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The influence of humic substances oxygen and pH on the effect of light on faecal coliforms in waste stabilization ponds

Lookup NU author(s): Professor Thomas CurtisORCiD


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Simple beaker experiments established that light damages fecal coliforms in waste stabilization ponds by an oxygen-mediated exogenous photosensitization. Wavelengths of up to 700 nm were able to damage bacteria. The ability of wavelengths of >425 nm to damage fecal coliforms was dependent on the presence of dissolved sensitizers. The sensitizers were ubiquitous in raw sewage, unaffected by sewage treatment, not derivatives of bacteriochlorophyll or chlorophyll, absorbed well in UV light, and had a slight yellowish color; they are therefore believed to be humic substances. The ability of light to damage fecal coliforms was highly sensitive to, and completely dependent on, oxygen. Scavengers of H2O2 and singlet oxygen could protect the bacteria from the effects of sunlight, but scavengers of hydroxyl radicals and superoxides could not. Light-mediated damage of fecal coliforms was highly sensitive to elevated pH values, which also enabled light with wavelengths of >425 nm (in the presence of the sensitizer) to damage the bacteria. We conclude that humic substances, pH, and dissolved oxygen are important variables in the process by which light damages microorganisms in this and other environments and that these variables should be considered in future research on, and models of, the effects of light.

Publication metadata

Author(s): Curtis TP, Mara DD, Silva SA

Publication type: Article

Publication status: Published

Journal: Applied and Environmental Microbiology

Year: 1992

Volume: 58

Issue: 4

Pages: 1335-1343

Print publication date: 01/04/1992

ISSN (print): 0099-2240

ISSN (electronic): 1098-5336

Publisher: American Society for Microbiology