High-rate ethanol production at low pH using the anaerobic granular sludge process

Area of Science:

• Biotechnology
• Environmental Microbiology
• Biochemical Engineering

Background:

• Anaerobic granular sludge reactors are crucial for bioprocessing.
• Product spectrum control in fermentation is key for downstream applications.
• Microbial community structure significantly influences fermentation outcomes.

Purpose of the Study:

• To investigate the operational performance and product spectrum of glucose-fermenting anaerobic granular sludge reactors at pH 4.
• To understand the impact of low pH on microbial community structure and fermentation products.
• To assess the potential for tailoring precursor compounds for biopolymer production.

Main Methods:

• Operation of an anaerobic granular sludge reactor at pH 4 with specific settling phase, hydraulic retention time (HRT), and solid retention time (SRT).
• Analysis of fermentation products including ethanol, lactate, and volatile fatty acids (VFA).
• Microbial community structure analysis using advanced sequencing techniques.

Main Results:

• At pH 4, fermentation yielded ethanol (0.55 gCOD/gCOD), lactate (0.15 gCOD/gCOD), and VFA (0.20 gCOD/gCOD).
• The product spectrum significantly differed from higher pH conditions (4.5-5.5), which were VFA-dominated.
• Microbial community shifted to dominance by Candida tropicalis, Pichia jaroonii, and Lactobacillus species, unlike Clostridia at higher pH.

Conclusions:

• Controlling the pH of anaerobic granular sludge reactors allows for targeted manipulation of the microbial community.
• This control enables the selective production of specific fermentation products like ethanol and lactate.
• Bioprocess engineers can tailor precursor compound mixtures for subsequent processes such as chain elongation or PHA biopolymer production.