Biochar-assisted anaerobic digestion of sugarcane vinasse for enhanced energy recovery: Experimental evaluation and environmental assessment

Sugarcane vinasse is a high-strength industrial wastewater that presents treatment challenges due to its high organic load and instability of anaerobic digestion (AD) caused by volatile fatty acid (VFA) accumulation. This study explored biochar (BC)-assisted thermophilic AD as an engineering strategy to enhance process stability, treatment performance, and energy recovery from vinasse. Batch experiments were conducted using BC dosages of 5, 10, and 15 g L −1 , followed by consequential life cycle assessment (CLCA). The optimal BC dosage (10 g L −1 ) significantly improved AD performance, increasing biogas and methane yields by 36% (568 mL g −1 VS) and 43% (362 mL g −1 VS), respectively, while enhancing COD removal to 81% and reducing residual total VFAs from 7.1 to 4.1 g L −1 relative to the control. Kinetic analysis further showed increased methane production potential and a shorter lag phase, indicating improved digestion stability. The CLCA showed that BC-assisted AD achieved a greater net global warming (GW) benefit than conventional AD (−62.72 vs. −44.10 kg CO 2 -eq), but the benefits were impact-category dependent, with water consumption shifting from a net saving to a net burden. Sensitivity analysis further showed that the comparative results were strongly influenced by avoided electricity and fertilizer substitution and by the geographical configuration of the BC supply chain. Localizing BC production reduced transportation-related burdens but did not proportionally improve the overall GW result. These findings demonstrate that BC can enhance vinasse AD, while its life-cycle implications depend on consequential substitutions and regional supply-chain conditions.