Association of a UASB reactor and a submerged aerated biofilter for domestic sewage treatment

This paper presents exploratory results on the association of an Upflow Anaerobic Sludge Blanket - UASB reactor (46 L) and a submerged aerated biofilter – BF (6.3 L) for domestic sewage treatment. The experimental period extended for 322 days, during which the hydraulic and organic loads were gradually increased in both reactors. Having the UASB as a reference, the following hydraulic loads were tested: 0.4 m³/m².h (θ = 16 h); 0.6m³/m².h (θ = 10h); 0.8 m³/m².h (θ = 8 h); 1.0 m³/m².h (θ = 6 h) and 1.45 m³/m².h (θ = 4h). During the experiments carried out with the UASB reactor operating at a hydraulic detention time of 6 hours, related to a θ < 11′ in the granular media of the BF, the mean removal efficiency in terms of SS, BOD₅ and COD, in both reactors, were respectively 94%, 96% and 91%. The final effluent, related to the BF effluent, presented the following mean characteristics: SS = 10 mg/L, BOD₅ = 9 mg/L and COD = 38 mg/L. The results obtained in the last phase of the experiments, when the hydraulic load in the UASB reactor reached 1.45 m³/m².h (θ = 4h), were similar to those obtained in the previous phase. These results demonstrate that submerged aerated biofilters can be considered a viable alternative for the post-treatment of effluents from UASB reactors treating domestic sewage. These reactors are capable of being operated with very short hydraulic detention times.