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The need to pre-treat lignocellulosic biomass prior to dark fermentation results primarily from the composition of lignocellulose because lignin hinders the processing of hard wood towards useful products. Hence, in this work a two-step approach for the pre-treatment of energy poplar, including alkaline pre-treatment and enzymatic saccharification followed by fermentation has been studied. Monoethanolamine (MEA) was used as the alkaline catalyst and diatomite immobilized bed enzymes were used during saccharification. The response surface methodology (RSM) method was used to determine the optimal alkaline pre-treatment conditions resulting in the highest values of both total released sugars (TRS) yield and degree of lignin removal. Three variable parameters (temperature, MEA concentration, time) were selected to optimize the alkaline pre-treatment conditions. The research was carried out using the Box-Behnken design. Additionally, the possibility of the re-use of both alkaline as well as enzymatic reagents was investigated. Obtained hydrolysates were subjected to dark fermentation in batch reactors performed by Enterobacter aerogenes ATCC 13048 with a final result of 22.99 mL H2/g energy poplar (0.6 mol H2/mol TRS).

Abstract:Pre-treatment is a significant step in the production of second-generation biofuels from waste lignocellulosic materials. Obtaining biofuels as a result of fermentation processes requires appropriate pre-treatment conditions ensuring the highest possible degree of saccharification of the feed material. An influence of the following process parameters were investigated for alkaline pre-treatment of Salix viminalis L.: catalyst concentration (NaOH), temperature, pre-treatment time and granulation. For this purpose, experiments were carried out in accordance to the Box-Behnken design for four factors. In the saccharification process of the pre-treated biomass, cellulolytic enzymes immobilized on diatomaceous earth were used. Based on the obtained results, a mathematical model for the optimal conditions of alkaline pre-treatment prediction is proposed. The optimal conditions of alkaline pre-treatment are established as follows: granulation 0.75 mm, catalyst concentration 7%, pre-treatment time 6 h and temperature 65 • C if the saccharification efficiency and cost analysis are considered. An influence of the optimized pre-treatment on both the chemical composition and structural changes for six various lignocellulosic materials (energetic willow, energetic poplar, beech, triticale, meadow grass, corncobs) was investigated. SEM images of raw and pre-treated biomass samples are included in order to follow the changes in the biomass structure during hydrolysis.

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This paper presents the theoretical screening of 23 low-cost deep eutectic solvents (DESs) as absorbents for effective removal of the main impurities from biogas streams using a conductor-like screening model for real solvents (COSMO-RS). Based on thermodynamic parameters, i.e., the activity coefficient, excess enthalpy, and Henry’s constant, two DESs composed of choline chloride: urea in a 1:2 molar ratio (ChCl:U 1:2), and choline chloride: oxalic acid in a 1:2 molar ratio (ChCl:OA 1:2) were selected as the most effective absorbents. The σ-profile and σ-potential were used in order to explain the mechanism of the absorptive removal of CO2, H2S, and siloxanes from a biogas stream. In addition, an economic analysis was prepared to demonstrate the competitiveness of new DESs in the sorbents market. The unit cost of 1 m3 of pure bio-methane was estimated to be in the range of 0.35–0.37 EUR, which is comparable to currently used technologies.

This paper concerns the comparison of the efficiency of two-stage hydrolysis processes, i.e., alkaline pre-treatment and acid hydrolysis, as well as alkaline pre-treatment followed by enzymatic hydrolysis, carried out in order to obtain reducing sugars from triticale straw. For each of the analyzed systems, the optimization of the processing conditions was carried out with respect to the glucose yield. For the alkaline pre-treatment, an optimal catalyst concentration was selected for constant values of temperature and pre-treatment time. For enzymatic hydrolysis, optimal process time and concentration of the enzyme preparation were determined. For the acidic hydrolysis, performed with 85% phosphoric acid, the optimum temperature and hydrolysis time were determined. In the hydrolysates obtained after the two-stage treatment, the concentration of reducing sugars was determined using HPLC. The obtained hydrolysates were subjected to ethanol fermentation. The concentrations of fermentation inhibitors are given and their effects on the alcoholic fermentation efficiency are discussed.

Processing of lignocellulosic biomass includes four major unit operations: pre-treatment, hydrolysis, fermentation and product purification prior to biofuel generation via anaerobic digestion. The microorganisms involved in the fermentation metabolize only simple molecules, i.e., monosugars which can be obtained by carrying out the degradation of complex polymers, the main component of lignocellulosic biomass. The object of this paper was to evaluate the saccharification conditions and identify the process parameters that should be applied to improve the saccharification efficiency of lignocellulosic biomass, defined as the simple sugars concentration, which was considered as a crucial parameter for hydrogen generation via dark fermentation. Drawing global conclusions about the occurring changes in the biomass requires learning about the nature of the biomass structure and composition at different stages of the process. Therefore, techniques for analysis, as FTIR, HPLC and SEM were applied. The experiment was planned employing Box-Behnken design. The advantageous operating conditions and the composition of saccharification enzymatic cocktail were identified and their values occurred similar in the applied border conditions for all tested biomass types. Analysis of the intermediate solid and liquid streams generated during the pre-treatment procedure revealed several structural and compositional changes in the biomass.

Volatile organochlorine compounds (VOXs) presented in biogas can cause many technological and environmental problems. During the combustion of biogas containing VOXs, the corrosion of installation, as well as the formation...