Rural Sewage Treatment Performance of Constructed Wetlands with Different Depths

The treatment performance, for low concentration rural sewage, through constructed wetlands of different depths(60cm and 40cm), was comparatively investigated by using pilot-scale apparatus in Lake Dian-chi area, Yunnan province, China. The experiment results showed, under a high hydraulic loading rate of 30cm/d, that the removal efficiencies of COD, total nitrogen, ammonia-nitrogen and total phosphorus in the constructed wetland of 60cm depth were 66.4%, 57.7%, 78.7% and 63.2%, respectively, and were 63.8%, 59.1%, 82.1% and 61.3% in the 40cm depth, respectively. The removal efficiencies of COD and total phosphorus in the constructed wetland of 60cm depths were higher than those in the 40cm depth, but the nitrogen removal efficiency in the latter was higher than that in the former. Nitrogen and phosphorus removal mechanisms were studied. The results showed that nitrogen removal through nitrification/denitrification and the phosphorus revmoal through absorb and sedimentation were their main removal mechanisms. The nitrogen and phosphorus removed by plant harvesting were amounting to 10% and 9% of input TN and TP, respectively, which was also an important removal pathway for nitrogen and phosphorus.