Impact of a natural coagulant pretreatment for colour removal on solar water disinfection (SODIS)

Abstract

Solar water disinfection (SODIS) is the process of treating microbiologically contaminated water in clear plastic bottles through exposure to sunlight. One of the major limiting factors of this treatment is source water quality. This work investigates the impact of source water colour on SODIS efficiency and evaluates a natural coagulant for colour removal. The ability of Moringa oleifera seed emulsion to both clarify and decolourize source waters was investigated as a coagulation pretreatment for SODIS. This coagulant reduced the colour by more than two-thirds and achieved up to 1-log10 bacterial removal (90%). The combined Moringa oleifera coagulation-SODIS treatment sequence was tested in highly coloured natural source water and was found to reduce the sunlight exposure time required by up to 2 hours. However, despite being an effective clarification and decolouring process, the pretreatment may not shorten the overall treatment time because of its own labour and time requirements, potentially decreasing the treatment compliance rates. In addition, while total coliform and heterotrophic bacteria regrowth was observed during overnight storage of the treated water, no Escherichia coli regrowth was found to occur.