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In questo lavoro sono riportati e discussi i dati raccolti in un anno sul digestore anaerobico del Centro Biotrattamenti di ETRA di Camposampiero (PD). Sono stati studiati i parametri che influenzano la produzione e la composizione del biogas. Sono stati inoltre confrontati due sistemi di desolforazione in scala ridotta, un biofiltro a percolazione e un filtro a carboni attivi.
The overall pollution targets as well as issues related to human and animal health and food safety require increasingly sustainable solutions for waste landing and recycling. The Directive 2009/28/EC on renewable energy, sets the target of a 20% share of energy from renewable sources by 2020. A major part of the renewable energy will originate from bio-sources. At least 25% of all bioenergy in the future could originate from biogas, produced from wet organic wastes. Anaerobic digestion (AD) is one of the most economic ways to produce biogas from various feedstocks. The process is accomplished in four stages: bacterial hydrolysis, acidogenesis, acetogenesis and methanogenesis. The methanogenic archaea populations play a key role in the AD. The biogas composition (methane, carbon dioxide and traces of other contaminant gases)depends on the quality of the treated wastes and on the process management parameters. Despite of the increasing attention on AD as a source of renewable energy, in form of biogas, there is still a lack of information about the effect of the activity of methanigens during the conversion of biomass to methane. Besides, each biogas plant receives various types of wastes and runs in different operational and environmental conditions, according to the type of substrates to be digested. In this study the AD plant of ETRA Biotreatment Centre in Camposampiero has been monitored for one year. This plant treats three different kind of wastes: Organic Fraction of Municipal Solid Waste, industrial agrifood liquid wastes and thickened sludge from the wastewater treatments. The produced biogas feeds a CHP (Combined Heat and Power) system. The aim of this work is to point out the parameters that control the biogas production in term of quantity and composition, according to the technical specifications of CHP systems. Moreover, as the hydrogen sulphide is harmful to some CHP technologies, two different pilot scale desulfurizers, an activated carbon filter and a biotrickling filter, were compared. Desulfurization tests were carried out in parallel using a raw biogas flow rate of the order of 2 m²/h. The activated carbon filter was impregnated with 3% of potassium iodide (KI). This filter is suitable for the removal of H₂S, SO₂ and mercaptans and the best performance is obtained with a gas containing water vapor and a small percentage of O ₂ ( 0.5%). The biotrickling filter was provided by Profactor GmbH and it was designed to clean up biogas with sulphur loads up to 15 gS m-3h-1. The biofilter was operated using a mixed culture of sulphide oxidizing bacteria, preliminary Thiobacillus sp.. Results highlight that methane concentration depends on OLR and HRT and is related to H₂S content. The filters experimentation under the same operating conditions allowed us to compare the management costs and the yield of the chemical and biological desulfurization processes. The biological filtration has low operating costs and it produces secondary substances having low disposal costs, while chemical filtration collect the contaminants in the pores until saturation. At the same yield, the activated carbons regeneration costs are much higher than those for the treatment of the acid solution produced by biological filtration.
31 Dicembre 2013
Energia elettrica da biomasse (BIOMASSE2013)