Towards zero waste: A valorization route of washing separation and liquid hot water consecutive pretreatment to achieve solid vinasse based biorefinery

Abstract

With increasing accumulation of solid vinasse from liquor industries of China, the valorization of solid vinasse become an urgent concern. Given its high content of rice husk (56 wt %), lactic acid (106 g/kg), and levulinic acid (50 g/kg), the roles of washing and liquid hot water pretreatment on anaerobic digestion of original solid vinasse were investigated. Washing pretreatment enhanced the methane yield of original solid vinasse by 38.09%, while the pretreatment of liquid hot water increased the methane yield of washed solid (rice husk) by 225.70%. The maximum methane yield of 214.14 L/kg TS was obtained by consecutive washing separation and liquid hot water at 170 °C for 2 h. Various analysis methods were conducted to explain the insight mechanism hidden in the pretreatment routes. The poor methane yield from direct liquid hot water pretreated original solid vinasse was due to formation of oligolactic acid from original lactic acid, resulted in the loss of carbon source for methane production. Furfural and phenolic oligomers contained in hydrolysate were found to inhibit methane production. A complete utilization of original solid vinasse was proposed, where the liquid fractions obtained after consecutive washing and liquid hot water pretreatment of solid vinasse were used for the mixed anaerobic digestion, while the solid fractions obtained after liquid hot water containing the crystalline cellulose and lignin covered by humins was a promising material for biochar preparation. These findings opened a door to develop a sustainable solid vinasse based biorefinery.