Removal of pathogens from greywater using green roofs combined with chlorinationRemoval of pathogens from greywater using green roofs combined with chlorination Peer-Reviewed Journal Publication Δημοσίευση σε Περιοδικό με Κριτές 2024-02-162023enGreywater is an important alternative water resource which could be treated and reused in buildings, reducing the freshwater demand in drought affected areas. For the successful implementation of this solution, it is important to ensure the microbial safety of treated greywater. This study examined the microbiological quality of treated greywater produced by an emergent nature-based technology (green roofs) and a chlorination process. Specifically, the effect of substrate, substrate depth, and vegetation on the removal of total coliforms, Escherichia coli, and enterococci in experimental green roofs treating greywater was examined for a period of about 12 months. In addition, the ability of chlorination to inactivate the abovementioned pathogen indicators was evaluated and their potential regrowth was examined. Results shown that green roofs filled with 10 cm of perlite reduce total coliform concentration by about 0.4 log units while green roofs filled with 20 cm of vermiculite reduce total coliform concentration by about 1.2 log units. In addition, the use of vegetation in green roofs improves the removal of pathogenic bacteria by about 0.5 log units in comparison with unvegetated systems. In all cases, the effluents of green roofs failed to satisfy the criteria for indoor reuse of treated greywater for non-potable uses such as toilet flushing without a disinfection process. The addition of 3 mg/L of chlorine in the effluent provided safe greywater microbiological quality for storage periods of less than 24 h, while longer periods resulted in the significant regrowth of pathogens. In contrast, a chlorination dose of 7 mg/L completely secured inactivation of pathogen indicators for periods of up to 3 days.This research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme «Human Resources Development, Education and Lifelong Learning 2014–2020 in the context of the project “Development of constructed wetlands on rooftops for greywater treatment and indoor reuse” (MIS 5048920).http://creativecommons.org/licenses/by/4.0/Environmental Science and Pollution Research30922560–22569Petousi_et_al_Environ. Sci. Pollut. Res._30(9)_2023.pdfChania [Greece]Library of TUC2024-02-16application/pdf1.1 MBfree Petousi Ioanna Thomaidi Vasiliki Kalogerakis Nikos Καλογερακης Νικος Fountoulakis Michalis Springer Nature Wastewater Regrowth Green spaces Water reuse Disinfection Coliforms