Intensive cropping of microalgae on pig manure: performance, constraints, use of biomasses. Thesis 125 pages by Lionel DABBADIE
This thesis concerns the depollution of pig manure not microalgae but contains information on the culture of microalgae for other applications, in particular 3rd generation biofuel. See the example of BFS
Green microalgae from the volvocales and chlorococcales group are used to mobilize the nutrients contained in pig manure. These are essentially Scenedesmus falcatus and S. quadricauda, mixotrophic species which have a strong affinity for ammoniacal nitrogen, the predominant form of nitrogen in slurry. For the purification to be effective, the algal biomasses produced must be exported. The simplest way is to have these algae ingested by a cladoceran crustacean (Daphnia magna) which, thanks to its relatively large size (up to 8 mm), is more easily harvested than algae.
To provide management information for the pilot station set up in the summer of 1992 at Chateau-Thierry, numerous small-scale experiments were carried out at the National Museum of Natural History in Paris.
Although, in some cases, very good algal production (up to 315 g DM / m2.sem) and sometimes total purification of certain nitrogenous elements such as ammoniacal nitrogen have been obtained, it has emerged from experiments that mixing is absolutely necessary to achieve high biomass and satisfactory nutrient removal. In unstirred crops, many nuisances occur: flotation or sedimentation of algae, deoxygenation and production of toxic gases.
The accumulation of organic matter causes the formation of flocs (agglomerates of algae) which further increases the sedimentation process.
Another nuisance that causes a decrease in algal biomass is due to the turbidity caused by the presence of parenchyma of decaying terrestrial plants (leaves). It is therefore imperative that crops are placed outside forested areas. The experiments also showed that the proliferation of rotifers (up to 10 ind / l) which had been held responsible for the collapse of the phytoplankton could be an effect and not a cause of it and that the development of algae would be more limited by low temperatures than by low light.
Relatively large algae (15 to 20 µm) are favored by a lengthening of the water retention time in cultures (23 days instead of 15 in winter). The biomass produced is then more stable.
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