Influence of Conventional and Hybrid Septic Tank-Anaerobic Filter Configurations on the Hydrodynamics and Performance of Wastewater Treatment

Decentralized treatment is an adequate strategy to more sustainably treat municipal wastewater in rural and peri-urban areas. In light of the above, this study evaluated, on a pilot scale, the performance of an anaerobic configuration consisting of a septic tank (ST) and an anaerobic filter (AF) in two modalities: (i) a conventional system (CS) in separate reactors and (ii) a hybrid system (HS) with a ST and an AF in a single reactor –both with theoretical hydraulic retention times (HRTs) of 36, 30, 24, and 18 hours. The results indicated that the HS had a better performance (less variability) under the different conditions evaluated, achieving, at an HRT of 18 hours, higher reduction efficiencies (52,0±16,8% COD and 73,06±18,5% TSS) compared to the CS (39,8±13,1% COD and 65,8±20,52% TSS). Although hydrodynamic analysis showed dual flow (full mix and plug flow) in both configurations, the HS exhibited a greater predominance of plug flow (62%) than the CS (52%), which allowed the former to reach a real HRT closer to the theoretical value than the latter (23/24 vs. 19/24 hours). This behavior guarantees the lowest occurrence of dead zones and short circuits, as well as a higher Persson hydraulic efficiency (0,62) and lower area requirements for the HS in comparison with the CS (0,5).