Reduction of Faecal Indicators and Elimination of Pathogens from Sewage Treated Effluents by Heat Treatment

Different pathogens may be found in the sewage treated effluents generated by sewage treatment plants (STPs). The United States Environmental Protection Agency (U.S. EPA) regulations have established pathogen reduction requirements for faecal coliforms (FC). Therefore, the effectiveness of mesophilic treatments at 45°C and thermophilic treatment at 55°C, as well as heat pasteurisation at 65°C, to reduce FC and eliminate the pathogens were investigated (Shigella sp, E. coli, Salmonella spp., K. pneumonia, P. aeruginosa, and S. aureus), after 0.5, 1, 1.5, 2, 4, 24, 48, 96 and 192 h. Isolation of bacteria was carried out by membrane filtration on appropriate selective media. The results show that the sewage treated effluents met the U.S. EPA Guidelines for water reuse (FC < 14 cells/100 ml) after 192 h at 45°C. Shigella sp., E. coli and Salmonella spp. were eliminated after 4, 48 and 96 h at 55°C, respectively, and 2 h at 65°C. No regrowth of these pathogens was observed in treated effluents. Mesophilic treatment has the potential to be one of the tertiary treatments used to reduce FC to meet the U. S. EPA standards limits, and thermophilic treatment and heat pasteurisation are sufficient to eliminate pathogens.