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  • Production of liquid hydrocarbons from autotrophic microbial biomass by low temperature autocatalytic conversion Part 3 : Harvesting procedures of microalgae in seawater


Large quantities of biomass suitable for conversion into oil can be achieved by large-scale production of fast growing microalgae. The most promising procedure for harvesting is flocculation followed by either settling or floating at the surface due to gas bubbles. Cultures of Tetraselmis tetrathele and Tetraselmis suecica were selected because of their high growth rate. After they reached pH 9.4-9.7, the pH was artifically raised to 10 which brought about flocculation by forming Magnesium Hydroxide as coagulation centres for algal cells. About 90% of the algae in a culture could be harvested in this way. The chemical procedure has been tested under pilot plant conditions involving sedimentation tanks of 1000 - 1300 l. A local raising of the pH in the surface region of these tanks was sufficient to flocculate the algae in the whole volume. This technique is simple, reliable and economically acceptable. To flocculate and harvest a Tetraselmis t. culture with a cell concentration of 0.5g (dry weight) per litre, 40g NaOH/kg algae harvested were needed and only 25g NaOH/kg algae to induce the flocculation of a Tetraselmis s. culture with a cell concentration of 0.9 g/l. These expenditures correspond to 5-10 US cents per kg oil produced by the subsequent conversion process.

Additional information

Authors: WAGENER K, Technische Hochschule, Aachen (DE)
Bibliographic Reference: EUR 11874 EN (1988)
Availability: (2)
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