Continuous acidogenic fermentation: Narrowing the gap between laboratory testing and industrial application

Area of Science:

• Environmental Engineering
• Biotechnology
• Waste Management

Background:

• Sewage sludge (SS) presents a significant waste stream with potential for resource recovery.
• Acidogenic fermentation is a promising technology for converting organic waste into valuable volatile fatty acids (VFAs).
• Optimizing fermentation conditions is crucial for maximizing VFA yield and productivity.

Purpose of the Study:

• To investigate the potential of acidogenic fermentation of sewage sludge (SS) for volatile fatty acid (VFA) production.
• To evaluate the impact of co-fermentation with organic fraction of municipal solid waste (OFMSW) on VFA production.
• To explore the role of pH control strategies in enhancing acidogenic fermentation.

Main Methods:

• Utilized an 80 L automatized pilot scale platform for acidogenic fermentation of SS.
• Investigated high-rate VFA production at specific hydraulic retention times (HRT) and pH levels.
• Performed co-fermentation of SS with OFMSW and monitored pH shifts.
• Applied ultrafiltration to recover VFA-rich permeate.

Main Results:

• Achieved high VFA yield (336 mg VFA/g VS) and productivity (2.15 kg VFA/m³d) at HRT 5d and pH 9.
• Co-fermentation with OFMSW and a reversible pH shift (pH 9 to 6) promoted butyrate production.
• Observed a VFA peak of 23.2 g COD/L during co-fermentation, with butyric acid reaching 13.97 g COD/L.
• Ultrafiltration successfully recovered 12.3-26.6 g COD/L of VFA-rich permeate.

Conclusions:

• Mixed culture fermentation systems exhibit flexibility, allowing for non-steady pH control to enhance acidogenesis.
• Co-fermentation strategies and dynamic pH adjustments can significantly boost VFA production, particularly butyric acid.
• Ultrafiltration is an effective method for concentrating VFAs from fermentation broth, enabling resource recovery.