Performance Evaluation of a Modified SODIS under Sub-Tropical Climate Condition in Bangladesh

Abstract

The World Health Organization (WHO) has acknowledged solar disinfection (SODIS) as a low-cost, efficient, sustainable, and simple approach for getting rid of certain germs in drinking water. According to studies, SODIS' primary drawbacks are longer exposure times (>6h), inefficiency in the monsoon and winter months, and the regeneration of microorganisms following treatment. To get around these restrictions, this study used test water and drinking water collected from restaurants, slums, and household areas in accordance with the WHO protocol during the monsoon and winter seasons in Bangladesh's subtropical climate to evaluate the performance of a modified SODIS with a photo catalyst (H2O2). Regression analysis was also carried out to forecast the rate of bacterial disinfection utilizing the modified SODIS with H2O2. The WHO protocol was followed in the preparation of two different test waters. Reactors with a 500 ml capacity made of polyethylene terephthalate (PET) bottles and plastic bags were used for the SODIS experiment. In order to each PET or plastic bag (PB), 5 cc of H2O2 was added. Six PET or PB with test water or collected drinking water samples were utilized in each batch, and they were exposed to sunlight using a made-up SODIS chamber for six hours during the monsoon season (June–October, 2022) and the winter season (November–February, 2023) respectively. The physicochemical and bacteriological water quality parameters were measured prior to the SODIS experiment. Along with bacteriological characteristics like Escherichia coli (E. coli) tests, physicochemical parameters including dissolved oxygen (DO), electrical conductivity (EC), pH, turbidity, and water temperature were evaluated in every test. One sample was taken for physicochemical and bacterial analysis during each hour of the SODIS experiment, and the sun irradiance was measured every 1 min. To test the microbes' potential for regrowth, the SODIS-treated water was left at room temperature in the dark for 12 and 24 hours after being treated for 6 hours. To test the improved SODIS, drinking water samples were also taken from Dhaka City eateries, slums, and residential establishments. The variations in the physicochemical parameters before and after SODIS demonstrated that there were no notable changes other than in the EC values. The effectiveness of modified SODIS with H2O2 shows that the PET bottle only needed 2 hours to inactivate germs, while PB only needed one hour during the monsoon season to obtain a 6.7 log reduction value (LRV). However, during the winter, it took 2 hours for bacteria in a PET bottle and PB to become inactive, resulting in a 5.49 LRV. After the 12 and 24 hours post-SODIS periods in the monsoon and winter seasons, respectively, there was no regrowth. Based on microbial inactivation (LRV >4), SODIS with H2O2 was deemed to be "Highly Protective" in performance. With an R2 value of 0.95-0.98, the Weibull bacterial inactivation model matches the data of PET bottles and PB in the monsoon and winter seasons well. The minimum and maximum safe exposure times for achieving the four LRV were 1 and 2 hours, respectively. Regression analysis showed that PB (TW-1) with an R2 value of 0.79 (79%), where the equation coefficients are turbidity, water temperature, solar irradiation, and DO, had the highest degree of accuracy. According to regression analysis, the rate of disinfection increased with rising water temperature, solar irradiation, and DO and reduced with rising turbidity. The statistical analysis findings from the regression analysis also showed how well the model suited the data from this investigation. Drinking water samples were taken from eateries, slums, and residential areas. The findings of the water parameter tests show that the majority of the water was microbially contaminated and included iron. The application of the modified SODIS with H2O2 in comparison to the traditional SODIS shows that the modified SODIS functions better and does not experience regrowth. The findings of this investigation are consistent with the literature on SODIS for inactivating bacteria. If properly promoted, SODIS has the potential to be a viable technology for drinking safe water and giving access to water in water-stressed parts of Bangladesh and other developing countries. The findings of this study will enable people in Bangladesh and other developing nations to recognize the usefulness of SODIS and use it for potable water.