Anaerobic treatment of nightsoil and toilet sludge from on-site sanitation systems in Ghana

The feasibility of faecal sludge treatment by an upflow anaerobic sludge blanket (UASB) reactor was studied using first, untreated primary sludge from a sewage treatment works treating only domestic sewage, and then actual faecal sludge. The primary sludge was diluted in the ratio 1:20 - 1:10 while the faecal sludge was diluted in to the ratio 1:6. The UASB reactor treating the primary sludge had a
volume of 15 litres and was operated at a mean hydraulic retention time (HRT) of 9.8 h, at a temperature of 37 °C, and at an organic loading rate (OLR) in the range of
5.6 - 15.0 kg COD/m\d. The UASB reactor treating the faecal sludges had a volume of 50 litres and was operated at a mean HRT of 12.1 h, at ambient temperatures in the range of 23.0 - 31.2 °C, and at OLR in the range of 1 2 .5 -2 1 .5
kg COD/nr\d. The first experiment involving the untreated primary sludge was run for 114 days while the second was run for 119 days. The results from both experiments indicate that it is feasible to treat faecal sludges using the UASB reactor. The average removal efficiencies obtained for the first experiment were: 78% for COD, 62% for total solids (TS), 75% for total volatile solids (TVS) and 91% for total suspended solids (TSS). The pH was in the range of 6.9 - 7.4. With regards to faecal sludges, the average removal efficiencies were: 71% for COD, 61% for TS, 74% for
TVS and 73% for TSS. The removal efficiencies are comparable to those obtained for a UASB reactor treating for domestic sewage. High removal efficiencies were obtained in a much shorter time compared to UASB reactors treating domestic sewage. The COD concentration in the effluents is too high for direct discharge and hence a form of post-treatment would be necessary. The calculated volume of methane in the biogas collected ranged from 4 - 8 1/kg COD, not accounting for practical losses.