the experimental manifolds outperformed the conventional (11 and 12% greater nitrate and total suspended solids removal, respectively) when wastewater was more concentrated. Both bioreactor manifold designs successfully treated aquaculture wastewater over the 784-d study, indicating viable treatment longer than has been previously evaluated. Results from both studies affirm the potential for denitrifying woodchip bioreactors to be integrated with RAS facilities.
Denitrification, denitrifying woodchip bioreactors, aquaculture, recirculating aquaculture systems, inflow manifold design, water reuse, toxicity
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign