Solar disinfection - An appropriate water treatment method to inactivate faecal bacteria in cold climates

Anni Juvakoski; Gaurav Singhal; Manuel A Manzano; Miguel Ángel Moriñigo; Riku Vahala; Irina Levchuk

doi:10.1016/j.scitotenv.2022.154086

Solar disinfection - An appropriate water treatment method to inactivate faecal bacteria in cold climates

Sci Total Environ. 2022 Jun 25:827:154086. doi: 10.1016/j.scitotenv.2022.154086. Epub 2022 Feb 23.

Authors

Anni Juvakoski¹, Gaurav Singhal², Manuel A Manzano³, Miguel Ángel Moriñigo⁴, Riku Vahala⁵, Irina Levchuk⁶

Affiliations

¹ Department of Built Environment, School of Engineering, Aalto University, PO Box 15200, FI-00076 Aalto, Finland; Department of Environmental Technologies, INMAR-Marine Research Institute, Faculty of Marine and Environmental Sciences, University of Cádiz, Poligono Rio San Pedro s/n, Puerto Real, 11510 Cádiz, Spain. Electronic address: anni.juvakoski@aalto.fi.
² Department of Built Environment, School of Engineering, Aalto University, PO Box 15200, FI-00076 Aalto, Finland; Department of Environmental Technologies, INMAR-Marine Research Institute, Faculty of Marine and Environmental Sciences, University of Cádiz, Poligono Rio San Pedro s/n, Puerto Real, 11510 Cádiz, Spain; Department of Chemical and Metallurgical Engineering, School of Chemical Engineering, Aalto University, Kemistintie 1, P.O. Box 16100, Espoo, FI-00076, Aalto, Finland.
³ Department of Environmental Technologies, INMAR-Marine Research Institute, Faculty of Marine and Environmental Sciences, University of Cádiz, Poligono Rio San Pedro s/n, Puerto Real, 11510 Cádiz, Spain.
⁴ Department of Microbiology, Faculty of Sciences, Campus Universitario de Teatinos s/n, University of Málaga, Spain.
⁵ Department of Built Environment, School of Engineering, Aalto University, PO Box 15200, FI-00076 Aalto, Finland.
⁶ Department of Built Environment, School of Engineering, Aalto University, PO Box 15200, FI-00076 Aalto, Finland; Fine Particle and Aerosol Technology Laboratory, Department of Environmental and Biological Sciences, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland. Electronic address: irina.levchuk@uef.fi.

PMID: 35218818
DOI: 10.1016/j.scitotenv.2022.154086

Abstract

Solar disinfection (SODIS) is an inexpensive drinking water treatment method applied in tropical and sub-tropical low-income countries. However, it has been unclear whether it functions adequately also in colder climates. To investigate this issue, SODIS experiments were performed in the humid continental climate of Finland by exposing faecally contaminated drinking water to natural solar radiation at different water temperatures (8-23 °C) and UV intensities (12-19 W/m²) in polyethylene (PE) bags. To establish an adequate benchmark, SODIS experiments with the same experimental design were additionally conducted in the Mediterranean climate of Spain in typical conditions of SODIS application (~39 °C and 42 W/m²). Out of all experiments, the highest coliform and enterococci inactivation efficiencies in terms of lowest required doses for 4-log disinfection (25 Wh/m² and 60 Wh/m², respectively) were obtained in humid continental climate at the lowest studied mean water temperature (8-11 °C). Despite the low mean UV irradiance (~19 Wh/m²), 4-log disinfection of coliforms and enterococci were also reached fast in these conditions (1 h 27 min and 3 h 18 min, respectively). Overall, the doses required for disinfection increased as the water temperatures and UV intensities of the experiments rose. Disinfection of 4-logs (> 99.99%) of both bacteria was reached in all SODIS experiments within 6 h, suggesting SODIS could be a sufficient household water treatment method also in colder climates, unlike previously thought. The effects of different water temperatures on bacterial inactivation were also tested in the absence of sunlight. Together the obtained results indicate that while water temperatures below or close to the optima of coliforms and enterococci (~10 °C) alone do not cause inactivation, these temperatures may enhance SODIS performance. This phenomenon is attributed to slower bacterial metabolism and hence slower photorepair induced by the low water temperature.

Keywords: Emergency water purification; Frugal technologies; Household water treatment and safe storage (HWTS); Low temperature disinfection; SODIS; Waterborne disease.

MeSH terms

Bacteria
Cold Climate
Disinfection / methods
Drinking Water*
Sunlight
Water Microbiology
Water Purification* / methods

Substances

Drinking Water