Abstract
A subsurface flow-constructed wetland with a zeolite substratum (S.F.Z.) is characterized by a high removal rate of ammonium nitrogen due to its high ion-exchange capacity. However, after the saturation of ammonium ions (NH4+) in the zeolite, the rate is markedly decreased. We investigated the effect of nighttime drainage operation for the recovery of the NH4+ ion-exchange capacity of zeolite using a large-scale experimental S.F.Z plant. The experiment was carried out using two channels which had different influent water loads and frequencies of drainage operation. Channel 1 was drained every night and Channel 2 was drained three times per week in the nighttime (0:00∼6:00). The results showed that the amount of adsorbed NH4+ in the zeolite was decreased by nitrification after the operation. NO3--N concentration was increased in the effluent of Channel 1, however, it was not increased in Channel 2. The increase in NO3--N by nitrification could be reduced by controlling the frequency of the drainage operation and the influent water load. High removal rates of NH4+ and inorganic nitrogen were observed for 9 months after the start of drainage operation. Therefore, the S.F.Z. can be used long-term with a high performance in nitrogen removal through the introduction of a suitable drain operation.
