Low-dosage enzymatic hydrolysis of organic municipal waste for sugar and ethanol production

Enzymatic hydrolysis (EH) of the organic fraction of municipal solid waste (OFMSW) is challenging due to its complexity and heterogeneous character. This study investigated the effects of OFMSW compositional characteristics and pretreatment techniques on the efficiency of EH. The experiments involved varying enzymatic dosages and pretreatment methods, including heat pretreatment and anaerobic incubation of raw OFMSW. Remarkably, after thermal pretreatment, a saccharification yield exceeding 50% was achieved with only 1 filter paper unit (FPU) of Cellic® Ctec3 and 0.5 glucoamylase unit (AGU) of AMG® 300 L BrewQ per g of dry OFMSW. This resulted in the recovery of 239 g of sugar per kilogram of dry OFMSW. The study revealed that the decomposition of OFMSW by enzymes is limited after reaching about 50% of the sugar recovery yield, and high concentrations of inhibitors such as organic acids, alcohols, and potentially other organics and inorganics may contribute to this limitation. These compounds, however, serve as excellent preservatives, achieving contamination control during biological conversion. Sugar-rich hydrolysates were subjected to ethanol fermentation using Saccharomyces cerevisiae, leading to the conversion of most hexose sugars into ethanol, reaching 331 g of ethanol per kilogram of dry OFMSW, and indicating that the limitation of OFMSW saccharification was not due to product inhibition. These findings highlight the need for further investigation of the saccharification process of biowaste to overcome inhibitory effects and subsequently achieve higher efficiency of the following bioprocesses.