Ulrike Tschirner

Process modeling and analysis of pulp mill-based integrated biorefinery with hemicellulose pre-extraction for ethanol production: a comparative study.

Pulp and paper mills represent a major platform to use more effectively an abundant, renewable bio-resource - wood. Modification of the modern day pulp mills into integrated forest biorefineries (IFBR) presents an excellent opportunity to produce, in addition to valuable cellulose fiber, co-products including fuel grade ethanol and additional energy, thus resulting in increased revenue streams and profitability and potentially lower the greenhouse gas emissions. A process model to simulate the integrate forest biorefinery manufacturing pulp and other co-products has been developed. This model has been used to compare three integrated biorefinery scenarios: the conventional Kraft pulping process, the pulp mill-based IFBR with hemicelluloses extraction prior to pulping for ethanol production, and the pulp mill-based IFBR with both pre-extracted hemicelluloses and the short fiber for ethanol production. Based on a fixed feedstock throughput of 2000 dry Mg wood/day, results show that the pulp mill-based IFBR with both pre-extracted hemicelluloses and the short fiber cellulose converted to ethanol can produce 0.038 MM m(3) (10.04 MM gal) ethanol per year at a minimum ethanol selling price (MESP) of

Improved pretreatment of lignocellulosic biomass using enzymatically-generated peracetic acid.

491/m(3) (

Student Peer Teaching: An Innovative Approach to Instruction in Science and Engineering Education

1.86/gal). The economic feasibility of IFBR can be further improved by using further improvements in the pre-extraction process, other biomass such as corn stover for producing ethanol, and taking advantage of the economies of scale.

Fiber length and pulping characteristics of switchgrass, alfalfa stems, hybrid poplar and willow biomasses

Release of sugars from lignocellulosic biomass is inefficient because lignin, an aromatic polymer, blocks access of enzymes to the sugar polymers. Pretreatments remove lignin and disrupt its structure, thereby enhancing sugar release. In previous work, enzymatically generated peracetic acid was used to pretreat aspen wood. This pretreatment removed 45% of the lignin and the subsequent saccharification released 97% of the sugars remaining after pretreatment. In this paper, the amount of enzyme needed is reduced tenfold using first, an improved enzyme variant that makes twice as much peracetic acid and second, a two-phase reaction to generate the peracetic acid, which allows enzyme reuse. In addition, the eight pretreatment cycles are reduced to only one by increasing the volume of peracetic acid solution and increasing the temperature to 60 °C and the reaction time to 6h. For the pretreatment step, the weight ratio of peracetic acid to wood determines the amount of lignin removed.

Lignocellulose modifications by brown rot fungi and their effects, as pretreatments, on cellulolysis

This paper reports the results of a pilot-study in a senior paper science and engineering class, of an innovative instructional method designed to foster student problem-solving and in-depth learning of material, namely, student peer teaching. We review related literature focusing on active learning methods in science and engineering education, describe the method of student peer teaching used in this pilot-study, present the evaluation method and results, and discuss implications for further development of this method of instruction. Results suggest that students were able to effectively teach significant curricular content. In addition, the method of student peer teaching served important purposes in helping students develop in-depth understanding and expertise in the issues related to their teaching session, as well as teaching and presentation skills which will be useful in their professional practice. However, students expressed concern that, while achieving in-depth learning of the content of their teaching session, they tended to focus on the content area of their teaching session at the expense of other content areas and may not have learned as well from other students as from the Professor. We recommend a modified structure for student peer teaching which incorporates cooperative learning methods; increased Professor involvement in class sessions, in the role of the mentor; and modifications in performance evaluation methods to ensure ongoing student monitoring of progress and self-assessment. The method of student peer teaching, in science and engineering education, combined with cooperative learning methods, is viewed as a major extension of cooperative learning methods, used in the service of preparation for professional careers.

Improved ethanol production from various carbohydrates through anaerobic thermophilic co-culture.

Switchgrass (Panicum virgatum), alfalfa stems (Medicago sativa), second year growth hybrid poplar (Populus) and willow (Salix spp.) were examined to determine fiber characteristics, pulping behavior and paper properties. Alfalfa stems and switchgrass both showed length weighted average fiber length (LWW) of 0.78 mm, a very narrow fiber length distribution and high fines content. Willow and hybrid poplar have lower fines content but a very low average fiber length (0.42 and 0.48 mm LWW). In addition, the four biomass species showed distinctly different chemical compositions. Switchgrass was defibered successfully using Soda and Soda Anthraquinone (AQ) pulping and demonstrated good paper properties. Both fast-growing wood species pulped well using the Kraft process, and showed acceptable tensile strength, but low tear strength. Alfalfa stems reacted very poorly to Soda and Soda AQ pulping but responded well to Kraft and Kraft AQ. Pulps with tensile and tear strength considerably higher than those found for commercial aspen pulps were observed for alfalfa. All four biomass species examined demonstrated low pulp yield. The highest yields were obtained with poplar and switchgrass (around 43%). Considering the short fibers and low yields, all four biomass types will likely only be used in paper manufacturing if they offer considerable economic advantage over traditional pulp wood.

Process Modeling of Comprehensive Integrated Forest Biorefinery—An Integrated Approach

Brown rot fungi Gloeophyllum trabeum and Postia placenta were used to degrade aspen, spruce, or corn stover over 16 weeks. Decayed residues were saccharified using commercial cellulases or brown rot fungal extracts, loaded at equal but low endoglucanase titers. Saccharification was then repeated for high-yield samples using full strength commercial cellulases. Overall, brown rot pretreatments enhanced yields up to threefold when using either cellulase preparation. In the best case, aspen degraded 2 weeks by G. trabeum yielded 72% glucose-from-cellulose, a 51% yield relative to original glucan. A follow-up trial with more frequent harvests showed similar patterns and demonstrated interplay between tissue modifications and saccharification. Hemicellulose and vanillic acid (G6) or vanillin (G4) lignin residues were good predictors of saccharification potential, the latter notable given lignins potential active role in brown rot. Results show basic relationships over a brown rot time course and lend targets for controlling an applied bioconversion process.

Performance of agricultural residue media in laboratory denitrifying bioreactors at low temperatures

Saccharification is one of the most critical steps in producing lignocellulose-based bio-ethanol through consolidated bioprocessing (CBP). However, extreme pH and ethanol concentration are commonly considered as potential inhibitors for the application of Clostridium sp. in CBP. The fermentations of several saccharides derived from lignocellulosics were investigated with a co-culture consisting of Clostridium themocellum and Clostridium thermolacticum. Alkali environments proved to be more favorable for ethanol production. Fermentation inhibition was observed at high ethanol concentrations and extreme pH. However, low levels of initial ethanol addition resulted in an unexpected stimulatory impact on the final ethanol productions for all cultures under selected conditions. The co-culture was able to actively ferment glucose, xylose, cellulose and micro-crystallized cellulose (MCC). The ethanol yield observed in the co-culture was higher (up to twofold) than in mono-cultures, especially in MCC fermentation. The highest ethanol yield (as a percentage of the theoretical maximum) observed was 75% (w/w) for MCC and 90% (w/w) for xylose.

Bagasse alkaline sulfite-anthraquinone ( AS/AQ ) pulping and totally chlorine free ( TCF ) bleaching

The key to expanding the energy supply, increasing energy security, and reducing the dependency on foreign oil is to develop advanced technologies to efficiently transform our renewable bioresources into domestically produced bioenergy and bioproducts. Conventional biorefineries, i.e., forest products industry’s pulp and paper mills with long history of sustainable utilization of lignocellulose (wood), offer a suitable platform for being expanded into future integrated forest biorefineries. Due to the pre-existing infrastructure in current forest products operations, this could present a very cost-effective approach to future biorefineries. In order to better understand the overall process, technical, economic, and environmental impacts, a detailed process modeling of the whole integrated forest biorefinery is presented here. This approach uses a combination of Aspen Plus®, WinGEMS®, and Microsoft Excel® to simulate the entire biorefinery in detail with sophisticated communication interface between the three simulations. Preliminary results for a simple case study of an integrated biorefinery show the feasibility of this approach. Further investigations, including additional details, more process options, and complete integration, are currently underway.

Separation and purification processes for lignocellulose-to-bioalcohol production

Denitrifying bioreactors can be effective for removing nitrate from agricultural tile drainage; however, questions about cold springtime performance persist. The objective of this study was to improve the nitrate removal rate (NRR) of denitrifying bioreactors at warm and cold temperatures using agriculturally derived media rather than wood chips (WC). Corn ( L.) cobs (CC), corn stover (CS), barley ( L.) straw (BS), WC, and CC followed by a compartment of WC (CC+WC) were tested in laboratory columns for 5 mo at a 12-h hydraulic residence time in separate experiments at 15.5 and 1.5°C. Nitrate-N removal rates ranged from 35 to 1.4 at 15.5°C and from 7.4 to 1.6 g N m d at 1.5°C, respectively; NRRs were ranked CC > CC+WC > BS = CS > WC and CC ≥ CC+WC = CS ≥ BS > WC for 15.5 and 1.5°C, respectively. Although NRRs for CC were increased relative to WC, CC released greater amounts of carbon. Greater abundance of nitrous oxide (NO) reductase gene () was supported by crop residues than WC at 15.5°C, and CS and BS supported greater abundance than WC at 1.5°C. Production of NO relative to nitrate removal (NO) was consistently greater at 1.5°C (7.5% of nitrate removed) than at 15.5°C (1.9%). The NO was lowest in CC (1.1%) and CC-WC (0.9%) and greatest in WC (9.7%). Using a compartment of agricultural residue media in series before wood chips has the potential to improve denitrifying bioreactor nitrate removal rates, but field-scale verification is needed.