TECHNOLOGY FOCUS - BIOLOGY - Preferred Process: The algae suspension is thickened to (5-30, preferably 18-25) wt.%. The excess water coming from the thickening section is recycled both to the ponds/containers of the phototrophic and heterotrophic microalgae. The thermal treatment is performed at 150-330 degrees C, and at a pressure of 0.5-18 MPa, for 0.5-2 hours. The thermal energy required for the thermal treatment derives from solar energy and/or from solar pond. Preferred Composition: The growth water of the phototrophic and heterotrophic microalgae is fresh or salty water, of natural or artificial origin (preferably brackish water with salts concentration of (5-350 g/1); especially sea water or brackish water associated to the wells for producing natural gas/oil). EXAMPLE - An integrated process for producing bio-oil from both phototrophic and heterotrophic microorganisms, was carried out as follows. Cultivation ponds with seawater were used, with a total surface, for phototrophic microalgae, of 377 hectares and 30 cm deep. The phototrophic microalga belonged to the genus Nannochloropsys. Cultivation ponds with seawater were used, with total surface area, for heterotrophic microalgae, of 8 hectares and 1 m deep. The heterotrophic microalga was heterotrophic strain belonging to the genus Nannochloropsys. The following products were fed to the pond of phototrophic microalgae under regime conditions, such as make-up water (1500 tons/hour) to compensate the water lost in purging and by evaporation; CO2 (8.5 tons/hour); sodium nitrate and sodium phosphate to maintain a concentration of 200 and 20 ppm, respectively; and recycled water. When phototrophic microalga had matured, 9450 tons/hour of a suspension at 0.05 wt.% of microalgae in water fed to the thickening area (decanting), was discharged from the ponds. The stream coming from cultivation containers for heterotrophic microalga, consisting of 500 tons/hour of suspension at 0.5 wt.% of heterotrophic microorganisms, reached the same thickening area. Approximately 20 wt.% of the suspension was thickened in the thickening section. An aqueous suspension of 36 tons/hour at 20 wt.%, was continuously removed form the thickened suspension from this area, preheated in a heat exchanger to 150 degrees C, brought to 300 degrees C and 12 MPa in heat generator, fed to pressurized container, and maintained under these conditions for 1 hour. The water discharged from the thickening (9170 tons/hour) was respectively recycled to the cultivation ponds for phototrophic microalgae, after purging 260 tons/hour to keep salinity constant; and in 470 tons/hour in cultivation ponds of heterotrophic microalgae. The biomass thermally treated in pressurized container was cooled in heat exchangers and transported to separator. Bio-oil (2.5 tons/hour) was recovered from this biomass, together with gas (1.5 tons/hour) and an aqueous suspension (32 tons/hour) was fed to the closed containers of the heterotrophic microalgae, after dilution with stream of recycled water. The method allowed specific productivity of 20000 tons/year of bio-oil to be reached, using overall surface of 385 hectares and with a volume of make-up water equal to 12000000 tons/year. For the same production of bio-oil, using a technology based on phototrophic micro-organisms alone, cultivation ponds for 755 hectares and 24000000 tons/year of make-up water would have been necessary.