Trattamento di Biomasse vegetali e algali finalizzato all'ottenimento di energia. Potenziali sviluppi in Sardegna

The biomass employ for energy purposes is the subject of debate and controversy, especially as regards the use of plant species of interest to food and agricultural land. Indeed, the cultivation of plant species for energy enables diversification of agricultural activities, the recovery of wild areas or the exploitation of land not suitable to food production, but requires the use of resources and energy, which must then assess the environmental impacts. The use of biomass in the energy production is a complex issue that involves many aspects such as the knowledge of the actual extractability in a given territory, the chemical and physical properties, the availability of efficient technologies for energy conversion and last, but not least, the management of the supply chain. This aspect is very important when using residual biomass. This doctoral thesis has been carried out to evaluate the biomass energy production in Sardinia, considering the availability and the distribution of these resources in the region, the economic and environmental context. Specifically, it has been taken into account the potential of plant, residual and algal biomass. In this work are examined the main technologies used for biomass energy conversion, with a special reference to thermochemical and biochemical processes. In the thermochemical, combustion, gasification, pyrolysis, pyro gasification, hydrogen production are described. In the biochemical, anaerobic digestion and energy production from microalgae are illustrated. The biorefinery concept is highlighted and the major hurdles to the production of energy from biomass are considered. The amount and distribution of biomass in the whole region in terms of dedicated crops, both agricultural residues and agro-industrial are subjected to a detailed analysis. It is also evaluated the potential energy of each resource and the thermochemical and biochemical energy conversion technologies are identified as the most practicable with a high degree of effectiveness in Sardinia. Regional planning of the biomass energy production requires the exact calculation of the energy needs, the mapping of all the resources available and finally, the definition and implementation of specific strategies. The Biomass Regional Plan is viewed in the overall Regional Action Plan for Renewable Energy and the detailed strategy for this sector is illustrated. Particular emphasis has been given to the segment of the residual biomass because these represent available low cost raw materials for energy production, but are also very important from an environmental point of view. The results of many tests carried out on a pilot plant for anaerobic digestion, are showed in detail. Several tests were carried out by the treatment of the residue of the vegetable market of Sardinia, the waste of the processing of potatoes and the by-products of the oil and dairy industry in the co-digestion with energy crops. To identify the specific relations between the most significant variables for the process, even when subjected to a wide range of variation, the multivariate statistical analysis was employed. The forest biomass have a wide use in the thermal energy production in large areas of the planet. The largest share of biomass fuel comes from the woods and is represented from the direct combustion of the trees or the forestry residues. The construction of a forest biomass-energy chain, however, must take into account many technical, economic and environmental aspects. A study in Ogliastra, for the assessment of availability and distribution of forest biomass, targeted planning of a specific energy supply chain is presented. The study required a methodology of recognition and assessment of forest resources based on GIS method with the use of soil paper integrated with the vegetation chart. The forest biomass have been subjected to a chemical-physical analysis for the evaluation of the energy potential of the territory. The choice of the best energy conversion technology was performed by applying a multi attribute method (MADM). The ability of algal biomass to grow rapidly and to store high amounts of oil has long been known and a lot of studies have been undertaken to make possible its use in replacing fossil fuels. To achieve this goal is necessary to maximize the microalgae yield and know the influence of different variables on their growth. The results of the growth conditions study of the Nannochloropsis oculata, species suitable for the oil production and aquaculture, using two sizes of reactors (6l and 120l) of the type "bubble column" is presented. The main parameters influencing microalgal growth and their interactions are studied through the approach of the design of experiment (DoE). The growth of microalgae is modelled using the modified Gompertz equation. This model allowed calculating the specific speed of growth and to determinate the biomass and oil productivity. The evaluation of the influence of nitrates concentration has made to assess the use of the Nannochloropsis oculata, contextually in the treatment of waste water and in the oil production. The energy characterization of the algal biomass, obtained in the different operating conditions, complete the study. In summary, the plant, residual and algal biomass, may be relevant not only for the energy sector, but also for the whole agro-industrial economy of the island. The biomasses are totally renewable raw materials and can allow to completely rethinking the agro-industrial production. A new approach is the application of the biorefinery concept that allows designing integrated production systems with the production of foods, animal feeds, chemicals and energy, achieving great benefits from an economical and environmental point of view. A plant biomass, widely available in Sardinia, is represented by the artichoke that residues at the end of the culture. Sardinia is, in fact, the third largest producer of this Italian Ortiva with about 12,000 ha divided into four basins in different parts of the region. The crop wastes amount, is estimated prudentially, to about 180,000 t a-1 and is theoretically possible to exploit these to obtain energy, chemicals such as inulin and phenolic substances for food and pharmaceutical industry, fresh and processed vegetable fibres for packaging use. This will require in the future a specific research to assess the real feasibility, but the sector seems to be certainly promising.