Effects of acid/alkali pretreatments on lignocellulosic biomass mono-digestion and its co-digestion with waste activated sludge

The present study investigated the effects of acid/alkali pretreatments on wheat straw mono-digestion and its co-digestion with waste activated sludge (WAS). The effects of pretreatment conditions on different anaerobic digestion (AD) stages (hydrolysis, acidogenesis, acetogenesis and methanogenesis) were discussed. At first, this study analyzed the impacts of acid/alkali pretreatments on wheat straw morphology, lignocellulosic components and evaluated these impacts on subsequent AD process by SEM, XRD, FT-IR and 3D-EEM analysis. The results of AD process showed that both acid and alkali pretreatments can enhance the hydrolytic performance of substrates. W12 (0.01 mol/L NaOH pretreated wheat straw mono-digestion) obtained the highest cumulative specific methane yield (CSMY) of 227.4 mL/g·VS. However, due to the formation of humic substances in liquid fraction, 0.1 mol/L NaOH pretreated wheat straw (W13) presented inhibition in converting propionic acid into acetic acid process. Co-digestion with sludge can relieve this inhibition and obtain the highest CSMY of 221.4 mL/g·VS. This study also exhibited the effects of pretreatments on microbial community and diversity: the inhibition of acetogens in AD process was revealed. Eventually, this study summarizes the positive and negative effects of acid/alkali pretreatments on the different digestive stages, aiming to provide references for future research and engineering implementation.