Reducing carbon footprint in high HS 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 (HS) formation (up to 50,000 ppm) during acidogenic fermentation. The resulting HS and high carbon dioxide (CO) 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 HS abatement and CO 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 % HS and 98.2 % CO removal efficiencies within 72 h, with a maximum HS elimination capacity of 30.3 gS-HS m⁻ h⁻. 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), ensuring complete HS oxidation to sulfate without inhibitory intermediate accumulation or clogging. The system's robustness was further supported by Chloroidium ellipsoideum's adaptation to high HS loads (up to 72.0 gS-HS m) and optimized inorganic carbon (1.8-3.4 g L⁻). 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.