Abstract
A subsurface flow-constructed wetland (S.F.C.W.) with a zeolite substratum is characterized by a high removal rate of ammonium nitrogen due to its high ion-exchange capacity. However, after saturation of zeolite by NH4+, the rate is markedly decreased. Therefore, it is necessary to restore the ion-exchange capacity of zeolite by removing the adsorbed NH4+. We examined the possibility of restoring the ion-exchange capacity of zeolite by nitrification using two tanks with a continuous supply system for secondary treatment wastewater from a rural sewage treatment plant. In this study, water supply was stopped at night (21:00-6:00). The water in the tank A was retained at night and that in tank B was drained in order to supply oxygen in the tank and promote nitrification. The nitrification activity in tank B was higher than that in tank A. In tank B, NH4+ adsorbed to zeolite was nitrified at night and a high concentration of NO3-N was observed. This result shows that the ion-exchange capacity of zeolite is easily restored by nitrification, and which nitrification is promoted by water drainage from the tank when the water supply has been stopped. It is suggested that S.F.C.W. with a zeolite substratum extends the time to saturation by NH4+.
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