Ammonium removal using ion exchange and biological regeneration

A new concept for ammonium removal from secondary effluent by zeolite followed by bioregeneration has been studied. In contrast to other studies of hybrid biological-ion exchange multireactor Systems, the proposed process uses the ion exchange material, zeolite, as a carrier for the nitrifying biomass. Therefore, the entire process is carried out in a single reactor. Since all the ammonium from the original effluent is concentrated in the zeolite and released gradually during regeneration, nitrification is carried out in a small volume reactor in an almost batch mode where optimal conditions for nitrification can easily be maintained. Moreover, the conversion of ammonium cations to nitrate anions allows for regenerate recycle, where the amount of chemicals added for desorption is reduced to the amount of sodium bicarbonate added as a buffer for nitrification. As a result, operational costs and production of large volumes of brine are minimized. To achieve sufficient NH4+ concentration in the solution to allow for high rate nitrification, the cation-rich regenerant solution (or part of it) is reused from one cycle to the next. A theoretical model including ion exchange and bioregeneration modes, indicates that the total cation concentration and each cation in the recycled regenerant should reach constant values after several cycles of adsorption-regeneration and remain constant as long as the influent characteristics and operation conditions stay similar. Experiments results verified the predicted values. (C) 1998 Elsevier Science Ltd. All rights reserved.