Enhanced Nitrification in Constructed Wetlands Using Ion-Exchange and Biological Regeneration

摘要

Constructed wetlands built in northern climates do not adequately remove nitrogen, especially ammoniacal nitrogen, in the winter. Clinoptilolite, an ion-exchange crystal, can be used to store ammonium from wetland effluents during the colder winter months when nitrification is limited by environmental constraints. The ammonium-sorbed clinoptilolite can be biologically regenerated during the summer months, when conditions are more conducive for nitrification. Laboratory scale and pilot scale studies were conducted to prove this hypothesis and develop design criteria for a clinoptilolite supplemental system. Ultimately, two small pilot scale clinoptilolite columns were built that utilized an in-situ nitrifying biomass (Nitrosomonas and Nitrobacter) and draw and fill technology. The study showed that ammonium-sorbed clinoptilolite can be bioregenerated using tap water, an in-situ nitrifying biomass, and draw and fill aeration. The process can remove almost 100% of the adsorbed ammonium. The nitrifying biomass can remove at least 94% of the ammonium as nitrate at ambient temperatures as low as 14 degrees centigrade.. Oxygen utilization is extremely efficient in the draw and fill bioregeneration scheme. The nitrifying biomass utilized from 68 - 95% of the available oxygen to oxidize the ammonium adsorbed by the clinoptilolite during the initial stages of regeneration. In practice, a clinoptilolite bed system will reduce constructed wetland design requirements. The design can be optimized for year-round BOD removal and summer-time nitrogen removal which will reduce the CW size under normal municipal waste conditions. Theoretically, a clinoptilolite bed system coupled with a CW system can be used to remove almost 100% of the wetland's effluent ammonia during the six month adsorption phase. After the ammonia is converted to nitrate, the nitrate can be used to decrease the influent BOD concentration into the CW.