This paper introduces a novel approach to optimization of the anaerobic co-digestion (AcoD) process by developing enriched versions of first-order kinetic, modified Gompertz, and single-stage combined kinetic models. The key innovation of these enriched models lies in the introduction of new kinetic parameters that depend on both temperature and substrate composition, resulting in a set of new model parameters. These parameters are calibrated simultaneously across various process conditions, unlike existing models where kinetic constants are calibrated for only one operating regime. The enriched models are successfully calibrated and validated with experimental data from a batch AcoD of chicken manure with sawdust and fungal-pretreated Miscanthus; the relative index of agreement is higher than 0.99 for the produced biogas under all considered process conditions. By using the calibrated models to optimize the substrate composition and the AcoD process temperature profile, the results indicate that biogas production can increase by up to 50 %. Moreover, the proposed optimization allows for a favorable cost-benefit ratio; the estimated net energy gain can increase by up to 40 %. The proposed enriched models enable accurate prediction of biogas production at various process conditions and optimization of the AcoD process, representing a significant advancement over existing empirical models.

The esterification reaction of oleic acid with methanol practically does not occur at the temperature of most current industrial processes. If you raise the temperature, significant conversion occurs only above 200°C and after several hours. For the above reasons, all of today's industrial oleic acid esterification technologies are based on catalyzed esterification. Catalysts based on silicates are often used as catalysts in the mentioned reactions because they are cheap, easy to synthesize, insoluble in most organic solvents, and recyclable. In this work, modified mesopo-rous silica SBA-15 was used, which is suitable for a wide range of organic reactions. The effect of the amount of this catalyst on the yield of the esterification reaction was studied. It has been shown that with an increase in the amount of catalyst, the degree of conversion, i.e. the yield of methyl oleate, increases.

In the chapter, milk fermentation for kefir production is studied. The traditional kefir production process based on inoculating kefir grains into milk is considered. The quality and quantity of the produced kefir also depend on the dynamics of the fermentation process. The chapter presents the design and synthesis of the closed-loop control system in which changing the bioreactor’s temperature is used to control the time course of the concentration of dissolved CO2. In the chapter: (1) a nonlinear dynamic mathematical model of the fermentation process, which allows evaluating the influence of the bioreactor’s temperature on the dynamics of the fermentation process, is presented; (2) the design and synthesis of a conventional linear control system with constant parameters are carried out; (3) an adaptive control system that enables the tracking of the courses of the quantities of the fermentation process to the desired reference trajectories without the time-consuming preliminary identification of the parameters of the fermentation process model is developed. The numerical, experimental, and analytic outcomes of the study are presented.

In this research catalyzed degradation of polyethylene terephthalate was performed. For that purpose, ZSM-5 zeolite was synthesized as an acid catalyst. For its characterization N2 adsorption, scanning electron microscopy, NH3 temperature programmed desorption, differential scanning calorimetry, thermogravimetric analysis, dynamic light scattering, and Fourier transform infrared spectroscopy were utilized. Degradation reactions were performed in high pressure crucibles using differential scanning calorimeter at different temperatures (200, 250 and 300) °C and time intervals (2.5, 5, 10 and 15) min. Samples were analyzed using high performance liquid chromatography coupled with UV-VIS detector. The results revealed that the highest conversion was achieved at 300 °C and 10 min. The analysis of obtained results showed that despite the differences in conversions being not as high as expected, reactions with the catalyst were slightly more effective than without it. For the future work, we plan to finetune the synthesis procedure to obtain more active catalyst. And for the upgrade of the study the kinetic analysis of the reaction will be conducted.

The usability of glass fibers as immobilization support with a porous open structure was investigated. We developed a method to immobilize the enzyme β-galactosidase on special glass fiber rolls. The new method is simple, non-expensive and industrially applicable. Glutaraldehyde was used as a non-specific cross-linking agent for the covalent binding of β-galactosidase on modified glass fibers. The efficiency of immobilization was tested with the known hydrolysis of lactose. All experiments were performed in a continuous laboratory reactor. The influence of the reaction temperature (20, 25 and 30 °C), the substrate flow rate (1, 2 and 3 mL/min) and the pH of the reaction medium (6, 7 and 8) on the conversion was investigated. The reaction efficiency was monitored by measuring the glucose concentration with a spectrophotometer. High immobilization efficiency, enzyme activity and stability were obtained. The optimal reaction temperature, substrate flow rate and pH were found. The activity and stability of the enzyme entrapped on the glass fiber rolls remained almost unchanged during reuse, which is promising for potential industrial applications.

Catalysis and catalysts play an important role in modern technology. Catalysis means a change in the rate of a chemical reaction under the influence of a substance that does not change chemically as a result of the reaction. This substance is called a catalyst. The catalyzed reaction proceeds on a different reaction path than the uncatalyzed reaction, thanks to the participation of the catalyst. The reactants are absorbed on the surface of the catalyst, and then a mutual reaction of the adsorbed species occurs. The reaction produc- es a product that is desorbed from the surface, while the catalyst remains unchanged and ready for a new reaction cycle. An important piece of information for evaluating the quality of a catalyst is the rate of the reaction in which it participates. The subject of kinetic research is the study of the influence of process pa- rameters on the reaction rate. It is safe to say that the study of reaction kinetics is a central part of chemical reaction engineering. Therefore, the study of the kinetics of real heterogeneous catalysts is of particular im- portance, both for the improvement of existing catalysts and for the development of new ones. These tests involve determining the influence of process parameters such as the type of catalyst present, temperature, pressure, and concentration of reactants and products on the reaction rate. In this work, the influence of the mass of the catalyst at a certain temperature on the rate constant of the chemical reaction of esterification of oleic acid with methanol was studied. The catalyst used was mesoporous silica, an amorphous solid that can be obtained by drying hydrogels. It was found that as the mass of the catalyst increases, the rate of the chemical reaction constant also increases, i.e. the rate of the esterification reaction increases.

Kombucha tea is produced by fermenting sweetened tea with a mixture of a symbiotic colony of bacteria and yeast. As it is consumed almost all over the world transport of the kombucha starter is very important. Besides controlled transport conditions, the storage conditions before delivery can have a significant impact on the final quality of this beverage. The aim of this study was to determine the influence of storage time and temperature of the kombucha starter on the activation rate and quality of the final product. The pH value, CO2 and sugar concentrations in the fermentation media were monitored during the fermentation. We used starters with different ages, 1 year, half a year and fresh ones. Kombucha starter cultures were frozen, refrigerated, stored at room temperature and at 40 °C for 72 h, to investigate the impact of the storage temperature. Some differences were detected in the quality of the final product using kombucha starters with different ages. On the other hand, the results obtained after changing the storage temperature of the starter show that higher temperature accelerates the fermentation. The final product has higher CO2 concentration, lower sugar content and lower pH value compared to the product which was produced using frozen and refrigerated starter cultures. The novel finding of this study revealed that storage time and storage temperature of a kombucha starter is important for production of this slightly alcoholic beverage. This could be useful information for distributors of that specific starter culture.

Kinetics of hydrothermal degradation of colorless polyethylene terephthalate (PET) waste was studied at two temperatures (300 °C and 350 °C) and reaction times from 1 to 240 min. PET waste was decomposed in subcritical water (SubCW) by hydrolysis to terephthalic acid (TPA) and ethylene glycol (EG) as the main products. This was followed by further degradation of TPA to benzoic acid by decarboxylation and degradation of EG to acetaldehyde by a dehydration reaction. Furthermore, by-products such as isophthalic acid (IPA) and 1,4-dioxane were also detected in the reaction mixture. Taking into account these most represented products, a simplified kinetic model describing the degradation of PET has been developed, considering irreversible consecutive reactions that take place as parallel in reaction mixture. The reaction rate constants (k1–k6) for the individual reactions were calculated and it was observed that all reactions follow first-order kinetics.

Fermentation is a crucial bioengineering process, existentially important for modern society. The most commonly used production unit for this process is the batch bioreactor. Its main advantage is unsophisticated construction, which unfortunately results in its incapability of controlling the transient state of the fermentation process. Control of the fermentation can significantly improve the quality of the product and the economy of the process; therefore, it is useful for bioreactors to be equipped with a control system. Based on the experimental results, we used an optimization method to identify a mathematical model that describes the impact of the bioreactor's temperature on the fermentation's transient process. The obtained model was applied for the design and synthesis of the closed-loop control system. Simulations and experiments confirmed the effectiveness of the proposed control system. In this way, we can ensure the consistent quality of the produced probiotic product, increase the amount of the product, and shorten the fermentation time. The original results display the feasibility of the closed-loop control of the batch bioreactor's fermentation process by changing the temperature. So far, the process has been carried without a closed-loop control system. The problem is current and has not yet been solved sufficiently. There are many attempts published; one of the last shows the possibility of controlling the fermentation process by changing the oxygen supply, which is more complex and expensive for realization than the solution from our study.

Knowledge of the mathematical models of the fermentation processes is indispensable for their simulation and optimization and for the design and synthesis of the applicable control systems. The paper focuses on determining a dynamic mathematical model of the milk fermentation process taking place in a batch bioreactor. Models in the literature describe milk fermentation in batch bioreactors as an autonomous system. They do not enable the analysis of the effect of temperature changes on the metabolism during fermentation. In the presented extensive multidisciplinary study, we have developed a new mathematical model that considers the impact of temperature changes on the dynamics of the CO2 produced during fermentation in the batch bioreactor. Based on laboratory tests and theoretical analysis, the appropriate structure of the temperature-considered dynamic model was first determined. Next, the model parameters of the fermentation process in the laboratory bioreactor were identified by means of particle swarm optimization. Finally, the experiments with the laboratory batch bioreactor were compared with the simulations to verify the derived mathematical model. The developed model proved to be very suitable for simulations, and, above all, it enables the design and synthesis of a control system for batch bioreactors.

Animal waste is generated at an increased rate, and its disposal is attracting wide public attention. Anaerobic digestion is considered the most promising option for reducing this waste, and simultaneously, it produces renewable energy. Lignin contained in lignocellulosic biomass is hardly biodegradable, thus pre-treatment has to be considered prior to digestion. The possibility of biological pre-treatment of chicken manure with sawdust using Pleurotus ostreatus fungi was investigated in our study. This animal waste was used as a substrate for further biogas production. To provide a better nutrient balance, we added two different co-substrates, wheat straw and Miscanthus. Mixtures with different mass ratios of chicken manure with sawdust/ordinary wheat straw, as well as chicken manure with sawdust/pre-treated wheat straw were incubated for 30 d. The same experiments were performed with Miscanthus. During incubation, samples were taken at predetermined time intervals, and the concentration of acid-insoluble lignin was determined. Additionally, concentrations of glucose and xylose in the filtrate taken at the end of the Klasson procedure were determined in the initial samples and in the samples after 30 d of incubation. Despite our expectations, almost no lignin degradation was observed. Insignificant decreases in glucose and xylose concentrations after 30 d is attributed to fungi ingestion. Obtained results show that Pleurotus ostreatus, as a white-rot fungi with a unique enzymatic system and as generally preferred organisms for lignin degradation, is, therefore, not suitable for delignification of this particular animal waste.

The present study investigates the possibility to increase methane production during the anaerobic digestion of different mass ratios of chicken manure with sawdust to barley straw pre-treated with two fungal strains, Pleurotus ostreatus and Trametes versicolor. Ordinary barley straw was used as a control. Digestions were performed in laboratory equipment. Results showed that the mixture of chicken manure with sawdust to ordinary barley straw generally produced the highest volume of biogas at all mass ratios; only the mixture of chicken manure with sawdust to barley straw pre-treated with Pleurotus ostreatus fungi at mass ratio 50:50 produced slightly more biogas. The least biogas was produced during digestion of mixture of chicken manure with sawdust to barley straw pre-treated with Trametes versicolor fungi at mass ratio 60:40. Final concentrations of methane were more or less the same for all mixtures, regardless of whether the substrates were overgrown by fungi or not. We conclude that biological pre-treatment with selected white-rot fungi strain is not a proper choice to increase methane production.

This paper presents the advanced control theory's original utilisation to realise a system that controls the fermentation process in batch bioreactors. Proper fermentation control is essential for quality fermentation products and the economical operation of bioreactors. Batch bioreactors are very popular due to their simple construction. However, this simplicity presents limitations in implementing control systems that would ensure a controlled fermentation process. Batch bioreactors do not allow the inflow/outflow of substances during operation. Therefore, we have developed a control system based on a stirrer drive instead of material flow. The newly developed control system ensures tracking of the fermentation product time course to the reference trajectory by changing the stirrer's speed. Firstly, the paper presents the derivation of the enhanced mathematical model suitable for developing a control system. A linearisation and eigenvalue analysis of this model were made. Due to the time-consuming determination of the fermentation model and the variation of the controlled plant during operation, the use of adaptive control is advantageous. Secondly, a comparison of different adaptive approaches was made. The model reference adaptive control was selected on this basis. The control theory is presented, and the control realisation described. Experimental results obtained with the laboratory batch bioreactor confirm the advantages of the proposed adaptive approach compared to the conventional PI-control.

In this paper, modelling and control of a batch bioreactor is studied. A main disadvantage of batch bioreactors compared to other types of bioreactors is their inability to introduce biological or/and chemical substances during operation. Therefore, possibility of bioreactor's control by means of changing temperature was proposed, analyzed, and implemented. A new supplementary input/output dynamical mathematical model, which considers influence of heating and cooling on a bioprocess, was developed. On a basis of this model, a control system was designed and a method for tuning of the controller was suggested. Results show characteristics, applicability, and advantages of the presented approach.

The goal of this study was to determine the kinetic parameters of methane production during anaerobic fermentation of mixtures of chicken manure with sawdust and wheat straw overgrown with fungi. Pretreatment of wheat straw was carried out with Pleurotus ostreatus and Trametes versicolor white-rot fungi. Mixtures of chicken manure with sawdust and wheat straw overgrown with fungi at different mass ratios (50:50, 60:40 and 80:20) were used as a substrate for anaerobic fermentation. For the control, ordinary wheat straw was used. Anaerobic fermentations were performed at (35, 40 and 45) degrees C. An individual process of anaerobic fermentation was maintained at constant temperature for 21 days. During the process, the volume and concentration of biogas produced were monitored. The most biogas produced was recorded for the straw overgrown with Pleurotus ostreatus fungi (ratio 50:50) at 45 degrees C, and the least in the case of straw overgrown with Trametes versicolor fungi (ratio 80:20) at 35 degrees C. At the beginning of anaerobic fermentation, the methane concentration increased faster at a higher temperature, while after 21 days, it was between 53 and 56% regardless of temperature. (C) 2019 Elsevier Ltd. All rights reserved.

2. mednarodna konferenca Tehnologije in poslovni modeli za krožno gospodarstvo (Zbornik referatov). Fakulteta za kemijo in kemijsko tehnologijo Univerze v Mariboru je organizirala 2. mednarodno strokovno/znanstveno konferenco Tehnologije in poslovni modeli za krožno gospodarstvo (Technologies & Business Models for Circular Economy; TBMCE), ki je potekala od 24. do 25. oktobra 2019 v Grand Hotelu Bernardin v Portorožu. TBMCE 2019 je bila namenjena predstavitvi konceptov krožnega gospodarstva in tehnologij ter metodologij, ki prispevajo k preusmeritvi gospodarskih subjektov in družbe kot celote k bolj odgovornemu, tj. krožnemu ravnanju z viri. V zborniku so predstavljeni prispevki s tem konference, ki so bile: trajnostna energija, biomasa in alternativne surovine, krožni poslovni modeli, sekundarne surovine in funkcionalni materiali, IKT v krožnem gospodarstvu, procesi in tehnologije. Konferenca je potekala pod pokroviteljstvom Ministrstva za gospodarski razvoj in tehnologijo.

The aim of our work was to synthesize a sulfonic acid functionalized SBA-15 catalyst in a single step process. For the characterization, we used nitrogen adsorption–desorption (BET), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), dynamic light scattering (DLS), and thermogravimetric analysis (TGA). The effectiveness of the synthesized solid acid catalyst was checked on a model esterification reactions of benzoic and myristic acid with methanol. All reactions were carried out in an automated batch reactor system at different temperatures and different mass of the catalyst. The benzoic acid esterification catalysed with the functionalized catalyst SBA-15 was successfully described by the first order kinetic expression and myristic acid by the Langmuir–Hinshelwood–Hougen–Watson model.

BACKGROUNDMilk fermentation takes place in the presence of various micro-organisms, producing a variety of dairy products. The oldest of them is kefir, which is usually produced by the fermentation of milk with kefir grains. Carbon dioxide (CO2 ), as one of the process products, also contributes to the characteristic flavor of kefir. The amount of CO2 generated during fermentation depends on bioprocessing conditions and may change, which is not desirable at the industrial level.RESULTSIn this study we developed a simplified mathematical model of CO2 release in the milk-fermentation process. An intuitive approach based on superposition and experimental analysis was used for the modeling. The chemical system studied was considered as a two-input (temperature, rotational frequency of the stirrer) one-output (CO2 concentration) dynamic system.CONCLUSIONBased on an analysis of CO2 release transients in the case of non-simultaneous stepwise changed input quantities, two differential equations were defined that describe the influence of the two input quantities on the output quantity. The simulation results were verified by experiments. The proposed model can be used for a comprehensive analysis of the process that is being studied and for the design and synthesis of advanced control systems, which will ensure a controlled CO2 release at the industrial level. © 2018 Society of Chemical Industry.

ABSTRACT In our study, we synthesized two types of solid acid catalysts. Silica gel with a particle size of 0.063–0.2 mm was silanized first at reflux (S1) and second at room temperature (S3) using (3-mecaptopropyl)trimethoxysilane in toluene, and further oxidized with H2O2, and methanesulfonic acid. Characterization of the synthesized catalysts was performed using adsorption/desorption of nitrogen (BET), Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. Both catalysts were used in esterification reactions of benzoic acid with methanol. All reactions were performed in a batch reactor at temperatures, ϑ = 55, 60, and 64.5°C, stirrer speed, fs = 400 min−1, and catalyst loading, m = 5, 10, and 15 g. The concentration of produced methylbenzoate was determined by HPLC. The study was supplemented with a kinetic study of the reaction. First-order kinetics was confirmed for this esterification reaction. Using catalyst S1, higher conversion was reached, while catalyst S3 is much more suitable for reuse.