Enhanced bio-energy recovery in a two-stage hydrogen/methane fermentation process

Area of Science:

• Biotechnology
• Environmental Engineering
• Renewable Energy

Background:

• Wastewater treatment offers potential for bio-energy recovery through two-stage fermentation.
• Hydrogen-producing bacteria (HPB) generate hydrogen from carbohydrates, with subsequent methane production from organic acids.
• Acid pre-treatment is explored as a method to enhance bio-energy yields.

Purpose of the Study:

• To evaluate the efficacy of strong acid pre-treatment (HCl, H2SO4, HNO3) on hydrogen production.
• To assess the impact of acid pre-treatment on subsequent methane production in a two-stage system.
• To identify the optimal acid for enhancing overall biogas recovery.

Main Methods:

• Three strong acids (HCl, H2SO4, HNO3) were used for sludge pre-treatment.
• Hydrogen production rates were measured after acid pre-treatment.
• Fluorescent in situ hybridization (FISH) was employed to analyze bacterial populations.
• Methane production rates were measured in a subsequent fermentation stage.

Main Results:

• HCl and H2SO4 pre-treatment significantly increased hydrogen production rates (230 and 290 L/kg-glucose/day, respectively) compared to HNO3 (20 L/kg-glucose/day).
• FISH analysis revealed selective enrichment of HPB, including Clostridium sp. cluster I, after acid pre-treatment.
• Methane production was highest with HCl pre-treatment (100 L/kg-glucose/day), while sulfate and nitrate appeared to inhibit methane-producing bacteria.

Conclusions:

• Acid pre-treatment is a feasible strategy to enhance biogas recovery in two-stage fermentation.
• HCl pre-treatment is optimal for enriching HPB and achieving continuous methane production.
• The choice of acid is critical, as sulfate and nitrate can negatively impact methane fermentation.