Solar water disinfection by a Parabolic Trough Concentrator (PTC): flow-cytometric analysis of bacterial inactivation

An innovative solar water pasteurizer was developed to directly heat the water by solar radiation using a “Parabolic Trough Concentrator” (PTC). The efficiency of drinking water pasteurization by using the PTC was studied with a combination of analytical methods including flow-cytometric determination of total cell concentration and enumeration of cells with damaged membranes before and after treatment. Fluorescent staining of all microbial cells with two nucleic acid stains, SYBR®Green I and Propidium Iodide (live/dead staining), was used. The effectiveness of the pasteurizer to inactivate spiked Escherichia coli cells in contaminated water was also investigated. Flow-cytometric analysis revealed that cellular membranes of all microbial cells were strongly damaged after exposure in all the tested water samples. The pasteurizer reached a maximum daily water production of 66 L on a sunny day and was stable in its E. coli reduction rates. The results of this study suggest that the pasteurization temperature of 87 °C is able to inactivate bacterial cells in drinking water. Despite this, water pasteurized in this way is not sterile and has to be consumed quickly, since treated water samples incubated at 30 °C for 72 h exhibited a potential microbial regrowth. •We investigated the behaviour of a solar pasteurizer under real weather conditions.•The pasteurizer produced 66 L of hygienically safe drinking water during a sunny day.•Flow cytometry was used to quantify number and state of microbial cells after treatment.•After pasteurization most cells had a damaged membrane (>90%).•The pasteurizer inactivated up to 9 log10 of Escherichia coli.