Life cycle assessment of microalgae-based aviation fuel: Influence of lipid content with specific productivity and nitrogen nutrient effects

Emission characteristics of cellulosic jet biofuel blend under laminar and turbulent combustion

Alternative biofuels have the potential to reduce greenhouse gas emissions and particulate matter due to free of aromatics compared to traditional petroleum-based aviation fuel. The potential mitigating emission of hydrothermal-condensation-hydrotreating jet biofuel (HCHJ) derived from agriculture residue was investigated. The effects of aviation biofuel components, blend ratio and equivalent ratio on emission characteristics were conducted by Premixed Pre-evaporated Bunsen burner (PPBB) for laminar combustion and ZF850 jet engine for turbulent combustion. In compositions, HCHJ had a higher concentration of cycloparaffins (mostly in C8-C10) while petroleum-based aviation fuel (RP-3) had a higher concentration of alkylbenzenes (mostly in C8-C11). In laminar combustion, HCHJ and both 50% blend HCHJ appear no unburned hydrocarbon (UHC) due to low aromatics content and no sulfur in the biofuel. Moreover, there were no significant differences in NO and NO2 concentration for HCHJ and HCHJ blends. In turbulent combustion, HCHJ blends and RP-3 were compared engine emissions at various state points. Considering all complex effects of fuel and combustion environment, HCHJ blend had a noticeable reduction in PM2.5 emissions in comparison with RP-3 due to their lower aromatics and sulfur content. As HCHJ is similar to RP-3 in C/H ratio, density and heat value and the different aromatics contents have different tendencies to generate PM2.5 at different condition, PM2.5 emission is not only related with the total aromatic content and individual aromatic structure but also the combustion environment at thrust setting and coexisting pollutants including NOx and UHC emissions. CO and NOx emission indicated that both of turbulent state and fuel type influence emissions. HCHJ blend can be benefit for PM2.5 reduction and combustion efficiency growth. PM2.5 reduction can be obtained 77.5% at 10% HCHJ blend and 9.5% at 5% HCHJ blend while combustion efficiency can be obtained 0.05% at 5% HCHJ blend and 0.36% at 10% HCHJ blend through all thrust output.

Emerging microalgae-based biofuels: Technology, life-cycle and scale-up

Microalgae biomass is a versatile feedstock with a variable composition that can be submitted to several conversion routes. Considering the increasing energy demand and the context of third-generation biofuels, algae can fulfill the increasing global demand for energy with the additional benefit of environmental impact mitigation. While biodiesel and biogas are widely consolidated and reviewed, emerging algal-based biofuels such as biohydrogen, biokerosene, and biomethane are cutting-edge technologies in earlier stages of development. In this context, the present study covers their theoretical and practical conversion technologies, environmental hotspots, and cost-effectiveness. Scaling-up considerations are also addressed, mainly through Life Cycle Assessment results and interpretation. Discussions on the current literature for each biofuel directs researchers towards challenges such as optimized pretreatment methods for biohydrogen and optimized catalyst for biokerosene, besides encouraging pilot and industrial scale studies for all biofuels. While presenting studies for larger scales, biomethane still needs continuous operation results to consolidate the technology further. Additionally, environmental improvements on all three routes are discussed in light of life-cycle models, highlighting the ample research opportunities on wastewater-grown microalgae biomass.

A comprehensive review on carbon source effect of microalgae lipid accumulation for biofuel production

Energy is a major driving force for the economic development. Due to the scarcity of fossil fuels and negative impact on the environment, it is important to develop renewable and sustainable energy sources for humankind. Microalgae as the primary feedstock for biodiesel has shown great application potential. However, lipid yield from microalgae is limited by the upstream cost, which restrain the realization of large-scale biofuel production. The modification of lipid-rich microalgae cell has become the focus over the last few decades to improve the lipid content and productivity of microalgae. Carbon is a vital nutrient that regulates the growth and metabolism of microalgae. Different carbon sources are assimilated by microalgae cells via different pathways. Inorganic carbon sources are mainly used through the CO₂-concentrating mechanisms (CCMs), while organic carbon sources are absorbed by microalgae mainly through the Pentose Phosphate (PPP) Pathway and the Embden-Meyerhof-Pranas (EMP) pathway. Therefore, the addition of carbon source has a significant impact on the production of microalgae biomass and lipid accumulation. In this paper, mechanisms of lipid synthesis and carbon uptake of microalgae were introduced, and the effects of different carbon conditions (types, concentrations, and addition methods) on lipid accumulation in microalgal biomass production and biodiesel production were comprehensively discussed. This review also highlights the recent advances in microalgae lipid cultivation with large-scale commercialization and the development prospects of biodiesel production. Current challenges and constructive suggestions are proposed on cost-benefit concerns in large-scale production of microalgae biodiesel.

Optimization upstream CO2 deliverable with downstream algae deliverable in quantity and quality and its impact on energy consumption

Algae CO₂ biofixation provides a promising opportunity due to earn carbon credits and valuable end uses. For balancing technology, energy and economy issues in practical utilization, this approach quantitively interprets the contradictions from upstream CO₂ source with a wide range of initial concentration to downstream CO₂ biofixation product including edible algae and algal biomass. The influence of upstream CO₂ deliverable on algal quantity and quality have been assessed, and the influence of CO₂ concentration on CO₂ transport mode choice has been also assessed coupling the transportation distance. In downstream algal fixation, quantitively relationship of algal growth have been established. The assessment discovered that direct energy consumptions complied with logarithmic relationship with specific productivities while both direct energy and indirect energy consumption complied with linear relationship with protein content. According to sensitive uncertainty analysis, initial CO₂ concentration is a critical parameter to influence significantly energy consumption in upstream CO₂ deliverables and algal quality while the contents of protein and specific productivity are the critical sensitive parameters in downstream algae deliverables. Potential modification systems are achieved for significantly reducing energy consumption by improving specific productivity and carbon abundance with low protein content in algae.