Disinfection of Fecal Sludge Using Solar Thermal Water Heating: Sludge Management Option for Developing Countries

This study investigates a solar thermal water heating system that is effective in drying and disinfecting fecal sludge (FS) and recovering nutrients and water resources that happen to have fertility values for agricultural use. The fertilization value of the dried sludge and condensate was tested in a laboratory-scale plantation using three types of plants used as fodder for animals. Results showed average sludge temperatures reached during sludge drying and disinfection were 39.5°C and 33.9°C in dry and wet seasons, respectively. The sludge’s water content decreased from 99.32% to 5.3% and 81.57% to 5.5% in 40 and 54 days of dry and wet seasons, respectively. Pathogen reduction in the dry season was 100% for 13 days compared to 42 days in the wet season. The evaporation rate was higher in the dry season at $9.099\times {10}^{-4}\mathrm{kg}{\mathrm{H}}_2\mathrm{O}/{\mathrm{m}}^2·\mathrm{d}$, compared to $6.4514\times {10}^{-4}\mathrm{kg}{\mathrm{H}}_2\mathrm{O}/{\mathrm{m}}^2·\mathrm{d}$ in the wet season, whereas condensation rate was higher in the wet season at $5.59\times {10}^{-5}\mathrm{kg}{\mathrm{H}}_2\mathrm{O}/\mathrm{day}$ compared to $4.94\times {10}^{-5}\mathrm{kg}{\mathrm{H}}_2\mathrm{O}/\mathrm{day}$ in the dry season. Dried sludge increased the soil porosity by 9.39% compared to 8.41% for raw FS. Also, it increased the soil permeability from $0.06302\times {10}^{-6}$ to $5.773\times {10}^{-6}\mathrm{cm}/\mathrm{s}$, whereas raw FS decreased the soil permeability to $0.02163\times {10}^{-6}\mathrm{cm}/\mathrm{s}$. Moreover, dried sludge improved soil pH values between 7.04 and 7.39. Statistical analysis results at a 95% confidence level revealed that plants in the soil treated with dried sludge had significantly better growth characteristics than others.