Biofuel Production Systems Research Articles

Life cycle and techno-economic analyses of biofuels production via anaerobic digestion and amine scrubbing CO2 capture

The global energy landscape highlights the importance of the hydrogen economy, emphasizing its critical role in worldwide energy policies. This study explores a system designed for producing biomethanol and biomethane by integrating anaerobic digestion, biogas upgrading, and high-temperature electrolysis. The system builds on real-scale industrial data from an existing anaerobic digestion plant, which has been expanded to include biogas upgrading, an oxy-fuel gas turbine, a Solid Oxide Electrolysis Cell (SOEC), and a methanol production unit. Hydrogen, generated through electrolysis, synthesizes biomethanol by reacting with CO2. Additionally, the system produces biomethane through biogas upgrading. The system incorporates thermal energy integration with an oxy-fuel gas turbine. Life cycle assessment (LCA) results demonstrate the system’s environmental potential, achieved negative CO2 emissions of −0.0075 kgCO2eq/kgBiomass in case of photovoltaic panels and −0.0096 kgCO2eq/kgBiomass in case of wind turbines as electricity sources, attributed to efficient conversion of sewage sludge into valuable biofuels. Thermodynamic modeling in Aspen Plus shows an energy efficiency of 58.09 %, with outputs of 188 kg/h of biomethane and 269 kg/h of biomethanol. The techno-economic analysis reveals a payback period of 6.11 years and a levelized cost of biomethanol of 294.37 € per ton, indicating the system’s economic viability. The LCA further underscores the system’s sustainability, supporting its environmental benefits. This comprehensive analysis provides valuable insights into the viability and environmental impact of the proposed biofuel production system.

Energy Utilization and Conversion in Modern Biomass Conversion Technologies

This paper provides a review on the current state of biomass conversion technologies that are in use and those that could play a significant role in the future, such as those that might be linked to carbon dioxide (CO2) collection and sequestered technology. Since the transportation industry is poised to become the most important new market for large-scale efficient biomass usage, here is where most of the focus will be placed. Bio-energy contribution, now estimated at 40EJ to 55 EJ per year, is expected to expand significantly in the future. Nevertheless, the precise objective of bio-energy will be dependent on the competitiveness aspect with bio-fuels and on agriculture policy globally. For the rest of this century as least, observations suggest a range of 200–300 EJ, rendering biomass a more significant alternatives of energy supply compared to mineral oil. The need to update bio-energy practices so they are compatible with sustainable development strategies is a major concern. It is expected that within the next two to three decades, the cost of electricity generated using sophisticated conversion concepts (such as gasification and contemporary co-firing and gasification) and contemporary biomass sourced fuels (e.g., hydrogen, methanol, and ethyl alcohol from the lignocellulosic biomass) will be competitive with conventional energy sources (partly based on price development with petroleum). An even more efficient and cost-effective biofuel production system may be developed from sugarcane-centric ethanol within the tropical climates.

Replacing All Fossil Fuels With Nuclear-Enabled Hydrogen, Cellulosic Hydrocarbon Biofuels, and Dispatchable Electricity

Abstract We describe a roadmap using three sets of technologies to enable base-load nuclear reactors to replace all fossil fuels in a low-carbon world. The technologies integrate nuclear, wind, solar, hydroelectricity and biomass energy sources. Base-load nuclear reactors with large-scale heat storage enable dispatchable electricity to the grid. The low-cost heat storage enables buying excess wind and solar electricity to charge heat storage for later electricity production while providing assured generating capacity. Nuclear hydrogen production facilities at the scale of global oil refineries produce hydrogen to replace natural gas (gaseous fuel) as a chemical feedstock and heat source. Single sites may have tens of modular reactors produced in a local factory to lower costs by converting to a manufacturing model for reactor construction. Nuclear heat and hydrogen convert cellulosic biomass into drop-in liquid hydrocarbon biofuels to replace fossil-fuel gasoline, diesel, jet fuel, and hydrocarbon feed stocks for the chemical industry. External heat and hydrogen inputs increase the quantities of biofuels that can be produced per unit of cellulosic feedstock, thus assuring sufficient biomass feed stocks to replace all crude oil without major impacts on food and fiber prices. The biofuel production system enables the removal of large quantities of carbon dioxide from the atmosphere that is sequestered as carbon char in the soil while recycling plant nutrients (potassium, phosphorous, etc.) to assure agricultural and forest sustainability.

A comparative study of thermodynamic equations and artificial neural networks in modeling the behavior of glycerol+methanol+CO2 and glycerol+ethanol+CO2 systems in biodiesel production

Classical thermodynamic methods often encounter challenges when applied to model the intricate behavior of liquid-liquid equilibria within biofuel production systems. To overcome these limitations, Artificial Neural Networks (ANNs) have emerged as a promising avenue for effectively describing such complex systems. This study developed and evaluated ANNs to predict the behavior of two key systems, glycerol+ethanol+CO2 and glycerol+methanol+CO2, employing diverse configurations and parameters. A total of 516 distinct ANNs were methodically crafted and evaluated. Notably, the Cascade Feed-Forward architecture exhibited optimal performance in predicting the CO2+glycerol+ethanol system, while the Elman networks excelled in predicting the CO2+glycerol+methanol system. The optimized ANNs were subsequently benchmarked against analogous systems in the literature by applying established thermodynamic equations. Remarkably, the results of this research work underscore the superior predictive accuracy of the ANN approach, yielding significantly diminished error values. Specifically, the mean squared error (MSE) values of 0.1283 and 0.0892 were achieved for the methanol and ethanol systems, respectively. This study contributes substantively by showcasing the ability of ANNs to surpass classical methods for accurate prediction within the intricate domain of biofuel production systems.

Life-cycle assessment of microwave-assisted pyrolysis of pine sawdust as an emerging technology for biodiesel production

Although biofuels are often presented as a renewable and eco-friendly substitute to fossil fuels, it is crucial to have a comprehensive understanding of the complete environmental consequences of biofuel production to make well-informed choices about their usage. This study evaluated the environmental impacts of producing biodiesel from microwave-assisted pyrolysis (MAP) of pine sawdust using life-cycle assessment. A cradle-to-gate system boundary approach encompassing pine cultivation, biomass pre-processing, pyrolysis, and biofuel synthesis via transesterification was used. The ecoinvent v3.7 in openLCA v2.0 software was used to assess the environmental sustainability of the system. The ReCiPe 2016 (H) midpoint impact assessment methodology was used to analyze 18 environmental impact categories. The results showed that producing 1 kg of biofuel from MAP of pine sawdust had environmentally favorable impacts for most categories except global warming potential (1.18 kg CO2 eq.), photochemical oxidant formation (0.71 kg NMVOC eq.), and human toxicity (2.46 kg 1,4-DCB eq.). Biomass production contributed significantly to global warming, freshwater ecotoxicity, human toxicity, and marine ecotoxicity. Pyrolysis contributed 33 % of global warming potential due to non-condensable gas emissions. Biofuel synthesis impacted human toxicity, photochemical oxidant formation, and terrestrial ecotoxicity, mainly due to methanol use. Implementing sustainable practices such as using organic fertilizers, optimization of transportation routes, implementing gas cleaning technologies and effective waste management practices can enhance the environmental performance of this biofuel production system.

Development of yeast and microalgae consortium biofilm growth system for biofuel production

BackgroundThe current study aimed to develop a laboratory-scale biofilm photobioreactor system for biofuel production. Scope & ApproachDuring the investigation, Jute was discovered to be the best, cheap, hairy, open-pored supporting material for biofilm formation. Microalgae & yeast consortium was used in this study for biofilm formation. ConclusionThe study identified microalgae and yeast consortium as a promising choice and ideal partners for biofilm formation with the highest biomass yield (47.63 ± 0.93 g/m2), biomass productivity (4.39 ± 0.29 to 7.77 ± 0.05 g/m2/day) and lipid content (36%) over 28 days cultivation period, resulting in a more sustainable and environmentally benign fuel that could become a reality in the near future.

Efficient coupling of sulfadiazine removal with microalgae lipid production in a membrane photobioreactor

This study explored the feasibility of a coupled system for antibiotic removal and biofuel production through microalgae cultivation. Initial, batch culture experiments demonstrated that sulfadiazine (SDZ) had an inhibitory effect on Chlorella sp. G-9, and 100.0 mg L-1 SDZ completely inhibited its growth. In order to improve SDZ removal efficiency by microalgae, three membrane photobioreactors (MPBRs) with different hydraulic retention times (HRTs) were established for continuous microalgae cultivation. The efficient coupling of SDZ removal and microalgal lipid production was achieved through the gradual increment of influent SDZ concentration from 0 to 100.0 mg L-1. The reduction in SDZ ranged between 57.8 and 89.7%, 54.7–91.7%, and 54.6–93.5% for the MPBRs with HRT of 4 d, 2 d, and 1 d, respectively. Chlorella sp. Was found to tolerate higher concentrations of SDZ in the MPBR system, and the resulting stress from high concentrations of SDZ effectively increased the lipid content of microalgae for potential biodiesel production. With the increase of influent SDZ concentration from 0 to 100.0 mg L-1, the lipid content of microalgae increased by 43.5%. Chlorophyll content, superoxide dismutase activity, and malondialdehyde content of microalgae were also evaluated to explore the mechanism of microalgae tolerance to SDZ stress in MPBR.

Progress of social assessment in the framework of bioeconomy under a life cycle perspective

The bioeconomy is positioned as a sustainable pathway to address the climate crisis and decrease the consumption of fossil resources. Life cycle methodologies are recognised as useful tools for assessing sustainability issues of production and consumption patterns. Nevertheless, the Social Life Cycle Assessment (S-LCA) methodology is less explored despite its potential, although it is true that social sustainability assessment in promoting bioeconomy strategies requires more attention. This study describes the state of the art of the S-LCA methodology under the bioeconomy framework, critically analysing the main procedural and practical issues of its implementation, and the eventual specificities, as well as providing some of the challenges for future studies. This review highlights methodological weaknesses that require further research, related to the definition of system boundaries and cut-off criteria, the method of impact assessment, and the selection of societal issues and stakeholders, as well as uncertainty, among others. In addition, particularities of the bioeconomy in the life perspective were noted, such as multifunctionality and allocation issues of bio-based products, as well as the strong interest in biofuel production systems. Therefore, more efforts are desirable to address the diversity of challenges towards the progress of the S-LCA method in line with other life cycle approaches (environmental and economic). However, the updated S-LCA Guidelines represent a useful and valuable starting point on the way towards a comprehensive (i.e., diverse social concerns) and standardised social assessment under a life cycle perspective.

Fuzzy set scoring methodology for multi-objective sustainability assessment of algal biofuel pathways

This work implements a multi-objective scoring methodology based on fuzzy set theory to evaluate and compare the sustainability metrics of microalgal biorefining concepts. Fuzzy membership functions are developed for three key metrics: minimum fuel selling price, global warming potential, and net energy ratio. Membership functions yield satisfaction scores ( λ ) between 0 and 1 for each objective; achieving λ = 1 indicates a sustainability metric has fully met its target, while λ = 0 is unacceptable for the standards of that metric. The individual λ are combined into an overall satisfaction score, λ o , also ranging from 0 to 1, which is used here to simplify the comparison of sustainability metrics. In addition to baseline biorefining conditions, uncertainties across the algal biofuel production system are assessed through a Monte Carlo analysis of λ o . A case study is developed to compare Combined Algal Processing (a biochemical conversion pathway) against hydrothermal liquefaction (a thermochemical conversion pathway). Baseline results show that lipids are always heavily favored for fuel production, but no practical cultivation operations would be able to achieve such lipid-heavy biomass. The Monte Carlo analysis reveals that current algal fuel conversion technologies cannot simultaneously satisfy all key sustainability objectives. If biomass productivity is doubled and the feedstock is high in lipids, hydrothermal liquefaction can achieve a mean λ o = 0.53 ± 0.12 , still well below a desirable λ o of 1. Combined Algal Processing struggles to achieve high satisfaction scores even in optimistic scenarios and requires a high-lipid feedstock to achieve a mean λ o = 0.10 ± 0.03 . Hydrothermal liquefaction can be integrated downstream of Combined Algal Processing to increase fuel yield and optimistically can achieve a mean λ o = 0.48 ± 0.07 . A combination of system improvements, including biomass productivity, feed composition, fuel yield, and implementation of co-product pathways must work together to satisfy all the relevant sustainability metrics for algal biofuels. The scoring methodology developed here can be readily applied to other microalgal biorefinery concepts and, more broadly, to sustainable fuel development and production. • Holistic evaluation of algal based biofuel systems. • Sustainability assessed through economic and environmental metrics. • Fuzzy set scoring system is applied to holistically assess algae fuel pathways. • Overall satisfaction of sustainability targets depends on algae composition. • Thermochemical pathway outscores biochemical pathway when biofuels are sole product.

Utilization of nanomaterials in accelerating the production process of sustainable biofuels

Around 84 % of the global energy needs are met by fossil fuels, notwithstanding their several drawbacks. Dependence on fossil fuels can be reduced when biofuels become more widely used. Compared to fossil fuel, biofuel is substantially less combustible and derived from renewable resources. Biofuel production from non-edible feedstocks can be enhanced by utilizing nanotechnology. Biofuel research to date has produced promising results, but very few recent studies have underlined the use of nanotechnology to enhance the biofuel production process. This study comprehensively reviews the potential use of nanotechnology in improving biofuel production processes. It also highlights the factors that affect nanomaterial performance in the biofuel production process. The nickel oxide (NiO) nanoparticles (NPs) are shown to be highly efficient, with harvestingChlorella vulgarisbiomass at an efficiency of 98.75 % in 1 min at pH 7. In terms of cost-effectiveness, naked modified magnetic nanoparticles (MNPs) cost significantly less, ranging from £3-500 to £0.5–108 per kg following nanoparticle reactivation. Due to their toxicity, nanomaterials used in biofuel production systems have several detrimental effects on living organisms, the environment, and the economy. Developing non-toxic nanomaterials, utilizing cheaper nanoparticles, and doing additional research might increase knowledge availability and understanding to address the current issues.

Bubble functionalization in flotation process improve microalgae harvesting

Microalgae are a promising resource for biofuel production, although the lack of effective harvesting techniques limits their industrial use. In this context, flotation, and in particular dissolved air flotation (DAF), is an interesting separation technique that could drastically reduce harvesting costs and make biofuel-production systems more economically viable. But because of the repulsive interaction between cells and bubbles in water, the efficiency of this technique can be limited. To solve this problem, we propose here an original DAF process where bubbles are functionalized with a bio-sourced polymer able to specifically bind to the surface of cells, chitosan. In a first part, we modify chitosan by adding hydrophobic groups on its backbone to obtain an amphiphilic molecule, PO-chitosan, able to assemble at the surface of bubbles. Then, using a recently developed technique based on atomic force microscopy (AFM) combined with microfluidics, we probe the interactions between PO-chitosan coated bubbles and cells at the molecular scale; results show an enhanced adhesion of functionalized bubbles to cells (from 3.5 to 12.8 nN) that is pH-dependent. Separation efficiencies obtained in flotation experiments with functionalized bubbles are in line with AFM data, and a microalgae separation efficiency of approximately 60% could be reached in a single step. In addition, we also found that PO-chitosan could be used efficiently as a flocculant (nearly 100% of cells removed), and in this case AFM experiments revealed that the flocculation mechanism is based on hydrophobic interactions between cells and PO-chitosan. Altogether, this comprehensive study shows the interest of PO-chitosan to harvest cells in flotation or flocculation/flotation processes.

Technologies integration towards bio-fuels production: A state-of-the-art review

Biomass is concerned as a most promising alternative energy resource. There are a number of biomass utilization technologies, most of which can be classified to either biological technology or thermo-chemical technology. Both have their specific bottleneck problems. Individual technology is currently almost reaching the ceiling, and technologies integration is thus proposed to make up drawbacks of individual technology with synergy effect. Technologies integration towards bio-fuels production include integration of biological technologies (e.g. algae cultivation from anaerobic digestate, secondary digestion of anaerobic digestate, anaerobic digestion of aerobic digestate, etc.), integration of thermo-chemical technologies (e.g. hydrodeoxygenation of bio-oils, steam reforming of fast bio-oils, cascade pyrolysis, etc.), and integration of biological technologies with thermo-chemical technologies (e.g. gasification of anaerobic digestate, pyrolysis of anaerobic digestate, carbonization of anaerobic digestate etc.). a comprehensive review concerning the state-of-the-art conceptual designs of technologies integration as well as their performances is urgently needed. Accordingly, this paper critically reviews: (1) State-of-the-art conceptual designs of integrated bio-fuel production systems; (2) Overall evaluation of different integrated technologies; (3) Insightful discussion on the future perspectives in this field. Concerning carbon conversion as an overall indicator for the performance of different technologies, it was found that the average carbon conversions were 70.71%, 75.29%, and 70.44% for integration of biological technologies, integration of thermo-chemical technologies, and integration of biological technologies with thermo-chemical technologies, respectively. This review is hoped to be beneficial for promoting future development of integrated bio-fuels production technologies.

Response of Surface Runoff and Sediment to the Conversion of a Marginal Grassland to a Switchgrass (Panicum virgatum) Bioenergy Feedstock System

The land systems between the humid and arid zones around the globe are critical to agricultural production and are characterized by a strong integration of the land use and water dynamics. In the southern Great Plains (SGP) of the United States, lakes and farm ponds are essential components in the land systems, and they provide unique habitats for wildlife, and critical water resources for irrigation and municipal water supplies. The conversion of the marginal grasslands to switchgrass (Panicum virgatum) biofuel feedstock for energy production has been proposed in the region. However, we have limited experimental data to assess the impact of this potential land-use change on the surface runoff, which is the primary water source for surface impoundments. Here, we report the results from a paired experimental watershed study that compared the runoff and sediment responses that were related to the conversion of prairie to a low-input biomass production system. The results show no significant change in the relationship between the event-based runoff and the precipitation. There was a substantial increase in the sediment yield (328%) during the conversion phase that was associated with the switchgrass establishment (i.e., the site preparation, herbicide application, and switchgrass planting). Once the switchgrass was established, the sediment yield was 21% lower than the nonconverted watershed. Our site-specific observations suggest that switchgrass biofuel production systems will have a minimum impact on the existing land and water systems. It may potentially serve as an environmentally friendly and economically viable alternative land use for slowing woody encroachment on marginal lands in the SGP.

Effect of pH on biomass production and carbohydrate accumulation of Chlorella vulgaris JSC-6 under autotrophic, mixotrophic, and photoheterotrophic cultivation

Microalgal biomass, known as the third generation feedstock for biofuels production, is currently being explored mainly for lipids and functional components. However, the potential of microalgal carbohydrates has not been evaluated. In this investigation, Chlorella vulgaris JSC-6 was used for carbohydrates production from CO2 and fatty acids under different cultivation strategies to meet the requirements of a CO2-neutral and clean fermentation system for biofuel production. Autotrophic cultivation resulted in better carbon assimilation and carbohydrate accumulation; about 1.4 g CO2 could be converted to 1 g biomass, of which 50% are carbohydrates. Assimilation of fatty acids in photoheterotrophic and mixotrophic modes was influenced by pH, and pH 7–7.5 supported butyrate and acetate assimilation. The maximum carbohydrate content (49.86%) was attained in mixotrophic mode, and the ratio of the simple sugars glucose-xylose-arabinose was 1:0.11:0.02. The higher glucose content makes the microalgal biomass a suitable feedstock for sugar-based fermentations.

Potencijalni rizici i problemi kod gajenja višegodišnjih energetskih useva

Second-generation biofuel production systems are significantly better than first-generation systems. However, the size of areas in which the energy crops are grown depends on public support, and it decreases if public support is missing. Despite all the environmental and economic benefits, perennial energy crops do not currently play a significant role. It is believed that available land areas will be a basic limiting factor for cultivating biofuel crops in the EU. On the other hand, there is significant untapped potential for bioenergy production in abandoned and marginal land in Southeast Europe. At the same time, perennial energy crops are investments with certain risks. Economically viable production of dedicated energy crops will be difficult to achieve on most lands classified into V-VIII land capability classes. In terms of the risk of farming investments, maize has an advantage over all perennial energy crop systems. We have identified 10 types of risks for successful production of energy crops: (1) Crop water supply; (2) Weed infestation in crops; (3) Risks of frost damages; (4) Crop lodging; (5) Crop diseases and pests; (6) Short harvest periods and variable yields; (7) Economic viability of cultivation on land areas of lower land capability class; (8) Influences of agricultural practices and agro-ecological conditions on biomass quality; (9) Storage of harvested biomass and fire hazard; and (10) economic sanctions, war, and war surroundings. Although the cultivation of perennial energy crops has a perspective, it must be systematically planned and further improved.

Multi-Objective Target-Oriented Robust Optimization of Algal Biofuel Production Integrating Resource Recirculation

The production of algal biofuels has long-time been proven as an applicable alternative for fossil fuels. Yet, its economic performance is challenged by the inexpensive costs of fossil fuels. To address this, integrating various processes to the system yields high-value bioproducts to increase profitability and sustainability. Looking towards a circular economy perspective, the recirculation of resource flows is utilized to meet economic and environmental sustainability through the reduction of waste. Since the recovery of resources used within the production system is unpredictable in terms of output, uncertainty regarding resource recovery is assessed. Previous modelling studies have not looked into the opportunity of integrating continuous recirculation and reuse of resources along with its corresponding output uncertainty. In this work, a novel multi-objective target-oriented robust optimization model is developed centered on an algal biofuel production system that simultaneously optimizes profit and environmental impact, integrates inputs and processes aimed towards a closed-loop system, adopts the principle of resource recovery and recirculation along with the uncertainty of resource recovery outputs. A case study is solved as proof of concept and to illustrate the design methodology, optimal solutions based on economic and environmental performance are analyzed. Scenario analysis is also performed to analyze system behavior under varying conditions. Results show that to get a minimum profit, the robustness index is greater than one indicating the model is very much flexible to sudden changes in demand.

Dark fermentative biohydrogen production using pretreated Scenedesmus obliquus biomass under an integrated paradigm of biorefinery

In recent times, biohydrogen production from microalgal feedstock has garnered considerable research interests to sustainably replace the fossil fuels. The present work adapted an integrated approach of utilizing deoiled Scenedesmus obliquus biomass as feedstock for biohydrogen production and valorization of dark fermentation (DF) effluent via biomethanation. The microalgae was cultivated under different CO2 concentration. CO2-air sparging of 5% v/v supported maximum microalgal growth and carbohydrate production with CO2 fixation ability of 727.7 mg L−1 d−1. Thereafter, lipid present in microalgae was extracted for biodiesel production and the deoiled microalgal biomass (DMB) was subjected to different pretreatment techniques to maximize the carbohydrate recovery and biohydrogen yield. Steam heating (121 °C) in coherence with H2SO4 (0.5 N) documented highest carbohydrate recovery of 87.5%. DF of acid-thermal pretreated DMB resulted in maximum H2 yield of 97.6 mL g−1 VS which was almost 10 times higher as compared to untreated DMB (9.8 mL g−1 VS). Subsequent utilization of DF effluent in biomethanation process resulted in cumulative methane production of 1060 mL L−1. The total substrate energy recovered from integrated biofuel production system was 30%. The present study envisages a microalgal biorefinery to produce biohydrogen via DF coupled with concomitant CO2 sequestration.

A flexible biofuel and bioenergy production system with transportation disruption under a sustainable supply chain network

Increasing energy demand and the rising levels of greenhouse gas emissions have increased the necessity of bioenergy and sustainable energy generation. The sustainable bioenergy supply chain is the key to produce sustainable biofuel. This paper points to render an optimization model for planning a versatile and dependable biomass-to-bioenergy sustainable supply chain network in which crop residuals from several agricultural sectors, multi-transportation disruption modes, multi-biorefineries, multi-biogas plants, and multi-market centers are investigated for two bioenergy sources, namely biofuel and biogas. For this reason, supply chain cost optimization, emissions of feedstock transport, processing, and distributing end biofuel to respective markets are utilized. The multi-setup-multi-delivery (MSMD) concept is incorporated and lead time crashing cost is applied to minimize the lead time in this model. The carbon emission costs at all steps and the variable production rate for the production of bioenergy are included within the model. Finally, one small-scale data and another large-scale data of six agricultural areas, four biorefineries, four biogas plants, and six markets are considered to validate the model's usefulness. The model's goal is to show bioenergy's effect to make a sustainable supply chain of biofuel and biogas. The numerical results reveal that the cost of bioenergy production contributed 54.12%, a major extent of the whole cost in biorefinery and biogas plants. The transportation segment is the preeminent initiator of carbon emissions with 83.33% in the entire carbon emission within the whole supply chain. Although, transportation cost contributed 33.09% of the total cost, the multi setup-delivery-multi-delivery policy minimized the whole supply chain cost. The results provide a systematic guideline for developing a sustainable biofuel supply-chain by minimizing cost, various aspects of transportation logistics, and multi-model alternatives under reduced energy effects.

Green hydrogen from microalgal liquefaction byproducts with ammonia recovery and effluent recycle for developing circular processes

Hydrothermal liquefaction is a promising technology for microalgae-based biofuel production. However, hydrothermal liquefaction’s aqueous wastes have little established reuse, and contain significant fractions of toxic ammoniacal nitrogen. Careful reuse of this waste can assure microalgae-based biofuels are produced with less environmental impact and larger energy efficiency. Microbial electrolysis cells were investigated to valorize this waste product by converting the leftover organics into hydrogen and remove ammonia. Waste hydrothermal liquefaction aqueous phase from two microalgal strains, Tetraselmis sp. and Chlorella sp. were used as feedstocks for hydrogen production in microbial electrolysis cells. Chlorella and Tetraselmis aqueous phase-fed microbial electrolysis cells reach an average current density of 5.1 ± 0.19 A/m2 and 3.8 ± 0.08 A/m2. Compound removal rates and mass removal percentages were also investigated for each feedstock. Acetic acid, propionic acid, ethanol, and glycerol were effectively removed from the aqueous byproduct. Further, microbial electrolysis cells separated up to 34.3% of ammoniacal nitrogen present in the aqueous phase. Charge transfer analysis indicated that proton transfer, not ammonium transfer, contributed to the majority of the hydrogen production in the cathode. Finally, the microbial electrolysis cell effluent was reused to grow the same microalgal strains, leading to the development of a circular biofuel production system. Microalgae regrowth studies using microbial electrolysis cell effluent showed nearly complete removal of total organic carbon, but significantly less removal of total nitrogen. Tetraselmis sp. growth occurred with the Tetraselmis-derived MEC effluent, however, the control medium without effluent produced the most growth. These findings support the possibility of a circular biofuel framework using MECs, but additional constraints, including the removal of inorganic contaminants, are necessary to realize the circular processes.

Amino Acid Catabolism During Nitrogen Limitation in Phaeodactylum tricornutum.

Diatoms can accumulate high levels of triacylglycerols (TAGs) under nitrogen depletion and have attracted increasing attention as a potential system for biofuel production. In Phaeodactylum tricornutum, a model diatom, about 40% of lipid is synthesized from the breakdown of cellular components under nitrogen starvation. Our previous studies indicated that carbon skeletons from enhanced branched-chain amino acid (BCAA) degradation under nitrogen deficiency contribute to TAG biosynthesis in P. tricornutum. In this review, we outlined the catabolic pathways of all 20 amino acids based on the genome, transcriptome, proteome, and metabolome data. The contribution of these amino acid catabolic pathways to TAG accumulation was also analyzed.