A fundamentally different structure
Where lignocellulosic residues are defined by three structural polymers bound together, microalgae have essentially no lignin and comparatively little structural polysaccharide. The bulk of dry matter is protein — 50–70% in Spirulina — alongside lipids, pigments and other bioactives. The 'ash and extractives' figure shown in the composition bar is therefore doing very different work than it does for straw or cob.
What that means for processing
The absence of lignin removes the single hardest problem in lignocellulosic processing: there is no recalcitrant aromatic polymer to fractionate around. But it also removes the xylan that makes cob and bagasse valuable for prebiotic production. Algae is not an alternative feedstock for the same products — it is a different feedstock for different products.
Where the value sits
Commercial interest in microalgae centres on high-value fractions: phycocyanin and other pigments, omega-3 lipids, complete protein for food and feed, and specialised antioxidant compounds. Prices per kilogram can far exceed anything achievable from crop residue, but so can production cost — cultivation, harvesting and dewatering are all energy-intensive relative to collecting a residue that already exists.
The carbon-capture angle
Algae cultivation can consume concentrated CO₂ from industrial flue gas, which makes it interesting as a bolt-on to a facility already producing a CO₂ stream — turning an emission into a protein or pigment product rather than a disposal cost.
Practical status
Unlike crop residue, algae requires purpose-built cultivation infrastructure rather than a collection network. It is best understood as a complementary long-horizon route rather than a substitute for residue valorisation.
Sources and method. Composition ranges are literature-typical values and vary with variety, soil, climate and harvest timing. Figures are indicative and should be confirmed against local assay data before use in any project assessment.