Persulfate-driven sludge biorefinery toward value-added medium-chain fatty acids.

Area of Science:

• Environmental Science
• Biotechnology
• Chemical Engineering

Background:

• Waste activated sludge (WAS) transformation into biofuels is crucial for sustainable waste management and carbon neutrality.
• The recalcitrance of extracellular polymeric substances (EPS) and microbial cell walls impedes efficient medium-chain fatty acids (MCFAs) production via anaerobic fermentation.

Purpose of the Study:

• To develop and investigate a persulfate (PDS)-based pretreatment strategy for enhancing MCFAs production from WAS.
• To elucidate the mechanisms by which PDS pretreatment improves sludge disintegration and substrate bioavailability for anaerobic fermentation.

Main Methods:

• Persulfate (PDS) pretreatment of WAS at varying concentrations.
• Analysis of MCFAs yield and sludge characteristics (e.g., SCOD, EPS composition).
• Metagenomic functional annotation and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to analyze dissolved organic matter (DOM) and microbial metabolism.

Main Results:

• A PDS dose of 7.5 mM increased MCFAs yield by approximately 50% to 13,341.4 mg COD/L.
• PDS radicals effectively degraded tightly bound EPS, reducing protein and polysaccharide content and increasing soluble chemical oxygen demand (SCOD) 5.05-fold.
• The resulting DOM was more bioavailable, with high H/C and low O/C ratios, stimulating microbial glycolysis, amino acid metabolism, and carbon chain elongation.

Conclusions:

• Persulfate pretreatment is a viable strategy for efficient sludge biorefinery, enhancing MCFAs production through improved sludge disintegration and DOM bioavailability.
• The study elucidates the radical-EPS-DOM-metabolism cascade, enabling mechanism-guided design for high-efficiency sludge valorization.
• Techno-economic and life cycle assessments confirm the environmental sustainability and economic feasibility of this radical-driven approach.