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

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.