Biomethane Production Research Articles

A first-of-its-kind study on founding concatenated trio fuels production platform: Biodiesel from lipids, biomethane by anaerobic digestion of defatted biomass, and hydrochar by hydrothermal carbonization of Oscillatoria willei biogas slurry (OWBS)

Sustainable production of multiple biofuels from algae/spent algal biomass through a concatenated route imparts a new energy and environmental sustainability platform. Thus, this is a first-of-its-kind study on establishing a novel and integrated trio fuels production platform using a cyanobacterium Oscillatoria willei (O. willei); - (i) production of biodiesel from O. willei (ii) Anaerobic digestion of defatted biomass for biomethane production (iii) Hydrothermal carbonization (HTC) of O. willei biogas slurry (OWBS) for hydrochar production. Initially, a maximum dry weight of 1.63 g/L was obtained from O. willei on the 18th day, and further, it contains 12.86 % lipids, 41.37 % proteins, and 34.21 % carbohydrates. Biodiesel (Bioenergy- I) produced from the test strain was 67.87 % and it contains preferable fatty acids such as C16:0, C16:1, C18:1, C18:2, and C18:3. The defatted biomass was used for anaerobic digestion (AD) for biomethane (Bioenergy- II) production for up to 45 days. The OWBS from the AD process was used as a feedstock in HTC for the production of hydrochar (Bioenergy- III) under different HTC temperatures (200, 220, 240, 260, and 280 °C) and time (60, 90, 120, 150 and 180 min). The highest hydrochar yield from OWBS was estimated to be 41.65 % at 200 °C and 60 min. Further, elemental analysis of hydrochar revealed 37.6, 4.8, 1.7, 0.1, and 28.3 % of C, H, N, S, and O, respectively with 27.5 % ash content. Based on the results, it is concluded that this novel sequence of strategy delivering trio biofuels along with biogas slurry nutrient removal has not been investigated till now to the best of our knowledge, which will lay a road map for the production of multiple bioenergies along with waste management.

Anaerobic digestion of fat, oil, and grease (FOG) under combined additives: Enhanced digestibility, biogas production, and microbiome

Addition of a single additive (such as biochar or calcium) in anaerobic digestion has been studied previously. However, the effect of combined additives in anaerobic digestion (including fat, oil, and grease) has not been well-investigated yet. In this study, the biogas/biomethane, lipid degradation, and volatile fatty acids were investigated under various concentrations of combined additives. The effect on principal reactions, microbial community, and functional enzymes was also analyzed under different concentrations of calcium-modified biochar. The fat, oil, and grease was degraded up to 81.91 % resulting in 9.03-fold higher biomethane production. Acidogenesis and methanogenesis efficiencies were induced up to 53.31 % and 67.91 %, respectively, due to the enrichment of bacteria (such as Clostridium >50 %, Sporosarcina >18 %, Cellulosilyticum >8 %) and archaea (such as Methanosphaera >49 %). Increased abundance of Co-A ligase, short-chain acyl-CoA dehydrogenase, acetate kinase, and formylmethanofuran dehydrogenase, represented mixed hydrogenotrophic and acetoclastic methanogenesis. The current study demonstrated that co-additives can be added to overcome microbial inhibition and facilitate biomethanation at high fat, oil, and grease concentrations.

Effect of reactor operation modes on mitigating antibiotic resistance genes (ARGs) and methane production from hydrothermally-pretreated pig manure

Numerous efforts have been made to enhance the performance of anaerobic digestion (AD) for accelerating renewable energy generation, however, it remains unclear whether the intensified measures could enhance the proliferation and transmissions of antibiotic resistance genes (ARGs) in the system. This study assessed the impact of an innovative pig manure AD process, which includes hydrothermal pretreatment (HTP) and a two-stage configuration with separated acidogenic and methanogenic phases, on biomethane (CH4) production and ARGs dynamics. Results showed that HTP significantly increase CH4 production from 0.65 to 0.75 L/L/d in conventional single-stage AD to 0.82 and 0.91 L/L/d in two-stage AD. This improvement correlated with a rise in the relative abundance of Methanosarcina, a key methanogenesis microorganism. In the two-stage AD, the methanogenic stage offered an ideal environment for methanogens growth, resulting in substantially faster and higher CH4 production by about 10% compared to single-stage AD. Overall, the combined use of HTP and the two-stage AD configuration enhanced CH4 production by 40% compared to traditional single-stage AD. The abundance and diversity of ARGs were significantly reduced in the acidogenic reactors after HTP. However, the ARGs levels increased by about two times in the following methanogenesis stage and reached similar or higher levels than in single stage AD. The erm(F), erm(G), ant(6)-Ia, tet(W), mef(A) and erm(B) were the six main ARGs with significant differences in relative abundances in various treatments. The two-stage AD mode could better remove sul2, but it also had a rebound which elevated the risk of ARGs to the environment and human health. Network analysis identified pH and TVFAs as critical factors driving microbial communities and ARG proliferation in the new AD process. With the results, this study offers valuable insights into the trade-offs between AD performance enhancement and ARG-related risks, pinpointing essential areas for future research and practical improvements.

Data-Driven Circular Economy of Biowaste to Bioenergy with Conventional Prediction Modelling and Machine Learning

Rapid population growth has not only increased energy demand, but waste generation that has increased and introduced emerging pollutants into waste streams, posing sanitary and environmental risks. The purpose of this research was to investigate waste to energy (anaerobic digestion-bioenergy process) on integrated waste management and digitalization of biomethane production as a data-driven circular economy model across the value chain of the carbon cycle (transition from take-make-dispose to use-make-return) through waste quantification, characterization, biomethane potential test (BMP) to prediction of the biomethane production. Anaerobic digestion experiment was conducted at a laboratory scale to analyze biomethane production from diverse substrates such as food waste, cow manure, sewage sludge, and chicken manure, with an average pH of 7.58. The experimental results obtained were then modelled and simulated with Modified Gompertz, Logistic, and Richards models and compared to machine learning simulation using Python with Gompertz, Logistics, and Richards models. Modified Logistic model was shown to be the best-fit curve, with a coefficient of determination (R2) > 0.9 validating the conventional mathematical modeling and simulation performance. During simulation with machine learning (Python), the experimental results obtained from the cow manure substrate provided the best fitting curve to the training curve compared to other substrates with the highest average of R2 as 1.0 for training, validation, and test data. Cow manure had the best validation performance at MSE (mean squared error) of 25.36 at epoch 1.Graphical

Production of biomethane, biohydrogen, and volatile fatty acids from Nordic phytoplankton biomass grown in blended wastewater

Upgrading carbon-negative microalgal biomass to biofuels and value-added products presents a three-pronged solution for waste treatment, carbon capture, and economically viable bioenergy production. Acidogenesis and methanogenesis are versatile processes at the core of anaerobic digestion systems, facilitating the conversion of diverse biogenic substrates into energy and a wide range of biobased products. The present study was conducted to integrate acidogenesis and methanogenesis for coproduction of biohydrogen, biomethane, and volatile fatty acids from Nordic phytoplankton consortia. For this purpose, microalgal consortia was cultivated in a raceway pond equipped with high surface area structures. Harvested microalgal biomass was subjected to thermoalkaline (2% NaOH solution at 121 °C) and enzymatic (cellulase) pretreatments. The hydrolysates of the pretreated biomass were inoculated with thermally treated sludge for acidogenic fermentation and with mixture of untreated sludge and cow dung (1:1 v/v ratio) for anerobic digestion. The acidogenic process produced a significant amount of biohydrogen (maximum 164.8 mL bioH2/VSload) along with volatile fatty acids (maximum 7.9 g COD/L), while methanogenesis resulted in biomethane production of maximum 210.7 mL bioCH4/VSload, accompanied by an ammonium recovery of 1278 mg NH4+/L. These maximum yields were all achieved by enzymatic pretreatment of the biomass fraction harvested from high surface area brush head structures inserted in the raceway pond. These results have important implications for designing phytoplankton cultivation systems and upstream pathways to optimize energy production from carbon-negative phytoplankton biomass.

Potential of acetic acid to restore methane production in anaerobic reactors critically intoxicated by ammonia as evidenced by metabolic and microbial monitoring

BackgroundBiogas and biomethane production from the on-farm anaerobic digestion (AD) of animal manure and agri-food wastes could play a key role in transforming Europe’s energy system by mitigating its dependence on fossil fuels and tackling the climate crisis. Although ammonia is essential for microbial growth, it inhibits the AD process if present in high concentrations, especially under its free form, thus leading to economic losses. In this study, which includes both metabolic and microbial monitoring, we tested a strategy to restore substrate conversion to methane in AD reactors facing critical free ammonia intoxication.ResultsThe AD process of three mesophilic semi-continuous 100L reactors critically intoxicated by free ammonia (> 3.5 g_N L−1; inhibited hydrolysis and heterotrophic acetogenesis; interrupted methanogenesis) was restored by applying a strategy that included reducing pH using acetic acid, washing out total ammonia with water, re-inoculation with active microbial flora and progressively re-introducing sugar beet pulp as a feed substrate. After 5 weeks, two reactors restarted to hydrolyse the pulp and produced CH4 from the methylotrophic methanogenesis pathway. The acetoclastic pathway remained inhibited due to the transient dominance of a strictly methylotrophic methanogen (Candidatus Methanoplasma genus) to the detriment of Methanosarcina. Concomitantly, the third reactor, in which Methanosarcina remained dominant, produced CH4 from the acetoclastic pathway but faced hydrolysis inhibition. After 11 weeks, the hydrolysis, the acetoclastic pathway and possibly the hydrogenotrophic pathway were functional in all reactors. The methylotrophic pathway was no longer favoured. Although syntrophic propionate oxidation remained suboptimal, the final pulp to CH4 conversion ratio (0.41 ± 0.10 LN_CH4 g_VS−1) was analogous to the pulp biochemical methane potential (0.38 ± 0.03 LN_CH4 g_VS−1).ConclusionsDespite an extreme free ammonia intoxication, the proposed process recovery strategy allowed CH4 production to be restored in three intoxicated reactors within 8 weeks, a period during which re-inoculation appeared to be crucial to sustain the process. Introducing acetic acid allowed substantial CH4 production during the recovery period. Furthermore, the initial pH reduction promoted ammonium capture in the slurry, which could allow the field application of the effluents produced by full-scale digesters recovering from ammonia intoxication.

Dual valorization of coastal biowastes for tetracycline remediation and biomethane production: A composite assisted anaerobic digestion

Harnessing coastal biowaste for dual valorization in water treatment and biofuel production holds paramount importance for sustainability and resource challenges. This study investigated the potential of engineered composite (CABC) derived from coastal biowaste-based materials for tetracycline (TC) removal and biomethane production. High-yield calcium carbonate (CaCO3; 95.65%; bivalve shells) and biochar (GA-BC; 41.50%; green macroalgae) were produced and used as precursors for CABC. The characterization results revealed presence of β-CaCO3 and ν2-CO3 aragonite in CaCO3, and composite homogeneity was achieved. The CABC exhibited a maximum TC sorption capacity of 342.26 mg/g via synergistic sorption mechanisms (i.e., surface/pore filling, electrostatic attraction, calcium ion exchange, and chelation). Supplementation of anaerobic digestion process with GA-BC, CaCO3, and CABC was investigated via three consecutive cycles. Biochemical methane potential of glucose as a sole substrate was increased from 157.50 to 217.00, 187.00, and 259.00 mL-CH4, while dual substrate (glucose+TC) treatment was increased from 94.5 to 146.5, 129.0, and 153.00 mL-CH4 for GA-BC, CaCO3, and CABC, respectively. Moreover, system stability and TC removal were increased with the addition of GA-BC (40.90%), CaCO3 (16.30%), and CABC (53.70%). Therefore, this study exemplifies the circular bioeconomy approach, demonstrating the sustainable use of biowaste-derived composite for water treatment and biofuel production.

Detailed performance analysis of a novel small-scale biomethane liquefaction plant

In the current global energy scenario, an important role is played by the increasing production of biomethane, which is carbon-neutral when burned. In addition to production processes, it is paramount to increase the construction of liquefaction plants, in order to simplify the transportation and use of biomethane. However, biomethane liquefaction plants have limited diffusion because of the complexity of current biomethane liquefaction technologies, which have been adapted from natural gas liquefaction plants. Therefore, novel biomethane liquefaction plants are needed to assist the increasing demand of biomethane in the global market. In previous papers, an innovative biomethane liquefaction plant was proposed and studied; compared to current liquefaction technologies, the main advantage is given by the use of simplified heat exchangers. In this paper, the plant performance is explored in more detail by changing some operating parameters to study the efficiency of the whole process by means of a parametric analysis. The results confirm a high potential of the proposed plant, in terms of coefficient of performance and compactness of the heat exchangers.

Biogas potential of biowaste: A case study in the state of Rio de Janeiro, Brazil

Anaerobic digestion has been widely applied for waste treatment, renewable energy generation and biofertilizer production. The biogas potential in Brazil is sizable, but the state of Rio de Janeiro is largely dependent on fossil fuels, and there is a lack of biogas potential assessments in the state. Thus, this study evaluated biomethane, electricity and biofertilizer potentials in the region. Three different scenarios of biomass supply were considered for four major biowaste streams: sewage sludge; cattle manure; sugarcane processing waste; and food waste. Biomethane generation from the assessed sources could reach 0.6–1.3 billion Nm3 year−1, corresponding to 1,768–3,961 GWh year−1 of electricity and 1.6–3.3 million Mg year−1 of biofertilizer. Cattle manure was responsible for 73–84% of the projected biomethane production, presenting an opportunity to reduce the significant emissions from livestock farming. The estimated biofertilizer production could meet the demands of the state, and the produced electricity could offset up to 10% of the demand. The gas grid could facilitate the distribution of upgraded biomethane, and 10–22% of the natural gas demand could be met. The findings of this work highlight the high potential for biogas generation in Rio de Janeiro, which is up to seven times larger than the current production.

Decision support tool to determine the suitability of demand side management implementation in continuously operated processes – A biorefinery case study

AbstractThe time‐dependent adjustment of a system's power demand simultaneously with current power generation is commonly referred to as demand side management (DSM). DSM strategies are based on the flexibility to purchase electricity at times when prices are low, which can result in monetary benefits. One option to increase the flexibility of continuously operated processes is to oversize them. From an economic point of view, this leads to an increased investment. DSM only serves an economic purpose if the monetary benefits exceed this increase in capital costs. The main goal of this contribution is to develop a decision support tool to help evaluate unit operations regarding their feasibility for DSM implementation. In a case study, the decision support tool was applied to show its functionality on a biomethane production plant. The results show that with the help of the decision support tool, evaluating unit operations concerning their economic DSM potential is possible.

Unlocking the power of synergy: Cosubstrate and coculture fermentation for enhanced biomethane production

The energy crisis, shortage of conventional fuels, and increasing pollution have directed the research toward renewable energy. Methane is one such form of energy that can be used as fuel directly or for electricity generation. It is one of the conventional fuels produced as biogas in triable and rural areas from organic waste using household biogas digesters. However, adapting such technology at commercial and global scales needs to withstand many challenges like purity and quality of methane, yield, cost of production, and efficient utilization of biomass residues. Generally, organic residues from industries and agricultural fields have higher applicability due to availability in abundance but their complex nature slower down the degradation process. In addition, some of the residues are rich in carbon while some are rich in nitrogen which might affect the product yield hence coculture and codigestion are effective approaches to valorize the waste. Coculture provides the possibility to exploit multiple pathways to degrade polymer compounds along with transformation into methane while codigestion might balance the availability of nutrients. The approach has proved promising but commercial exploitation needs further exploration for the compatibility and stability of coculture.

Environmental impact assessment of a novel third-generation biorefinery approach for astaxanthin and biofuel production

A novel third-generation biorefinery approach, including two paths of Ethanol/methane production pathway (EMP) and the direct methane production pathway (DMP), for astaxanthin and ethanol and biogas production from the freshwater microalgae Haematococcus pluvialis was developed previously. To ensure its environmental sustainability, a comprehensive life cycle assessment (LCA) study was conducted based on 1-GJ energy generation from biomethane as the functional unit. Results indicate that the EMP pathway had higher environmental impacts on all categories due to more stages and chemicals/energy consumption (at least five times greater effect). Results showed that while the enzymatic hydrolysis step followed by the fermentation stage was the main contributor to all environmental categories in the EMP route, astaxanthin induction dominated all environmental categories in the DMP route. The results showed that sodium nitrate, phosphate salts, inoculum sludge, acetone, and electricity had considerable environmental impacts. Moreover, despite low enzyme usage in enzymatic hydrolysis, these proteins significantly impacted all environmental categories in this stage. The baseline analysis concluded that to produce 1 GJ energy from methane, about 88 kg and 13 kg CO2 were generated from the EMP and DMP pathways, respectively. A sensitivity analysis was also conducted to compare various ratios of chemicals, such as phosphate salts, with high contributions to enzymatic hydrolysis and astaxanthin induction stages in the EMP and DMP routes, respectively. Finally, the LCA results revealed that the DMP pathway is more environmentally friendly with the same economic value of biomethane and astaxanthin production. This LCA study updated the data related to the environmental assessment of processes to utilize H. pluvialis to produce biofuels and astaxanthin simultaneously.

Biomethane production enhancement from waste activated sludge with recycled magnetic biochar: Insights into the recycled strategies and mechanisms

Adding conductive materials for enhancing methane production from biomass has caused widespread attention. However, the discharge of digestive residues inevitably causes the loss of conductive materials, which not only weakens the roles of conductive materials but also increases the operating cost. This study aims to reveal the potentials of recycled magnetic biochar (MBC) in sludge anaerobic digestion. Results suggested that the direct utilization was better than the indirect utilization. Compared to raw MBC group, methane production further increased by 6.5–7.0 % in multi-cycle MBC groups. The mechanism analysis illustrated that the recycled MBC accelerated the conversion of intermediates. Besides, the recycled MBC promoted the content of redox-active substances and the activity of intracellular electron transfer systems. In addition, the acetoclastic methanogenesis pathway was improved in recycled MBC biofilms while the hydrogenotrophic methanogenesis was reduced. More interestingly, the microbial communities in biofilms presented directional evolutions with the increased cycle numbers of MBC. Correspondingly, the dominant direct interspecies electron transfer patterns changed from Geobacter &Methanosaeta to Clostridium &Methanosarcina, and the electron mediators converted to MBC and c-type cytochrome. The findings provided new insights into reutilization of conductive materials in anaerobic digestion.

Optimizing biogas methanation over nickel supported on ceria-alumina catalyst: Towards CO2-rich biomass utilization for a negative emissions society

Biogas methanation emerges as a prominent technology for converting biogas into biomethane in a single step. Furthermore, this technology can be implemented at biogas plant locations, supporting local economies and reducing dependence on large energy producers. However, there is a lack of comprehensive studies on biogas methanation, particularly regarding the technical optimization of operational parameters and the profitability analysis of the overall process. To address this gap, our study represents a seminal work on the technical optimization of biogas methanation obtaining an empirical model to predict the performance of biogas methanation. We investigate the influence of operational parameters, such as reaction temperature, H2/CO2 ratio, space velocity, and CO2 share in the biogas stream through an experimental design. Based on previous research we selected a nickel supported on ceria-alumina catalyst; being nickel a benchmark system for methanation process such selection permits a reliable data extrapolation to commercial units. We showcase the remarkable impact of studied key operation parameters, being the temperature, the most critical factor affecting the reaction performance (ca. 2 to 5 times higher than the second most influencing parameter). The impact of the H2/CO2 ratio is also noticeable. The response surfaces and contour maps suggest that a temperature between 350 and 450 °C and an H2/CO2 ratio between 2.5 and 3.2 optimize the reaction performance. Further experimental tests were performed for model validation and optimization leading to a reliable predictive model. Overall, this study provides validated equations for technology scaling-up and techno-economic analysis, thus representing a step ahead towards real-world applications for bio-methane production.

Evaluating the efficiency of the enhanced ultrasonic–assisted hydrogen peroxide degradation of low–rank coal biogenic gas

ABSTRACT The efficiency of biogas formation from low-rank coal was improved through ultrasonic-assisted hydrogen peroxide degradation. We investigated various aspects of this process, including the mass of the small-molecule organic matter, changes in the composition of biogas components in three systems, and alterations in the microscopic morphology of coal before and after biogas formation. Our analytical methods included UV-vis spectrophotometry, drainage gas collection method, gas chromatography, infrared spectroscopy, and scanning electron microscopy. Optimal pretreatment conditions were identified with an ultrasonic power of 400 W, a reaction time of 90 min, and a reaction temperature of 60°C. The biogenic methanogenic cycle was delineated into three stages, with the raw coal and filtrate systems exhibiting fast and slow gas production stages during the first and second stages, respectively. In contrast, the residual coal system displayed slow and fast gas production stages during these stages. Methane yields were measured at 270.72 μmol g−1 (raw coal), 303.50 μmol g−1 (residual coal), and 293.43 μmol g−1 (filtrate). Pretreated coal exhibited biomethane yields (residual coal and filtrate) approximately 120% higher than untreated raw coal. Notably, the gas-forming potential of the filtrate should not be underestimated. Ultrasonic-assisted hydrogen peroxide pretreatment disrupted the macromolecular reticulation structure within the raw coal, resulting in the opening of a portion of the aromatic ring structure. This innovative approach offers a novel strategy for augmenting biomethane production from low-rank coal and furnishes a scientific foundation for advancing industrial applications.

Techno-economic analysis of solvent-based biogas upgrading technologies for vehicular biomethane production: A case study in Prados de la Montaña landfill, Mexico City

This study examines the feasibility of utilizing biogas from the Prados de la Montaña landfill (PML) in Mexico City to produce vehicular biomethane. Five solvent-based biogas upgrading technologies are analyzed: water scrubbing (WS), propylene carbonate (PC), dimethyl ether of polyethylene glycol (DPEG), monoethanolamine solution (MEA), and potassium carbonate solution (K2CO3). Process modeling and economic analysis are conducted, focusing on the levelized cost of energy (LCOE) as a comparative indicator. The results indicate that the quality and production capacity of biomethane are comparable across all evaluated technologies. The carbon capture system, which significantly impacts the LCOE, represents the largest component cost of the biogas upgrading plant. Among the case studies, the PC solvent demonstrates the most favorable economic performance ($14.5/MMBTU), followed by the solvents K2CO3, DPEG, and WS, which exhibit similar LCOE values ($17.1–17.5/MMBTU). Conversely, the MEA solvent exhibits the highest cost ($20.3/MMBTU). While these LCOEs exceed the historical average cost of natural gas in the market, the PC solvent remains competitive at a carbon tax price ≥ $9.6/tCO2eq. In conclusion, the commercial viability of producing vehicular biomethane at PML using these technologies is primarily dependent on the projected price of imported natural gas and the carbon tax.

Lignocellulosic biomass pretreatment: Industrial oriented high-solid twin-screw extrusion method to improve biogas production from forestry biomass resources

Forestry lignocellulosic waste is an important, largely untapped source of biomass for producing clean energy. In this study, a high-solids twin-screw extrusion approach is developed as a novel pretreatment method to effectively increase the biogas production rate to better fit commercial requirements. Multiple screw designs are progressively introduced with increasingly intensified mechanical shear. The experiments also looked at the impact of feed solids content and several cost-effective processing aids along with these screw designs. Various characterization methods were used to relate the physical state of the biomass based on its specific surface area and volatile fraction, to the rate of biomethane generation possible from a 14- and 31-day biomethane potential test. An increase in biomethane production over this period by up to 190% was possible with the optimal screw design compared to a benchmark sample. This is a promising finding for the industrialization of biomethane production from forestry lignocellulosic biomass.

A solar-assisted liquefied biomethane production by anaerobic digestion: Dynamic simulations for harbors

This work presents a dynamic simulation model for the production of liquefied biomethane by anaerobic digestion. This layout includes anaerobic digesters supplied by the organic municipal solid wastes, biogas upgrading and biomethane liquefaction units, photovoltaic panels, evacuated solar collectors, electric and thermal storages. Solar collectors provide the heat to anaerobic digesters. Photovoltaic panels supply electricity to the electric devices of the plant. The dynamic model evaluates the electric consumption for the biogas upgrading and biomethane liquefaction units and the thermal load of the anaerobic digesters. The produced liquified biomethane is supplied as fuel to some ships traveling from the mainland to the islands of the Gulf of Naples. The simulation models of the anaerobic digester, biogas upgrading and biomethane liquefaction units are developed in MATLAB® environment and subsequently integrated in TRNSYS18, where the whole plant is modelled. The model of anaerobic digester takes into account both the biological and thermal processes and it considers the digester geometrical and structural features. The biogas upgrading unit consists of a three-stages selective membrane system, whereas the liquefaction system is modelled by the conventional Linde cycle. Significant energy savings and CO2 emissions reduction are obtained, that is a strategic outcome for harbours located in densely populated cities. When the proposed system is compared with the reference system consisting of an existing fleet, equipped with very old ferries using internal combustion diesel engines, the primary energy saving is about 50 %. Considering the present Italian funding policy for biomethane, such system exhibits a good economic profitability.

New green biorefineries from cyanobacterial-microalgal consortia: Production of chlorophyll-rich extracts for the cosmetic industry and sustainable biogas

Microalgae are promising and sustainable candidates for developing biorefineries to obtain valuable bioproducts and bioenergy. However, key challenges, such as low biomass production, high-cost harvesting, and non-efficient extractions, are restricting its large-scale production. Symbiotic relationships between microalgae and cyanobacteria can simultaneously mitigate these technical and economic restrictions. This research aims to develop sustainable and cost-effective biorefineries from two microalgae-cyanobacteria consortia to produce valuable ingredients for the cosmetic field (chlorophylls) and bioenergy (biogas). Solvent screening and cell disruption experiments were carried out to optimise the chlorophyll extraction protocols. Green solvents were chosen for both consortia. The mildness method (vortexing) was enough to achieve the maximum extraction level of chlorophylls (4.8 ± 0.2 mg/g) using 96% ethanol from a consortium composed of Chlorella vulgaris, Tetraselmis sp., and Kamptonema sp. The use of bead-beating was even more effective using water in the case of the consortium of C. vulgaris and Arthrospira platensis (13.5 ± 1.1 mg/g). High-potential antioxidant chlorophyll extracts were obtained for the cosmetic sector. As ethanol traces were found in the residual biomass of the C. vulgaris, Tetraselmis sp., and Kamptonema sp. consortium, the highest cumulative biomethane production (472 ± 32 mLCH4/gVS) was achieved with this residual biomass, the corresponding value for the initial consortium being significantly lower (239 ± 32 mLCH4/gVS). The study concludes through the overall mass balances of the best biorefineries that it is possible to recover up to 100% of both consortia weight as cosmetic ingredients, biogas, and fertilisers or cultivation media.

Metabolic heat production impacts industrial upscaling of ex situ biomethanation trickle-bed reactors

Conversion of electrical energy and CO2 to a chemical energy carrier in the form of biomethane, can be carried out through the process chain of biomethanation. Although this process provides a promising source of fossil-free natural gas, limited experience with upscaling still hampers its industrial maturation. Through methanation of raw biogas in a 225 L pilot-scale trickle-bed reactor by use of electrolysis-derived H2, this work uniquely elucidates how metabolic heat from the exothermic biomethanation process present both a challenge and opportunity for upscaling the biomethanation technology. For the first time, a trickle-bed reactor subject to periodic trickling is characterised based on axial temperature profiles as a result of exothermic heat release, in up-flow and down-flow gas configurations. At maximum, reactor core temperatures in the upper thermophilic range (78 and 83 °C) were recorded in certain axial locations, respectively, for substrate gas flow rates of 3.0 and 7.5 NLCO2/Lreactor/d. During a long-term continuous period at 3.0 NLCO2/Lreactor/d, biomethane production with a CH4 content of ≥95 vol% was measured, in both the reactor’s up-flow and down-flow gas configurations. The alternating flow directions and periodic trickling affected both hydrodynamic factors and thermal stability, showing the importance of preheating and humidifying gaseous feed streams and the implementation of a metabolic heat management strategy, by way of cooling, to provide thermal and reaction stability for future upscaling of trickle-bed biomethanation reactors for biological power-to-gas.