Disinfection of contaminated water by using solar irradiation

Abstract

Contaminated water causes an estimated 6 to 60 billion cases of gastrointestinal illness annually. The majority of these cases occur in rural areas of developing nations where the water supply remains polluted and adequate sanitation is unavailable. A portable, low-cost, and low-maintenance solar unit to disinfect unpotable water has been designed and tested. The solar disinfection unit was tested with both river water and partially processed water from two wastewater treatment plants. In less than 30 min in midday sunlight, the unit eradicated more than 4 log10 U (99.99%) of bacteria contained in highly contaminated water samples. The solar disinfection unit has been field tested by Centro Panamericano de Ingenieria Sanitaria y Ciencias del Ambiente in Lima, Peru. At moderate light intensity, the solar disinfection unit was capable of reducing the bacterial load in a controlled contaminated water sample by 4 log10 U and disinfected approximately 1 liter of water in 30 min.

FIG. 1.

(a) Solar disinfection unit base. Dimensions are in inches. (b) Solar water disinfection apparatus. The reactor is made of a 12- by 24- by 1/2-in. dark gray PVC base with a UV transmitting cover. The feed and collecting bottles are 2-liter transparent plastic bottles covered with white contact paper.

FIG. 2.

Change in total coliform counts with increasing residence times in the continuous solar disinfection unit for municipal wastewater samples. Each data point represents the average of three samples. Error bars indicate standard errors.

FIG. 3.

Change in total coliform counts with increasing residence times in the continuous solar disinfection unit for Delaware River water. Each data point represents the average of three samples. Error bars indicate standard errors.

FIG. 4.

Effect of turbidity on the time to achieve a 4-log₁₀-U reduction in bacterial load for wastewater samples in the continuous solar disinfection unit. Water from four points in the Easton wastewater treatment facility (0.20 to 1.16 NTU) was treated in the solar disinfection unit. Each data point represents the average of three samples.

FIG. 5.

Change in total coliform counts with increasing residence times in the continuous solar disinfection unit for a controlled contaminated water sample at CEPIS. Tap water samples were inoculated with 10⁵ CFU of a culture of mixed coliforms/100 ml and processed in the solar disinfection unit at about 500 W of radiation/m² and an 0.4-ml/s flow rate. Each data point presents the average of three samples.