Temperature-Phased Conversion of Acid Whey Waste Into Medium-Chain Carboxylic Acids via Lactic Acid: No External e-Donor

Abstract

Summary Acid whey is a Greek-yogurt waste stream and can be a resource to produce biofuel precursors. Our objective was to convert acid whey into medium-chain carboxylic acid (MCCA) oil with the open-culture carboxylate platform. Here, we developed a temperature-phased bioprocess with different anaerobic reactor microbiomes, performing thermophilic lactic acid production and mesophilic chain elongation, to produce MCCAs (C6–C9) from acid whey via lactic acid as an intermediate. For the lactic acid-producing bioreactor, we achieved a volumetric lactic acid production rate of 1,230 mmol C L −1 day −1 (1.54 g L −1 hr −1 ). For the chain-elongating bioreactor, we achieved a volumetric MCCA production rate of 111 mmol C L −1 day −1 and a volumetric n -caproic acid (C6) production rate of 81 mmol C L −1 day −1 (0.07 g L −1 hr −1 ). We converted a real waste stream into mainly MCCAs without the external addition of an electron donor.