Avaliação do processo de desinfecção solar (SODIS) e de sua viabilidade social no estado do Ceará

Abstract

Despite the importance of sanitation for well-being of the mankind and the natural resources conservation, still today a large number of people do not have access to wastewater system neither to public water supply. One technique which has being studied and applied in developing countries as a safe household water treatment method is solar disinfection, SODIS. The only two elements demanded to this method are PET bottles and the sun. Nowadays, around one million people use SODIS regularly in 20 different countries. This study evaluated the feacal coliform bacteria inactivation efficiency according to the effect of bottles’ agitation and the use of differents exposition surfaces under of State of Ceará climatic conditions, as well as SODIS social viability in four communities at distinct geographical location (peri-urban, rural and coastal). To achieve this, agitated and non-agitated samples and five diferrents surfaces: concrete spotted in white color, concrete spotted in black color, abobe roofing tile, asbestos roofing tile and aluminum basins were investigated. To evaluate social acceptability, questionnaires had been applied to all users SODIS and raw water and treated water by SODIS were analyzed. It was verified that despite the agitation surveying a concentration more than 0,75mg/L of OD in the agitated samples, this effect was not capable to increase significantly the inactivation efficiency in these samples. The mean decay constant for bacterial population in agitated bottles was found to be a factor of 1.10 higher than in non-agitated bottles. The surface investigation indicated that no significant difference (paired Student´s T-test at P=0,05 significance level of log10 transformed data) in inactivating feacal coliforms by exposing the bottles over the five surfaces examined were observed. The mean decay constant for bacterial population was: 0,3049h-1, 0,2624h-1, 0,3152h-1, 0,2747h-1, 0,2874h-1, respectively for the sample exposed over concrete spotted in white color, concrete spotted in black color, abobe roofing tile, asbestos roofing tile and aluminum basins. The maximum water temperature reached was 44ºC and still thus, it was obtained reduction more than 99.99% of feacal coliforms. In 67% of the assays, SODIS was capable to completely inactivate concentrations of feacal coliforms above 105 NMP.100mL-1 within six hours of exposition. The field study had shown that SODIS improved the microbiological water quality in the four communities. However, the permanence and in some cases the increase of feacal coliforms was verified when the users exposed the bottles in shaded areas. SODIS was well received in rural and coastal communities reaching acceptance levels over than 45%, compared to urban community, with only 8%. Beyond the great acceptance of the method, over 80% of the users answered that they would continue to use SODIS.