Resumo

COTA-ESPERICUETA, Alma Delia  e  PONCE-CORRAL, Carlos. Removal of patogenic bacteria in wastewater sludge during solar drying. Rev. Int. Contam. Ambient [online]. 2008, vol.24, n.4, pp.161-170. ISSN 0188-4999.

This paper describes the performance of a solar dryer capable of bacterial pathogen removal from the physicochemical sludge of the main wastewater treatment plant for Ciudad Juárez, México. The solar setup was proposed as an alternative solution, technically feasible, for reducing the volume of the 135 tons of sludge produced per day in this plant. The experimental-greenhouse prototype has a 4.5 m² collection area, a 1 m³-drying bed, and automatic systems for ventilation, extraction, and data acquisition. The automatic operation was controlled by temperature and humidity differences between internal and external conditions. Global solar radiation, pH and water content of the sludge were monitored. The overall effectiveness of the solar dryer was determined by assessing thermal and microbiological performance. Water content in sludge during the process was used as an indicator of thermal effectiveness. The microbiological elimination was quantified at different residence times considering two contamination indicators: faecal coliforms and Salmonella spp. Quantification of the pathogenic microorganisms was carried out by the multiple-tube fermentation technique presented in the Mexican regulation NOM-004-SEMARNAT-2002. The thermal results related to the water content showed an exponential decay that achieved up to a 99 % reduction. Regarding microbiological removal effectiveness, there was a strong dependence between the number of bacteria present and the water content in the sludge. As a consequence, with the removal of 92 % of water, it was verified that the elimination of faecal coliforms fell from 3.8x10⁶ to 1.6 MPN per gram of dried sludge; and for Salmonella spp. the reduction was from 1.5x10¹³ to 1.9x10³ MPN per gram of dried sludge.

Palavras-chave : solar dryer; sewage sludge; faecal coliforms; pathogens.