Evaluation of the natural coagulant Moringa oleifera as a pretreatment for SODIS in contaminated turbid water

Solar Disinfection of water (SODIS) is a treatment method that traditionally exposes low turbidity water filled in clear bottles to direct sunlight up to 6 h. Typically, water should have turbidity lower than 30 NTU before solar exposure; however turbidities of water sources in communities vary and can reach higher than 200 NTU. In order to reduce turbidity, flocculating agents like Moringa oleifera (Moringa) may be used. In this study we assess the efficacy of Moringa to clear turbid water as a pretreatment for SODIS. We initially evaluate two preparations- powdered seeds and an aqueous filtrate of the seeds, to determine if these can benefit SODIS in turbid, E. coli contaminated water (Experiment 1). We show that powdered Moringa seeds reduce turbidity best and that SODIS treatment of highly turbid water was effective regardless of reduced turbidity. Overnight, however; a bio-active sludge layer formed. We then determined if 24 h Moringa pretreatment and decanting can maintain water quality over an extended period (Experiment 2). After 24 h Moringa treatment showed a 2.1 log reduction in E. coli, increasing following SODIS (6-log) E. coli without nightly recovery or sludge formation. Untreated turbid controls showed SODIS disinfection after 6 h direct sunlight; however, nightly regrowth and sludge layer formation occurred by 48 h. These results suggest that SODIS is capable of inactivating bacteria in highly turbid water at 6 h; however, active biofilm sludge layers formed by 48 h. We conclude that, for longer term water storage, we find a combination of Moringa seed powder pretreatment prior to SODIS to be optimal.