Research on Biogas Yield from Macroalgae with Inoculants at Different Organic Loading Rates in a Three-Stage Bioreactor

Abstract

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 VSadded, and the methane yield was 306.5 ± 9.2 L CH4/Kg VSadded. 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 VSadded 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.

Assessment of the Seasonal Potential of Macroalgae and Grass in the Sea of Azov for Methanogenesis and Optimization of the Digestate’s Carbon/Nitrogen Ratio

“…The concentrations of C and N were determined using an EA 3000 elemental composition analyzer (Eurovector, Pavia, Italy). The research results showed that, in the three-stage bioreactor, ΔC reached 10.0 ± 0.03 g/kg TS d and ΔN-0.3 ± 0.001 g/kg TS d. These results were obtained when the initial Cbefore of the substrate supplied to the TSB was 650.0 ± 19.5 g/kg TS, and the Nbefore was 25.0 ± 0.1 g/kg TS [22]. Using these data, the prospects for the use of methanogenesis products as organic fertilizers were evaluated, taking into account the carbon-to-nitrogen (C/N) ratio of the digested substrate in the TSB.…”

“…Studies have shown that high biogas yields can be achieved in a three-stage bioreactor. By using this type of bioreactor, up to 15% more biogas is extracted, and due to its structural features, the energy costs of bioreactor operation are reduced [21,22]. A three-stage bioreactor could be a promising tool for fertilizer production from the excess plant biomass of the Sea of Azov.…”

Changes in Microbiota Composition during the Anaerobic Digestion of Macroalgae in a Three-Stage Bioreactor

“…The preparation chamber prevents oxygen from entering the second chamber together with the biomass. From the preparation chamber, the biomass is fed to the secondary chamber, where the substrate is shifted from aerobic (containing dissolved oxygen) to anaerobic conditions [ 21 ]. Previous research has shown that methanogenesis works effectively when the temperature is maintained at 37 °C [ 4 , 22 , 23 ].…”

Current trends and future directions of global research on wastewater to energy: a bibliometric analysis and review

“…Improving biogas recovery from anaerobic digestion systems represents another hotspot for further research. Two main areas attracting increased research in this aspect are process enhancement through optimising key parameters such as digestion time, process stability, biogas yield and rate, and exploring the use of new and improved microbial inoculants (Zagorskis et al 2023 ). Recent studies have been conducted on the optimisation of the systems for biogas generation from anaerobic digestion by increasing the organic content of feedstock (Freund et al 2020 ), through modelling the energy generation with machine learning algorithms (Kerem and Yuce 2023 ), biogas steam reforming (Park et al 2020 ), and combined optimisation with nitrogen removal (Vergara-Araya et al 2022 ).…”