Lope G. Tabil

Technoeconomic analysis of wheat straw densification in the Canadian Prairie Province of Manitoba

This study presents a technoeconomic analysis of wheat straw densification in Canadas prairie province of Manitoba as an integral part of biomass-to-cellulosic-ethanol infrastructure. Costs of wheat straw bale and pellet transportation and densification are analysed, including densification plant profitability. Wheat straw collection radius increases nonlinearly with pellet plant capacity, from 9.2 to 37km for a 2-35tonnesh(-1) plant. Bales are cheaper under 250km, beyond which the cheapest feedstocks are pellets from the largest pellet plant that can be built to exploit economies of scale. Feedstocks account for the largest percentage of variable costs. Marginal and average cost curves suggest Manitoba could support a pellet plant up to 35tonnesh(-1). Operating below capacity (75-50%) significantly erodes a plants net present value (NPV). Smaller plants require higher NPV break-even prices. Very large plants have considerable risk under low pellet prices and increased processing costs.

Effects and mechanism of ball milling on torrefaction of pine sawdust

The effects and mechanism of ball milling on the torrefaction process were studied. Ball- and hammer-milled (screen size 1mm) pine sawdust samples were torrefied at three temperatures (230, 260, and 290°C) and two durations (30 and 60min) to investigate into their torrefaction behavior and physicochemical properties. The results showed that, under identical torrefaction conditions, torrefied ball-milled pine sawdust had a higher carbon content and fixed carbon, and lower hydrogen and oxygen contents than torrefied hammer-milled pine sawdust. Torrefied ball-milled pine sawdust produced lower mass and energy yields, but higher heating values than torrefied hammer-milled pine sawdust. Ball milling destroyed the crystalline structure of cellulose and thus reduced the thermal stability of hemicellulose, cellulose, and lignin, causing them to degrade at relatively lower temperatures. In conclusion, biomass pretreated with a combination of ball milling and torrefaction has the potential to produce an alternative fuel to coal.

Enhanced biomass delignification and enzymatic saccharification of canola straw by steam-explosion pretreatment.

BACKGROUND In recent decades, bioconversion of lignocellulosic biomass to biofuel (ethanol and biodiesel) has been extensively investigated. The three main chemical constituents of biomass are cellulose, hemicellulose and lignin. Cellulose and hemicellulose are polysaccharides of primarily fermentable sugars, glucose and xylose respectively. Hemicellulose also includes small fermentable fractions of arabinose, galactose and mannose. The main issue in converting lignocellulosic biomass to fuel ethanol is the accessibility of the polysaccharides for enzymatic breakdown into monosaccharides. This study focused on the use of steam explosion as the pretreatment method for canola straw as lignocellulosic biomass. RESULTS Result showed that steam explosion treatment of biomass increased cellulose accessibility and it hydrolysis by enzyme hydrolysis. Following 72 h of enzyme hydrolysis, a maximum cellulose conversion to glucose yield of 29.40% was obtained for the steam-exploded sample while the control showed 11.60% glucose yields. Steam explosion pretreatment increased glucose production and glucose yield by 200% and 153.22%, respectively, compared to the control sample. The crystalline index increased from 57.48% in untreated canola straw to 64.72% in steam-exploded samples. CONCLUSION Steam explosion pretreatment of biomass increased cellulose accessibility, and enzymatic hydrolysis increased glucose production and glucose yield of canola straw.

Effect of Drying Conditions and Level of Condensed Distillers Solubles on Protein Quality of Wheat Distillers Dried Grain with Solubles

Reduced protein quality is one of the concerns currently confronting the supply and utilization of wheat distillers dried grain with solubles (DDGS) as an animal feed ingredient. This study assessed the protein quality of wheat DDGS, expressed as acid detergent insoluble crude protein (ADICP) and lysine content, by blending wet distillers grain (WDG) with varying condensed distillers solubles (CDS) levels and drying using forced air convection, microwave, and microwave–convection methods. As the CDS level was increased, the protein content of wheat DDGS generated from the three drying methods increased. Interactions of CDS level with drying air temperature, microwave power, and microwave–convection settings had a significant effect (p < 0.05) on average ADICP and lysine contents. Higher ADICP and lower lysine contents were observed in samples dried at higher temperature, microwave power, and microwave convection settings. Further, the CDS level significantly affected the color parameters of microwave- and microwave–convection-dried samples and the drying air temperature–CDS level interaction significantly affected the color of forced air convection–dried samples. Significant lysine content–redness, ADICP–lightness color parameter, and ADICP–total color difference correlations were found in forced air convection–, microwave-, and microwave–convection-dried samples, respectively. Microwave and microwave–convection drying achieved desirable protein quality associated with low-temperature drying at much shorter times.

Biomass Feedstock Pre-Processing – Part 2: Densification

1.1 The need for densification Agricultural biomass residues have the potential for the sustainable production of bio-fuels and to offset greenhouse gas emissions (Campbell et al., 2002; Sokhansanj et al., 2006). Straw from crop production and agricultural residues existing in the waste streams from commercial crop processing plants have little inherent value and have traditionally constituted a disposal problem. In fact, these residues represent an abundant, inexpensive and readily available source of renewable lignocellulosic biomass (Liu et al., 2005). New methodologies need to be developed to process the biomass making it suitable feedstock for bio-fuel production. In addition, some of the barriers in the economic use of agricultural crop residue are the variable quality of the residue, the cost of collection, and problems in transportation and storage (Bowyer and Stockmann, 2001; Sokhansanj et al., 2006). In order to reduce industry’s operational cost as well as to meet the requirement of raw material for biofuel production, biomass must be processed and handled in an efficient manner. Due to its high moisture content, irregular shape and size, and low bulk density, biomass is very difficult to handle, transport, store, and utilize in its original form (Sokhansanj et al., 2005). Densification of biomass into durable compacts is an effective solution to these problems and it can reduce material waste. Densification can increase the bulk density of biomass from an initial bulk density of 40-200 kg/m3 to a final compact density of 600-1200 kg/m3 (Adapa et al., 2007; Holley, 1983; Mani et al., 2003; McMullen et al., 2005; Obernberger and Thek, 2004). Biomass can be compressed and stabilized to 7–10 times densities of the standard bales by the application of pressures between 400–800 MPa during the densification process (Demirbas and Sahin, 1998). Because of their uniform shape and size, densified products may be easily handled using standard handling and storage equipment, and they can be easily adopted in direct-combustion or co-firing with coal, gasification, pyrolysis, and utilized in other biomass-based conversions (Kaliyan and Morey, 2006a) such as biochemical processes. Upon densification, many agricultural biomass materials, especially those from straw and stover, result in a poorly formed pellets or compacts that are more often dusty, difficult to handle and costly to manufacture. This is caused by lack of complete understanding on the natural binding characteristics of the components that make up biomass (Sokhansanj et al., 2005).

Pretreatment of Lignocellulosic Biomass Using Microorganisms: Approaches, Advantages, and Limitations

Much of Earth’s recent geologic history is dominated by periods of extensive glaciation, with relatively low global mean temperatures and correspondingly low atmospheric CO2 concen‐ trations [1]. The current interglacial period stands out as an anomaly because the atmospheric CO2 concentration has risen sharply above the range of approximately 180-280 parts per million by volume that has defined the past 420,000 years to reach levels that are nearly 40% higher than the biosphere has experienced over this time frame [2]. This rapid increase in CO2 concentration is primarily due to the release of ancient fixed atmospheric CO2 into the modern atmosphere through the combustion of fossil fuel resources over the past 200 years. Since it is clear from ice core records that atmospheric CO2 concentration has a strong positive correlation to global temperature, it is expected that changes to global climate are forthcoming [3]. There are substantial uncertainties regarding the ability of terrestrial and oceanic carbon sinks to absorb this anthropogenic CO2 on time scales that are relevant to human society [2], so the continued release of ancient CO2 into the modern atmosphere at current rates carries with it an important risk of inducing climate changes of unknown amplitude along with a host of ancillary changes that are difficult to predict with certainty. This has led to the search for alternatives to fossil fuels to meet a rising global energy demand, and one such option is the use of extant organic matter to produce energy. This resource contains carbon that was fixed from the modern atmosphere, which means it does not result in a net increase in atmospheric CO2 upon combustion.

Adsorptive Isotherms and Removal of Microbial Inhibitors in a Bio-Based Hydrolysate for Xylitol Production

Adsorption isotherms and thermodynamics of microbial inhibitors generated by the acid-catalyzed hydrolysis of hemicellulose were investigated using activated carbon as the adsorbent. Parameters of temperature (25–65°C) and pH (1.0–10.0) were employed to study the adsorption isotherms of phenol, acetic acid, and furfural. The results based on the Langmuir model indicated that a higher efficiency of adsorption could be achieved at a lower pH and lower temperature for phenol and acetic acid. Furfural removal from the aqueous solution was only dependent on temperature, with a higher performance at 25°C. Negative values obtained for the heat of adsorption (ΔH), entropy (ΔS), and free energy (ΔG) indicated that the adsorption of all three components is exothermic (physisorption) in nature, with a mechanism based on the affinity of the solute toward the adsorbent and non-spontaneous. The adsorptive removal of the main inhibitors (8.7 g/L phenols and 4.2 g/L acetic acid) from the concentrated hydrolysate of oat hull hemicellulose was dependent on the activated carbon dosage, temperature, and pH. Under operational conditions of pH 1.0 and 25°C with an incremental carbon dosage of 1.25–5% in the hydrolysate, the removal of phenols was 64–95.4% and that of acetic acid was 6–13.2%, respectively. The xylitol fermentation process indicated that oat hull hemicellulosic hydrolysate is low in toxicity to Candida guilliermondii. Meanwhile, a mild adsorptive detoxification using activated carbon resulted in over 10% increase in xylitol yield (≈ 0.8 g/g) and productivity (0.5 g/L/h).

Microwave-Assisted Alkali Pre-Treatment, Densification and Enzymatic Saccharification of Canola Straw and Oat Hull

The effects of microwave-assisted alkali pre-treatment on pellets’ characteristics and enzymatic saccharification for bioethanol production using lignocellulosic biomass of canola straw and oat hull were investigated. The ground canola straw and oat hull were immersed in distilled water, sodium hydroxide and potassium hydroxide solutions at two concentrations (0.75% and 1.5% w/v) and exposed to microwave radiation at power level 713 W and three residence times (6, 12 and 18 min). Bulk and particle densities of ground biomass samples were determined. Alkaline-microwave pre-treated and untreated samples were subjected to single pelleting test in an Instron universal machine, pre-set to a load of 4000 N. The measured parameters, pellet density, tensile strength and dimensional stability were evaluated and the results showed that the microwave-assisted alkali pre-treated pellets had a significantly higher density and tensile strength compared to samples that were untreated or pre-treated by microwave alone. The chemical composition analysis showed that microwave-assisted alkali pre-treatment was able to disrupt and break down the lignocellulosic structure of the samples, creating an area of cellulose accessible to cellulase reactivity. The best enzymatic saccharification results gave a high glucose yield of 110.05 mg/g dry sample for canola straw ground in a 1.6 mm screen hammer mill and pre-treated with 1.5% NaOH for 18 min, and a 99.10 mg/g dry sample for oat hull ground in a 1.6 mm screen hammer mill and pre-treated with 0.75% NaOH for 18 min microwave-assisted alkali pre-treatments. The effects of pre-treatment results were supported by SEM analysis. Overall, it was found that microwave-assisted alkali pre-treatment of canola straw and oat hull at a short residence time enhanced glucose yield.

Physico-chemical characteristics of microwave-dried wheat distillers grain with solubles.

Abstract Laboratory-prepared samples of wheat distillers grain with solubles with varying condensed distillers solubles (CDS) content were dried under varying microwave power, and microwave convection settings using a domestic microwave oven to examine their effect on the chemical, structural, color, flow, compression, thermal, and frictional properties of the product, which is dried distillers grain with solubles (DDGS). As CDS level increased, protein and ash content increased, while fat and fiber content decreased in wheat-based DDGS. Fat content was also markedly effected by the microwave oven drying conditions. While CDS level, microwave power or microwave convection setting, and/or their interactions significantly effected a number of physical properties; results indicated that CDS level had a stronger influence compared to the other factors. DDGS samples with high CDS levels were significantly denser, finer but more differentiated in size, less flowable, and less dispersible. These also produced denser and stronger pellets.

Interaction of medium detoxification/supplementation and cell recycling in fermentative xylitol production

Abstract To study the importance and interactions of pH control and delignification of a medium derived from oat hull hemicellulose, as well as the influence of supplemental nitrogen source and cell recycling, Candida guilliermondii was used as the biocatalyst in repeated batch bioconversion processes in three successive batches each lasting 144 h. The research study was conducted based on a factorial design with three factors consisting of: a) pH control (pHs: pH constant during the process; pHi: pH adjusted to 6.0 at the beginning of bioconversion with no control thereafter; and pHt: pH set to 6.0 before sterilization of the medium with no control thereafter); b) medium detoxification/supplementation (Conc.: medium used directly with no treatment; AC1.25: medium treated with 1.25% activated carbon; AC2.5: medium treated with 2.5% activated carbon; AC5: medium treated with 5% activated carbon; and AC2.5-N: medium detoxified with 2.5% activated carbon and then supplemented with ammonium sulphate); and c) cell recycling [three cycles (C1, C2, and C3)]. Results from the bioconversion process indicated that detoxification of the medium was the least important factor affecting product yield and productivity, while cell recycling and medium supplementation were much more important parameters which needed to be considered to achieve a successful process. Results also indicated that medium supplementation by inorganic nitrogen (ammonium sulphate) could be a requirement to achieve a consistent process performance in consecutive cycles of bioconversion using recycled biocatalyst. However, there is no need to use a supplemental nitrogen source in a single-cycle process.