Survival of Thermotolerant Coliforms in Tropical Soil Cultivated with Eucalyptus and Fertilized with Sewage Sludge.

The class B sewage sludge contains several pathogens, including bacterias, funghi, viruses, and helminth ova, which may suggest risk for public health when using this residue for land application. This risk was the main cause for banning the use of sewage sludge as fertilizer without previous treatment in Brazil. This study aimed to evaluate the survival time of thermotolerant coliforms in sandy tropical soil, cultivated with eucalyptus and fertilized with sewage sludge, comparing the results with some studies developed in other countries, under temperate climate conditions, once there is no concrete result about the time of survival of thermotolerant coliforms in tropical regions. The experiment were conducted at the city of Avaré, State of São Paulo, Brazil, for 52 weeks, using two different types of sewage sludge: one (Sewage Sludge 1 – SS1) generated by a conventional model system of sewage treatment, and other (Sewage Sludge 2 – SS2) from a conventional activated sludge system with tanks aerated with pure oxygen. The average temperature of soil and sludge fluctuated between 15 °C and 30 °C and the average moisture of sludge fluctuated between 60% and 90% during almost all of the reporting period. The estimated time of survival of thermotolerant coliforms after land application was 54 weeks for SS1, and 93 weeks for SS2. Both of the time of survival were higher than the time presented by some studies in Europe, North America, and Asia, what suggests that the climate conditions, mainly temperature, could be an important point for the survival of this kind of pathogen.