Innovative pretreatments for the valorisation of the invasive macroalga Rugulopteryx okamurae

Abstract

Rugulopteryx okamurae is a macroalgae with a high rate of spread, being accumulated in significant quantities in the Strait of Gibraltar (Spain). The use of this macroalgae biomass for the production of value-added compounds represents an interesting alternative to address the environmental problem, while also lowering the economic costs associated with its removal and management. In this work, the application of innovative pretreatments to improve the macroalgae conversion for biorefinery processes was studied, which were compared with thermoacid pretreatment using H2SO4 or HCl, the most widely described in the scientific literature. For this purpose, pretreated and non-pretreated macroalgae were subjected to enzyme hydrolysis. All pretreatments tested increased the glucose bioconversion in the solid phase by 96.7 % concerning the control. The highest glucose concentration was achieved with the biomass pretreated by plasma-activated water (19.21 g·L−1). However, due to its high concentration of hydrolysable sugars, it resulted in lower yields. The highest yield was achieved with the biomass pretreated biologically using Aspergillus oryzae, increasing by 46.5 % compared to the control, which may be attributed to the action of the alginate lyases and xylanases produced by the fungus, promoting glucans accessibility. Finally, the use of acidified broth of Acidithiobacillus thiooxidans for the pretreatment of the macroalgae biomass is promising to minimize the environmental impact and costs associated with the use of synthetic chemicals. This article also highlights the importance of the harvesting time on the macroalgae composition, which affects the saccharification yields.