Impacts Of Media Structures On Nitrogen Removal And Clogging In Vertical Flow Constructed Wetlands

Vertical flow constructed wetland has wide application fields. It can be used to deal with sewage or advanced treatment of sewage and industrial wastewater. Nitrogen removal from the wastewater is CWs’one of the most important functions. Media structure is the core content of wetland construction. At present, the impacts of media structure on CWs’purification research are not thorough, the nitrogen removal mechanism, synergy of plants, treatment ability to cope with changeable water quality and clogging prevention are need to be studied carefully.In this paper, aiming at nitrogen removal performance of progressively-sized, anti-sized and uniform-sized media structures, considering influencing factors such as:plant, temperature organic loading, a year-round purification experiment was performed in the home-made experimental base, treating the simulative wastewater. So as to investigate the nitrogen removal ability in each media structure and choose the best clogging resistance one.The main results were as following:The differences of reoxygenation ability lead to a different DO level of each kind of media structure. Large particle size in top layer in anti-sized reactor lead to a relative great reoxygenation, the overall DO level was high, nitrification ability was strong, while the TN removal rate was not high; progressively-sized reactors presented aerobic-anaerobic regions and the ideal condition facilitated total nitrogen removal; uniform-sized reactors was not obvious on both nitrification and denitrification compared to the fist two.Great oxygen transfer of anti-sized reactors helped to cope with high organic loadings treatment. This kind of media structure ensured the nitrification and provided a comfortable environment for denitrification. TN removal rate was higher than low organic loadings. Uniform-sized was similar to anti-sized reactor, but the denitrification effect was inferior to the former. The ability of progressively-sized reactor to cope with high organic loading was the worst, TN removal rate decreased.The present of plants contributed little to wetlands’ DO level, just around the root area, the DO value slightly higher. However, at high organic loading treatment, plant groups’ nitrogen removal rate were high than no plant, progressively-sized reactor was the most obvious. Plants in progressively-sized reactor had well developed root systems, while plants in anti-sized reactor had maximum extension. Tiny particles in progressively-sized reactor made it a good insulating ability to cope with cold climate.The porosity of both the first layer of progressively-sized and uniform-sized reactors decreased serious, while anti-sized reactor appeared at the bottom layer. Clogging was connected with the position of biomass accumulated, while the reduction of the internal void space was not the determining factor. Progressively-sized reactors had the strongest ability of clogging prevention, while the weakest of anti-sized reactors. High organic loading made each media structure’s porosity decrease serious, bed resting was not effective in anti-sized reactor.