Valorisation of solid biowastes: The lactic acid alternative

[Display omitted] •Solid biowastes are in general good fermentation substrates.•Production of lactic acid is possible from each type of solid biowaste.•Chemical or enzymatic hydrolysis is often required as pretreatment step.•Addition of exogenous enzymes can enhance the fermentation process.•Complexity of solid biowastes varies according to their source. Solid biowastes (SBW) are organic residues from gardens and parks, food wastes from kitchens, organic municipal solid wastes and comparable side streams from food processing plants. Without proper treatment, SBW represent an environmental hazard. Several initiatives around the world are dedicated to developing more effective systems for the treatment of this constantly growing ‘resource’. The chemical composition of SBW, rich in carbohydrates, proteins and lipids, makes it a good substrate to produce biobased materials through fermentation. Amongst them, lactic acid (LA), considered one of the top ten green molecules of the future, has attracted huge interest because of its many uses as an intermediate chemical. This review gathers the most important learnings from fermentation of SBW to LA, providing an overview of the process steps while highlighting some of the current limitations to overcome. Despite their complexity, results suggest that some of the SBW could be good substrates in LA fermentations and that biosynthesis of LA should be regarded as part of the whole waste management solution.