Enhanced anaerobic digestion of food waste using purified lactonic sophorolipids produced by solid-state fermentation of molasses and oil waste : A circular approach

In the present work, the effect of pure lactonic sophorolipids (SL) on the anaerobic digestion of biowaste was investigated. For this purpose, crude SL were produced from organic waste (a mixture of molasses and winterization oil cake) through solid-state fermentation (SSF) in a 22L pilot-scale aerobic bioreactor using the yeast Starmerella bombicola as SL-producing microorganism. The crude material extracted from the SSF exhaust solid contained several forms of SL and it was purified using High-Performance Liquid Chromatography (HPLC) and characterized by means of Liquid Chromatography-Mass Spectrometry (LC-MS) yielding a high-purity C18 lactonic SL (>99%). This pure SL was used to enhance the batch anaerobic digestion of source-selected biowaste, mainly composed by kitchen waste. The best dosage of SL was in the range of 0.02-0.04 g SL/g TS, with an increment of methane yield of 41% in NmL/g VS. The presence of SL did not significantly alter the structure of the microbial community or general biodiversity. In summary, we propose a circular approach for waste valorisation in which different organic waste streams are combined in a biorefinery-like configuration, where the solid-state fermentation is used to produce SL and results in an enhanced bioenergy production.