Does the Existence of Obstructions Help the Treatment Efficiency? Case Study in the Guandu Constructed Treatment Wetland, Taipei, Taiwan

摘要

Since the existence of jetties, a kind of obstruction, occupies the volume of a wetland, it would decrease usable volume and restrain treatment efficiency. However, the treatment efficiency would promote, because the jetties are able to be the habitat for plants and microorganisms. Degradation by microorganisms and adsorption by plants are the two major treatment mechanisms in wetlands. In addition, the jetties cause inflow pollutant to meander, so the treatment time by the two mechanisms would increase. It shows that the existence of jetties could restrain or promote the treatment efficiency. Does a wetland be demanded to the jetties for the treatment efficiency? Rely on the comparison between simulated results and field survey data, we found that the existence of jetties in the wetland could promote the treatment efficiency in the constructed treatment wetland in Guandu Nature Park, Taipei, Taiwan, China. This study applied a two-dimension model: TABS2, which agrees with wide and shallow situation as wetlands, to simulate the Guandu wetland, which contains four surface wetland systems. According to the simulation, theoretical treatment efficiency would decrease from 48% to 32% in BOD and from 41% to 27% in NH4+because the jetties occupy about 50% volume of the wetland (from 7789 m3 to 4228 m3). The existence of the jetties seems to restrain the treatment efficiency. However, the treatment efficiency by field survey is about 76% in BOD and 68% in NH4+(there are jetties in the wetland). It explicitly shows that the theoretical treatment efficiency by one-dimension plug flow is underestimated and the jetties could promote the treatment efficiency. The treatment efficiency can not be quantified yet because the mechanisms of degradation by microorganisms and adsorption by plants have not been distinctly investigated.