Synergistic effect of hydraulic upflow velocity and TSS concentration on biogranule formation in fluidized bed reactors (FBR)

Abstract

Urban population growth in Andean cities like Huancayo, Peru has exacerbated municipal wastewater challenges, particularly from suspended solids (SS) in stormwater runoff that compromise treatment efficiency. This study investigates the dual influence of upflow velocity (UV) and SS concentration on biogranule development in an upflow anaerobic sludge blanket reactor (UASBR), proposing operational optimizations for tropical highland conditions. Kaolinite clay (characterized by SEM-EDS as 83.17% SiO₂, 13.52% Al₂O₃, with 0.32-0.87 µm particle size via DLS) simulated typical inorganic SS. The reactor was operated at three UVs (0.3, 0.6, 0.9 m/h) and SS concentrations (212.5, 220, 280 mg TSS/L), with weekly granule size monitoring by SEM. Key findings demonstrated UV's pivotal role: 0.3 m/h induced excessive sludge compaction (10.8 µm granules), while 0.9 m/h caused biomass washout (11.6 µm). The intermediate UV of 0.6 m/h combined with 212.5 mg TSS/L yielded optimal granulation (13.05 µm) and system stability. Elevated SS loads impaired granule consistency, reducing diameters to 7.6-12.91 µm due to hindered microbial aggregation. The study establishes that maintaining 0.6 m/h UV and ≤212.5 mg TSS/L promotes robust biogranule formation, offering a practical solution for anaerobic treatment of SS-rich wastewater in high-altitude urban environments. These parameters balance hydraulic selection pressure with microbial retention, addressing a critical gap in tropical Andes wastewater management.