Enzymatic hydrolysis and additional mild pretreatments for recovery of valuable compounds from organic fraction of municipal solid waste at high-solids loading

The organic fraction of municipal solid waste (OFMSW) is usually processed via composting or anaerobic digestion. Thereby, the potential of OFMSW as a renewable feedstock is not fully exploited. Here, a systematic evaluation of enzymatic hydrolysis among the mild pretreatments of OFMSW from a waste treatment plant aiming to increase the total amount of soluble compounds within the liquid fraction is provided. Pretreatment combinations and conditions tested were shredding for size reduction, autoclaving to lower the microbial activity, enzyme addition and two different dry matter contents at high-solids loading. The results provide valuable information about the enzymatic hydrolysis of OFMSW and subsequent solid–liquid separation. Shredding prior to enzyme addition led to higher amounts of soluble molecules released (e.g. glucose), which indicates an enhanced enzymatic hydrolysis. As a result of improved hydrolysis, an overall increase of the liquid fraction obtained after solid–liquid separation was observed. Thereby, the yield of lactic acid that is already present within the OFMSW and the yield of other soluble compounds were increased. Enzymatic hydrolysis of OFMSW with dry matter content of 25% (w/w) was more effective compared to dry matter content of 30% (w/w). The presented findings help to further develop suitable pretreatment methods and find appropriate process characteristics in terms of the solid load for OFMSW. This will facilitate the utilisation of OFMSW at high-solids loading to produce value-added products within a circular economy.

Graphical Abstract