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Abstract: With the world facing the twin pressures of a warming climate and an ever-increasing amount of waste, it is becoming increasingly clear that we need to rethink the way we generate energy and use materials. Despite growing awareness, our energy systems are still largely dependent on fossil fuels and characterized by a linear ‘take-make-dispose’ model. This leaves us vulnerable to supply disruptions, rising greenhouse gas emissions, and the depletion of critical raw materials. Hydrogen is emerging as a potential carbon-free energy vector that can overcome both challenges if it is produced sustainably from renewable sources. This study reviews hydrogen production from a circular economy perspective, considering industrial, agricultural, and municipal solid waste as a resource rather than a burden. The focus is on the reuse of waste as a catalyst or catalyst support for hydrogen production. Firstly, the role of hydrogen as a new energy carrier is explored along with possible routes of waste valorization in the process of hydrogen production. This is followed by an analysis of where and how catalysts from waste can be utilized within various hydrogen production processes, namely those based on using fossil fuels as a source, biomass as a source, and electrocatalytic applications.
Keywords: hydrogen production, waste-derived catalysts, renewable energy, biomass conversion
Published in DKUM: 25.09.2025; Views: 0; Downloads: 7
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Abstract: Pistachio and walnut shells accumulate in large quantities as waste during food processing and represent a promising lignocellulosic biomass for the extraction of valuable components. Subcritical water technology was used as an environmentally friendly technique to study the extraction of active ingredients and other valuable degradation products from walnut and pistachio waste. Subcritical water extraction (SWE) was carried out under different process conditions (temperature (150–300 ◦C) and short reaction times (15–60 min)) and compared with conventional extraction using different organic solvents (acetone, 50% acetone and ethanol). The extracts obtained from pistachio and walnut shell waste are rich in various bioactive and valuable components. The highest contents of total phenols (127.08 mg GA/g extract at 300 ◦C for 15 min, from walnut shells), total flavonoids (10.18 mg QU/g extract at 200 ◦C for 60 min, from pistachio shells), total carbohydrates (602.14 mg TCH/g extract at 200 ◦C for 60 min, from walnut shells) and antioxidant activity (91% at 300 ◦C, for 60 min, from pistachio shells) were determined when the extracts were obtained via subcritical water. High contents of total phenols (up to 86.17 mg GA/g extract) were also determined in the conventional extracts obtained with ethanol. Using the HPLC method, sugars and their valuable derivatives were determined in the extracts, with glucose, fructose, furfurals (5-hydroxymethylfurfural (5-HMF) and furfural) and levulinic acid being the most abundant in the extracts obtained by subcritical water. The results show that subcritical water technology enables better exploitation of biowaste materials than conventional extraction methods with organic solvents, as it provides a higher yields of bioactive components such as phenolic compounds and thus extracts with high antioxidant activity, while at the same time producing degradation products that are valuable secondary raw materials.
Keywords: pistachio shells, walnut shells, subcritical water extraction, conventional extraction, waste biomass, valuable compounds, sugars, furfurals
Published in DKUM: 01.07.2025; Views: 0; Downloads: 8
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Abstract: The environment hosts a diversity of microorganisms whose potential for biotechnological applications has not yet been exhausted. The quest of our study was to find isolates of Pichia kudriavzevii from the environment that could be used as new biotechnological agents. Moreover, we aimed to explore the resource efficiency for microbial cultivation, in particular the efficiency of spent coffee grounds (SCG), an easily accessible waste coffee product with a high unutilized organic content. In this study, Pichia kudriavzevii strain ZMUM_K002, a yeast strain isolated from a grape pomace compost, was investigated. Antifungal susceptibility, particularly fluconazole susceptibility, was assessed, and the strain’s biotechnological potential by comparing its ability to utilize low-cost carbon sources, including SCG, with a natural isolate of Saccharomyces cerevisiae (strain ZMUM_K003) was assessed. The P. kudriavzevii strain ZMUM_K002 exhibited higher fluconazole susceptibility and yielded more than 30% more biomass in optimized media formulations compared to S. cerevisiae ZMUM_K003. These findings demonstrate that P. kudriavzevii ZMUM_K002 has the potential for efficient biomass production in sustainable industrial biotechnology, particularly in processes requiring high biomass yields on alternative substrates.
Keywords: Pichia kudriavzevii, Candida krusei, environmental sampling, biomass production, sauerkraut, safety assessment, spent coffee grounds
Published in DKUM: 21.03.2025; Views: 0; Downloads: 8
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Abstract: Lignocellulosic biomass has been widely recognized as a renewable feedstock that has enormous potential for the production of bio-based fuels and platform chemicals. Obtained from the dehydration of sugars, 5-hydroxymethylfurfural (HMF) in particular has received extensive consideration due to its diverse functionality and versatility. However, despite its potential, major technical and economic challenges still need to be addressed before HMF valorization technologies can be competitive with current processes that rely on fossil fuels. This doctoral study specifically focuses on the catalytic hydrogenation of HMF into various platform chemicals while utilizing nickel-based catalysts. The overall goal of this dissertation is to advance these technologies through innovative catalyst design and catalyst characterization techniques that allowed for a systematic investigation into the major catalyst surface properties that influence activity and product selectivity. Various characterization techniques were applied to acquire relevant catalyst surface and structural properties including temperature-programmed reduction, temperature-programmed desorption, X-ray powder diffraction, and transition electron microscopy, N2 physisorption, and diffuse reflectance infrared Fourier transform spectroscopy. A detailed kinetic model was also established that takes into account the number of metallic active sites that provides comparative kinetic parameters to better understand catalyst activity. The main discoveries obtained during this doctoral thesis include the determination of the critical influence that the support material has on catalyst activity and tuning the reaction network. Particularly, it was found that carbon as a relatively neutral support was effective for hydrodeoxygenation, however, an alumina support was necessary to activate the furan ring and facilitate ring saturation and ring opening reactions. The solvent system was also found to be impactful where incorporating water as a co-solvent completely eliminated all dehydration side reactions. Structural-activity correlations indicate that both acid and basic active sites could play a pivotal role in dictating between the two competing reactions of ring saturation and ring opening. The results presented in this doctoral dissertation provide crucial details for more optimal catalyst design and operating conditions for the effective conversion of 5-hydroxymethylfurfural via hydrogenation for the purpose of advancing sustainable bio-based chemical production.
Keywords: biomass, catalysis, kinetics, hydrogenation, 5-hydroxymethylfurfural
Published in DKUM: 19.09.2024; Views: 0; Downloads: 19
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Abstract: In this work, the thermochemical properties of municipal solid waste (MSW) are studied using the torrefaction process as the main method for investigation. Torrefaction experiments were carried out using an electric laboratory furnace, at temperatures of 200, 250, and 300 °C. The residence time was set to 90 min. Proximate and ultimate analysis were performed on the torrefied MSW samples and compared with the properties of the raw MSW samples. In addition, the thermal properties of the obtained torrefied MSW samples were evaluated by thermogravimetric analysis (TGA) and derivative thermogravimetric analysis (DTG). The following could be stated: the obtained results showed that mass and energy yields (MY and EY, respectively) decrease with increasing when torrefaction temperature, while the heating values (HHV) increased under the same conditions (from 24.3 to 25.1 MJ/kg). Elemental analysis showed an increase in carbon content (C), from 45.7 ± 0.9 to 52.8 ± 1.05 wt.%, and decrease in oxygen content (O), from 45.6 ± 0.9 to 39.5 ± 0.8 wt.%, when torrefaction temperature is increased, which is consistent with the general definition of the torrefaction process. In addition, enhancement factors (EFs) and fuel ratios (FRs) were calculated, which ranged from 1.00 to 1.02 and 0.16 to 0.23, respectively. Some anomalies were observed during the thermal analysis, which are assumed to be related to the composition of the selected MSW. This study therefore shows that torrefaction pretreatment can improve the physicochemical properties of raw MSW to a level comparable to coal, and could contribute to a better understanding of the conversion of MSW into a valuable, solid biofuel.
Keywords: biomass, municipal solid waste, torrefication, energy yield, thermogravimetric analysis
Published in DKUM: 10.05.2024; Views: 255; Downloads: 27
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