The subject of the study is the profitability of selected substrates used in agricultural biogas plants. Dry matter, organic dry matter, COD, total nitrogen, organic acids, biogas potential and methane content in biogas were investigated in the analyzed substrates. The measurements for biogas potential were performed as a batch-test at 38°C. The results enabled to estimate the energy balance, which was the basis for economic calculation for each of the analyzed substrates. As a result of the analysis it was found that maize silage provides the highest energy gain, while the lowest energy gain is acquired from cattle slurry and whey.

The research carried out in this work determined the biochemical methane potential of the solid fraction remaining after acid fermentation with the recovery of volatile fatty acids and hydrogen, in which kitchen waste was used as the substrate. The methane fermentation process was carried out in bath bioreactors without pH regulation during the process, with the addition of digestate sludge from wastewater treatment plants and without its addition, at various substrate concentrations. It was found that the solid fraction after acid fermentation with the addition of digested sludge, is a good substrate for biogas production. The highest biochemical methane potential of 640 cm³ CH ×gsmo^-1 was found in the process in which the waste solid fraction after acid fermentation concentration was 100 gm×dm^-3.

The production of secondary metabolites by microorganisms depends on many factors. Therefore, it is crucial to establish the main conditions of microbial growth to obtain products with biotechnological potential. The aim of the research was to determine the optimal culture conditions of the Rhodococcus opacus FCL1069 strain producing an exopolymer with flocculating properties. Different carbon (e.g. glucose, lactose) and nitrogen (e.g. yeast extract, peptone) sources were used for optimization of bacterial growth. Moreover, the impact of addition of ions to the culture broth was established. During bacterial growth, the protein content was determined with the Bradford method and flocculating activity was tested using a kaolin and calcium chloride mixture. The total sugar concentration in the culture broths on the subsequent days of cultivation was measured with the Dubois method. The investigations presented in this study allowed obtaining an exopolymer with the highest possible flocculating activity in the shortest incubation time.

The paper presents research on the possibility of using textile wastewater (TW) as a culture medium for microalgae and cyanobacteria. Thermophilic strains of the microorganisms Synechococcus sp. PCC 6715 as well as mesophilic Chlorella sp. 155, Chlorella sp. 179 and isolates from the sewage treatment plants PTx1 and PTx2 were used in the research. The highest production of biomass in 100% textile wastewater demonstrated PTx1. The effects of supplementation TW with NaHCO₃ as an inorganic source of carbon and NaNO₃ as an additional source of nitrogen in reference to BG11 were also studied. The processes were carried out in shake flasks with a working volume of 250 cm³ under both sterile and non-sterile conditions. The highest biomass production was achieved for 100% TW. The Biochemical Methanogenic Potential (BMP) of the biomass was in the range of 372–398 cm³_CH4×g_SMO^-1. The proposed process allows obtaining energy-rich microalgae biomass.

The paper presents results of the study on efficient production of microalgae (Chlorella sp.) biomass. Culture was conducted on the basis of synthetic medium, in a laboratory storage tank photobioreactor with an active volume of 5 dm³, under forced aeration and mixing conditions. The culture control consisted in the spectrophotometric measurement of changes in the optical density of the culture medium as well as the determination of basic nutrients (total nitrogen and phosphorus) in the culture medium. In addition, Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) values were measured in biomass suspension. Within 35 days, algae absorbed about 230 g of nitrogen (over 30% by weight) and about 36 mg of phosphorus (over 90% by weight), and the OD₆₈₆ exceeded 1.2. During this time, the COD value increased by over 80% and the total organic carbon content by over 20%. The high efficiency of algae biomass production has been achieved by limiting the possibility of bacterial infection and ensuring appropriate conditions, including aeration, circulation and availability of biogenic compounds.

Filamentous fungi are microorganisms widely used in the biotechnology industry. Belonging to this group Aspergillus terreus and Mucor racemosus show different mechanisms of morphogenesis. In the conducted submerged cultures various morphological forms of A. terreus and M. racemosus were observed. The case of the first microorganism confirmed a well-known agglomerative mechanism of hairy pellets formation. The second studied microorganism is a non-agglomerative fungus, therefore the pellets formation in M. racemosus cultivation did not take place. The observed with the use of microscope mycelial objects were photographed and subjected to digital image analysis. As a result, the following morphological parameters were calulated: mean projected area (A, µm²), elongation (E,-), roughness (R,-) and morphology number (Mo,-). The analysis of the obtained values confirmed the presence of different mycelial objects in A. terreus and M. racemosus cultures as well as various morphogenesis mechanisms.

The aim of the research was to examine the effect of the light color (yellow, green, blue and red) on the biomass production of microalgae Chlorella sp. under laboratory conditions. The changes in the content of total nitrogen, total phosphorus and total organic carbon were monitored in the culture medium. The increase in algae biomass was evaluated using the optical density measurements of the media at 686 nm and weight measurements. It was found that the spectral composition of light that illuminates the cultivation affects the production of algae biomass. The best results were obtained for those cultures illuminated with blue and red light. From the beginning of algae cultivation, 29 and 27% by weight decreases in the total nitrogen content and 98 and 94% by weight decrease in the total phosphorus content were obtained, respectively. During this time, the total organic carbon content increased by 45 and 38%, by weight and optical density increased to 1.42 and 1.13, respectively. In the cultures illuminated with blue and red light, microalgae biomass growth was at the level of 2.86 and 2.56 g/dm³.

The study concerns the purification of synthetic and industrial textile wastewater containing the most common dye, Reactive Black 5 (RB5), by electrocoagulation. The experiments were carried out under conditions of high salinity (35 g×dm^-3 NaCl) in a strongly alkaline environment (pH 11–12). These conditions are characteristics of dye-baths. The color and chemical oxygen demand (COD) removal were compared while the use of iron (steel) and aluminum (iron) electrodes. The biological oxygen demand (BOD₅) was tested as well. High efficiency of color removal, about 90%, was observed in a very short time: 3 and 10 minutes for iron and aluminum electrodes, respectively. The experiments showed that the effectiveness of color reduction depends on the material of the electrodes. However, there was no significant reduction in COD for both types of electrodes, which was related to the residual impurities in the liquid phase (by-products of RB5 and dissolved iron and aluminum compounds). At the same time, the BOD₅ increased 10 times after the purification, which indicates enhance in biodegradability of the wastewater. The main conclusion was that the electrocoagulation is a complex process, which is determined by the physical and chemical phenomena associated with the electrodes material as well as the environment of the reaction.