Abstract

NWANKWO, Ekene Jude  and  AGUNWAMBA, Jonah Chukwuemeka. Effect of reactor characteristics on the seasonal effectiveness of solar disinfection: a factorial study. Water SA [online]. 2021, vol.47, n.1, pp.113-122. ISSN 1816-7950.  http://dx.doi.org/10.17159/wsa/2021.v47.i1.9451.

Solar disinfection (SODIS) involves exposing water stored in transparent polyethylene terephthalate (PET) containers to the sun for about 6 h of strong sunlight, after which the water is rendered safe for consumption. This study investigated the seasonal effect of reactor characteristics on the inactivation kinetics/constant of faecal coliforms by conducting a 2³ factorial experiment, involving two levels of PET bottle size, PET bottle thickness, and PET bottle rear surface, uniquely combined to form 8 SODIS reactors/experimental units. The faecal coliform population of hourly samples taken from the 8 SODIS reactors showed that the inactivation kinetics/constant depends on the irradiation energy and maximum water temperature as dictated by the reactor characteristics. The average rate constant of the reflective reactors (1.37 ± 0.43 h^-1) was significantly better (p < 0.001) than the absorptive reactors (1.17 ± 0.59 h^-1) between June and October. The average rate constant of the small PET bottles (1.73 ± 0.65 h^-1) is significantly higher (p < 0.002) than the large PET bottles (1.46 ± 0.51 h^-1) from December to May; while the average rate constant of the light PET bottles (1.58 ± 0.64 h^-1) is significantly better (p < 0.001) than the thick PET bottles (1.41 ± 0.52 h^-1) year-round. Analyses of results confirmed a two-way interaction effect between PET bottle size and PET bottle thickness and between PET bottle rear surface and PET bottle thickness for periods with average radiation intensity of 450-500 W-m^-2. Although container size and thickness were the most significant factors, combining light PET bottles with absorptive rear-surface could extend the applicability of SODIS to regions that fall short of the recommended radiation intensity threshold of 500 W-m^-2 for 5 h.

Keywords : solar disinfection; factorial experiment; kinetics; drinking water; faecal coliform; diarrhoea.

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