Hydraulic and organic rates applied to pilot scale UASB reactor for sugar cane vinasse degradation and biogas generation

Highlights: • Pilot-UASB reactor for assess vinasse degradation and biogas generation. • Stable performance under stepped organic loading rate applied to reactor. • Low concentration of acetic, propionic, butyric and valeric acids at the reactor effluent over the operational period. • High COD removal and methane productivity under high organic loading rate. A pilot-scale upflow anaerobic sludge blanket (UASB) reactor (120 L) was operated for biogas production by vinasse degradation. The reactor was operated for 700 days using a recirculation rate of 1:3 with organic loading rates (OLR) ranging from 0.5 to 32.4 kgCOD.m⁻³.d⁻¹, upflow velocities ranged from 0.008 to 0.292 m h⁻¹(feed added with recirculation) and the hydraulic retention time ranged from 33.33 to 0.86 days. The reactor demonstrated a stable performance at OLR at all applied loads. The COD removal efficiencies throughout the experiment were 87.5 ± 5.3 and 90.5 ± 3.6% for raw and soluble COD, respectively. Total volatile acids ranged from 59 mg L⁻¹ to 585 mg L⁻¹. The concentration of acetic and propionic acids at the reactor effluent reached 28 mg L⁻¹ on OLR 20 kgCOD.m⁻³.d⁻¹. The methane content in the biogas was 68.8 ± 7.14%.The methane yield of 0.299 ± 0.066 LCH₄.g⁻¹COD corresponds to about 76.4% of the theoretical methane yield. The methane productivity reached the highest value of 8.059 LCH₄.L⁻¹.d⁻¹ at 32.27 kgCOD.m⁻³.d⁻¹., corresponding to 83.9% of the theoretical value (9.611 LCH₄.L⁻¹.d⁻¹). This result is very promising for power generation in the sugar and ethanol industry, complementing the energy balance of sugarcane, as shown by an energy balance evaluation.