The concept of a biorefinery that integrates processes and technologies for biomass conversion demands efficient utilization of all components. Hydrothermal processing is a potential clean technology to convert raw materials such as lignocellulosic materials and aquatic biomass into bioenergy and high added-value chemicals. In this technology, water at high temperatures and pressures is applied for hydrolysis, extraction and structural modification of materials. This review is focused on providing an updated overview on the fundamentals, modelling, separation and applications of the main components of lignocellulosic materials and conversion of aquatic biomass (macro-and micro-algae) into value-added products.

a b s t r a c tIncreasing microalgal starch content by nutrient limitation has been regarded as an affordable approach for the production of third generation bioethanol. This work evaluated starch accumulation in Chlorella vulgaris P12 under different initial concentrations of nitrogen (0-2.2 g urea L À1 ) and iron (0-0.08 g FeNa-EDTA L À1 ) sources, using a central composite design (CCD) for two factors. The obtained model: Starch content (%) = 8.220 À 16.133X 1 + 13.850X 2 1 , relating starch accumulation in microalgae with the coded level for initial urea concentration in the growth medium (X 1 ) presented a good concordance between the predicted and experimental values (R 2 = 0.94). Since accumulation of starch occurred at nitrogen depletion conditions under which the cell growth was much slower than that observed during nitrogen supplemented cultivations, a two-stage cultivation process for high starch accumulation (>40%) and cell growth of C. vulgaris was proposed: a first cultivation stage using nitrogen-and iron-supplemented medium (initial urea and FeNa-EDTA concentrations of 1.1 and 0.08 g L À1 , respectively), followed by a second cultivation stage in a nitrogen-and iron-free medium. The high starch content obtained suggests C. vulgaris P12 as a very promising feedstock for bioethanol production.

Growth parameters and biochemical composition of the green microalga Chlorella vulgaris cultivated under different mixotrophic conditions were determined and compared to those obtained from a photoautotrophic control culture. Mixotrophic microalgae showed higher specific growth rate, final biomass concentration and productivities of lipids, starch and proteins than microalgae cultivated under photoautotrophic conditions. Moreover, supplementation of the inorganic culture medium with hydrolyzed cheese whey powder solution led to a significant improvement in microalgal biomass production and carbohydrate utilization when compared with the culture enriched with a mixture of pure glucose and galactose, due to the presence of growth promoting nutrients in cheese whey. Mixotrophic cultivation of C. vulgaris using the main dairy industry by-product could be considered a feasible alternative to reduce the costs of microalgal biomass production, since it does not require the addition of expensive carbohydrates to the culture medium.