Understanding the effects of glycolipid biosurfactants produced through the solid-state fermentation of organic waste on the anaerobic digestion of biowaste

This study examined the effects of two different microbial glycolipid biosurfactants on the anaerobic digestion of source-selected biowaste. Sophorolipids and mannosylerythritol lipids were produced through solid-state fermentation using a combination of wheat straw, molasses, and winterization oil cake. The characterization of the biosurfactants was conducted via liquid chromatography-mass spectrometry, which revealed their diverse configurations, highlighting the importance of the purification of biosurfactants produced from waste. When utilized as additives in anaerobic digestion, both sophorolipids and mannosylerythritol lipids demonstrated high biodegradability, facilitating the degradation of recalcitrant matter in the absence of readily biodegradable substrates. Sophorolipids yielded 785-800 mL of methane per gram added, depending on the purification level. Meanwhile, mannosylerythritol lipids produced 948 mL of methane per gram added. Overall, addition of biosurfactants lowered methane production when taking their own production into account, highlighting a key control that many other studies lack. Furthermore, in conjunction with biowaste, sophorolipids augmented the initial concentration of volatile fatty acid by 52%. Sophorolipids showed a high inhibition of the methanogenesis process. A complete microbial analysis of selected samples revealed distinct changes in community composition, with sophorolipids favouring hydrolytic and acidogenic populations, while mannosylerythritol lipids increased methanogenic Archaea. This fact can have important implications in the further use of these additives to improve biowaste AD. In the case of novel biosurfactants such as sophorolipids and mannosylerythritol lipids, which are produced from organic waste, it is evident that there is a lack of studies supporting their effectiveness in anaerobic digestion and their biodegradability in such environments, as well as the real consequences of adding them.