This study investigates digestibility enhancements of lignocellulose from shock pretreatment, alkaline pretreatment, and combination. Shock pretreatment subjects aqueous slurries of lignocellulose to shock waves, which disrupts its structure rendering it more susceptible to hydrolysis. Alkaline pretreatment submerges the biomass in aqueous alkali (NaOH, Ca(OH) 2 ), which removes lignin and acetyl groups. As indicators of digestibility, cellulase (CTec3) and hemicellulase (HTec3) were used to saccharify the pretreated corn stover and the resulting filtrate which contains about 10% of the sugars. Shock is most effective when it precedes alkaline pretreatment, presumably because it opens the biomass structure and enhances diffusion of pretreatment chemicals. Lignocellulose digestibility from calcium hydroxide treatment improves significantly with oxygen addition. In contrast, sodium hydroxide is a more potent alkali, and thereby eliminates the need for oxygen to enhance pretreatment.At low hydroxide loadings (<4 g OH À /100 g dry biomass), both NaOH and Ca(OH) 2 provide similar increases in digestibility; however, at high hydroxide loadings, NaOH is superior. For animal feed, Ca(OH) 2 treatment is recommended, because residual calcium ions are valuable nutrients. In contrast, for methane-arrested anaerobic digestion, NaOH treatment is preferred because NaHCO 3 is a stronger buffer. At 50 C, shock pretreatment improves sugar yields at all NaOH loadings. The effect of shock is most pronounced when the no-shock control employed the same soakingand-drying procedure as the shock treatment. The recommended conditions are shock treatment (5.52 bar [abs] initial H 2 /O 2 pressure) followed by 50 C alkaline treatment with NaOH loading of 4 g OH À /100 g dry biomass for 1 h.

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To address climate change, liquid biofuels are an essential alternative to fossil fuels, especially for transportation. The carboxylate platform uses methane‐arrested anaerobic digestion (MAAD) to ferment biomass to carboxylic acids, which can be chemically converted to liquid fuels via the carboxylate platform. Most biomass sources require expensive pretreatments to remove lignin; however, prickly pear (Opuntia ficus‐indica) cladodes have low lignin content and therefore do not require pretreatment. Furthermore, this sugar‐rich feedstock is readily digested to high concentrations of carboxylic acids. At various substrate concentrations, batch MAAD of prickly pear cladodes yielded primarily acetic, butyric, and caproic acids. From these batch data, continuum particle distribution modeling (CPDM) simulated four‐stage countercurrent digestion. At a non‐acid volatile solid (NAVS) concentration of 100 g/Lliq, CPDM predicts a high total acid concentration of 93 g/L and conversion of 0.93 g NAVSdigested/NAVSfed at a volatile solid loading rate of 6 g/(Lliq·d) and liquid retention time of 35 days. Without chemical pretreatment, co‐digestion, or in situ product removal, prickly pear produced high yields, biomass conversion, product concentration, and selectivity compared to previously studied lignocellulosic feedstocks.