Removal of stormwater dissolved organic nitrogen through biotransformation using activated carbon

Conventional bioretention systems are not effectively designed to remove stormwater dissolved organic nitrogen (DON). Biotransformation study on five organic nitrogenous compounds with different values for adsorption on coal activated carbon (AC) and bioavailability revealed that adsorption is a greater controlling factor for ammonification than bioavailability. This study also showed three apparent benefits: enhancement of the ammonification rate, ammonification of the bio-recalcitrant organic nitrogenous compounds, for example, pyrrole, and bio-regeneration of the adsorbent (coal AC). Low temperature (4°C) did not impact ammonification of leucine at a velocity of 34 cm/h, but negatively affected it at 61 cm/h. It was also observed that bed media height > 30 cm would not appreciably increase ammonification. Under intermittent wetting/draining conditions, the DON removal efficiency was more than 90%, indicating that DON was successfully removed through concurrent adsorption/ammonification, although generated ammonium in the effluent must be properly addressed. PRACTITIONER POINTS: Coal activated carbon appears a better material for DON ammonification compared with charcoal and quartz sand. A temperature as low as 4°C may not adversely impact DON ammonification at a velocity of 34 cm/h or less. A bed media depth of 30 cm is considered as adequate to promote DON ammonification. A larger depth may not be expected to improve ammonification. Ammonification of the bio-recalcitrant organic nitrogenous compounds, for example, pyrrole, and bio-regeneration of the adsorbent, for example, coal activated carbon, may be achieved.