<p>Sugarcane vinasse biodigestion presents challenges due to its sulfate-rich nature (2–3&#xa0;g-SO₄^2– L^–1), causing microbial competition, inhibition, and H₂S-rich biogas production. The high H₂S content (up to 45,000&#xa0;ppm) is considered a significant economic drawback for energy recovery purposes, mainly for the upgrading routes toward biomethane. Despite the potential benefits, the adoption of two-stage biodigestion faces obstacles because of high alkalinization costs. However, the fermentative-sulfidogenic process is promising by producing bicarbonate alkalinity as a by-product of the organic matter oxidation and consuming H⁺ ions through ionized sulfide generation. This pathway mitigates the need for expensive alkalinizing inputs and enhances the biogas energetic value (CH₄ &gt; 80%, H₂S-free), providing favorable conditions for cost-effective and environmentally sustainable upgrading strategies. Moreover, the H₂S- and CO₂-rich biogas produced during the fermentative-sulfidogenic stage must be addressed from an environmental perspective as an “off-gas”, enabling promising biotechnological routes for sulfur and biogenic CO₂ recovery. Although significant progress has been made at laboratory scale, further understanding is needed regarding the role of the fermentative-sulfidogenic step as a biological alkalinity source for methanogenesis. In parallel, developing low-cost and environmentally advantageous strategies to support sulfidogenic activity remains critical. This review elucidates the fermentative-sulfidogenic pathway’s central role in vinasse biodigestion, highlighting its dual potential for biogas upgrading and recovery of valuable by-products such as elemental&#xa0;sulfur and biogenic CO₂.</p> Graphical abstract <p></p>