Temperature-phased conversion of acid whey waste into medium-chain carboxylic acids via lactic acid: no external e-donor.

Waste streams can be renewable feedstocks to produce biofuels and chemicals. Acid whey is an example waste stream and is produced by the Greek-yogurt industry in large volumes. This whey and other waste streams have been successfully converted into methane gas by anaerobic digesters with open cultures of microbial consortia (microbiomes). However, the revenue from methane has been relatively low. Until now, no other products could be produced with microbiomes from this waste stream. This has now changed. Here, we showed that acid whey was converted into valuable medium-chain carboxylic acids (MCCAs), such as n-caproic acid (n-hexanoic acid) and n-caprylic acid (n-octanoic acid), without addition of external electron acceptors. MCCAs can be precursors for biofuels or chemicals or can be used as green antimicrobials or livestock feed additives. Due to biological chain elongation, the oil-like MCCAs were extracted with relatively low energy consumption. However, capital costs should be further reduced during scale-up.