Spatial–temporal variation of treatment performance and bacterial community diversity in a hybrid constructed wetland

Abstract

A hybrid pilot-scale constructed wetland (HSSF-FWS) with three horizontal flow components and a free water surface in series (HF-CW1 + HF-CW2 + HF-CW3 + FWS) was designed and investigated to evaluate seasonal wastewater treatment performance, the microbial diversity and community structure. The HF-CW1 component was planted with Scirpus holoschoenus and Cyperus papyrus; HF-CW2 was unplanted, whereas HF-CW3 was planted with Scirpus validus. In FWS, the wastewater was covered with Lemna minor and Daphnia magna. HSSF-FWS has a great potential to reduce chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total suspended solids (TSS), fecal coliforms (FC) and fecal streptococci (FS), while the removal efficiencies of nitrate nitrogen (NO3−) and orthophosphorus (PO43−) were relatively low. The best removal efficiency was achieved in spring for COD and BOD5, in summer for TSS, in autumn for NO3− and in winter for PO43−, while no seasonal difference was found for the removal of FC and FS. The seasonal treatment performance is generally less influenced by the plant species than by the presence or absence of vegetation. HF-CW3 and FWS had different influences on treatment parameters; the FWS component improved the removal of TSS and PO43− during winter and the removal of COD and NO3− during spring season. Seasonal changes affect the microbial diversity and community structure throughout the hybrid constructed wetland and are enhanced by the presence of plants, with diversity changing with different plant species. Cluster analysis indicated that bacterial community structure from influent and FWS samples was closely related in autumn.