Assessment of Clogging in Constructed Wetlands

The main goal of this thesis is the assessment of the clogging degree in the horizontal subsurface flow constructed wetland of Martinlongo and Barrada WWTP, included in Algarve Multi-Municipal Sanitation System Despite of constructed wetland treatment processes being natural and constructed wetlands easy to operate, clogging phenomena can be quite complex and challenging in a way that it is necessary to understand what is going on in the whole system. In order to do so, a deep search of relationships between the wetland components and the interactions of these with the operation mode was needed, as well as an identification of the influence factors and impact of each one. The main symptom of clogging is water insurgence, which leads often to pond formation and surface runoff. This are undesired consequences due to the risk associated with the wastewater exposure at the surface. Ultimately, clogging problem can be so severe that deep intervention is needed and so it is definitely an issue that shortens the life span of these equipment’s. The assessment of the two constructed wetlands clogging degree used saturated hydraulic conductivity measurements obtained with the Falling Head Method. The investigation reported in this document reveals that Martinlongo WWTP constructed wetland is really clogged in the majority of its area, with the exception of the inlet zone (recently rehabilitated), and that Barrada WWTP constructed wetlands has already some preoccupying dispersed values meaning the existence of preferential flow paths and showing where the first symptoms of clogging will occur.