Short chain and medium chain fatty acids production using food waste under non-augmented and bio-augmented conditions

Bioprocess for conversion of ethanol and short chain fatty acids (SCFAs) into medium chain fatty acids (MCFAs) is termed as microbial chain elongation. MCFAs are saturated monocarboxylic acids with applications as antimicrobials, corrosion inhibitors and are precursors for the production of biodiesel and bioplastics. In the present study, a two-stage mixed culture fermentation was employed for the production of SCFAs and MCFAs from food waste (FW). In the first stage, FW was hydrolyzed into leachate (contains SCFAs) by the addition of anaerobic bacteria and in the second stage SCFAs present in leachate were converted in to MCFAs by the chain elongation bioprocess. The production of MCFAs such as caproic, heptanoic, caprylic and decanoic acids were demonstrated for 91 days in four different experimental conditions, i.e., control (no bacteria), pure culture (Clostridium kluyveri), non-augmentation (only enriched mixed culture), and bio-augmentation (C. kluyveri bio-augmented with enriched mixed culture). Produced SCFAs, MCFAs and biogas were analysed at different time intervals. Bio-augmented culture showed highest SCFAs (8.9 g/l of butyric acid) and MCFAs (8.1 g/l of caproic acid) production than other conditions. Microbial population was characterized by using denaturing gradient gel electrophoresis (DGGE) analysis with the highest MCFAs producing culture. The bacterial diversity observed contained predominantly Clostridia, Sphingobacteriales, Desulfobacteraceae and Bacillus groups in the bioaugmented mixed culture. Results have depicted the potential of employing the bio-augmentation strategy for the valorization of food waste into useful products like SCFAs and MCFAs.