Restoration of Ion-Exchange Capacity of Zeolite by Nitrification of Adsorbed Ammonium Nitrogen

A subsurface flow constructed wetland (S.F.C.W.) with a zeolite substratum has been developed in Japan. It is characterized by the high removal rate of ammonium nitrogen due to its ion-exchange capacity. However, after saturation of zeolite with ammonium nitrogen, this rate rapidly decreases. Therefore, it is necessary to restore the ion-exchange capacity of the zeolite by removing the adsorbed ammonium nitrogen. In this study, we examined nitrification by microorganisms grown on zeolite for this purpose. We prepared zeolite with adsorbed ammonium and incubated it in secondary-treated wastewater of a rural sewage treatment plant. Nitrification activity was measured using zeolite incubated for different periods. The following results were obtained: 1) Nitrification activity was observed after only 10 days of incubation. 2) Nitrifying bacteria attached to the zeolite incubated in the secondary treated wastewater with organic matter. 3) Ammonium adsorbed to zeolite was metabolized by nitrifying bacteria and released into the medium. 4) Nitrification rate was estimated as 5.2×10-3mg N·h-1·cm-3 zeolite after one month of incubation.