Towards the definition of treatment wetland pathogen log reduction credits

Treatment wetlands have the potential to treat a range of water and wastewater pollutants while using less energy and chemicals than conventional treatment processes, making them a viable option for improving the sustainability of water treatment systems. However, water treatment systems used for water reuse must also be protective of human health. To date, the human health protection benefits of treatment wetlands have not been rigorously quantified in the context of current human health risk frameworks. This study presents a comprehensive review of the ability of treatment wetlands to provide reliable pathogen reduction to meet risk-based treatment targets for water reuse. Following an existing protocol for establishing log reduction credits, we systematically reviewed the documented pathogen reduction performance of major treatment wetland types in terms of core components of that protocol, including pathogen removal mechanisms, identification of target pathogens, and influencing factors. Results of the review point to design and operational conditions under which treatment wetlands could likely be credited with a log reduction value of approximately 0.5 or greater for virus, protozoa and bacteria. These conditions are specified in terms of preliminary operating envelopes, or design and operational parameter windows associated with optimal performance. Important caveats are noted, as are specific and tractable recommendations for future research and data collection efforts that would help refine operating envelopes and define log reduction credits for these promising water treatment technologies. As a resource to other practitioners, we have also included the detailed performance characterization database as Supplemental Information. This database includes a detailed tracking of log reduction values as well as design and operational parameters reported in the literature.