Lime pretreatment to improve methane production of smooth cordgrass (Spartina alterniflora)

Abstract Anaerobic conversion of smooth cordgrass (SC; Spartina alterniflora ) to methane for energy production presents a viable option for effective management. The effect of lime pretreatment of SC on methane production was investigated in this study. The effect of three selected independent variables (lime loading (0.02–0.12 g Ca(OH) 2 /g SC), pretreatment time (7–28 days) and temperature (25–55 °C)) on material composition and methane production was explored. Lime pretreatment resulted in significant changes in SC composition: 5.7–60.5% hemicellulose and 10.2–36.2% lignin reductions, and 91–98.7% cellulose remaining in the solid residues after lime pretreatment. Lime pretreatment increased methane yield by between 122% and 180% and the methane production rate constant in the range of 56–212%. The highest methane yield was 218.4 mL/g total solids from pretreatment conditions of lime loading 0.12 g Ca(OH) 2 /g SC, for 28 days at 45 °C. These results were based on a 30-day biochemical methane potential assay. Lime loading had the greatest influence on methane yield of the three pretreatment factors. Considering the energy balance, the optimization of pretreatment experiment was carried out under the condition of 0.10 g Ca(OH) 2 /g SC dry mass, at 25 °C for 14 days. Based on this study, the pretreatment condition of high lime loading, low temperature and short pretreatment time was a preferential consideration for lime pretreatment.