Performance of Four Types Constructed Wetlands on Domestic Wastewater Treatment under Low C/N Ratio Loading and Emission of N2O and CH4 from Them

摘要

Constructed wetland (CW) systems are reliable, flexible in design, and can be built, operated, and maintained at lower costs compared to conventional methods of chemical treatment. There for CW systems are widely used for controlling water-body eutrophication as an ease-operation and cost-effective ecological technology in developing countries. However, growing attention has been directed to its greenhouse side-effect and global-warming potential in recent years. In this study, three typical constructed wetlands: Vertical Flow (VF), Free Water Surface (FWS) and Subsurface Flow (SF), and combined VF-SF-FWS constructed wetlands were used not only to compare the nutrients removal performance for treatment of low C/N ratio loading domestic wastewater, but also to investigate and compare their CH4 and N2O greenhouse gas emissions characteristics. The results indicated that the four types of CWs had high removal efficiencies for organic matter and SS. Moreover,the combined wetlands and SF CW also showed comparatively good performance for nitrogen and phosphorus removal, which was 95.7%, 99.3%, 75.8% and 91.1% for BOD5, SS, TN and TP for the prior, and 98.5%, 98.7%, 75.7% and 91.0% for the latter, respectively, in reverse the efficiency of FWS CW was lowest among all CWs. The VF CW was most effect on phosphorous removal and ammonia oxidizing, which were 91.4% and 98.6%, respectively, but not effective for denitrification, which was only 53.5% for T-N removal rate. The FWS CW had the highest tendency to emit CH4 and led to a higher global warming potential among four types of CWs, maximum flux was about the same as 768mgCO2.m -2 .h -1 .