Algal biomass valorization for biofuel production and carbon sequestration: a review

Abstract

The world is experiencing an energy crisis and environmental issues due to the depletion of fossil fuels and the continuous increase in carbon dioxide concentrations. Microalgal biofuels are produced using sunlight, water, and simple salt minerals. Their high growth rate, photosynthesis, and carbon dioxide sequestration capacity make them one of the most important biorefinery platforms. Furthermore, microalgae's ability to alter their metabolism in response to environmental stresses to produce relatively high levels of high-value compounds makes them a promising alternative to fossil fuels. As a result, microalgae can significantly contribute to long-term solutions to critical global issues such as the energy crisis and climate change. The environmental benefits of algal biofuel have been demonstrated by significant reductions in carbon dioxide, nitrogen oxide, and sulfur oxide emissions. Microalgae-derived biomass has the potential to generate a wide range of commercially important high-value compounds, novel materials, and feedstock for a variety of industries, including cosmetics, food, and feed. This review evaluates the potential of using microalgal biomass to produce a variety of bioenergy carriers, including biodiesel from stored lipids, alcohols from reserved carbohydrate fermentation, and hydrogen, syngas, methane, biochar and bio-oils via anaerobic digestion, pyrolysis, and gasification. Furthermore, the potential use of microalgal biomass in carbon sequestration routes as an atmospheric carbon removal approach is being evaluated. The cost of algal biofuel production is primarily determined by culturing (77%), harvesting (12%), and lipid extraction (7.9%). As a result, the choice of microalgal species and cultivation mode (autotrophic, heterotrophic, and mixotrophic) are important factors in controlling biomass and bioenergy production, as well as fuel properties. The simultaneous production of microalgal biomass in agricultural, municipal, or industrial wastewater is a low-cost option that could significantly reduce economic and environmental costs while also providing a valuable remediation service. Microalgae have also been proposed as a viable candidate for carbon dioxide capture from the atmosphere or an industrial point source. Microalgae can sequester 1.3 kg of carbon dioxide to produce 1 kg of biomass. Using potent microalgal strains in efficient design bioreactors for carbon dioxide sequestration is thus a challenge. Microalgae can theoretically use up to 9% of light energy to capture and convert 513 tons of carbon dioxide into 280 tons of dry biomass per hectare per year in open and closed cultures. Using an integrated microalgal bio-refinery to recover high-value-added products could reduce waste and create efficient biomass processing into bioenergy. To design an efficient atmospheric carbon removal system, algal biomass cultivation should be coupled with thermochemical technologies, such as pyrolysis.

Prospects of carbon capture, utilization and storage for mitigating climate change

“…In the USA, a model study confirmed that pure CO 2 from the corn ethanol production process could be used for algae cultivation in an open pond, thus reducing GHG emission and water stress and can avoid the energy-intensive carbon capturing process for CCU (68). A wide range of value-added products for industrial applications can also be produced from algae-based biomass, such as food, feed and cosmetics (69). It seems that algae have a promising future not only for removing atmospheric CO 2 but also can play an important role in producing food, feed and biofuels.…”

“…68 A wide range of value-added products for industrial applications can also be produced from algae-based biomass, such as food, feed and cosmetics. 69 It seems that algae not only have a promising future for removing atmospheric CO 2 but also can play an important role in producing food, feed and biofuels.…”

Microalgal-Based Bioenergy: Strategies, Prospects, and Sustainability

“…Such efficient sequestration of carbon by microalgae can theoretically generate ∼65 million tons of biofuel, costing around $8.52/gallon . On average, microalgal farming in an open/closed system can utilize ∼513 tons of CO 2 to generate ∼280 tons of dry biomass/hectare annually . Such carbon fixation efficacy of microalgal cells not only provides biomass/biofuels but also has greener prospects of remediating industrial flue gases that are rich in CO 2 .…”

“…For example, with the aeration level of 10–20% CO 2 , Chaetoceros muelleri achieved high lipid productivity of 51 mg L –1 day –1 . Other marine strains, such as Nannochloropsis sp., Isochrysis sp., Chlorella salina, Pavlova salina, etc., having oil-rich biomass, have also been explored for their adaptability to varying amounts of CO 2 . Further, the species ability to fix CO 2 and produce bioenergy is primarily dependent upon the specificities of the microalgal physiology and the environmental conditions.…”

Activation temperature and particle size of palm kernel shell vs. the surface properties of activated carbon

“…The use of biomass wastes as starting materials has sparked intense research interest due to their physiochemical stability, light weight, low cost, and environmental friendliness (Aslam et al 2021). Oil palm biomass is an efficient source of carbon for conversion to high-value products especially palm kernel shells (PKS) as activated carbon precursors (Norrrahim et al 2022;Sarwer et al 2022). The high carbon percentage in PKS is promising for the production of activated carbon (AC), as it contributes to a high product yield.…”