Wavy Subsurface Flow and Vertical Flow Constructed Wetlands: Effects of Aeration and Wastewater Composition on Wetland Clogging

In this study, effects of aeration and wastewater composition were evaluated on the clogging process in four laboratory-scale wavy subsurface-flow and vertical-flow constructed wetlands (WSVFCWs) used for secondary and tertiary treatment. The relationship between the accumulated solid material and infiltration rate, the content and particle size distribution as well as the ratio of organic and inorganic matter of the accumulated material in the filter media were determined, and the mechanisms of clogging were elucidated. The clogging mainly occurred in the upper 0-40 cm layer, and the accumulated material decreased with filter depth (along the flow direction). The main particle size contributing to clogging was ∼40 μm in the WSVFCWs for secondary treatment and >110 μm in those for tertiary treatment. The accumulated material had 30-40% of organic matter. The clogging mechanisms varied as the composition of influent and aeration conditions are different in WSVFCWs. Aeration promoted the growth of biofilm and mineralization of the accumulated material as well as provided shear force in the WSVFCWs. Aeration has a good effect in extending operational time in the tertiary WSVFCW but has a mild effect in the secondary WSVFCWs because of high organic loading rate there. Both the organic and suspended solids (SS) loading rate are important factors and should be controlled to mitigate the clogging problem in WSVFCWs.