Activated carbon column adsorption of compounds that mimic urban stormwater dissolved organic nitrogen

Nutrients mobilized by stormwater can exacerbate eutrophication in receiving waters. While bioretention systems are increasingly employed to improve stormwater quality, they do not normally incorporate design attributes for removal of dissolved organic nitrogen (DON). Thus, the current study concentrated on continuous column adsorption of stormwater DON using a media mixture of coal activated carbon and quartz sand. Adsorption of eight model organic nitrogenous compounds was studied and only pyrrole showed an appreciable adsorption performance; other organic nitrogen compounds were weakly adsorbed. The breakthrough depth for pyrrole was 88 m (equivalent to 4.4 m simulated rainfall depth), at a superficial velocity of 61 cm/hr and influent DON concentration of 1 mg N/L. Subsequent experiments revealed that adsorption of pyrrole was minimally affected by superficial velocity, such that its DON removal efficiency was greater than 91% for all tested superficial velocities (7-489 cm/hr). Accordingly, adsorption processes may be employed for removing stormwater DON fractions behaving similarly to pyrrole; data suggest DON removal initially at greater than 95%, gradually falling to 30% through 25 years of service. PRACTITIONER POINTS: Adsorption of eight different organic nitrogenous compounds onto coal-based activated carbon was investigated. Amino acids and an amino sugar were weakly adsorbed onto the activated carbon. Pyrrole, a moderately hydrophobic heterocyclic organic nitrogen compound was effectively adsorbed. A 30-cm depth was considered as adequate for removal of pyrrole and compounds that would similarly adsorb. Evidence of biological ammonification was present in all studies except for pyrrole.