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The article deals with the creation of a calibration model of lactic acid content in an aqueous solution. The research concept included the preparation of a control tool for the process of modifying the properties of the food fraction for methane fermentation bacteria. The thesis was formulated that it is possible to prepare a systemic solution for real-time observation and monitoring of lactic acid secretion during the digestion of a hydrated mixture of food fractions. The scientific aim of the work was to develop and verify a calibration model of lactic acid content in an aqueous mixture with limited transparency for visible light waves. The research methodology was based on near-infrared spectroscopy with multivariate analysis. Stochastic modeling with noise reduction based on orthogonal decomposition was used. A calibration model was created using Gaussian processes (GP) to predict the lactic acid concentration in an aqueous solution or mixture using an NIR-Vis spectrophotometer. The design of the calibration model was based on absorbance spectra and computational data from selected wavelength ranges from 450 nm to 1900 nm. The measurement data in the form of spectra were limited from the initial wider range (400–2250 nm) to reduce interference. The generated calibration model achieved a mean error level not exceeding 2.47 g∙dm−3 of the identified lactic acid fraction. The coefficient of determination R2 was 0.996. The effect of absorbing the emitter waves was achieved despite the limited transparency of the mixture.

The paper presents an analysis of methods for utilizing digestate for energy purposes from two different biogas plants using different technologies. Biogas plant A used only cattle manure and corn silage as substrates, while biogas plant B used technology based on the utilization of food production waste. The analysis showed differences in the chemical, elemental, and thermogravimetric composition of both types of digestate. An analysis of the energy inputs required to produce fuel from digestate was also performed, along with energy balance calculations. The research and analysis led to the conclusion that both types of digestate are suitable for energy recovery. The possibilities of optimizing the process using excess heat from the biogas plant were also analyzed. In the case of digestate A, the combustion heat of digestate B was 17.20 MJ·kg−1, while for digestate A, it was 14.80 MJ·kg−1. The calorific value of digestate A at 8.79% moisture content was 13.40 MJ·kg−1, while for digestate B at 6.03% moisture content, it was 15.80 MJ·kg−1, respectively.

Biorefining and biorefineries are the future of industry and energy. It is still a long way to complete its implementation, but small biorefineries focused mainly on the production of fuels and energy are more and more frequent in rural areas and large areas located near big cities in which, in addition to fuels and energy, various organic substances of high market value are also produced. In order to optimize biogas production and to control methane fermentation processes, fast and accurate identification of carboxylic acid concentrations, including propionic acid as a precursor to acetic acid, is needed. In this study, a process quality control method was developed to evaluate the propionic acid content of an aqueous solution from the fermentation mass. The proposed methodology is based on near infrared spectroscopy with multivariate analysis and stochastic metamodeling with a denoising procedure based on proper orthogonal decomposition (POD). The proposed methodology uses the Bayesian theory, which provides additional information on the magnitude of the correlation between state and control variables. The calibration model was, therefore, constructed by using Gaussian Processes (GP) to predict propionic acid content in the aqueous solution using an NIR-Vis spectrophotometer. The design of the calibration model was based on absorbance spectra and calculation data from selected wavelength ranges from 305 nm to 2210 nm. Measurement data were first denoised and truncated to build a fast and reliable metamodel for precise identification of the acid content of an aqueous solution at a concentration from 0 to 5.66%. The mean estimation error generated by the metamodel does not exceed 0.7%.

The article explores passive systems for regulating microclimates in residential settings, with a focus on modular constructions. It investigates the use of the trombe wall system for passive ventilation to ensure comfort and hygiene. The study examines building designs that enable effective air circulation without using mechanical systems. Furthermore, the effectiveness of the passive system of using solar energy with the trombe wall as a ventilation device in modular houses has been experimentally confirmed. Although the research confirms the effectiveness of this solar system in modular homes, there is limited documentation regarding its overall efficiency, particularly concerning the impact of the surface pressure coefficient on ventilation. The study establishes the correlations governing the thermosiphon collector’s effectiveness at varying air layer thicknesses. Optimal parameters, such as maximum air consumption (L = 120 m3h−1), are identified at an air layer thickness (δ) of 100 mm and outlet openings area (F) of 0.056 m2. These findings pave the way for improving passive systems aimed at maintaining optimal thermal and air conditions in modern homes. The findings suggest the potential for more efficient and sustainable housing solutions. Further research is essential to understand how factors like building design and wind speed affect ventilation system efficacy.

The aim of this work was to analyze the influence of thermal conditions and the presence of biomass in the chamber on the composting process. The work analyzed the process of the aerobic decomposition of grass, the inoculating fraction and the structure-forming fraction. The analysis covered the batch composting process using veterinary biomass in the treatment chamber. Observations of the process included the following: determining the rate of mineralization, process temperatures, pH, process gas concentrations, chemical composition, physical properties of the compost, and the maturity of the compost. In all analyzed samples, the composting process works correctly in terms of thermal parameters; the obtained fresh compost, after the thermophilic phase has ended, requires action be taken with reference to the values of the seed generation index and the respiration activity (AT4) parameter. After the thermophilic phase, after 60 days of composting, it was noted that for P1 (Probe 1) and P2 (Probe 2) mixtures, the seed germination level decreased below 10%. The AT4 parameter for the P1 and P2 compost samples was between 29.8 and 26.2 mg O2∙g−1. The improvement of the germination level to values in the 30% to 40% range for the maturing compost samples was caused by the thermal conversion of biomass with the regulation of air and water conditions. The phytotoxicity of the compost was overcome, while an improvement in the value of the AT4 index was achieved.

This article considers the distribution of the pressure coefficient on the surface of a modular house model in order to further assess the possibility of operation of a thermosyphon solar collector integrated into the external protection. The experiment was planned to estimate the factors influencing the value of the aerodynamic coefficient. The results of experimental studies conducted in a wind tunnel are presented. The obtained graphical dependences were compared with the results of computer simulations and convergence was evaluated.

Small power generators (up to 5 kW) with a dual-fuel function rely on the use of fuels with standardized quality parameters. The use of gaseous and liquid biofuels, produced by the prosumers themselves, to power the engines of these generators poses the problem of their impact on the operation of the fuel system and on exhaust gas emissions. The goal of this study was to indicate the environmental effects of adapting the internal combustion engine of a 2 kW multi-fuel generator to burn gaseous and liquid biofuels produced by the prosumer. Exhaust emission tests were carried out for the combustion of biogas, methanol, natural gas (methane) and conventional fuel. Forms of propellants that were generated at laboratory scale were used during the tests. Anaerobic organic waste management technologies were used in the tests. Biogas and biomethanol were generated for the tests. A modified SI generator fuel system: pressure reduction and fuel pre-conditioning, was tested burning gasoline, methanol, biogas and natural gas with 98% methane content. Exhaust gas emission tests in three operating states (idle, 50% load, 100% load) indicated CO2, CO, NOx and HC emission levels. The feasibility of using renewable fuels in a low-power generator was demonstrated, as well as the correct operation of the author’s system for supplying the generator with gaseous fuels. In the case of bioethanol, better complete combustion of the fuel was achieved than with gasoline, which was characterized by, among other things, 20% lower carbon monoxide emissions at full load. NOx emissions from the combustion of bioethanol compared to gasoline were 1.75 times lower at full load, and HC emissions were almost twice as low. In the case of biogas, there were significant carbon dioxide emissions due to the high carbon dioxide content of the fuel (40%). The other emission results for biogas were not significantly different from those from natural gas combustion.

This article aims to present the results of research on anaerobic digestion (AD) of waste wafers (WF-control) and co-substrate system—waste wafers and cheese (WFC-control), combined with digested sewage sludge. The aim of this study was to assess the physicochemical parameters of the diatomaceous earth/peat (DEP; 3:1) carrier material and to verify its impact on the enzymatic activity and the process performance. The experiment was conducted in a laboratory, in a periodical mode of operation of bioreactors, under mesophilic conditions. The results of analyses of morphological-dispersive, spectroscopic, adsorption, thermal, and microbiological properties confirmed that the tested carrier material can be an excellent option to implement in biotechnological processes, especially in anaerobic digestion. As part of the experiment, the substrates, feedstock, and fermenting slurry were subjected to the analysis for standard process parameters. Monitoring of the course of AD was performed by measuring the values of key parameters for the recognition of the stability of the process: pH, VFA/TA ratio (volatile fatty acids/total alkalinity), the content of NH4+, and dehydrogenase activity, as an indicator of the intensity of respiratory metabolism of microorganisms. No significant signals of destabilization of the AD process were registered. The highest dehydrogenase activity, in the course of the process, was maintained in the WFC + DEP system. The microbial carrier DEP, used for the first time in the anaerobic digestion, had a positive effect on the yield of methane production. As a result, an increase in the volume of produced biogas was obtained for samples fermented with DEP carrier material for WF + DEP by 13.18% to a cumulative methane yield of 411.04 m3 Mg−1 VS, while for WFC + DEP by 12.85% to 473.91 m3 Mg−1 VS.

The manner of storage of sugar beets largely influences their physical and chemical properties, which may subsequently determine their biochemical methane potential. In this study, samples of fresh sugar beets as well as beets stored in two ways—in airtight conditions and in an open-air container—were tested. In both cases, measurements were taken on specific dates, i.e., after 4, 8, 16 and 32 weeks of storage. A decrease in pH was observed in all samples, with the lowest decrease occurring in hermetically stored samples. The lowest pH value of 3.71 was obtained for sugar beets stored in an open-air container after 32 weeks of storage. During storage, a gradual decrease in total solids was also recorded along with accompanying losses of organic matter, more significant in the case of storage in an open-air container. In subsequent storage periods, the biogas/methane production efficiency differed slightly for both methods. The highest volume of biogas was obtained for fresh sugar beets—148.23 mL·g−1 fresh matter (FM)—and subsequently in the 8th and 16th weeks of storage: 139.35 mL·g−1 FM (H—airtight conditions) and 144.14 mL·g−1 FM (O—open-air container), and 147.58 H mL·g−1 FM (H) and 148.22 mL·g−1 FM (O), respectively. The storage period affected the time of anaerobic decomposition of the organic matter—fresh sugar beets took the longest to ferment (26 days), while the material stored for 32 weeks took the shortest to ferment. In the experiment, the content of selected organic compounds in individual samples, i.e., sugar, methanol, ethanol, lactic acid and acetic acid, was also analysed. Within these results, significant differences were found between the samples stored using the two different methods. A high content of sugar, methanol, ethanol and other chemical compounds in the “O” materials showed the hydrolysis and acidogenesis processes taking place in an open-air container, with the participation of catalytic microorganisms.

The article aims to present results of research on anaerobic digestion (AD) of waste wafers (WF-control) and co-substrate system–waste wafers and cheese (WFC-control), combined with digested sewage sludge, as inoculum. The purpose of this paper is to confirm the outcome of adding silica/lignin (S/L; 4:1) material, as a microbial carrier, on the process performance and genetic diversity of microbial communities. The experiment was conducted in a laboratory under mesophilic conditions, in a periodical operation mode of bioreactors. Selected physicochemical parameters of the tested carrier, along with the microstructure and thermal stability, were determined. Substrates, batches and fermenting slurries were subjected to standard parameter analysis. As part of the conducted analysis, samples of fermented food were also tested for total bacterial count, dehydrogenase activity. Additionally, DNA extraction and next-generation sequencing (NGS) were carried out. As a result of the conducted study, an increase in the volume of produced biogas was recorded for samples fermented with S/L carrier: in the case of WF + S/L by 18.18% to a cumulative biogas yield of 833.35 m3 Mg−1 VS, and in the case of WFC + S/L by 17.49% to a yield of 950.64 m3 Mg−1 VS. The largest total bacterial count, during the process of dehydrogenase activity, was maintained in the WFC + S/L system. The largest bacterial biodiversity was recorded in samples fermented with the addition of cheese, both in the case of the control variant and in the variant when the carrier was used. In contrast, three phyla of bacteria Firmicutes, Proteobacteria and Actinobacteria predominated in all experimental facilities.