Ion-Exchange Removal of Ammonium Ions from Secondary Treatment Wastewaters and Dilute Solutions Using Clinoptilolite

Abstract

Secondary treatment wastewaters contain considerable concentrations of calcium, magnesium, potassium, and sodium as well as ammonia in the cation form. It also accommodates biological activity due to high concentrations of aerobic and anaerobic bacteria. Previous work shows that clinoptilolite, a naturally occurring alumino silicate, has a high selectivity for NH₄ ⁺ relative to other ions present in wastewater making it an effective zeolite for the process of ion exchange. Investigations have been made through isotherm measurements into the effect of other cations, individually and in combination, on the ion-exchange process. It has been found that the uptake capacity of clinoptilolite falls by 20% with typical secondary wastewaters compared to a control solution of de-ionised water and NH₄C1.

The role of surfaces on microbial growth has also been shown to be significant and nitrification kinetics are increased for attached cultures rather than suspended cultures. Theory would suggest that clinoptilolite effectively concentrates ammonium on its surface. This accumulation of substrate is then available to bacteria and these micro organisms will respond to this condition and concentrate on the solid surface. Significant increases in clinoptilolite cycle life due to biological activity have been seen and results are presented through breakthrough curve in this paper. Results presented in this work show increased nitrification kinetics through a clinoptilolite packed bed compared to an inert packing. These findings suggest that the bacteria can break down ammonium cations, attached to the zeolite surface, to nitrite and nitrate anions hence relieving sorption sites and making them available to other cation.