Influence of long-term storage operating conditions on the reduction of viable Ascaris eggs in sewage sludge for agricultural reuse

Abstract

The National Environment Council (CONAMA Resolution 375/06) defined to achieve sanitation quality parameters, for the use of sewage sludge in agriculture, the adoption of additional pathogen reduction processes is necessary. Sludge that is stored for longer periods generally shows higher levels of sanitation, particularly on the helminth egg inactivations which are among the most resistant pathogens. The objective of this study was to monitor the Ascaris egg removal and inactivation efficiency of long-term storage of sludge from septic tanks and up-flow anaerobic sludge blanket (UASB) reactors, besides evaluating the influence of covering and manually revolving or stirring the sludge over a 2-year period. The study was undertaken in the cities of Fazenda Rio Grande and Apucarana, Southern Brazil. In total, 18 experimental treatments were installed and nine samples were assessed at weeks 0, 4, 9, 13, 17, 30, 47, 61, and 104. The standard defined in the CONAMA for class A sludge (one viable egg per 4 g TS) was reached for all treatments at 9 weeks of storage. Two years of storage were necessary in order for the covered, UASB-centrifuge sludge to reach CONAMA standards. Of the six treatments using septic sludge, only one achieved the established standard. This treatment was realized in Apucarana and involved a revolving/stirring process. The period of 104 weeks of storage of the septic sludge was not sufficient to completely inactivate Ascaris eggs for the other treatments. Between study locations, Apucarana performed better than Curitiba which is likely due to greater levels of insolation and temperature.