New doctoral dissertation

June 15, 2026

VILNIUS TECH Library invites you to follow the published new dissertations. The dissertation „Research and application of biofiltration materials in the purification of biogas from hydrogen sulfide“ prepared at VILNIUS TECH by Kamyab Mohammadi. The dissertation was prepared in 2022–2026. Scientific consultant – Assoc. Prof. Dr Rasa Vaiškūnaitė.

The dissertation was defended at the public meeting of the Dissertation Defense Council of the Scientific Field of Environmental Engineering in the Aula Doctoralis Meeting Hall of Vilnius Gediminas Technical University at 10 a.m. on 15 June 2026.

This dissertation analyzes the removal of hydrogen sulfide (H₂S) from biogas via biofiltration. The study addresses one of the major challenges in biogas utilization, effective H₂S removal, since this compound is toxic and corrosive, and significantly reduces the operational efficiency and service life of biogas energy systems. The main object of the research is biofiltration materials intended for hydrogen sulfide removal from biogas: biochar produced from sewage sludge, cellular lightweight concrete (CLC) waste, and polyurethane foam (PUF). The doctoral dissertation aims to increase the efficiency of hydrogen sulfide removal from biogas and to enhance the operational stability of the biofilter by applying physically and chemically modified as well as unmodified waste-derived materials within the biofiltration process. The dissertation consists of an introduction, a literature review, chapters on methodology and results, general conclusions and recommendations, and lists of references and the author’s publications related to the dissertation topic. The Introduction presents the research problem and its relevance, describes the research object, formulates the aim and objectives, outlines the research methodology, scientific novelty, and practical significance of the results, and states the defended propositions. The First Chapter reviews biotechnologies for hydrogen sulfide removal from biogas, with particular emphasis on biofiltration mechanisms, the properties of biofilter packing materials, and the key factors determining process efficiency. The Second Chapter describes the experimental methodologies used to select biofiltration materials, determine their physicochemical and adsorption properties, inoculate and cultivate microorganisms, evaluate hydrogen sulfide removal efficiency, and the mathematically model the biofiltration process. The Third Chapter presents the results of theoretical and experimental investigations of innovative filtration materials, revealing the relationship between their properties and modification with microbial establishment, biofilm formation, and filter performance in hydrogen sulfide removal, and compares experimental results with mathematical modeling outcomes. Eight scientific papers related to the dissertation topic have been published: two in Web of Science-indexed journals with an impact factor, one in a Web of Science-indexed journal without an impact factor, four in other internationally indexed journals, and one in a conference proceedings volume indexed in the Scopus database. Seven presentations on the dissertation topic were given at national and international scientific conferences.

Doctoral dissertation readers can search via VILNIUS TECH Virtual Library.

 

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New doctoral dissertation
New doctoral dissertation
VILNIUS TECH Library invites you to follow the published new dissertations. The dissertation „Performance investigation of a hybrid car engine fuelled with gasoline and gaseous mixtures“ („Benziną ir dujų mišinius naudojančio hibridinio automobilio variklio efektyvumo tyrimas“) prepared at VILNIUS TECH by Tadas Vipartas. The dissertation was prepared in 2021–2026. Scientific consultant – Prof. Dr Alfredas Rimkus. The dissertation was defended at the public meeting of the Dissertation Defence Council of the Scientific Field of Transport Engineering in the Aula Doctoralis Meeting Hall of Vilnius Gediminas Technical University at 9 a.m. on 12 June 2026. This dissertation investigates the use of alternative fuels (natural gas and hydrogen) to increase the efficiency of a spark-ignition engine. The impact of different fuels and engine control algorithms on the combustion process and on energy and ecological indicators was determined and evaluated by analysing the emerging technological constraints within the context of a power-split (series-parallel) hybrid powertrain. The dissertation presents a review of scientific literature, analysing the directions for internal combustion engine improvement, the properties of gaseous fuels and the challenges of their application, along with the operating principles of automotive hybrid powertrains. Bench tests were conducted to investigate the effect of late intake valve closing timing on an engine operating on natural gas, and the influence of hydrogen additives on the combustion process and knock control. The numerical analysis of the engine’s combustion process was performed using AVL BOOST™ software, while the energy and ecological indicators of the hybrid vehicle were evaluated through experimental research and numerical simulation in the AVL CRUISE™ software. The following main results were obtained in the dissertation: retarding the intake valve closing timing increased the brake thermal efficiency and NOx emissions while reducing carbon dioxide emissions when the engine operates on natural gas. It was determined that a hydrogen additive in the fuel improves the engine’s energy indicators, but increases nitrogen oxides emissions and the risk of engine knock. Engine knock is effectively managed by retarding the ignition advance angle. Numerical simulation results confirmed that these trends persist during the Worldwide Harmonized Light-duty Vehicles Test Cycle: the use of hydrogen reduces fuel consumption and carbon dioxide emissions, but increases nitrogen oxides emissions. The dissertation results revealed the potential of these technologies and strategies for their application. The obtained data can be applied in the development and selection of advanced engine control algorithms and in the formulation of technologically sound environmental standards. Nine scientific articles have been published on the topic of the dissertation: six in scientific journals indexed in the Clarivate Analytics Web of Science database with an impact factor, one in a scientific journal indexed in the Clarivate Analytics Web of Science database without an impact factor, one in conference proceedings indexed in the Clarivate Analytics Web of Science Conference Proceedings Citation Index, and one in peer-reviewed conference proceedings not indexed in international databases. The research results were presented at three scientific conferences in Lithuania and Poland. Doctoral dissertation readers can search via VILNIUS TECH Virtual Library.
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