Optimization of solar disinfection considering log reduction values (LRV) for treated urban wastewater

Solar disinfection is becoming increasingly popular around the world for eliminating pathogens present in wastewater. The goals of this study were to identify the significant variables and to maximize the log reduction values (LRV) of total coliforms present in treated urban wastewater using solar disinfection. To achieve the goals, a 23 full factorial design of experiments and response surface methodology were used. Solar disinfection was carried out in an open-air batch reactor and in a solar batch reactor. The three variables considered were solar irradiation, volume of sample and exposure time at two markedly different levels: solar irradiation (1100 Wh/m2 and 1700 Wh/m2), volume of sample (0.2 L and 2L), and exposure time (0.5 h and 3 h). When compared to other variables, exposure time was the most significant factor in the analysis of variance (ANOVA) study for both the reactor conditions. The regression equation developed for a solar reactor does not adequately explain the variability of the experimental data when compared to the regression equation developed for an open-air reactor. According to the response optimizer, the optimum values of the factors for solar disinfection using a solar reactor to achieve an LRV of 2 for 0.25 L of sample volume are 1700 Wh/m2 solar irradiation and 2.97 hours of exposure time. With an open-air reactor, 0.2 L of sample must be exposed to 1700 Wh/m2 of solar irradiation for 3 hours to achieve LRV of 2.