Practice of integrated system of biofilter and constructed wetland in highly polluted surface water treatment

To find an appropriate process for highly polluted surface water, an integrated system with a double-layer biofilter and a constructed wetland was developed. In the biofilter packed with carbon-rich ceramic granules, alternation of nitrification and denitrification was realized resulting in prominent TN (total nitrogen) removal. The constructed wetland was designed in subsurface flow mode with 0.15 m depth filled with calcium-rich ceramic granules, which improved phosphorus removal greatly. COD (chemical oxygen demand), TN, NH4+-N and TP (total phosphorus) in the final effluent were mostly below 30, 15, 5 and 0.5 mg/L, respectively. The overall phosphorus removal rate in the constructed wetland reached 158.9 g/m2 year, in which granules' interception and plants' uptake respectively contributed 74.7% and 25.3%. After one year's operation, the calcium content on the surface of the granules in the constructed wetland decreased obviously, whereas phosphorus content increased greatly.