Development of passive bioreactors treating different types of low carbon wastewater in cold climate conditions

Woodchip bioreactors have been used as an engineered solutions for mitigating nitrate from contaminated water. However, their year-round treatment performance and possible solutions for enhancing their removal efficiency under cold climate conditions still needs more research. In this thesis, we investigated nitrogen removal from aquaculture and mine-influenced water as an indoor and outdoor treatment system under several experimental conditions. This thesis attempts to identify design parameters (e.g., optimal hydraulic retention time (HRT) and nitrate removal rate) and enhancement solutions for woodchip bioreactors under cold climate conditions such as additional carbon source, hydraulic design and use of a floating aquatic as a hybrid system. The results show that woodchip bioreactors can successfully remove nitrate from recirculating aquaculture system (RAS) discharge and mine-influenced water under cold climate conditions. Two-year results from a full-scale woodchip bioreactor showed that selected design parameters from a laboratory-scale were sufficient to complete denitrification at the full-scale. The denitrification followed first-order reaction for RAS effluent and optimal HRT ranged between 1.5 to 2 d to achieve a nitrate removal rate of 25.8 g NO-3-N m-3d-1 and 74% removal efficiency. A layer of 50 cm of dry woodchips combined with snow cover (20‐30 cm) was sufficient to prevent frost, the water temperature never dropped lower than 7.3 °C during cold winter conditions (minimum air temperature = -24.7 ℃). Design of the hybrid unit was improved by inserting two inner plates along the water flow and adding floating hook-moss improved the hydraulic efficiency from poor (λ=0.06) to satisfactory (λ=0.51) which led to higher removal rates.