Marine macroalgae waste: A potential feedstock for biogas production

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

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 (VSadded). 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 VSadded to 323.5 L CH4/kg VSadded.

Understanding Macroalgae: A Comprehensive Exploration of Nutraceutical, Pharmaceutical, and Omics Dimensions

Driven by a surge in global interest in natural products, macroalgae or seaweed, has emerged as a prime source for nutraceuticals and pharmaceutical applications. Characterized by remarkable genetic diversity and a crucial role in marine ecosystems, these organisms offer not only substantial nutritional value in proteins, fibers, vitamins, and minerals, but also a diverse array of bioactive molecules with promising pharmaceutical properties. Furthermore, macroalgae produce approximately 80% of the oxygen in the atmosphere, highlighting their ecological significance. The unique combination of nutritional and bioactive attributes positions macroalgae as an ideal resource for food and medicine in various regions worldwide. This comprehensive review consolidates the latest advancements in the field, elucidating the potential applications of macroalgae in developing nutraceuticals and therapeutics. The review emphasizes the pivotal role of omics approaches in deepening our understanding of macroalgae's physiological and molecular characteristics. By highlighting the importance of omics, this review also advocates for continued exploration and utilization of these extraordinary marine organisms in diverse domains, including drug discovery, functional foods, and other industrial applications. The multifaceted potential of macroalgae warrants further research and development to unlock their full benefits and contribute to advancing global health and sustainable industries.

Algae biogas production focusing on operating conditions and conversion mechanisms - A review

Global warming is the result of traditional fuel use and manufacturing, which release significant volumes of CO₂ and other greenhouse gases from factories. Moreover, rising energy consumption, anticipated limitations of fossil fuels in the near future, and increased interest in renewable energies among scientists, currently increase research in biofuels. In contrast to biomass from urban waste materials or the land, algae have the potential to be a commercially successful aquatic energy crop, offering a greater energy potential. Here we discuss the importance of Anaerobic Digestion (AD) for enhanced biogas yield, characterization, and comparisons between algae pretreatment methods namely, mechanical, thermal, microwave irradiation, and enzymatic and catalytic methods. The importance of anaerobic digestion enhances biogas yield, characterization, and comparisons between mechanical, thermal, microwave irradiation, and enzymatic and catalytic treatment. Additionally, operational aspects such as algal species, temperature, C/N ratio, retention period, and particle size impact biofuel yield. The highest algal biogas yield reported was 740 mL/gVS, subtracted from Taihu de-oiled algae applying thermos-chemical pretreatment under conditions of temperature, time, and catalyst concentration of 70 °C, 3 h, and 6%, respectively. Another high yield of algal-based biogas was obtained from Laminaria sp. with mechanical pretreatment under temperature, time, and VS concentration of 38 ± 1 °C, 15 min, and 2.5% respectively, with a maximum yield of 615 ± 7 mL/g VS. Although biofuels derived from algae species are only partially commercialized, the feedstock for biogas might soon be commercially grown. Algae and other plant species that could be cultivated on marginal lands as affordable energy crops with the potential to contribute to the production of biogas are promising and are already being worked on.

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

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.

Anaerobic co-digestion of marine macroalgae waste and fruit waste: Effect of mixture ratio on biogas production

Marine macroalgae waste (MMW) was used at different mixing ratios with fruit waste (FW) to evaluate the potential of co-digestion in enhancing methane yield. The process was conducted at mesophilic conditions (37 °C) with a fixed amount of biomass (10 g, 3.5% TS) and inoculum (150 mL; digested sewage sludge) and using MMW:FW ratios from 40:60 to 70:30. The results showed inhibition of the process for most of the studied substrate ratios, and in the mono-digestion of both substrates, possibly due to the accumulation of volatile fatty acids. A maximum biogas yield of 295 mL/g VS with 72% of methane was however obtained for the 60MMW:40FW ratio, corresponding to an estimated maximum methane yield of 213 mL/g VS and around 46% of the theoretical maximum methane production (49% of organic matter removal). The results show that the co-digestion of MMW with FW enhances the methane yield of both independent substrates.

Biogas production from residual marine macroalgae biomass: Kinetic modelling approach

Modelling the conversion of residual biomass to renewable fuels is of high relevance to promote the development of effective technological solutions. The present study compares the performance of five different kinetic models (pseudo-first-order kinetics, logistics, modified Gompertz, double-Gompertz, and multi-Gompertz) to describe the cumulative methane production during a low-solids anaerobic digestion of marine macroalgae waste. Different substrate concentrations were evaluated (0.9, 1.7 and 2.5% TS) with the best methane yield (105.2 mL CH₄.g VS^-1) being obtained at the highest amount of biomass. All models fitted the experimental data with R² > 0.988. The innovative multi-Gompertz model herein proposed led to the best performance indexes for all tested experimental conditions, allowing to predict methane yields more accurately when the digestion occurs in two or more steps, as it was the case with marine macroalgae waste.