Application of azo dyes as dosimetric indicators for enhanced photocatalytic solar disinfection (ENPHOSODIS)

The use of azo dyes as dosimetric indicators to measure the efficiency of enhanced photocatalytic solar disinfection has been developed based upon the solar dose required to inactivate helminth ova, a highly resistant waterborne pathogen frequently found in surface water sources in developing countries. A range of treatment conditions were examined to determine the optimal inactivation conditions required for a range of pathogens. The inactivation data were fitted using a modification of the Chick–Watson kinetic model. It was determined that the radiation dose required for >5-log helminth egg inactivation was approximately 140 kJ L−1 (using photo-Fenton reaction at [Fe(II)] = 10 mM and initial [H2O2] = 280 mM). In order to develop a dosimetric indicator providing a visual color change corresponding to this dose, a range of reaction conditions were examined to achieve removal of a dye, Acid Orange 24 (AO24). For experiments performed at [Fe(II)] = 0.7 mM and initial [H2O2] = 5 mM, complete color removal was achieved following receipt of a dose equal to 155 kJ L−1. 6-log inactivation of Escherichia coli and Pseudomonas aeruginosa was achieved following receipt of less than 10 kJ L−1. No significant increase in the inactivation dose was required when up to 5 mg L−1 natural organic matter (NOM) was added to the bacterial suspension. These results confirm that helminth eggs are an appropriate index for microbiologically safe water following enhanced photocatalytic solar disinfection. AO24 dye degradation was determined to serve as an accurate dosimetric indicator. The indicator employed is easy to use in the laboratory and field conditions, where the dye solutions may be prepared on-site and submitted to solar radiation in a glass vial in close proximity with water being disinfected in the solar collector. The user can easily and quickly monitor the treatment efficiency and be confident that the water disinfection process is complete when complete discoloration has been reached.