Spatial-temporal dynamics of organics and nitrogen removal in surface flow constructed wetlands for secondary effluent treatment under cold temperature

Abstract

Surface flow CWs (SFCWs) are widely applied as a potential alternative to treat secondary effluent in past several years, but its long-term application under cold temperature regimes is still a challenge because little quantitative information is available on the distribution of organics and nitrogen and their degradation modeling in the ‘‘black-box’’ CW in cold climates. A lab-scale SFCW was operated under a cold temperature (below 10 °C) in this study to investigate the spatial–temporal dynamics of organics and nitrogen removal from secondary effluent. The obtained results indicated that the distinct spatial–temporal variation of organics and nitrogen was observed in the experimental SFCW under the cold temperature. Organics degradation primarily occurred in the surface water and water–sediment-plant interface, while nitrogen removal was mainly accomplished in the water–sediment-plant interface. Cold temperature had much more important effect on the TN removal. Based on the degradation model, organics and NH4+-N could be degraded significantly in a short time because of the appropriate oxygen level, but the TN removal might be hindered due to the limited carbon supply for denitrification in a longer time. The obtained findings would contribute to a better understanding of organics and nitrogen biodegradation processes in SFCWs treating low carbon wastewaters in low-temperatures regions.