Massa, Marina (2016) Sustainable production of microalgae biomass in liquid digestates and by products from agro-food industries. [Tesi di dottorato]

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Abstract

Globally, there is growing interest in microalgae production as innovative vegetable biomass rich in phytochemicals at high added value to apply in different commercial sectors (food, feed, nutraceutical, cosmetician and wastewaters depuration) and as future biodiesel source for the high lipid content and fatty acid profile of some species. To date the microalgae market for food and feed is a niche market but it is increasingly relevant and strictly correlate to their chemical composition (in particular lipids, fatty acids profile, proteins, carbohydrates, pigments and vitamins), underlying that microalgae biomass has the potential to be competitive respect the others conventional vegetable sources. From a point of view of biodiesel source the microalgae production is yet too expensive, both for fertilizers cost both for energy consumption for harvesting, drying and extraction. To develop the competitiveness of microalgae based products, some technical and economic aspects, that play a key role in biomass production costs and in production environmental sustainability, have to be considered. In the present research liquid digestates from anaerobic digestion of organic waste and food industry by-products were analyzed as alternative cheap fertilizer for autotrophic and heterotrophic microalgae production. An overview in terms of possible application of produced biomass in commercial sector on the basis of EU legislation was also considered. The thesis work consists of four experiments: 1) An overview of the use of liquid digestates and food industry by-products as microalgae grow media; 2) Heterotrophic production of Galdieria sulphuraria in spent cherry brines and its effects on the biomass productivity and composition; 3) The growth and the ability to metabolize the nutrients presents in different liquid digestates of two species of freshwater microalgae (S. obliquus, B. braunii), a marine diatom (P. tricornutum), and a photosynthetic cyanobacterium (A. maxima); 4) The evaluation of biomass productivity, the carbon dioxide fixation rate and the biochemical composition of two microalgal species, P. tricornutum and S. obliquus, grew indoors in high-tech photobioreactors and open ponds and low photobioreactors technology in greenhouses in southern Italy. Microalgae were cultivated using standard medium and two liquid digestates obtained by anaerobic digestion of vegetable biomass and zootechnical wastes. In conclusion the alternative media applied showed the ability to support sustainably the microalgae production, leading a reduction of productivity of about 25% with the use of by-products of confectionary industry, and a productivity in line with the standard medium with the use of liquid digestates for S. obliquus and P. tricornutum. Furthermore, the biochemical profile changes of biomass produced with the use of the liquid digestates were highlighted, in terms of lipids (average increase of 55%) and carbohydrates (average decrease of about 5%). With the use of by-products from the confectionary industry was observed a variation in the nutritional composition of the biomass, with an average reduction of about 35% of the protein and lipid content and, with an increase of about 70% in terms of polyphenols, in particular anthocyanins, and with an increase of 12% of carbohydrates. Also the lipid profile showed the variations, a decrease of about 70% of saturated fatty acids and an increase of 10% of unsaturated FA for liquid digestates and by products from confectionary industry utilized. The different microalgae species utilized were metabolized and reduced by about 90% the NH4 + -N The different microalgae species were highlighted a good capacity of phyto-remediation with a reduction of about 90% the NH4 + -N and a reduction of PO4 of about 86%. The cultivation with liquids digestates and the wastewater of the preserved cherries production process allow in addition to a reduction in costs of fertilizer, also interesting changes on the composition of the biomass produced and in some cases the enrichment of the biomass with compound with high biological activity.

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