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.