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This paper evaluated the economic and environmental benefits of using riparian constructed wetlands (CWs) for municipal wastewater treatment in an urban watershed. The monitoring data were collected from seven CWs in Tan-Shui River basin of the metropolitan Taipei, and were compared with a centralized wastewater treatment plant in the same watershed. Operation parameters such as site conditions, effluent quality, construction and operation/maintenance (O&M) costs were analyzed and used to calculate the first order reaction kinetics ( k v20 ) of three pollutants, i.e. TSS, BOD, and NH 4 –N. The reaction kinetics and costs vary significantly among the CWs and treatment plant. The overall treatment performances of BOD and NH 4 –N generally confirmed with the references, with variation only among the different sites, but the removal of TSS was less desirable for all CWs. The total costs of the CWs were between 0.425 and 3.621 USD per kg total BOD removed, and the costs of the centralized wastewater treatment plant was approximately 1.186 USD per kg total BOD removed. The wetlands provide reasonable pollutants removal and show additional benefits on education and recreation while the sanitary sewer system and new treatment plants are under construction. The experiment results confirmed with the references and the methodology can be used to developing water quality management plans for urbanized watersheds in subtropical areas.

Flood damage as a result of an extreme weather event is always a potential threat to constructed riparian wetlands in subtropical regions, and such damage can significantly impair the pollutant-removing performance of these wetlands The present study compares the pollutant-removal performance of the Hsin-Hai Bridge constructed wetland in the Tan-shui River basin of metropolitan Taipei in September 2000 (before the system was inundated by flood as a result of Typhoon Aere’) and in mid-October 2004 (after reconstruction of the wetland). The study analyses biochemical oxygen demand (BOD), ammonia nitrogen (NH 4 -N), and total phosphorus (TP) of influents and effluents in each of several compartments and for the system as a whole before the typhoon and after reconstruction. The study finds that performance with respect to BOD and NH 4 -N was marginally reduced (with no statistical significance) after reconstruction, but that performance with respect to TP was markedly improved (with statistical significance) after reconstruction. The study provides possible explanations for these findings and concludes that wetlands can be successfully reconstructed after extreme flood damage.