Pathogen reduction effects of solar drying and soil application in sewage sludge

The responses of sludge faecal coliforms, Salmonella, and Ascaris lumbricoides to heat drying, solar dehydration, and inactivation in soil are examined in this study. The presence of Salmonella in raw sludge cake after treatment was low, and absent for most of the cases. Likewise, the viable Ascaris eggs were not determined because of absent or low prevalence. Faecal coliforms, on the other hand, drastically decreased from 4.2 × 10^7 MPN g^-1 Dry Solid (DS) to absence by heat drying. Faecal coliform numbers in solar and non-solar drying treatments were not declined below 1.0 × 10³ MPN g^-1 after drying to 90% DS and also during the storage of 12 weeks. After 6 weeks, faecal coliform and Salmonella levels in the soil surface application fell below undetectable limits. The coliform numbers below soil surface fell gradually over 12 weeks and numbers were below undetectable limits at end of the experiment. These results showed that although the solar drying has significant effects on removing pathogenic microorganisms during hot and dry periods, the soil treatment was still necessary for the final complete inactivation. Solar exposure on the soil surface was found to be effective on the elimination of pathogens.