Synergistic Effect of Hydraulic Upflow Velocity and TSS Concentration on Biogranule Formation in Fluidized Bed Reactors (FBR)

Rapid urbanization in Andean cities presents unique wastewater management challenges, particularly due to the high concentrations of suspended solids (SS) in stormwater runoff, which impair treatment efficiency. This study investigated the combined effects of upflow velocity (UV) and SS concentration on biogranule formation in an upflow anaerobic sludge blanket reactor (UASBR) under conditions simulating tropical highland environments. Synthetic wastewater containing kaolinite clay (83.17% SiO₂, 13.52% Al₂O₃, particle size 0.32–0.87 µm) was used to simulate inorganic SS. The reactors were tested at UVs of 0.3, 0.6, and 0.9 m.h-1 and SS concentrations ranging from 212.5 to 280 mg.L-1. Granule morphology and size were monitored weekly using scanning electron microscopy (SEM). The results showed that UV critically affected granulation: low velocity (0.3 m.h-1) led to excessive compaction (10.8 µm), while high velocity (0.9 m.h-1) caused biomass washout (11.6 µm). The optimal conditions (0.6 m.h-1 and 212.5 mg.L-1) yielded stable, well-formed granules (13.05 µm) and high reactor efficiency. Higher SS loads disrupted microbial aggregation, reducing granule size to 7.6–12.91 µm. The findings highlight that maintaining a UV of 0.6 m.h-1 and SS ≤212.5 mg.L-1 enhances granule development, offering a feasible strategy for the anaerobic treatment of SS-rich wastewater in high-altitude urban regions.