Aqueous ammonia soaking (AAS) as a biomass pretreatment method: pilot-scale study with switchgrass, bench-scale use with poplar, and methane potential from anaerobic digestion of pretreated switchgrass

The main objective of this thesis was to evaluate aqueous ammonia soaking (AAS) as a pretreatment method for lignocellulosic biomass preparation for biofuel production, in a variety of settings. This thesis, partially fulfills the Master of Science degree requirement, is prepared in the journal paper format, and includes three papers that have been published in or are prepared for submission to a journal. The objective of the first chapter was to design and fabricate a pilot-scale soaking and washing system to safely and effectively generate AAS-pretreated switchgrass. Based on economic, safety and convenience factors, a 75-L soaking vessel was constructed and demonstrated to be effective in pretreating 4 kg of dry switchgrass per run with 20-L of aqueous ammonia. This pilot-scale system increased cellulose content and decreased hemicellulose and Klason lignin content of the remaining solids in a similar manner as observed in bench-scale experiments. To our knowledge, this is the first description and report of design, operation, and handling of a pilot-scale AAS biomass pretreatment system. The objective of the second research paper was to quantify acid soluble lignin and acid insoluble lignin content following four pretreatment methods of eight transgenic and one wild type poplar varieties. The transgenic varieties of poplar (Populus spp) had modifications in the lignin biosynthesis pathway to reduce lignin content or make varieties more susceptible to delignification. All pretreatment techniques were successful in removing a fraction of both acid soluble lignin (ASL) and acid insoluble lignin (AIL) from the transgenic varieties removing 12-70% ASL and 5-52% AIL. The objective of the last paper was to evaluate the energy yields from the anaerobic digestion (AD) of AAS-pretreated switchgrass and AAS-pretreated switchgrass plus hydrolytic enzymes. The results show that anaerobic digestion of AAS-pretreated switchgrass significantly increases biogas energy production over the AD of untreated switchgrass, and that the addition of sufficient commercially available hydrolytic enzymes greatly increased biogas yields, methane concentration, and total methane yields. At the highest enzyme loading, gross energy production from AD was over twice the gross energy production from ethanol fermentation of the same material

Effect of Ammonia Soaking Pretreatment and Enzyme Addition on Biochemical Methane Potential of Switchgrass

This article presents the biochemical methane potential (BMP) results from the anaerobic digestion (AD) of switchgrass. Triplicate BMP assays were performed on: untreated switchgrass, aqueous ammonia soaking (AAS) pretreated switchgrass (soaked in 29.5% reagent-grade aqueous ammonia at 5 L kg-1 switchgrass for 5 d), and AAS-pretreated switchgrass plus cellulytic enzymes at 12.5, 25, 62.5, and 125 filter paper units (FPU) enzyme g-1 volatile solids (VS). Biogas production and biogas methane content were measured daily in all treatments for 21 d. Both biogas and corrected methane production varied significantly among treatments, especially during the first 7 d of the BMP period. Total methane production at 21 d was corrected for enzyme degradation, and methane yields ranged from 0.15 to 0.36 m3 CH4 kg-1 VS. We compared the corrected energy yield of biogas from switchgrass to prior reports of the energy yield of ethanol from switchgrass via simultaneous saccharification and fermentation (SSF). The AD of AAS-pretreated switchgrass at the highest enzyme loading rates resulted in a 120% increase in energy extracted as compared to AAS-pretreated switchgrass converted to ethanol via SSF. Overall, the addition of enzymes to AAS-pretreated switchgrass greatly accelerated the rate of methane production over the untreated switchgrass and AAS-pretreated switchgrass without enzymes. However, the process economics are not clear, and additional work is needed to determine whether pretreating switchgrass with aqueous ammonia and/or enzymes before AD is economically advantageous

Aqueous ammonia soaking (AAS) as a biomass pretreatment method: pilot-scale study with switchgrass, bench-scale use with poplar, and methane potential from anaerobic digestion of pretreated switchgrass

The main objective of this thesis was to evaluate aqueous ammonia soaking (AAS) as a pretreatment method for lignocellulosic biomass preparation for biofuel production, in a variety of settings. This thesis, partially fulfills the Master of Science degree requirement, is prepared in the journal paper format, and includes three papers that have been published in or are prepared for submission to a journal. The objective of the first chapter was to design and fabricate a pilot-scale soaking and washing system to safely and effectively generate AAS-pretreated switchgrass. Based on economic, safety and convenience factors, a 75-L soaking vessel was constructed and demonstrated to be effective in pretreating 4 kg of dry switchgrass per run with 20-L of aqueous ammonia. This pilot-scale system increased cellulose content and decreased hemicellulose and Klason lignin content of the remaining solids in a similar manner as observed in bench-scale experiments. To our knowledge, this is the first description and report of design, operation, and handling of a pilot-scale AAS biomass pretreatment system. The objective of the second research paper was to quantify acid soluble lignin and acid insoluble lignin content following four pretreatment methods of eight transgenic and one wild type poplar varieties. The transgenic varieties of poplar (Populus spp) had modifications in the lignin biosynthesis pathway to reduce lignin content or make varieties more susceptible to delignification. All pretreatment techniques were successful in removing a fraction of both acid soluble lignin (ASL) and acid insoluble lignin (AIL) from the transgenic varieties removing 12-70% ASL and 5-52% AIL. The objective of the last paper was to evaluate the energy yields from the anaerobic digestion (AD) of AAS-pretreated switchgrass and AAS-pretreated switchgrass plus hydrolytic enzymes. The results show that anaerobic digestion of AAS-pretreated switchgrass significantly increases biogas energy production over the AD of untreated switchgrass, and that the addition of sufficient commercially available hydrolytic enzymes greatly increased biogas yields, methane concentration, and total methane yields. At the highest enzyme loading, gross energy production from AD was over twice the gross energy production from ethanol fermentation of the same material.</p

Design and Testing of a Pilot-Scale Aqueous Ammonia Soaking Biomass Pretreatment System

Scale-up of the aqueous ammonia soaking (AAS) biomass pretreatment method to 75-L soaking vessel size was accomplished in this work. A novel, pilot-scale AAS system capable of pretreating 4 kg of switchgrass per cycle was designed, fabricated, and tested. The pretreatment process involved soaking biomass in 29.5% aqueous ammonium hydroxide at a liquid: solid ratio of 5 L/kg. Major vessel design criteria included (1) allowing thorough washing of the soaked biomass in the pretreatment reactor; (2) simple, low-cost fabrication; and (3) limiting safety hazards by minimizing ammonia fumes from the system. Based on these constraints, commercially available 75-L HDPE tanks were selected as the primary vessels for pretreatment. The pretreatments were conducted outside, without agitation during the summer months in Iowa, with ambient temperatures ranging from 15°C to 33°C. During the first experimental cycle, clogging of the outlet resulted in leakage from the vessel during rinsing, and led to redesign of the washout prevention system. The redesigned system used a "teabag" approach in which dry biomass was preloaded into a cylindrical mesh bag, and the filled bag was placed into the soaking vessel. This modification eliminated outlet clogging, simplified biomass loading and unloading, but slightly reduced washing efficiency. Through five soaking cycles, an average of 22% to 25% delignification was achieved (Klason lignin basis) compared to the 35% removal seen at the bench-scale as reported by our group. Approximately 50% to 60% of the pretreated switchgrass was recovered, dry basis, compared to 75% previously achieved at the bench-scale. Overall, the system successfully generated moderate quantities (10 kg/wk) of pretreated biomass for pilot-scale fermentation experiments while illustrating some of the materials handling challenges that must be addressed as pretreatment methods are scaled-up.This article is from Applied Engineering in Agriculture, 25, no. 6 (2009): 953–959.</p

Effect of Ammonia Soaking Pretreatment and Enzyme Addition on Biochemical Methane Potential of Switchgrass

This article presents the biochemical methane potential (BMP) results from the anaerobic digestion (AD) of switchgrass. Triplicate BMP assays were performed on: untreated switchgrass, aqueous ammonia soaking (AAS) pretreated switchgrass (soaked in 29.5% reagent-grade aqueous ammonia at 5 L kg-1 switchgrass for 5 d), and AAS-pretreated switchgrass plus cellulytic enzymes at 12.5, 25, 62.5, and 125 filter paper units (FPU) enzyme g-1 volatile solids (VS). Biogas production and biogas methane content were measured daily in all treatments for 21 d. Both biogas and corrected methane production varied significantly among treatments, especially during the first 7 d of the BMP period. Total methane production at 21 d was corrected for enzyme degradation, and methane yields ranged from 0.15 to 0.36 m3 CH4 kg-1 VS. We compared the corrected energy yield of biogas from switchgrass to prior reports of the energy yield of ethanol from switchgrass via simultaneous saccharification and fermentation (SSF). The AD of AAS-pretreated switchgrass at the highest enzyme loading rates resulted in a 120% increase in energy extracted as compared to AAS-pretreated switchgrass converted to ethanol via SSF. Overall, the addition of enzymes to AAS-pretreated switchgrass greatly accelerated the rate of methane production over the untreated switchgrass and AAS-pretreated switchgrass without enzymes. However, the process economics are not clear, and additional work is needed to determine whether pretreating switchgrass with aqueous ammonia and/or enzymes before AD is economically advantageous.This article is from Transactions of the ASABE, 53, no. 6 (2010): 1921–1927.</p