Acidic-alkaline shocks in vinasse fermentation shape methanogenesis and sulfate reduction dynamics

Area of Science:

• Biotechnology and Bioengineering
• Environmental Science
• Microbial Ecology

Background:

• Efficient two-phase anaerobic digestion (2nd-AD) of sugarcane vinasse requires suppressing methanogenesis during acidogenesis to maximize methane yield and minimize H2S risks.
• Controlling microbial pathways is crucial for optimizing biogas production and waste valorization from vinasse.

Purpose of the Study:

• To investigate the efficacy of sequential acidic and alkaline pH shocks for controlling methanogenesis in sugarcane vinasse 2nd-AD.
• To assess the impact of pH shocks on sulfate reduction, acetate production, and microbial community dynamics.
• To establish a novel operational strategy for enhancing vinasse biorefineries.

Main Methods:

• Utilized an anaerobic structured-bed reactor (AnSTBR) fed with sugarcane vinasse for 90 days at 30°C.
• Implemented sequential acidic and alkaline pH shocks across six operational stages.
• Analyzed microbial communities using molecular techniques and monitored key parameters like methane content, sulfate reduction, and acetate concentration.

Main Results:

• pH shocks effectively inhibited methanogenesis (methane content reduced to 3%) and promoted sulfidogenesis (sulfate removal up to 82%).
• The process yielded an effluent rich in acetate (>3.0 g-HAc L⁻¹) with increased buffering capacity, suitable for subsequent methanogenesis.
• Desulfovibrio was identified as the dominant sulfate reducer, while Bacteroides and Aminobacterium were key acetate producers.

Conclusions:

• Sequential pH shocks offer a robust strategy for modulating microbial pathways in sugarcane vinasse 2nd-AD.
• This approach enhances biogas potential, improves environmental safety by controlling H2S, and supports sustainable waste management.
• The findings advance the operational efficiency of vinasse biorefineries through targeted microbial control.