Presence of bacteria and bacteriophages in full-scale trickling filters and an aerated constructed wetland

Aerated Constructed Wetlands are a state-of-the-art design that provides a different physical and chemical environment (compared to traditional passive wetland designs) for the wastewater treatment processes and, thus, may
have different pathogen removal characteristics. In order to establish the fate of bacterial and viral indicators, a field studywas carried out at a Sewage Treatment Works (STW) in the UK (serving 20,000 pe). The STWconsists of primary
and secondary sedimentation tanks and tricklingfilters (TF) as the biological stage.Alarge (1,160m2) pilot aerated Vertical Flow Constructed Wetland (AVFCW) was constructed at the STW as tertiary stage receiving ¼ of the total flow
rate, i.e., 1250m3/day. Effluent quality of the AVFCW complied with national and international standards for environmental discharge and reuse. For the first time, two sets of bacterial (Faecal coliforms, E.coli and intestinal enterococci)
and viral indicators (Somatic coliphages, F-RNA specific bacteriophages and human-specific B. fragilis GB124 phages) were simultaneously investigated in an AVFCW and TF. High elimination rates were detected (up to 3.7 and 2.2 log reduction for bacteria indicators and phages, respectively) and strong correlations between the two sets were found. The superior efficiency of the aerated ConstructedWetlands inmicrobiological contamination removal compared to passive wetland systems was established for the first time, whichmay have implications for process selection for wastewater reuse. This field study therefore provides new evidence onthe fate of bacteriophages and a first indication of their potential use for performance evaluation in TF and aerated ConstructedWetlands. It also demonstrates that the combination
of TF with aerated constructed wetlands could be a novel and effective treatment scheme for new STWor for the upgrade of existing STW.