Stripping‐based approach for the recovery of volatile fatty acids from anaerobic digestion digestate: preliminary experimental investigations and modelling

BACKGROUND: Volatile fatty acids (VFAs) are widely used across industries: as intermediates in chemical production (e.g., solvents and polymers), in pharmaceuticals and cosmetics, and as preservatives and health-promoting additives in food and animal feed. Emerging applications also include bioplastics, bioenergy, and biotechnology. Recovering VFAs from digestate requires downstream processing. Gas stripping has emerged as a promising technique. It transfers VFAs from liquid to gas using air or nitrogen and then recovers them through absorption or condensation. This method is simpler, scalable, and effective even at low concentrations, highlighting its potential for sustainable VFA recovery. RESULTS: Using a real digestate at 95 °C and a space velocity of 6 min−1, the stripping efficiency ranged from 23% for acetic acid to 73% for hexanoic acid. The stripping coefficient varied from 3.4 × 10−4 min−1 for acetic acid to 1.0 × 10−2 min−1 for hexanoic acid; the mass transfer coefficient varied from 2.2 × 10−3 min−1 for acetic acid to 1.0 × 10−2 min−1 for hexanoic acid. The model showed R2 between 0.62 and 0.997, with 90% of parity-plot data on the real digestate within ±30%. CONCLUSIONS: Air stripping under alkaline conditions is confirmed as a viable and efficient method for recovering VFAs from a real digestate. Increasing the stripping temperature and the stripping carrier space velocity enhanced VFA recovery performance, with the same trend confirmed for the stripping coefficient and the mass transfer coefficient. Higher molecular weight VFAs exhibited higher recovery efficiencies, notably given the higher market value of hexanoic (caproic) acid compared to the other acids. © 2026 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).