Effectiveness of Large SODIS Reactor Under Tropical Climate Condition with H2O2

Abstract

Access to safe drinking water remains a critical public health concern in developing countries, where conventional water treatment technologies are often expensive or unavailable in rural areas. Solar Water Disinfection (SODIS) offers a simple, affordable, and sustainable method that uses solar radiation to inactivate waterborne pathogens. However, its efficiency can decline under cloudy conditions, high turbidity, or when sunlight exposure is insufficient. To enhance the effectiveness of the process, this study investigated the performance of an H₂O₂-assisted SODIS system using a large-scale 10 L transparent PET reactor under natural tropical sunlight in Gazipur, Bangladesh. Experiments were conducted during both the summer and monsoon seasons to capture variations in solar irradiance and temperature. Two types of test waters were prepared: tap water (TW-1) and a mixed lake water sample (TW-2) containing 5% surface water to simulate natural contamination. Escherichia coli (ATCC 25922) was introduced as an indicator organism, and the effects of pH (5.5-12) and H₂O₂ concentration (5-15 mg/L) were analyzed. Samples were collected hourly over 6 hours of exposure and examined using the m-TEC membrane filtration method to determine bacterial log reduction. The results showed that the combined solar-hydrogen peroxide process achieved faster and more consistent disinfection compared to conventional SODIS. Under summer conditions, with average solar irradiance exceeding 800 W/m² and water temperatures above 45°C, complete E. coli inactivation (≥5-log reduction) was achieved within 4-5 hours at an optimized 10 mg/L H₂O₂ and pH 7.5. During the monsoon season, lower irradiance required a longer exposure of 6-7 hours to reach similar reductions. Higher H₂O₂ doses (15 mg/L) reduced efficiency slightly due to radical self-scavenging, while extreme pH values (5.5 and 12) negatively affected inactivation. The presence of organic matter in TW-2 also slowed the process, indicating that water quality influences radical availability and light transmission. Kinetic modeling revealed that bacterial inactivation followed a Double Weibull pattern, characterized by an initial rapid kill phase followed by a slower tailing phase. The inactivation rate constant (k) was higher in summer (1.56 h⁻¹) than in monsoon (0.92 h⁻¹), confirming seasonal dependence. Statistical analysis (R² > 0.95) demonstrated strong correlations between solar intensity, temperature, and disinfection efficiency. Moreover, regrowth analysis showed that the residual 1-2 mg/L H₂O₂ vi remaining after treatment effectively prevented microbial recovery during 24-hour storage, addressing a major limitation of traditional SODIS. This study demonstrates that integrating a low concentration of hydrogen peroxide into SODIS significantly improves its disinfection efficiency, reduces treatment time, and prevents bacterial regrowth under tropical conditions. The optimized configuration: 10 mg/L H₂O₂ at pH 7.5 with 6 hours of sunlight exposure, proved to be both effective and practical. These findings suggest that photo-assisted and H2O2 modified SODIS can serve as a sustainable, low-cost solution for providing safe drinking water in resource-limited tropical regions.