Production of Cellulases and Xylanases from Trichoderma reesei QM9414 using microalgae biomass as substrate.

Abstract

As a result of the current oil crisis, there is an increasing interest in the development of alternative energy sources characterized for being renewable, economically competitive and environmentally friendly. The production of biofuels through biomass conversion from lignocellulosic materials, or more recently, from microalgae biomass, seems to be an attractive option among them. Within the biofuel production, enzymatic hydrolysis represents a key point that must be carefully considered, as the costs derived from the commercial enzymes used during the hydrolysis can compromise the economical feasibility of the process. The microalgae biomass has proved to be an effective wastewater treatment with high nutrient contents. The nutrients accumulation (N and P) in the biomass, which was produced in these processes of treatment, becomes an attractive substrate for the enzyme production. This work aims at implementing the biorefinery concept by valorising the microalgae biomass produced from agro-food industry wastewater treatment as a substrate for enzyme production and the subsequent biofuel generation through enzymatic hydrolysis. Thus, the production of cellulases and xylanases has been tested for the fungal specie Trichoderma reesei QM9414 using microalgae biomass through solid-state fermentation (SSF).

The microalgae biomass was obtained from a mixture of primary wastewater and fertilizer treatment in raceway reactor and thin layer, respectively. This biomass produced was a cocktail of microalgae, principally Scenedesmus obliquus with a content of 45.03% C, 7.80% N and 1.99% P. The fungus, initially stocked at 4ºC in the private collection, was inoculated in commercial potato dextrose agar (PDA) at 28ºC during 7 days, and was suspended in water using it as pre-inoculum. Enzyme production was conducted with different substrates: microalgae, 1:1 sugarcane bagasse:microalgae and 1:1 sugarcane bagasse:wheat bran. It was worked by adding different concentrations of saline solution at 28ºC during 7 days, reducing the external nutrients supply, demonstrating the advantages of using microalgae as a substrate for enzyme production. Each 24 hours two flasks were taken and the enzymes were suspended in water at 150 rpm during 1 h and then centrifuged at 20000xg during 20 min. The supernatants were used for enzyme activity assays that were conducted according to IUPAC recommendations.

The enzymes, produced during this process, were used for the enzymatic hydrolysis of microalgae biomass, and other lignocellulosic materials such as sugarcane bagasse; reporting promising results compared with the commercial enzymes.