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Efficiency of solar based disinfection of Pseudomonas aeruginosa (P. aeruginosa) in rooftop harvested rainwater was evaluated aiming the potability of rainwater. The rainwater samples were exposed to direct sunlight for about 8–9 hours and the effects of water temperature (°C), sunlight irradiance (W/m2), different rear surfaces of polyethylene terephthalate bottles, variable microbial concentrations, pH and turbidity were observed on P. aeruginosa inactivation at different weathers. In simple solar disinfection (SODIS), the complete inactivation of P. aeruginosa was obtained only under sunny weather conditions (>50°C and >700 W/m2) with absorptive rear surface. Solar collector disinfection (SOCODIS) system, used to improve the efficiency of simple SODIS under mild and weak weather, completely inactivated the P. aeruginosa by enhancing the disinfection efficiency of about 20% only at mild weather. Both SODIS and SOCODIS systems, however, were found inefficient at weak weather. Different initial concentrations of P. aeruginosa and/or Escherichia coli had little effects on the disinfection efficiency except for the SODIS with highest initial concentrations. The inactivation of P. aeruginosa increased by about 10–15% by lowering the initial pH values from 10 to 3. A high initial turbidity, adjusted by adding kaolin, adversely affected the efficiency of both systems and a decrease, about 15–25%; in inactivation of P. aeruginosa was observed. The kinetics of this study was investigated by Geeraerd Model for highlighting the best disinfection system based on reaction rate constant. The unique detailed investigation of P. aeruginosa disinfection with sunlight based disinfection systems under different weather conditions and variable parameters will help researchers to understand and further improve the newly invented SOCODIS system.

The effects of different catchment types and storage conditions on Pseudomonas aeruginosa in harvested rainwater under wet and dry seasons were investigated. Both horizontal (roof intercepted to outlet point) and vertical (surface to bottom) quality variation inside storage tanks of different rainwater harvesting (RWH) systems was also monitored. The numbers of P. aeruginosa varied from 30 to 400 colony forming units (CFU)/100 mL during the dry season and 200 to 1800 CFU/100 mL during the wet season. A relatively good quality of harvested rainwater was observed in dry season. The horizontal and vertical quality variation of P. aeruginosa revealed best quality at the supply point. The number of P. aeruginosa was the highest (about 1800 and 1000 CFU/100 mL during wet and dry seasons, respectively) in rainwater harvested from mountain catchment while the lowest (about 30 and 1000 CFU/100 mL during dry and wet seasons, respectively) numbers was seen from concrete roof catchment. Dark, covered storage conditions resulting low rainwater temperatures showed better microbial quality of rainwater than uncovered and open storage conditions exposed to light. The study suggests that the improvement in the quality of harvested rainwater is possible when appropriate tank designs, maintenance of catchment surfaces, and proper storage conditions are considered in RWH systems.

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