Meeting daily drinking water needs for communities in Sub-Saharan Africa using solar reactors for harvested rainwater

Abstract

Two large reactors designed for solar water disinfection (SODIS) of harvested rainwater (HRW) were built and tested in Spain (controlled conditions) and Uganda (field testing). Both reactors use V-trough aluminium mirrors and UV-transparent poly(methyl-methacrylate) (PMMA) photo-reactor tubes of diameters, 100 mm and 200 mm, for treating 90L and 140L per batch, respectively. No differences in terms of treatment performances were obtained between both solar reactors. Complete disinfection of synthetic HRW spiked with a consortium of waterborne pathogens (E. coli, S. enteritidis, E. faecalis and MS2 coliphage) was achieved under natural sunlight, obtaining > 5-log reduction values (LRV) of all bacteria for a maximum solar UVA dose of 270 kJ/m2 or 120 min of solar exposure. A 5-LRV for MS2 virus was also achieved with a maximum of up to 620 kJ/m2 of UVA dose or 300 min of solar exposure. Accelerated and natural aging of the UV-transparent PMMA material were also investigated, showing that the material is highly transparent in the UVB (from 7 to 75 %) and UVA (87 %) and photostable, with no significant change in UVB&A transmittance for 9 months under extreme conditions of solar radiation, humidity and temperature. Results for the reactors in the field, in two rural primary schools in Uganda over 1 year, demonstrated excellent performances with complete reductions of the bacterial load in natural HRW to undetectable levels of E. coli, E. faecalis and Total coliforms (<1 CFU/100 mL), meeting Ugandan national standards for potable water, with the exception of the 50 % samples for Total Plate Count, where an average of >4 LRV were also attained. An analysis of cost , materials selection and solar resources needed has been carried out to determine the affordability and feasibility of this technology. The results of this analysis demonstrated the potential capability of the 140L solar V-trough reactor for treating HRW, with an estimated cost of €0.0012 per liter.