Paper Title
Evaluation of Nutrient Removal from Agricultural Subsurface Drainage using a Laboratory Woodchip Bioreactor

Abstract
The objective of this study was to evaluate nitrate and phosphate removal and nitrite accumulation in a laboratory woodchip bioreactor. The woodchip bioreactor was operated continuously for 100 days for an influent nitrate of 20 mg N/L, and influent phosphate of 1 mg P/L, and a hydraulic retention time (HRT) of 24 h. The results showed that the woodchip bioreactor completely removed nitrate during the 100 day operation. Nitrite accumulation within the bioreactor increased with increasing operating times. Nitrite concentrations peaked at 12 HRT and declined after that. Peak nitrate reached 1.78 mg/L in the bioreactor at the 100 day. Long HRT may be necessary to reduce the concentrations of nitrite in the final reactor effluent.The woodchip bioreactor showed the ability to remove phosphate in the influent. Phosphate removal through the woodchip bioreactor varied based on woodchip conditions and operation times. The phosphate removal by the woodchip bioreactor peaked at 70% at Day 60, but decreased to 53% at Day 100. Keywords - Agricultural Subsurface Drainage, Woodchip Bioreactors, Nutrient Removal, Denitrification, Nitrate, Phosphate