Grantee Research Project Results
Final Report: Biosynthesis and Application of Nanostructured Composites for Purification of Drinking Water: A Modification of the Solar Disinfection(SODIS)Technique
EPA Grant Number: SU839297Title: Biosynthesis and Application of Nanostructured Composites for Purification of Drinking Water: A Modification of the Solar Disinfection(SODIS)Technique
Investigators: Obuya, Emilly , Green, Naya , Perez, Jessica , Peterson, Kyle , Larson, Derek , Callahan, Lindsay , Legget, Sagan , Travis, Alicia , Frisbee, Megan , Tavolaro, Joanna , Epps, Lindsey Van , Gathiru, Marylyn
Institution: The Sage Colleges
EPA Project Officer: Page, Angela
Phase: I
Project Period: February 1, 2018 through January 31, 2019 (Extended to December 31, 2019)
Project Amount: $14,766
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2017) RFA Text | Recipients Lists
Research Category: Sustainable and Healthy Communities , P3 Awards , P3 Challenge Area - Safe and Sustainable Water Resources
Objective:
The importance of continuing research to achieve water sanitation through simple, efficient, and low-cost household water treatment and sanitation technologies cannot be overstated. Research specifically needs to look into development of point-of-use technologies that can be sustainably adopted by communities that do not have access to reliable infrastructure for centralized water treatment and distribution. While chlorination, boiling and filtration continue to be the preferred water disinfection methods among rural and urban communities in developing countries, SODIS has gained popularity within the last 10 years as an alternative technique that is simple, cost effective, non-toxic, and efficient in reducing disease incidences. SODIS technique uses solar radiation to disinfect microbial contaminated water that is placed in clear plastic PET bottles. Depending on the level of contamination, the illumination periods range from 6 – 48 hours.
Some of the problems that have been reported in the literature with SODIS are, (i) The long hours of constant illumination required to achieve complete bacterial destruction makes the process cumbersome hence prevents its large-scale adoption; (ii) The presence of bacterial re-growth after a SODIS treatment, indicating that the destruction pathways via UV energy alone is not sufficient to ensure complete contamination [5] and (iii) The technique is limited to specific bacterial destruction since the reactive oxygen species (ROS) formed through UV irradiation are not potent enough to target chemicals and more resistant pathogens like viruses and protozoa.
This research project seeks to improve the efficiency and sustainability of the SODIS technique by exploring technological solutions that ensure complete disinfection of a wide variety of pathogens with shorter illumination times and with the utilization of visible light irradiation. The purpose of this study was to develop SODIS as a simple, efficient, and low-cost water treatment technique for use in areas that lack municipal water treatment facilities or during natural disasters that compromise the centralized water distribution systems. We selected the Obunga slums in Kisumu, Kenya as our case study community.
The objectives for this research were:
1. To design, synthesize, and characterize the AgNPs (silver nanoparticels), TiO2 (nanofibers) NFs, and heterogeneous Ag-TiO2 nanocomposites.
2. To use the Disk Diffusion method as a quick quantitative assay of the relative antimicrobial activity of the as-synthesized catalysts.
3. To use the Time Kill method to perform photo-inactivation studies that will test the ability of the catalysts to destroy fecal bacteria using visible light radiation.
4. To test the viability of the nanomaterial catalysts with the actual SODIS devices (PET bottles) and field conditions (natural sunlight) in Obunga
The research scope was accomplished in three main stages:
- Stage I – A survey administered in Obunga slums in Kisumu, Kenya, was used to collect baseline data to identify residents’ current practices around water treatment and sanitation and how these practices correlate with disease incidences in the community. This information was used to assess the viability of SODIS as a household water treatment technology for residents of Obunga. Alongside the survey, a water quality test was conducted to determine the bacteriological quality of the drinking water used by residents.
- Stage II – A field-test of the SODIS technique was conducted to assess its ability to reduce (or completely remove) bacterial contamination – with a specific look at E. coli since it is the indicator mechanism for fecal contamination of drinking water. To achieve this, water samples from five of the most contaminated water sources in Obunga were treated using the SODIS technique and the levels of bacterial contamination monitored using Petrifilm Count Plates. UV intensity, humidity and temperature readings were recorded throughout the day in order to identify the ideal conditions required for SODIS treatment and bacterial quantification.
- Stage III – The green synthesis of the Ag-TiO₂ nanocomposites using Citrullus lanatus (watermelon) rind extract was conducted, and their antimicrobial efficacy tested using the Disc Diffusion and Time Kill methods. The goal was to assess whether the nanocomposites would be a viable additive to improve the efficiency of SODIS.
Summary/Accomplishments (Outputs/Outcomes):
- Stage I – Boiling was the most prevalent method of water treatment while SODIS and sedimentation were both the least commonly used techniques at 59% and 0.9% respectively. Correlation analysis indicated that even though most people in Obunga treated their drinking water by either boiling, cloth filtering, or by chlorination methods, most households still reported incidences of waterborne-related illnesses; an indication of lack of effectiveness of the most commonly utilized treatment methods in curbing waterborne diseases.
- Stage II – Out of the five water sources from Obunga that were treated with SODIS, the cumulative lethal dose required for complete bacterial decontamination ranged from 99.2– 445.8 kJ/m2. The cumulative UVA dose over the entire 6h SODIS treatment period was found to be 557.6 kJ/m2. Sources 1 & 4, which had moderate contamination, took 1 and 2 hours respectively to attain complete decontamination, while sources that were heavily contaminated (Sources 2, 3 & 5) required up to 4 hours of UV radiation to be completely clear of all pathogens. The least contaminated sources (1 & 4) achieved log reduction values of 3.1 and 2.6 respectively while sources 2, 3 & 5 achieved log reductions of between 3.4 and 3.6. The results from the UV intensity measurements indicate that UVA is the most intense of the UV radiations with peak intensities occurring between noon and 1 pm. From the UV intensity profile, the most convenient periods to carry out a SODIS experiment was reported to be between 10 am and 3 pm in order to take advantage of the high solar intensities during this period. The average daily temperature was found to be 30.5oC while the temperature of the corrugated roof where the PET bottles were placed averaged at 45.4oC. This reinforces the importance of placing the bottles on a metal roof that helps to conduct the infra-red radiation that has a synergistic effect in the bacterial decontamination process. The humidity readings, which fluctuated throughout the day with an average of 40.5%, created a conducive atmosphere for the incubation of the coliforms on the Petrifilm plates without the need for an incubator.
- Stage III – Higher watermelon rind extract concentrations of 400g/L were found to be optimum since at higher extract concentrations the polyphenols in the watermelon extract effectively reduced the Ag+ ions to Ag0 and provided enough capping agent for stabilization of the synthesized nanoparticles thus preventing their aggregation. At pH values above 10.0, a dark brown color was observed within the first five minutes. This change in color is indicative of the formation of nanoparticles. Additionally, as shown in the figure below, absorbance peaks were observed at wavelength 410, also indicating the formation of AgNPs. Disk Diffusion analysis indicated that the AgNPs had the highest average ZOI followed by the Ag-TiO2 nanocomposite. A higher ZOI value suggests that AgNPs had a higher efficacy for E. coli decontamination compared to the other catalysts tested.
Conclusions:
The results of this study demonstrate that SODIS is a viable treatment method for water that is contaminated by fecal bacteria since it was able to achieve a 3.16-Log reduction of E. coli, which is just above the WHO recommended minimum of 3-Log reduction. Contrary to previous research studies that report long illumination periods of 6 – 48 hours, none of the water sources from Obunga required the full 6-hour illumination period, with all of them being completely decontaminated of E. coli within 4 hours of illumination. To the best of our knowledge no previous study has tested SODIS as a viable treatment method in Kenya or utilized the Petrifilm Count Plates to assess the effectiveness of a SODIS treatment method. Based on the output results of this cross-sectional baseline survey and given the advantage of cost and its comparative effectiveness, it is reasonable to conclude that SODIS, though less preferred by Obunga residents, would be a better method of water treatment compared to other household water treatment and sanitation methods.
Journal Articles:
No journal articles submitted with this report: View all 6 publications for this projectSupplemental Keywords:
Solar disinfection (SODIS), Water Sanitation, TiO2 (Titanium dioxide), Heterogeneous Photocatalysis, Biosynthesis, Silver Nanoparticles, Nanotechnology, Green Chemistry, SustainabilityThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.