Assessment of the effect of alkaline additives in treating faecal sludge for pathogen inactivation

Currently, there is no effective, reliable, and independent natural method for complete sanitization of sludge. Hence, the objective of this study was to evaluate the effect of alkaline treatments on the sanitization of biosolids. The principle was based on increasing pH using quicklime, wood ash, and urea. To achieve this, the relationship between the quantities of adjuvant and the pH of the biosolids was first defined. Several concentrations of adjuvant were tested to achieve a pH ≥ 12 on 1kg of 40% dehydrated biosolids. Subsequently, treatments that reached the desired pH were subjected to further large-scale experiments (20kg of biosolids). Selected parameters to monitor sanitization were as follow: pH, EC, temperature, FC, FS, TC, presence of E. coli and helminth eggs, these were collected daily. Pathogen proliferation were evaluated on a weekly basis. Lime treatments (2.5%, 5%, and 8%) and wood ash treatments (80% and 100%) increased the pH of the biosolids to 12, whereas urea treatments (1.5%, 2.5%, and 5%) had a maximum pH of 10. Although pH values in the biosolids of mixed treatments were above 12, they were not statistically different from single treatments from quicklime and wood ash (p ≤ 0.05). The average temperature remained stable in all treatments and similar to ambient temperature (25°C) throughout the study period (30 days). However, electrical conductivity varied significantly (166.33 ± 8.08–555 ± 335 ms/cm). During this experiment, all treatments allowed complete removal of Fecal Coliforms, Fecal Streptococci, Total Coliforms, and E. coli . However, only the 5% lime treatment allowed for total elimination of helminth eggs.