Macroalgae can be a viable alternative to replace fossil fuels that have a negative impact on the environment. By mixing macroalgae with other substrates, higher quality biogas can be obtained. Such biogas is considered one of the most promising solutions for reducing climate change. In the work, new studies were conducted, during which biogas yield was investigated in a three-stage bioreactor (TSB) during the anaerobic digestion of Cladophora glomerata macroalgae with inoculants from cattle manure and sewage sludge at different organic loading rates (OLR). By choosing the optimal OLR in this way, the goal was to increase the energy potential of biomass. The research was performed at OLRs of 2.87, 4.06, and 8.13 Kg VS/m³ d. After conducting research, the highest biogas yield was determined when OLR was 2.87 Kg VS/m³ d. With this OLR, the average biogas yield was 439.0 ± 4.0 L/Kg VS_added, and the methane yield was 306.5 ± 9.2 L CH₄/Kg VS_added. After increasing the OLR to 4.06 and 8.13 Kg VS/m³ d, the yield of biogas and methane decreased by 1.55 times. The higher yield was due to better decomposition of elements C, N, H, and S during the fermentation process when OLR was 2.87 Kg VS/m³ d. At different OLRs, the methane concentration remained high and varied from 68% to 80%. The highest biomass energy potential with a value of 3.05 kWh/Kg VS_added was determined when the OLR was 2.87 Kg VS/m³ d. This biomass energy potential was determined by the high yield of biogas and methane in TSB.

Iron additives are effective in the anaerobic sewage sludge digestion process, but the composition and dosage of these additives are not precisely defined. This research investigates the effects of three iron oxides-based additives on the destruction of volatile solids, the production and quality of biogas, as well as the quality of the supernatant. Additive No 1 contained >41.5% of FeO and >41.5% of Fe₂O₃, additive No 2 contained ≥86% of Fe₃O₄, and additive No 3 contained ≥98% of Fe₃O₄. The best results were obtained by applying an iron oxides-based additive with a higher content of divalent iron oxide. The increase in efficiency of the VSs destruction was not significant and on average 2.2%. The increase in biogas production was on average 20% while the average increase in the content of methane in the biogas was 6.3%. Applying the additive, the reduction in the concentration of ammonium nitrogen in the supernatant was up to 28%, as well as a reduction in the concentration of phosphate phosphorus in the supernatant by up to 3.1 times could be expected compared to the case when the additive was not applied. The dose of additive No 1 was between 7.5 g/kg of dry solids and 15 g/kg of dry solids in the lab-scale test. The dose was specified in the full-scale test, and the recommended dose of the additive was 10 g/kg of dry solids to improve biogas production.

The use of microalgae as a raw material for biogas production is promising. Macroalgae were mixed with cattle manure, wheat straw, and an inoculant from sewage sludge. Mixing macroalgae with co-substrates increased biogas and methane yield. The research was carried out using a three-stage bioreactor. During biogas production, the dynamics of the composition of the microbiota in the anaerobic chamber of the bioreactor was evaluated. The microbiota composition at different organic load rates (OLRs) of the bioreactor was evaluated. This study also demonstrated that in a three-stage bioreactor, a higher yield of methane in biogas was obtained compared to a single-stage bioreactor. It was found that the most active functional pathway of methane biosynthesis is PWY-6969, which proceeds via the TCA cycle V (2-oxoglutarate synthase). Microbiota composition and methane yield depended on added volatile solids (VS_added). During the research, it was found that after reducing the ORL from 2.44 to 1.09 kg VS/d, the methane yield increased from 175.2 L CH₄/kg VS_added to 323.5 L CH₄/kg VS_added.

Augant bei plečiantis miestams, didėja ir nuotekų valymo įrenginių apkrova teršalais, todėl nuotekos ne visada tinkamai išvalomos, daromas neigiamas poveikis upių ekologinei būklei. Taip pat griežtėja reikalavimai valytų nuotekų užterštumui. Dėl šių priežasčių vis aktualesnis tampa tretinio nuotekų valymo etapas. Tyrimai atlikti komunalinių nuotekų valykloje. Jų metu buvo tirtas tretinio valymo įrenginio šalinimo efektyvumas pagal skirtingus teršalus, esant skirtingoms reagento fosforui šalinti dozavimo sąlygoms, kurios išskirtos į du etapus: kai reagento fosforui šalinti dozuojama mažiau nei reikia 0,5 mg/l bendrojo fosforo koncentracijai pasiekti ir kai dozuojama tiek, kiek reikia 0,5 mg/l bendrojo fosforo koncentracijai pasiekti. Tyrimo metu nustatyta, kad 1-ajame etape vidutinis bendrojo fosforo šalinimo efektyvumas siekė 28 %, fosfatų fosforo – 20 %, BDS7 – 66 %, Nb – 9,3 %, o SM – 83 %. 2-ojo etapo metu bendrojo fosforo ir fosfatų fosforo šalinimo efektyvumas siekė po 30 %, BDS7 – 36 %, Nb – 4,3 %, o SM – 68 %.