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Abstract The aim of the study was to determine the influence of the light source on the taxonomic structure and chemical composition of the harvested biomass, and on the fermentative biogas/methane production. Cultivation of a mixed microalgae culture was carried out in closed vertical photobioreactors equipped with different light sources. The effectiveness of anaerobic digestion was analysed by respirometric measurements. The harvested microalgae biomass was characterized by various taxonomic structures and varied chemical composition depending on the light source used during cultivation stage. In variants where warm white LED lighting and red light were used, species from the Cyanoprokaryota division predominated, characterized by a high concentration of organic compounds and nitrogen in the biomass. TOC values amounted to almost 430 mg/g TS. In the remaining variants, Chlorophyta predominated, and TOC values were in the range of 388.0–411.3 mg/g TS. A significantly higher biogas/methane production ( p = 0.05) was found in variants in which biomass with Cyanoprokaryota predominating was tested. The biogas yield was in the range of 383.2 L/kg VS to 400.8 L/kg VS, and the methane content was close to 55%. A lower effectiveness of biogas and methane formation were observed in variants with Chlorophyta as a predominating taxonomic group.

Microalgae-based technologies have huge potential for application in the environment sector and the bio-energy industry. However, their cost-efficiency has to be improved by drawing on design and operation data for large-scale installations. This paper presents a technical concept of an installation for large-scale microalgae culture on digestate liquor, and the results of a pilot-scale study to test its performance. The quality of non-treated digestate has been shown to be insufficient for direct use as a growth medium due to excess suspended solids, turbidity, and organic matter content, which need to be reduced. To that end, this paper proposes a system based on mechanical separation, flotation, and pre-treatment on a biofilter. The culture medium fed into photobioreactors had the following parameters after the processing: COD—340 mgO2/dm3, BOD5—100 mgO2/dm3, TN—900 mg/dm3, and TP—70 mg/dm3. The installation can produce approx. 720 kgVS/day of microalgal biomass. A membrane unit and a thickening centrifuge (thickener) were incorporated into the design to separate and dehydrate the microalgal biomass, respectively. The total energy consumption approximated 1870 kWh/day.

Waste glycerol can be subjected to various processing operations, including purification and refining, to obtain glycerol of an appropriate purity. Alternative methods for utilising waste glycerol are also being sought, e.g., by converting it into other valuable chemical products or biofuels. Therefore, various technologies are being developed to ensure effective and sustainable utilisation of this type of waste. The production of value-added products from waste glycerol strongly determines the improvement of the economic viability of biofuel production and corresponds to the model of a waste-free and emission-free circular economy. This paper characterises the mechanisms and evaluates the efficiency of existing methods for microbiological utilisation of waste glycerol into liquid biofuels, including biodiesel, bioethanol and biobutanol, and identifies further production avenues of value-added products. In addition, it presents the results of a bibliographical analysis of publications related to the production of liquid fuels and economically valuable products from glycerol, assesses the progress of research and application work and, finally, identifies areas for future research.

Increasing worldwide milk manufacturing and dairy processing resulted in producing more effluents, and thus effective management of wastewater is now the most important issue. This study used a new design of a pilot plant-scale hybrid anaerobic labyrinth-flow bioreactor (AL-FB) to increase the efficiency of anaerobic biodegradation and biogas productivity and improve anaerobic microflora performance. In addition, effluent recirculation was used to boost the treatment of dairy wastewater. Metagenomic analyses of the anaerobic microbial community were performed. It was found that an organic loading rate (OLR) of 4.0–8.0 g COD/L·d contributed to the highest CH4 yield of 0.18 ± 0.01–0.23 ± 0.02 L CH4/g COD removed, which corresponded to a high COD removal of 87.5 ± 2.8–94.1 ± 1.3%. The evenest distribution of the microorganisms’ phyla determined the highest biogas production. In all tested samples, Bacteroidetes and Firmicutes abundance was the highest, and Archaea accounted for about 4%. Metagenomic studies showed that methane was mainly produced in acetoclastic methanogenesis; however, higher OLRs were more favorable for enhanced hydrogenotrophic methanogenesis. Effluent recirculation enhanced the overall treatment. Thus, at OLR of 10.0 g COD/L·d, the highest COD removal was 89.2 ± 0.4%, and methane production yield achieved 0.20 ± 0.01 L CH4/g COD removed, which was higher by 25% compared to the achievements without recirculation.