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

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 degrees 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.