Separation of Short-Chain Fatty Acids from Primary Sludge into a Particle-Free Permeate by Coupling Chamber...

Area of Science:

• Biotechnology and biochemical engineering
• Environmental science and engineering
• Waste valorization

Background:

• Short-chain fatty acids (SCFAs) are key metabolic intermediates from sludge fermentation, with potential as biotechnological precursors.
• High solid content in hydrolyzed sludge hinders downstream SCFA recovery processes.
• Efficient separation of SCFAs from solids is essential for their industrial application.

Purpose of the Study:

• To develop and optimize a pilot-scale process for recovering SCFAs from primary sludge into a particle-free permeate.
• To overcome challenges associated with solid removal and membrane fouling during SCFA recovery.

Main Methods:

• Primary sludge underwent dark fermentation to produce SCFA-rich hydrolyzate.
• Hydrolyzate was treated using a chamber filter-press (100 µm polyester) after conditioning with hydroxypropyl trimethyl ammonium starch (HPAS).
• Cross-flow microfiltration (0.2 µm α-Al2O3) was employed, with optimized backwashing and surface charge modification to mitigate HPAS-induced fouling.

Main Results:

• Filter press reduced total solids by at least 60%, yielding filtrate with 100–1300 mg/L suspended solids.
• Microfiltration, despite fouling, achieved sustained permeate flux between 20–80 LMH through optimized backwashing and surface modification.
• The process recovered approximately 4 gC_SCFAs/capita/day from primary sludge with a purity of 0.85–0.97 C_SCFAs/DOC.

Conclusions:

• A combined filter-press and microfiltration system effectively recovers SCFAs from primary sludge, producing a particle-free permeate.
• Optimized microfiltration strategies, including backwashing and surface modification, are crucial for managing fouling and ensuring process efficiency.
• This approach offers a viable route for valorizing sludge by recovering valuable SCFAs for biotechnological applications.