Cascade approach of red macroalgae Gracilaria gracilis sustainable valorization by extraction of phycobiliproteins and pyrolysis of residue.

Phycobiliproteins extraction (primary refining) from Gracilaria gracilis seaweed, harvested in Lesina Lagoon (Italy) and further valorization of the residual algal via pyrolysis (secondary refining), were investigated with a cascade biorefinery approach. R-phycoerythrin (7 mg/g d.w.), allophycocyanin (3.5 mg/g d.w.) and phycocyanin (2 mg/g d.w.) were the main phycobiliproteins extracted. Pyrolysis of G.gracilis residue followed, aiming to investigate the production of bio-oil and biochar within a pyrolysis temperature range of 400-600 °C. Results showed that the bio-oil yield is high (∼65 wt%) at pyrolysis temperature ∼500 °C, but its high content in nitrogenous compounds prevents its use as a biofuel, unless some further de-nitrogenation takes place. Biochar yield ranged between 33 wt% (400 °C) and 26.5 wt% (600 °C). Interestingly, inorganic nutrients including P, K, Ca, Fe and Mg were detected in biochar, suggesting its potential use as recovering system of natural mineral resources from the oceanic reservoir.