Transfer of bacteria via vapor in solar desalination units

Abstract

Microbial contamination of drinking water is a major public health threat worldwide. Some studies have reported unusual findings of microbiological contamination in distilled water produced from solar stills. Not knowing the exact reason for this presence, they attributed it to possible cross contamination. In the complete absence of literature on the transfer of bacteria in solar stills, this research was conducted to investigate whether bacteria in water subjected to low temperature solar desalination finds its way into the effluent as a result of cross contamination or transfer through water vapor. This study looked at how the type of bacteria and the water temperature affected transfer in the absence of solar UV radiation. Simulated distillation experiments performed in darkness were conducted by spiking a pure culture of Escherichia coli or Enterococcus faecalis in tap water and heating it to low temperature ranges similar to those reached in solar stills under real sunlight. Results show that the two types of bacteria tested in the study were transferred with the vapor in a solar still when not exposed to solar UV radiation and that transfer at the 40–45°C range is significantly higher than transfer at other temperature ranges. Moreover, transfer is independent of bacterial type; however E. faecalis transfer rates are higher than E. coli at the 40–45 and 50–55°C ranges. While solar desalination can effectively inactivate bacteria in water, there exists a mode of transfer of bacteria in the humid medium of the solar still to the distillate that takes place under suboptimal weather conditions.

Keywords:

• Water contamination
• Low-temperature distillation
• Bacterial transfer
• Water vapor

Acknowledgment

This research was made possible by funding from the Lebanese National Council for Scientific Research (NCSR).

Notes

Presented at the International Conference WIN4Life, 19–21 September 2013, Tinos Island, Greece