Algae-based fuels are considered to be the most sustainable, renewable, effective and environment
friendly response to climate change and food–feed security, as well as the only renewable energy
resource that has the capacity to meet the global demand for fuels in the long-term. Therefore, an
extended overview of the composition, properties and challenges of algae biomass for biofuel application
was conducted based on reference peer-reviewed data plus own investigations. Initially, some general
considerations such as current bioenergy situation and significance of biofuel generations, as well as different
aspects related to biomass use as biofuels are discussed. Then, common issues concerning taxonomical
classification, habitat environment, carbon reserve capacity, production, use, and main
advantages and disadvantages of algae or algae biofuel are addressed. Further, more than 135 characteristics
related to the chemical, phase and mineral composition and properties of algae and algae ash are
evaluated and compared to those of terrestrial biomass, coal and their ashes. As a result specific benefits
and obstacles connected with the composition and properties of algae and algae ash are discussed. The
behaviour of organic and inorganic matter during algae combustion is also described. Finally, the major
technological and environmental challenges related to algae-based fuels are emphasized. The present
data demonstrate that the high contents of inorganic matter with unfavourable modes of element occurrences
(chlorides, sulphates, carbonates, oxalates, nitrates and some oxyhydroxides, phosphates and
amorphous material) in algae and algae ash provoke the most critical technological and environmental
challenges during algae processing for biofuel application and especially during algae thermochemical
conversion. Another very important challenge addressed is the indefinite availability of sustainable algae
resources for production of biofuels and biochemicals and certain recommendations are given. It was
found that the disadvantages of algae biofuel application prevail significantly over the advantages; however,
the major economic, environmental and social benefits appear to compensate the technological and
other barriers caused by the unfavourable composition and properties of algae.