Advanced Denitrification in Bioretention Systems Usinging Woodchips as a Primary Organic Carbon Source

Bioretention systems still lack the ability to effectively mitigate nitrogen concentrations from urban stormwater. Column tests were conducted to evaluate the effect of nitrate concentration, stormwater retention time, limestone addition, and woodchip species, size, and mass percentage on the bioretention denitrification process. Denitrification of artificial stormwater appeared to follow pseudo-first-order kinetics. A 0.8 day average retention time showed the highest nitrate removal percentage of 82.4 + 0.4%. Longer retention times correspond to greater removal efficiency. Willow Oak and Red Maple woodchips resulted in the highest total nitrogen removal efficiencies at 61.9 + 0.8% and 61.8%, respectively. Smaller woodchips and higher woodchip mass percentage corresponded to greater nitrate removal efficiencies, but also higher organic nitrogen leaching. Media containing 4.5% 5 mm Willow Oak woodchips by mass represented optimum conditions with a pseudo-first-order denitrification rate of 4.1 + 4.6 day-1 with nitrate concentrations of 1.5 to 4.5 mg/L N