The effect of change of hydraulic characteristic and microbial community on pollution removal efficiency of the infiltration systems in the bioclogging development process remain poorly understood. In this study, therefore, the pollutant removal as a response to hydraulic conductivity reduction and the change of diversity and structure of microbial communities in vertical flow constructed wetlands (VFCWs) was investigated. The results indicated that the richness and diversity of the bacterial communities in the columns at different depths were decreased, and the microbial communities of genus level were changed in the process of bioclogging. However, the variation of microbial communities has a low impact on the purification performance of VFCWs because the abundance of function groups, respiratory activity and degradation potentiality of microorganisms remain steady or even get improved in the columns after bioclogging. On the contrary, the hydraulic efficiency of VFCWs decreased greatly by 16.9%, 9.9%, and 57.1% for VFCWs filled with zeolite (Column I), gravel (Column II), and ceramsite (Column III) respectively. The existence of short-circuit and dead zones in the filter media cause the poor pollution removal efficiency of VFCWs due to the short contact time, decrease of oxygenation renewal as well as low activity in the dead zone.
COD removal rate decrease with the bioclogging in VFCWs
The substrate degradation rate of biomass were little changed during bioclogging.
The microbial variation during the bioclogging has a low impact on the purification performance.
The low hydraulic efficiency cause the poor pollution removal of VFCWs.