1. Zero-waste strategy of small wastewater treatment plants with integrated thermal treatment of generated solid wastesDanijela Urbancl, Christoph Hochenauer, Angelika Michaela Zachl, Nika Fekonja, Aleksandra Petrovič, Darko Goričanec, Marjana Simonič, 2025, original scientific article Abstract: The aim of the study was to analyse two small wastewater treatment plants (SWTPs) and compare their treatment performance with the aim of developing a zero-waste strategy. The analyses showed that the second wastewater treatment plant had a problem with an increased phosphorus concentration in the wastewater as well as fluctuations in nitrogen removal. One of the key aspects was the recovery of phosphorus in the form of struvite precipitated on zeolite, which can be used as a fertiliser due to its significant nutrient content. The main benefit of the same SWTP is the separate collection of cellulosic material (labelled as sample RS), which has the potential for reuse as biochar, while from the first SWTP the sludge sample (labelled as sample SS) was taken and torrefied for comparison with RS. Both samples were torrefied at 250 ◦C and 350 ◦C in nitrogen and carbon dioxide atmospheres. The RS products obtained in CO2 atmosphere at 350 ◦C showed the best biochar properties, as they had a higher heating value (HHV) and a higher C content. Elemental analysis showed that the carbon content in RS and SS increased from 43 to 65 % and from 35 to 39 %, respectively. Measurement of the HHV of the torrefied RS product showed an increase from 17 to 26 MJ/kg, while for SS it increased from 15 to 17 MJ/kg. The comprehensive combustion index and the EMCI index show higher values for the RS samples torrefied at 350 ◦C. The H/C and O/C ratios are favourable for these samples, as the high quality of torrefied biomass is associated with the highest prices on the market. According to the TGA and FTIR analysis, the type of torrefaction atmosphere, in contrast to the torrefaction temperature, has little influence on the subsequent use of the torrefied samples in combustion. The results show that the integration of torrefaction for biochar production with phosphorus recovery by struvite precipitation is an efficient solution for waste management in small wastewater treatment plants.
Keywords: wastewater treatment plant efficiency, torrefication, N2 atmosphere, CO2 atmosphere, solid biofuels, proximate and ultimate analyses, thermogravimetry
Published in DKUM: 29.10.2025; Views: 0; Downloads: 6
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2. Investigation of the influencing parameters of the ▫$H_2O_2-assisted$▫ photochemical treatment of waste liquid from the hydrothermal carbonization process in a microreactor flow systemAleksandra Petrovič, Tjaša Cenčič, Silvo Hribernik, Andreja Nemet, 2025, original scientific article Abstract: Due to its complex composition and toxicity, the waste liquid from hydrothermal carbonization (HTC) poses a serious environmental challenge that must be addressed before disposal. In this study, the photochemical treatment of HTC liquid in a microreactor flow system was investigated. The effects of wavelength, the presence of atmospheric oxygen, oxidizing agent (H2O2) and catalyst (FeSO4), residence time and pH on the efficiency of the photo-treatment were investigated. In addition, the influence of the addition of deep eutectic solvent (DES) on photo-treatment was studied. The results showed that the photochemical treatment was more efficient at 365 nm than at 420 nm, and that the acidic conditions gave better results than the basic ones. UV365 treatment in the presence of H2O2 (at a dosage of 1 vol%) resulted in removal efficiencies of 31.6% for COD, 17.6% for TOC, 16.9% for NH4-N and 17.2% for PO4-P. The addition of FeSO4 caused coagulation/flocculation effects, but improved phosphorus removal. The addition of DES resulted in slight discolouration of the liquid and proved unsuccessful in COD removal. The GC-MS analysis and 3D-EEM spectra showed significant changes in the fate of organics and in the fluorescence intensity of aromatic proteins and humic acid-like substances. Photochemical treatment in a microreactor flow system in the presence of H2O2 under the selected operating conditions reduced the content of organics and nutrients in the HTC liquid, but the process liquids still showed toxic effects on the organisms V. fischeri and Daphnia magna.
Keywords: hydrothermal treatment, waste process liquid, photochemical treatment, hydrogen peroxide, microreactor flow system
Published in DKUM: 25.09.2025; Views: 0; Downloads: 3
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3. Elektrokemijska razgradnja metilen modrega v pretočnem mikroreaktorskem sistemuUrška Žvarc, 2025, undergraduate thesis Abstract: V diplomskem delu smo preučili elektrokemijski razpad metilen modrega (MB) v pretočnem mikroreaktorskem sistemu, ter porabo električne energije za to analizo. MB je aromatska spojina, ki absorbira svetlobo in se vse pogosteje uporablja v različnih industrijskih panogah.
V eksperimentalnem delu smo s spreminjanjem napetosti, pretoka in koncentracije MB ugotavljali kako dani parametri vplivajo na razpad MB. Vpliv parametrov smo proučevali z metodo načrtovanja poskusov, metodo odzivnih površin, centralno kompozitno metodo. Te metode so vgrajene v program Design Expert, ki smo ga uporabljali najprej za načrtovanje poskusov nato pa še za analizo rezultatov, razvoj modela za učinkovitost razgradnje metilen modrega ter optimizacijo pogojev kemijske reakcije. Za izvedbo poskusa elektrokemijskega razpada smo uporabili elektrokemijski pretočni mikroreaktorski sistem, pri čemer smo kot katodo uporabili ogljikovo elektrodo, kot anodo pa elektrodo nerjavečega jekla.
Ugotovili smo, da je učinkovitost razpada pri nizkih koncentracijah MB zelo nizka, ne glede na napetost in pretok. Učinkovitost razpada višjih koncentracij MB je najboljša pri napetosti med 4,9 V in 6 V ter pri pretoku 1,63 mL/min.
Vzporedno smo izvedli še študijo porabe električne energije, s katero smo ugotovili, da se tok električne energije ni znatno spreminjal ne za črpalko in tudi ne za elektrokemijski modul. Do razlik je prišlo zaradi različnih zadrževalnih časov, in sicer daljši kot je bil zadrževalni čas večja je bila poraba električne energije.
Rezultati so pokazali, da so bili eksperimentalni podatki skladni s teoretičnimi napovedmi, kar potrjuje, da je metoda uporabna za čiščenje vodnih raztopin onesnaženih z MB.
Keywords: Metilen modro, mikroreaktorski sistem, elektrokemijski razpad, napetost, pretok
Published in DKUM: 18.09.2025; Views: 0; Downloads: 7
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4. Razpad metilen modrega v pretočnem fotokemijskem mikroreaktorju : diplomsko deloLaura Žajdela, 2025, undergraduate thesis Abstract: V diplomskem delu preučujemo razgradnjo sintetičnega barvila metilen modro v vodni raztopini s pomočjo pretočnega fotokemijskega mikroreaktorja. Namen raziskave je bil določiti optimalne pogoje procesa, ki omogočajo čim višjo učinkovitost čiščenja ob čim nižji porabi energije. Ker se metilen modro pogosto uporablja v tekstilni in farmacevtski industriji, njegova prisotnost v odpadnih vodah predstavlja pomemben okoljski problem.
Za izvedbo raziskave smo uporabili računalniški program Design Expert, s katerim načrtujemo poskuse po metodi odzivnih površin (RSM). Spreminjali smo štiri ključne parametre: pretok, začetno koncentracijo barvila ter količino dodanega železovega(II) sulfata in vodikovega peroksida, potek reakcije pa smo spremljamo s sprotnimi meritvami absorbance z UV-Vis spektrometrom. Na osnovi eksperimentalnih podatkov smo razvili matematični model za učinkovitost čiščenja in porabo energije. Rezultati kažejo, da ima na učinkovitost največji vpliv pretok, medtem ko začetna koncentracija barvila pomembno vpliva na porabo energije. Na koncu smo izvedli optimizacije z različnimi cilji kot so visoka učinkovitost čiščenje, minimalna poraba energije, pri čemer smo na podlagi razvite metod dobili kombinacije parametrov, ki vodijo do visoke učinkovitosti ob razmeroma nizki porabi energije.
Ugotovili smo, da je uporaba fotokemijskega mikroreaktorja učinkovita in energetsko primerna metoda za čiščenje barvil iz vode, ki ima potencial za širšo uporabo, tudi pri obdelavi industrijskih vod.
Keywords: metilen modro, mikroreaktor, fotokemija, Design Expert
Published in DKUM: 18.09.2025; Views: 0; Downloads: 7
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5. Energetska izraba ostankov fermentacije v trdnem stanjuEva Gradišnik, 2025, undergraduate thesis Abstract: V diplomskem delu smo preučili možnosti energetske izrabe konopljinih pogač, ki so ostanek
po fermentaciji v trdnem stanju (SSF) z glivo Thermomyces lanuginosus. Namen raziskave je
bil ovrednotiti vpliv biološke predobdelave in temperature pirolize na sestavo biomase ter
kakovost produktov termične obdelave. Pirolizo smo izvedli pri 300 °C in 700 °C v inertni
atmosferi ter analizirali nastale trdne in tekoče produkte.
Rezultati kažejo, da se je z višanjem temperature masni izkoristek zmanjšal, medtem ko so se
zgornja kurilna vrednost, delež aromatskih struktur in vsebnost fiksnega ogljika povečali.
Biološka obdelava je prispevala k znižanju vsebnosti hlapnih snovi in povečanju pepela, kar
kaže na razgradnjo organske komponente biomase. Termogravimetrična analiza, izvedena v
kisikovi in dušikovi atmosferi ter sklopljena s FTIR spektroskopijo, je pokazala sprembo v
reaktivnosti biološko obdelanih vzorcev, z nižjo začetno temperaturo razgradnje in manjšimi
izpusti hlapnih spojin. FTIR analiza je potrdila razgradnjo lignoceluloznih struktur ter večjo
prisotnost aromatskih skupin pri višjih temperaturah pirolize.
Ugotovili smo, da biološka predobdelava vpliva na sestavo biomase in lastnosti produktov
pirolize, kar odpira možnosti za optimizacijo procesa energetske izrabe lignoceluloznih
ostankov.
Keywords: energetska izraba, piroliza, ostanki fermentacije, termogravimetrična
analiza, gorivne lastnosti
Published in DKUM: 12.09.2025; Views: 0; Downloads: 20
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6. The torrefaction of agricultural and industrial residues : thermogravimetric analysis, characterization of the products and TG-FTIR analysis of the gas phaseDanijela Urbancl, Deniz Agačević, Eva Gradišnik, Anja Šket, Nina Štajnfelzer, Darko Goričanec, Aleksandra Petrovič, 2025, original scientific article Abstract: Four biomass residues–rosemary pomace, rosemary cake, grape seed and apple pomace– were torrefied at 250, 350 and 450 ◦C, and the physical, chemical and structural changes were characterized. The mass and energy yield decreased with increasing torrefaction temperature; the lowest mass (~10.4%) and energy yield (~10.6%) were observed for rosemary cake torrefied at 450 ◦C. The HHV increased the most for all feedstocks at 350 ◦C, with rosemary cake reaching a peak value of 36.4 MJ/kg at 350 ◦C. Ash content increased with temperature due to organic mass loss, while volatiles decreased and fixed carbon increased in most samples. The FTIR spectra showed the progressive loss of hydroxyl, carbonyl and C–O functionalities and the appearance of aromatic C=C bonds, indicating the formation of the biochar. TGA and DTG analyses revealed that the torrefied samples exhibited higher initial and maximum temperatures for decomposition, confirming improved thermal stability. The TGA-FTIR analyses of gas emissions during pyrolysis and combustion showed that the emissions of CO2, CH4, NOx and SO2 decreased with increasing degree of torrefaction. Overall, 350 ◦C was optimal to maximize energy density. The results show that agro-industrial residues can be effectively converted into sustainable biofuels, which offer the dual benefit of reducing waste disposal problems and providing a renewable alternative. In practice, such residues could be used for decentralized power generation in rural areas, co-combustion in existing power plants, or as feedstock for advanced bioenergy systems.
Keywords: torrefication, fuel, thermogravimetric analysis, biowaste, mass yield, energy yield
Published in DKUM: 04.09.2025; Views: 0; Downloads: 10
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7. Vpliv dodatka katalizatorja na produkte termične obdelave bioplastike : diplomsko delo univerzitetnega študijskega programa I. stopnjeMihaela Krajnc, 2025, undergraduate thesis Abstract: V diplomskem delu smo preučili vpliv dodatka različnih katalizatorjev na produkte termične obdelave (pirolize) bioplastike. Osredotočili smo se na dodatke, kot so Ca(OH)2, MgO, diatomejska zemlja, filtracijski pesek ter modificirano hidro-oglje, in preučili njihov vpliv na sestavo ter lastnosti trdne faze po pirolizi pri različnih temperaturah (300 °C, 400 °C in 500 °C).
V eksperimentalnem delu smo analizirali vzorce z vidika vsebnosti pepela, vlage, hlapnih snovi, kurilne vrednosti, elementne sestave, funkcionalnih skupin (FTIR) ter toplotne stabilnosti (TGA). Ugotovili smo, da se vsebnost hlapnih snovi pri neobdelani bioplastiki (70,88%) po dodatku katalizatorjev in pirolizi pri višjih temperaturah zmanjša tudi pod 25 %.
Rezultati FTIR analiz trdnih vzorcev kažejo na razgradnjo alifatskih skupin in tvorbo aromatskih struktur, TGA krivulje pa potrjujejo premike temperature začetka razgradnje (Ti) in temperature pri najvišji hitrosti razgradnje (Tmax) ob dodatku katalizatorjev. Pri termično obdelanih vzorcih z dodatki MgO oz. Ca(OH)2 se Ti zviša, kar kaže na izboljšano toplotno stabilnost, pri termično neobdelanih vzorcih pa se Tmax zniža, kar nakazuje na hitrejšo razgradnjo. Termično obdelani vzorci z dodatkom MgO in Ca(OH)2 so pokazali višje ostanke mase po obdelavi, kar potrjuje večji masni izkoristek trdne faze. Elementna analiza je razkrila znižanje vsebnosti ogljika pri višjih temperaturah, vendar so dodatki katalizatorjev pripomogli k ohranjanju večje vsebnosti ogljika v produktih.
Na splošno sta največji vpliv na sestavo produktov imela katalizatorja MgO in Ca(OH)2, medtem ko so modificirano hidro-oglje, filtracijski pesek in diatomejska zemlja pokazali nekoliko manj izrazite učinke.
Keywords: bioplastika, termična obdelava, piroliza, katalizatorji, termogravimetrična analiza
Published in DKUM: 15.07.2025; Views: 0; Downloads: 48
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8. Thermogravimetric, kinetic and thermodynamic behaviour of raw and hydrothermally pretreated oil cakes during pyrolysis and TG-FTIR analysis of the gaseous productsAleksandra Petrovič, Sabina Vohl, Sven Gruber, Klemen Rola, Tjaša Cenčič, Lidija Čuček, Danijela Urbancl, 2025, original scientific article Abstract: The pyrolysis of raw and hydrothermally (HTC) pretreated pumpkin (PC) and hemp (HC) oilseed cakes was investigated for the first time using thermogravimetric, kinetic and thermodynamic analyses. The influence of the HTC pretreatment and the type of reaction liquid (whey or water) on the pyrolysis was investigated and the pyrolysis gases were analysed. The HTC pretreatment increases the biochar yield with values of up to 44 wt.% compared to raw oil cakes (∼27 wt.%). The HTC pretreatment with whey resulted in a higher energy and biochar yield and better biochar properties than the pretreatment with water. The tested oil cakes provided comparable energy yields, although HC provided higher biochar yields, while PC biochar showed higher hydrophobicity. The kinetic modelling shows that the activation energies () for the pyrolysis of the raw oil cakes varied between 93.6 and 529.9 kJ/mol for PC and between 71.3 and 669.9 kJ/mol for the HC sample. HTC pretreatment in water media increased the values, while the use of whey led to a decrease in the values. TG-FTIR analysis of the emitted gases showed that the HTC treatment affected the release of CO2 and hydrocarbons as well as the pyrolysis mechanism and reaction pathways
Keywords: oilseed cake, hydrochar, pyrolysis, thermogravimetric analysis, kinetic analysis, gas emissions
Published in DKUM: 25.04.2025; Views: 0; Downloads: 15
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9. Improving lignocellulosic and non-lignocellulosic biomass characteristics through torrefaction processMaja Ivanovski, Danijela Urbancl, Aleksandra Petrovič, Janja Stergar, Darko Goričanec, Marjana Simonič, 2022, original scientific article Abstract: In this study, three locally available biomasses, namely miscanthus, hops, sewage sludge,
and additionally, their mixtures, were subjected to the torrefaction process to improve their fuel
properties. The torrefaction process was conducted at 250–350 ◦C and 10–60 min in a nitrogen
(N2) environment. The torrefaction temperature and time were studied to evaluate the selected
biomass materials; furthermore, heating values, mass and energy yields, enhancement factors,
torrefaction severity indexes (TSI), and energy-mass co-benefit indexes (EMCI) were calculated. In
addition, thermogravimetric (TGA) and Fourier transform infrared analyses (FTIR) were performed
to characterize raw and torrefied biomass under the most stringent conditions (350 ◦C and 60 min).
The results showed that with increasing torrefaction temperature and duration, mass and energy
yields decreased, and heating values (HHVs) increased for all studied biomasses. The results of the
TSI and EMCI indexes showed that the optimum torrefaction conditions were as follows: 260 ◦C
and 10 min for pure miscanthus and hops, whilst this could not be confirmed for the sewage sludge.
Furthermore, the combination of sewage sludge and the above-mentioned types of lignocellulosic
biomass exhibited better fuel properties than sewage sludge alone.
Keywords: lignocellulosic biomass, sewage sludge, torrefication, thermogravimetry, TSI
Published in DKUM: 10.04.2025; Views: 0; Downloads: 16
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10. Cu(II) and Ni(II) adsorption on torrefied wood waste biomassMarjana Simonič, Darko Goričanec, Aleksandra Petrovič, Ilda Silić, Danijela Urbancl, 2025, original scientific article Abstract: The aim of the research was to study the torrefaction processes of wood biomass, compare the product characteristics at different torrefaction temperatures, and assess both moisture adsorption on raw and torrefied samples, as well as metal (Cu(II) and Ni(II)) adsorption on torrefied biomass. The novelty of the research was to investigate whether the presence of adsorbed metals in torrefied biomass significantly affects the energetic properties of the torrefied biomass, compared to torrefied biomass without metals. First, wood samples were torrefied at temperatures of 250 °C, 350 °C, and 400 °C. Following torrefaction, thermogravimetric analysis (TGA) was performed to evaluate mass loss and thermal stability. Next, changes in surface functional groups were examined, and higher heating values (HHV) were measured to assess the energy content. The results showed that torrefaction significantly increased the hydrophobicity of the biomass, leading to reduced moisture adsorption and enhanced material properties. Additionally, the adsorption of Cu(II) and Ni(II) ions on torrefied biomass was investigated. The results showed that the adsorption efficiency for Cu(II) was higher, reaching 62.4%, compared to Ni(II) at 21.2%. The adsorption process followed a pseudo-second-order kinetic model, which indicated that chemisorption was the dominant mechanism.
Keywords: adsorption, torrefication, nitrogen atmosphere, metals
Published in DKUM: 12.03.2025; Views: 0; Downloads: 6
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