A study of the genotoxic implications and enhancement technologies for solar disinfection (SODIS) of drinking water

Solar disinfection (SODIS) is a household water treatment method that uses sunlight to inactivate pathogens in water. The work presented in this thesis aimed to show that SODIS is an appropriate, effective and acceptable intervention against waterborne disease. This was demonstrated by the inactivation of a highly infectious bacterial pathogen, increasing the volume of SODIS treatedwater using solar continuous-flow reactors, enhancing SODIS during sunny, cloudy and turbid water conditions by the use of compound parabolicconcentrator (CPC) mirrors and finally determining the genotoxicity of SODIS water.

This project identified the inactivation kinetics of E. coli 0157 under simulated light by following a natural temperature profile which would be comparable to inactivation under real sunlight conditions.

The use of CPC mirrors proved to be enhancement to SODIS in batch reactors under sunny and cloudy conditions and with clear and turbid water (< 300 NTU). Non-homogenous degradation of mirrors occurred in the field, under sunny conditions, there was no significant difference between using an old CPC and no CPC during solar disinfection. However, under cloudy conditions, only the systems with CPC either old or new achieved complete inactivation of bacteria.

An attempt to scale-up SODIS through continuous flow reactors by treating 14 L and 70 L volumes of water found that increasing flow rate was detrimental to inactivation of E. coli K-12, resulting in a residual active population after solar exposure. It was determined that a minimum UV dose, delivered in an interrupted manner was necessary to ensure complete inactivation of bacteria. However, successful inactivation of bacteria in large volumes of water (25 L) occurred in a CPC enhanced batch reactor (EBR) under periods of strong sunlight.

Under standard SODIS conditions, which included daily re-use of plastic bottles over a 6-month period, water contamination by genotoxic compounds was not observed with the Salmonella Arnes-Fluctuation assay in unconcentrated samples. The Ames-fluctuation test was successful in detecting potential genotoxicity in no-refill samples after 2 months for both dark-control and solar exposed samples. However, genotoxicity was higher for the solar exposed samples.