Plentiful seaweed along the coasts of India

Plentiful seaweed along the coasts of India

kdropcaps.S. Rajgopal writes in about a new study that demonstrates how macroalgal biomass from Gelidiella acerosa and Gracilaria dura collected from Adri and Veraval, both on the west coast of India, and Gelidium pusillum collected from Valinokam on the southeast coast could be used in a biorefinery process not only to produce bioethanol fuel, but also valuable coproducts including agar, pigments, lipids and fertilizer.

A ton of fresh biomass supplies several valuable extracts:

  • 0.3–0.7 kg of R-phycoerythrin (R-PE, pigment)
  • 0.1–0.3 kg of R-phycocyanin (R-PC, pigment)
  • 1.2–4.8 kg of lipids, 28.4–94.4 kg of agar (polysaccharide)
  • 4.4–41.9 kg of cellulose
  • 3.1–3.6 kilolitres of mineral solution (fertilizer)

The enzymatic hydrolysis and fermentation of cellulose thus obtained would yield 1.8–17.4 kg of ethanol. A highlight of the process is sequential extraction of the derivatives leading to full utilization of the feedstock.

The process, developed by Dr. C. R. K. Reddy, Chief Scientist, Seaweed Biology and Cultivation Group, Discipline of Marine Biotechnology and Ecology, Central Salt and Marine Chemicals Research Institute, Bhavnagar, Gujarat, and others, is published in the journal Green Chemistry.

Biofuel production alone from seaweed resources is not cost effective if other components remain unutilized. To date, the seaweed processing technologies allow extraction of one or the maximum of two products out of the three – agar, carrageenan, alginate – which constitute only 15-30 per cent of total mass. This means a larger proportion of biomass (70-85 per cent) remains unutilized and is drained off along with effluents.

With this in mind, Dr. Reddy and his team developed a biorefinery process enabling recovery of almost all primary constituents (water, pigments, lipids, polysaccharides and cellulose) of biomass. In this process, first biomass was crushed in a phosphate buffer and pigment was recovered using ultra membrane filtration. The buffer with minerals could be reused for extraction of pigments from fresh biomass. The residue remaining after extraction of pigments was subjected to solvent extraction for recovery of crude lipid and the solvents employed in lipid extraction could also be reused as earlier.

The residue left after lipid extraction was cooked in water at 120ºC for 90 minutes, blended, and then separated from the viscous solution by centrifugation. The viscous solution was cooled at room temperature to form a soft gel from which agar was prepared. The residue obtained during agar processing was finally used as a source for extraction of cellulose using different chemical treatments.