Reducing carbon footprint in high H2S emissions: A synergistic microalgal-bacterial solution for sugarcane biorefineries

Sugarcane vinasse, a major by-product of ethanol production, poses environmental and health risks due to its high sulfate content, promoting severe hydrogen sulfide (H₂S) formation (up to 50,000 ppm_v) during acidogenic fermentation. The resulting H₂S and high carbon dioxide (CO₂) levels in off-gas create serious hazards, often leading to conventional desulfurization systems' clogging and high maintenance. This study is the first to investigate a Chloroidium-based combined microalgal-bacterial (CMB) system for simultaneous, high-strength H₂S abatement and CO₂ sequestration from these challenging vinasse fermentation off-gas streams. Utilizing a 14 L bubble column photobioreactor under increasing gas flow conditions, the system achieved 100 % H₂S and 98.2 % CO₂ removal efficiencies within 72 h, with a maximum H₂S elimination capacity of 30.3 gS-H₂S m⁻³ h⁻¹. A comprehensive sulfur mass balance revealed that up to 99 % of theoretical sulfate was consumed by the consortium for biomass growth, demonstrating efficient sulfur valorization. Performance was sustained by elevated dissolved oxygen (averaging 15.0 g L^-1), ensuring complete H₂S oxidation to sulfate without inhibitory intermediate accumulation or clogging. The system's robustness was further supported by Chloroidium ellipsoideum's adaptation to high H₂S loads (up to 72.0 gS-H₂S m^-3) and optimized inorganic carbon (1.8-3.4 g L⁻¹). These results highlight the CMB system's potential as a biologically driven, low-input, clogging-resistant, and highly efficient alternative for acidogenic off-gas treatment and vinasse valorization, offering a scalable and sustainable solution for biorefineries.