Levulinic acid wastewater containing high concentration of sulfate was generated while producing levulinic acid by straw depolymerization with dilute sulfuric acid. In this study, levulinic acid wastewater was pretreated by calcium hydroxide precipitation, then co-digestion of pretreated levulinic acid wastewater and corn stalk was conducted for the further removal of sulfate from levulinic acid wastewater and production of bioenergy. Effects of sulfate loading and substrate level on methane production and sulfate removal from co-digestion were investigated. The results showed that the highest methane production potential of 249.93 mL/g volatile solid (VS) was achieved when the sulfate loading is 0.31 g/L and the substrate level is 32.3 g/L, which was significantly higher than 182.53 mL/g VS achieved for mono-digestion of corn stalk. The sulfate removal of 86.82-98.10% was obtained when sulfate loading is >0.31 g/L, and the concentration of sulfate in the biogas slurry was <0.09 g/L after 28 days of anaerobic co-digestion regardless initial sulfate loading. The results of microbial community analysis demonstrated that the relative abundance of methanogenic bacteria (such as Methanoculleus and Methanosarcina) had increased significantly at sulfate loading of 0.31 g/L, and the relative abundance of sulfate-reducing bacteria (Desulfotomaculum) increased from 0.01% to 2.11% when the sulfate loading rose from 0.10 g/L to 1.47 g/L under the substrate level of 32.3 g/L. This means that co-digestion of corn stalk and levulinic acid wastewater after calcium hydroxide pretreatment (CHP) was beneficial for methane production and sulfate removal.
Keywords: Co-digestion; Corn stalk; Levulinic acid wastewater; Methane production; Sulfate removal.
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