The antagonistic and synergistic effects of temperature during solar disinfection of synthetic secondary effluent

A 4-factor, multilevel, full factorial design of 240 experiments was performed in order to investigate the effect of temperature on the inactivation efficiency of spiked Escherichia coli in simulated solar disinfection of a synthetic secondary effluent. The initial population of the microorganisms was 10, 10, 10 and 10 CFU/mL, the exposure time 1, 2, 3 and 4 h, the treatment temperature 20, 30, 40, 50 and 60 ̊C and the sunlight intensity 0, 800 and 1200 W/m. Radical changes in bacterial behavior, process efficiency and remaining populations were observed, while treating effluents in discreet temperatures. Elevating treatment temperature from 20 to 40C drastically impaired disinfection. Thermal inactivation with no regrowth predominated at 50C and total inactivation of microorganisms was observed at 60C in non-irradiated samples. Irradiation at 800 and 1200 W/m much increased inactivation efficiency, especially at 50 and 60C, proving sensitive light-temperature synergy at those temperatures. Total inactivation was achieved within 4 hours under a range of treatment conditions, including all samples at 1200 W/m, or 60oC samples at 800 W/m. Also, 99.9-100% efficiencies and final population below 1000 CFU/100 mL were obtained at 800 W/m and temperatures of 50oC and above. Treatment time, temperature and intensity are the critical parameters for the disinfection process, while initial population is insignificant for removal efficiency. An explanation of the mechanism of the process as well as a general linear model predicting the outcome of the experiments are also suggested. NOTICE: this is the author’s version of a work that was accepted for publication in Journal of Photochemistry and Photobiology A: Chemistry. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Photochemistry and Photobiology A: Chemistry [Vol. 280, p. 14‐26, April 2014]. DOI: 10.1016/j.jphotochem.2014.02.003