Efficient conversion of municipal solid waste to biofuel by simultaneous dilute-acid hydrolysis of starch and pretreatment of lignocelluloses

Abstract

The organic fraction of municipal solid waste (OFMSW) is a complex mixture of easily digestible compounds, mainly starchy materials, and hardly digestible compounds, mainly lignocelluloses. Thus, OFMSW has a high potential for biofuel production after the hydrolysis of carbohydrates. In this study, dilute-acid treatment was used for the hydrolysis of starchy materials, eliminating the amylases enzymes requirement. Besides, the acid treatment acted as a pretreatment for the improvement of lignocelluloses fractions prior to the enzymatic hydrolysis of lignocelluloses. The acid treatment was conducted with 0.5 and 1% (w/w) sulfuric acid at 130 and 160 °C for 0, 30, and 60 min. The treatment with 1% acid at 130 °C for 60 min resulted in the hydrolysate with the highest glucose concentration of 43.2 g/L, mainly originated from starchy materials, and the subsequent enzymatic hydrolysis of the treated solids resulted in a hydrolysate containing 23.4 g/L glucose, mainly from cellulose. These hydrolysates, containing different sugars and inhibitors, were then subjected to ethanolic fermentation using a highly inhibitor-tolerant strain of Zygomycetes fungi, Mucor indicus. Using acid treatment with 1% at 130 °C for 60 min, without detoxification, the ethanol yield of 44.6 and 44.4 g per 100 g glucose was obtained from hydrolysate and acid treatment liquor, respectively. The liquid remained after the separation of ethanol from fermentation liquor and the residual solid remained after enzymatic hydrolysis were subjected to anaerobic digestion for biogas production. Overall, 194.0 g ethanol and 144.8 L methane were produced from each kg of dry OFMSW through the consecutive processes. Therefore, without detoxification and amylases requirement, all biodegradable parts of MSW were converted to bioenergy in the form of ethanol and biogas, resulting in the production of 10,453 kJ energy and 326.6 mL gasoline equivalent from each kg of dry OFMSW.