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 stu dies of hybrid biological-ion exchange multireactor Systems, the propo sed process uses the ion exchange material, zeolite, as a carrier for the nitrifying biomass. Therefore, the entire process is carried out i n a single reactor. Since all the ammonium from the original effluent is concentrated in the zeolite and released gradually during regenerat ion, nitrification is carried out in a small volume reactor in an almo st batch mode where optimal conditions for nitrification can easily be maintained. Moreover, the conversion of ammonium cations to nitrate a nions allows for regenerate recycle, where the amount of chemicals add ed for desorption is reduced to the amount of sodium bicarbonate added as a buffer for nitrification. As a result, operational costs and pro duction of large volumes of brine are minimized. To achieve sufficient NH4+ concentration in the solution to allow for high rate nitrificati on, 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 value s 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 E lsevier Science Ltd. All rights reserved.