Author, Institution: Egidijus Buivydas, Lithuanian Energy Institute
Science area, field of science: Technological Sciences, Environmental Engineering, T004
Research supervisor: Senior Researcher Dr. Kęstutis Venslauskas (Lithuanian Energy Institute, Technological Sciences, Environmental Engineering, T004)
Dissertation Defence Board of Environmental Engineering Science Field:
Prof. Dr. Egidijus Šarauskis (Vytautas Magnus University, Technological Sciences, Environmental Engineering, T004) – chairperson
Prof. Dr. Jonas Baltrušaitis (Lehigh University, United States, Natural Sciences, Chemistry, N003)
Prof. Dr. Jolanta Dvarionienė (Kaunas University of Technology, Technological Sciences, Environmental Engineering, T004)
Chief Researcher Dr. Darius Jakimavičius (Lithuanian Energy Institute, Technological Sciences, Environmental Engineering, T004)
Assoc. Prof. Dr. Alvydas Zagorskis (Vilnius Gediminas Technical University, Technological Sciences, Environmental Engineering, T004)
Dissertation defence meeting will be at the conference room at Lithuanian Energy Institute (Breslaujos 3 – 202, Kaunas)
The doctoral dissertation is available at the library of Kaunas University of Technology (Gedimino 50, Kaunas) and on the internet: E. Buivydas el. dissertation.pdf
© E. Buivydas, 2026 “The text of the thesis may not be copied, distributed, published, made public, including by making it publicly available on computer networks (Internet), reproduced in any form or by any means, including, but not limited to, electronic, mechanical or other means. Pursuant to Article 25(1) of the Law on Copyright and Related Rights of the Republic of Lithuania, a person with a disability who has difficulties in reading a document of a thesis published on the Internet, and insofar as this is justified by a particular disability, shall request that the document be made available in an alternative form by e-mail to doktorantura@ktu.lt.”
Annotation: A review of the literature has shown that animal waste fats are slowly biodegradable under both aerobic and anaerobic conditions. However, it can be expected that enriching animal manure, which is used to feed anaerobic biogas fermenters, with these fats will improve fat degradation and at the same time increase the methane concentration in biogas, the specific yields of biogas and methane from fat-enriched raw material mixtures. In addition, in the further purification process of such biogas, the need for electricity and methane emissions into the environment will decrease, i.e. the increasing methane concentration in biogas will mitigate the negative impact of the biogas purification process on the environment. To substantiate such a hypothesis at the research stage of the scientific work, the following were aimed:
- To determine the influence of animal waste fats added to chicken manure and cow slurry charges on the composition of these charges.
- To investigated experimentally the possibilities of processing waste fat together with chicken manure and cow slurry in anaerobic biogas production facilities and the influence of these additives on biogas production indicators.
- To determine the influence of increasing methane concentration in biogas on electricity consumption and methane gas emissions into the environment in the biogas purification process, using membrane gas separation technology devices for biogas purification.
- To assess comprehensively the impact of methane gas emissions on the environment from membrane gas separation facilities when purifying biogas with different methane gas concentrations.
After conducting experimental studies of biogas production with chicken manure and cow slurry, with the addition of waste fat, it was found that:
- Enrichment of chicken manure and cow slurry used for biogas production with animal waste fat increases the organic AD loads of both raw materials by 50%, shifts the C:N ratio to the optimal limits required for biogas production (20:1 – 30:1), and the mass of the charges themselves increases by only 5.26% and 2.91%, respectively.
- Increasing the organic loads of chicken manure and cow slurry AD by 50% waste fat differently affects all biogas production indicators for each type of raw material. Waste fat has the greatest impact on biogas production in cow slurry AD, i.e. an increase in the organic load of 50.0% increases the specific biogas yield from DOM by 123%, the methane concentration in biogas by 14.0%, and the specific methane yield from DOM by 140%, while the same indicators in chicken manure AD are almost twice as low and reach +63.1%, +7.73% and +75.8%, respectively.
- That enrichment of chicken manure and cow slurry feeds with waste fat improves the efficiency of decomposition not only of the raw material mixture, but also of the primary raw material to which they are added. In chicken manure studies, the highest decomposition efficiency was observed at an AD organic load of 4.0 kgdom/(m3·d). With an increase in the DOM of the feed by 3.51%, the DOM of the discharged substrate decreased by 8.41%. In cow slurry studies, the highest decomposition efficiency was observed at an AD organic load of 4.5 kgsom/(m3·d). With a 2.91% increase in feed DOM, the DOM of the discharged substrate decreased by 35.9%.
- Changes in methane concentration in biogas directly affect electricity consumption per PV, but do not directly affect methane losses, since methane losses in the studied facilities can be kept constant. When these losses are 0.5%, an increase in methane concentration in biogas from 50% to 80% reduces electricity consumption per PV by 39.2%. When these losses are reduced from 0.5% to 0.2%, electricity consumption at a methane concentration of 50% increases by 16.9%, and at 80% by 10.0%. The total electricity consumption at a methane loss of 0.2% and a methane concentration in biogas of 80% is 33.1% lower compared to the consumption at a loss of 0.5% and a methane concentration of 50%, i.e. increasing methane concentrations in biogas allows for reduced sustained methane losses, compensating for the resulting increased electricity costs.
- That when purifying biogas in membrane biogas purification technology facilities, when the methane concentration in the purified biogas increases, GHG emissions, calculated as FV, decrease in all impact categories. The smallest reduction of 31.1% is achieved in the global warming category, and the largest reduction of 39.1% is achieved in the fossil fuel consumption category, when methane losses to the environment are maintained at 0.5% at a methane concentration in biogas of 80%. In the case of the chicken manure study with waste fat, when methane losses to the environment are 0.5%, and the increase in methane concentration in biogas is 4.5%, the reductions in environmental impact in the global warming category are 5.9% and in the fossil fuel consumption category, 7.7%. In the case of cow slurry with waste fat studies, where methane losses to the environment are 0.5% and the increase in methane concentration in biogas is 4.6%, the reduction in environmental impact in the global warming category is 5.3% and in the resource depletion category is 7.0%.
