Solar-powered pumping at a remote denitrifying bioreactor

Area of Science:

• Environmental Engineering
• Water Quality Management
• Agricultural Science

Background:

• Denitrifying woodchip bioreactors are crucial for removing nitrate-nitrogen (N) from agricultural runoff.
• Flow variability in subsurface drainage systems can limit bioreactor efficiency.
• Few studies have assessed field-scale pumping configurations in bioreactors.

Purpose of the Study:

• To evaluate the impact of a solar-powered pumping system on a denitrifying woodchip bioreactor's performance.
• To assess nitrate-nitrogen removal rates and efficiencies with and without pumping.
• To determine the benefits and drawbacks of retrofitting bioreactors with pumping systems.

Main Methods:

• A field-scale "ditch diversion" bioreactor was retrofitted with a solar-powered pump.
• The pumped bioreactor was monitored for 29 days in 2022 and 93 days in 2023.
• Performance was compared to historic data from the non-pumped period (2019-2021).

Main Results:

• The pumped bioreactor achieved average N removal rates of 7.5 g N/m³-d (2022) and 5.2 g N/m³-d (2023).
• N removal efficiencies were 50% (2022) and 61% (2023), generally improving upon non-pumped periods.
• The diurnal batch operation from solar pumping led to increased overnight water temperatures, potentially boosting performance.

Conclusions:

• Pumping can enhance bioreactor performance, particularly for underloaded systems, by stabilizing flow.
• The addition of a pump showed a slight improvement in N load removal compared to conventional bioreactors.
• The increased complexity and cost associated with pumping systems must be carefully weighed against performance benefits.