• Energy Research

This study compared the effects on biogas production of suspended sludge versus a combination of suspended sludge and immobilized biomass, and microwave versus convection heating. Biogas production was the highest in the hybrid bioreactor heated by microwaves (385L/kg VS) and also the most stable, as shown by the FOS/TAC ratio and pH. Regardless of the type of heating, biogas production was 8% higher with immobilized biomass than without. Although the lag phase of biogas production was shorter with microwave heating than without, the log phase was longer, and biogas production in the microwave heated bioreactors took about twice as long (ca. 40days) to plateau as in the conventionally heated bioreactors. These differences in the profile of biogas production are likely due to the athermal effects of microwave irradiation.

This study compared the effects on biogas production of suspended sludge versus a combination of suspended sludge and immobilized biomass, and microwave versus convection heating. Biogas production was the highest in the hybrid bioreactor heated by microwaves (385L/kg VS) and also the most stable, as shown by the FOS/TAC ratio and pH. Regardless of the type of heating, biogas production was 8% higher with immobilized biomass than without. Although the lag phase of biogas production was shorter with microwave heating than without, the log phase was longer, and biogas production in the microwave heated bioreactors took about twice as long (ca. 40days) to plateau as in the conventionally heated bioreactors. These differences in the profile of biogas production are likely due to the athermal effects of microwave irradiation.

Disintegration of lignocellulosic biomass for energy purposes has been extensively studied. The study aimed to investigate the influence of crushed and uncrushed lignocellulosic biomass on biogas production in innovative reactor. The substrate fed to the reactor was Sida hermaphrodita silage mixed with cow manure. The bioreactor had innovative design mixing cage system. Mixing system of the bioreactor consisted of two cylindrical stirrers in the form of cage. The cages by rotation around the axis of the bioreactor at the same time turn against its own axis. The bioreactor is currently presented under the program Record Biomap (Horizon 2020). The bioreactor was operated at organic compounds loading 2 kg/(m3∙d) and 3 kg/(m3∙d) and hydraulic retention time was 50 d and 33 d, respectively. The biogas production under organic compounds loading 2 kg VS/(m3∙d) was 680 L/kg VS from crushed lignocellulosic biomass and 570 L/kg VS from uncrushed lignocellulosic biomass. The biogas production under organic compounds loading 3 kg VS/(m3∙d) was 730 L/kg VS from crushed lignocellulosic biomass and 630 L/kg VS from uncrushed lignocellulosic biomass. The crushing of substrate did not influence on methane content in the biogas. In all experiments about 54% of methane was in the biogas. The net energy efficiency was also calculated.

Disintegration of lignocellulosic biomass for energy purposes has been extensively studied. The study aimed to investigate the influence of crushed and uncrushed lignocellulosic biomass on biogas production in innovative reactor. The substrate fed to the reactor was Sida hermaphrodita silage mixed with cow manure. The bioreactor had innovative design mixing cage system. Mixing system of the bioreactor consisted of two cylindrical stirrers in the form of cage. The cages by rotation around the axis of the bioreactor at the same time turn against its own axis. The bioreactor is currently presented under the program Record Biomap (Horizon 2020). The bioreactor was operated at organic compounds loading 2 kg/(m3∙d) and 3 kg/(m3∙d) and hydraulic retention time was 50 d and 33 d, respectively. The biogas production under organic compounds loading 2 kg VS/(m3∙d) was 680 L/kg VS from crushed lignocellulosic biomass and 570 L/kg VS from uncrushed lignocellulosic biomass. The biogas production under organic compounds loading 3 kg VS/(m3∙d) was 730 L/kg VS from crushed lignocellulosic biomass and 630 L/kg VS from uncrushed lignocellulosic biomass. The crushing of substrate did not influence on methane content in the biogas. In all experiments about 54% of methane was in the biogas. The net energy efficiency was also calculated.

Annually, a few thousand tons of antibiotics and their transformation products (metabolites and degradation products) are introduced to wastewater treatment plants (WWTPs) as a result of human and animal excretion, or dispose of expired or unused medications. Antibiotics present in wastes might inhibit their treatment processes for instance during methane fermentation. In this study, β-lactams, tetracycline’s, fluoroquinolones, sulphonamides and metronidazole were selected as inhibitors of methane fermentation of sewage sludge collected from municipal WWTP. The experiments were performed in two series with different concentrations of antibiotics. The biogas production did not significantly differ between series, and was from 151.7 ± 18.9 mL/g VS (in the bioreactor with metronidazole addition—II series) to 208.3 ± 11.9 mL/g VS (in the bioreactor with amoxicillin addition—I series). In the control sample biogas production was 203.7 ± 21.1 mL/g VS. The methane content in all experiments was from 61.3 ± 2.1% to 66.4 ± 3.1%. The results indicated that microorganisms in anaerobic sludge from municipal wastewater are highly resistant to antibiotics in the tested concentrations. Antibiotic present in wastewater probably caused of antibiotic resistance in bacteria.

Annually, a few thousand tons of antibiotics and their transformation products (metabolites and degradation products) are introduced to wastewater treatment plants (WWTPs) as a result of human and animal excretion, or dispose of expired or unused medications. Antibiotics present in wastes might inhibit their treatment processes for instance during methane fermentation. In this study, β-lactams, tetracycline’s, fluoroquinolones, sulphonamides and metronidazole were selected as inhibitors of methane fermentation of sewage sludge collected from municipal WWTP. The experiments were performed in two series with different concentrations of antibiotics. The biogas production did not significantly differ between series, and was from 151.7 ± 18.9 mL/g VS (in the bioreactor with metronidazole addition—II series) to 208.3 ± 11.9 mL/g VS (in the bioreactor with amoxicillin addition—I series). In the control sample biogas production was 203.7 ± 21.1 mL/g VS. The methane content in all experiments was from 61.3 ± 2.1% to 66.4 ± 3.1%. The results indicated that microorganisms in anaerobic sludge from municipal wastewater are highly resistant to antibiotics in the tested concentrations. Antibiotic present in wastewater probably caused of antibiotic resistance in bacteria.

Carbon dioxide (CO2) is often a limiting factor for the growth of microalgal biomass. Consequently, the search for new CO2 sources that do not contain components inhibitory to microalgal metabolism remains a priority. An alternative to the solutions tested thus far may involve the use of CO2-rich gas derived from microbial fuel cells (MFCs). This concept served as the basis for the original experimental work described in this study. The objective of the research was to evaluate the effect of using gases from the anode chamber of an MFC as a CO2 source in the autotrophic cultivation of Tetraselmis subcordiformis. The highest biomass growth efficiency was observed when the CO2 concentration in the culture medium was maintained at 220.0 ± 8.0 mg/L. Under these conditions, the microalga proliferation rate reached 0.52 ± 0.03 g VS/(L∙day) and 11.54 ± 0.42 mg chl-a/(L∙day), with a final biomass concentration of 2.68 ± 0.10 g VS/L and 63.53 ± 2.44 mg chl-a/L at the end of the cultivation cycle. Moreover, the highest total hydrogen (H2) production of 312 ± 38 mL was achieved in the same experimental variant, corresponding to an H2 production rate of 62.4 ± 6.1 mL/day. The removal efficiency of ammonium nitrogen (N-NH4) was notably high in experimental variants using MFC-derived biogas, ranging from 97.0 ± 2.2% to 98.2 ± 1.8%. Additionally, the growing microalgal biomass effectively utilized phosphate phosphorus (P-PO4) and iron, further highlighting its potential for nutrient recovery.

Carbon dioxide (CO2) is often a limiting factor for the growth of microalgal biomass. Consequently, the search for new CO2 sources that do not contain components inhibitory to microalgal metabolism remains a priority. An alternative to the solutions tested thus far may involve the use of CO2-rich gas derived from microbial fuel cells (MFCs). This concept served as the basis for the original experimental work described in this study. The objective of the research was to evaluate the effect of using gases from the anode chamber of an MFC as a CO2 source in the autotrophic cultivation of Tetraselmis subcordiformis. The highest biomass growth efficiency was observed when the CO2 concentration in the culture medium was maintained at 220.0 ± 8.0 mg/L. Under these conditions, the microalga proliferation rate reached 0.52 ± 0.03 g VS/(L∙day) and 11.54 ± 0.42 mg chl-a/(L∙day), with a final biomass concentration of 2.68 ± 0.10 g VS/L and 63.53 ± 2.44 mg chl-a/L at the end of the cultivation cycle. Moreover, the highest total hydrogen (H2) production of 312 ± 38 mL was achieved in the same experimental variant, corresponding to an H2 production rate of 62.4 ± 6.1 mL/day. The removal efficiency of ammonium nitrogen (N-NH4) was notably high in experimental variants using MFC-derived biogas, ranging from 97.0 ± 2.2% to 98.2 ± 1.8%. Additionally, the growing microalgal biomass effectively utilized phosphate phosphorus (P-PO4) and iron, further highlighting its potential for nutrient recovery.