Microfaunal community in horizontal constructed wetlands with different design configurations

In comparison with conventional activated sludge treatment systems, for which a large body of research has been carried out on their microfauna and their role in bacteria and pollutant removal, only a few studies have focused on microfaunal communities inhabiting constructed wetlands (CWs). The aim of this study was to evaluate the microfaunal communities of horizontal CWs with differing design configurations in order to determine those design factors affecting their abundance and community structure and to discover their role in bacteria removal. Total bacteria, ciliates, amoebae and metazoa were counted in the effluents of an experimental plant combining the most common design configurations of CWs. Three different hydraulic designs (hydroponic, free water surface-FWS and subsurface flow-SSF), presence vs. absence of vegetation, two plant species (Typha angustifolia vs. Phragmites australis) and two organic loading rates were compared. SSF and vegetation favoured bacteria removal whereas abundance of protozoa and diversity of metazoa was greater in FWS-planted wetlands. Microfauna community structure and bacterial removal were clearly affected by vegetation and flow type, although no significant relationships were observed between microfauna and bacteria abundance at the outflow. Therefore, other mechanisms such as filtration, sedimentation or adsorption, seem to be more important than predation in removing bacteria from constructed wetlands. (C) 2016 Elsevier B.V. All rights reserved.