Biofuel technology seems to be a promising method for economically and environmentally prospective treatments of lignocellulosic wastes from various branches like food processing, forestry, or agriculture. Factors like the lignin content, crystallinity of cellulose, and particle size, limit the digestibility of hemicellulose and cellulose present in lignocelluloses. Biomass size reduction is a mechanical treatment process which due to increasing of the accessible surface area and decreasing of cellulose crystallinity improves the digestibility and the conversion of saccharides during hydrolysis. Informations about equipment design parameters and energy requirements are reviewed in relation to initial and final particle sizes, bulk density, and moisture content in biomass.
In this review, the effect of organic solvents on microalgae cultures from molecular to industrial scale is presented. Traditional organic solvents and solvents of new generation-ionic liquids (ILs), are considered. Alterations in microalgal cell metabolism and synthesis of target products (pigments, proteins, lipids), as a result of exposure to organic solvents, are summarized. Applications of organic solvents as a carbon source for microalgal growth and production of target molecules are discussed. Possible implementation of various industrial effluents containing organic solvents into microalgal cultivation media, is evaluated. The effect of organic solvents on extraction of target compounds from microalgae is also considered. Techniques for lipid and carotenoid extraction from viable microalgal biomass (milking methods) and dead microalgal biomass (classical methods) are depicted. Moreover, the economic survey of lipid and carotenoid extraction from microalgae biomass, by means of different techniques and solvents, is conducted.
Lightning belongs among critical process parameters that significantly affect growth and microalgal yield in photobioreactors. Sunshine or artificial lighting is applied to irradiate photobioreactors. Nevertheless, sunshine lighting is limited by locality and weather conditions. On the contrary, there is a typical demand for nonstop or 8000 annual working hours for industrial biorefineries using photobioreactors as an economic point of view. Thus the paper scopes to evaluate the fundamental economic feasibility of artificial lightning provided by electric energy from fossil fuels, renewable energy systems, or their mutual combinations. The economic feasibility is discussed concerning local annual sunshine hours for a model 1-ha microalgae cultivation plant. It was found that combined sunlight, solar energy- and electric energy-based artificial lighting has a significant positive effect on the economic behavior of a model biorefinery. The mutual combination of sunshine, solar energy- and electric artificial energy-based light evinces a profit increase of 2.18 for microalgal powder, 3.09 for microalgal lipids and 4.11 for microalga carotenoids production technologies all compared only to sun lighted photobioreactors. Nevertheless, capital investments in artificial lightings, solar systems, or photobioreactors, and high operating expenses represent the dominant risk factors of the discussed microalgal biorefinery. Developing cheap and reliable artificial lighting systems, solar and energy storage systems, and improving process characteristics of microalgal cultivation (process stability, high concentrated suspension in thin layer photobioreactors avoiding biofilm formation) were identified as the essential research needs and challenges to improve the economic feasibility of artificially lighted microalgal biorefinery.
Thermal-expansionary pretreatment is a novel environmentally friendly technology that has high potential to be installed in various industrial biofuel technologies where lignocellulosic biomass is processed. It is based on the boiling of biomass in water maintained by pressure in the liquid state, under a process temperature and a residence time with subsequent rapid batch decompression. The performance of the intensified pretreatment technology was shown in an intensified full-scale biogas plant. Wheat straw was used as the model processing substrate. To show the improvement, the results were compared with the regular non-intensified biogas plant. It was found that the intensified plant had a much higher power. The economic analysis and payback period were performed for both types of plant.
<p>Colloid mills and extruders are widely used for disintegrating wet fibrous biomass. However, their main disadvantages are a high energy requirement in the range of hundreds or thousands of kWh per ton of material, and the fact that they grind in process cycles. Efforts have therefore been made to design a new type of continuously operated grinder. Its disintegration principle uses a roller-plate grinding system with sharp-edged segments, where the compressive and shear forces combine to comminute the particles. Test experiments verified that the grinder disintegrates wet untreated straw to particles below 10mm in an effective manner in a single pass, with an energy requirement of 50 kWht<sup>−1</sup> TS. A 23% increase in biogas yield was achieved, leading to a net gain in electric energy of310 kWht<sup>−1</sup> TS.</p>
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