| dc.description.abstract | To improve biological digestibility, lignocellulose was pretreated by shock, alkali, and combinations thereof. 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. For animal feed, Ca(OH)₂ treatment is recommended because residual calcium ions are valuable nutrients. However, for methane-arrested, anaerobic digestion (MAAD), NaOH treatment is preferred because sodium is a better buffer. The effect of shock is most pronounced when the no-shock control employed the same soaking-and-drying procedure as the shock treatment.
MAAD is a more accurate assessment technique when lignocellulose is employed in the carboxylate platform, a promising approach that utilizes nearly all biomass components. Using recommended pretreatment conditions identified from a previous study, three corn stover pretreatments were compared using MAAD: (1) shock-only, (2) NaOH-only, and (3) shock + NaOH. Air-dried sewage sludge was used as nutrient source. At 100 g/L initial substrate concentration, compared to untreated corn stover, shock-only decreased conversion (amount of biomass digested) by 14%, NaOH-only increased conversion by 82%, and shock + NaOH increased conversion by 104%.
To sustainably produce carboxylic acids, paper and chicken manure were co-digested through semi-continuous countercurrent (MAAD) using a mixed culture of marine microorganisms grown at mesophilic conditions (40 °C). During the digestion, anion-exchange resin (Amberlite IRA-67) adsorption was applied to simultaneously recover inhibitory acid products from the digestion medium. The adsorption efficiency was enhanced by supplying CO₂ during in-situ adsorption. Compared with stand-alone digestion (control), integrating adsorption with MAAD significantly increased biomass conversion and acid yield by 2.28 and 2.09 times, respectively.
The effects of frozen (fresh), air-dried, and baked nutrients (chicken manure, sewage sludge) on MAAD was studied. Continuum particle distribution (CPDM) maps show the impact of liquid residence time (LRT) and volatile solids loading rate (VSLR) on conversion and product concentration. Baked chicken manure reduced conversion and acid concentration, which suggests that oven-drying damages nutrients. At high VSLR, air-dried nutrients have higher acid concentrations than fresh nutrients, but conversion is low; thus, fresh nutrients are preferred. At the same conditions, fresh chicken manure and sewage sludge have similar acid concentration; however, sewage sludge yields a larger proportion of caproic acid.
Most biomass sources require expensive pretreatment to remove lignin, a component that makes biomass less reactive. However, prickly pear cladodes have low lignin content and high sugar content. Batch MAADs of prickly pear cladodes were performed and CPDM maps were generated. With a product yield of ~50% and biomass conversion of ~70%, prickly pear performed better than previously studied lignocellulosic feedstocks. At 100 g solids/L liquid, the CPDM map predicts that high acid concentrations (93 g/L) and conversions (93%) are obtained at VSLR of 6 g/(Lliq·day) and LRT of 35 days. The high sugar content and low lignin content of prickly pear makes it a suitable feedstock for the carboxylate platform. | |
