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Manzini E.,University of Milan | Scaglia B.,University of Milan | Schievano A.,University of Milan | Schievano A.,Biomass and Bioenergy Laboratory | And 2 more authors.
International Journal of Energy Research | Year: 2015

In next generation bio-based refineries, hydrolysis and primary (or extractive) fermentations by undefined microbial cultures (UMC) are precursors of secondary bio-transformations, in which H2, CO2 and mixed carboxylates are used as substrate for achieving added-value target products (e.g. bio-based chemicals, bio-plastics and pigments). Dark fermentation (DF) is the most simple UMC-driven hydrolysis and primary fermentations to extract gaseous and soluble mixtures of compounds from raw biomass. Which solid fractions (types of macro-molecules) of mixed raw organic matter (OM) are efficiently hydrolyzed+fermented during DF is an aspect that was rarely considered in depth. Here, a first attempt was made to propose a new approach for understanding the effects of DF on different fractions of biomass. A set of seven different biomasses underwent optimized DF tests and, for simplicity, only the gaseous main product, i.e. bio-hydrogen potential (BHP) production, was used as parameter to assess DF efficacy. BHP was studied in relation with OM characteristics: on one side, chemical composition (macro-molecular fractions) and, on the other side, bioavailability to UMC attack (using two different biological assays). BHP was found significantly correlated (Pearson's test for p<0.05, n=7) only to acid detergent lignin (negatively), soluble sugars and sugars+starch (positively). Bioavailability was negatively correlated with fibrous fractions and to fat-like fractions, but correlations with BHP were poorer (p>0.05, n=7). A statistical model (partial least square regression) was proposed for predicting BHP from OM characteristics, with interesting predictability. In the next future, the proposed approach should be widened to better understand the DF effectiveness not only referred to its gaseous products, but especially focusing on the wide range of soluble products (carboxylates), thought as substrates for secondary biorefinery. © 2015 John Wiley & Sons, Ltd.

Riva C.,University of Milan | Schievano A.,University of Milan | Schievano A.,Biomass and Bioenergy Laboratory | D'Imporzano G.,University of Milan | And 3 more authors.
Waste Management | Year: 2014

The purpose of this study was to observe the economic sustainability of three different biogas full scale plants, fed with different organic matrices: energy crops (EC), manure, agro-industrial (Plants B and C) and organic fraction of municipal solid waste (OFMSW) (Plant A). The plants were observed for one year and total annual biomass feeding, biomass composition and biomass cost (€Mg-1), initial investment cost and plant electric power production were registered. The unit costs of biogas and electric energy (€Sm-3biogas, €kWh-1EE) were differently distributed, depending on the type of feed and plant. Plant A showed high management/maintenance cost for OFMSW treatment (0.155€Sm-3biogas, 45% of total cost), Plant B suffered high cost for EC supply (0.130 €Sm-3biogas, 49% of total cost) and Plant C showed higher impact on the total costs because of the depreciation charge (0.146€Sm-3biogas, 41% of total costs). The breakeven point for the tariff of electric energy, calculated for the different cases, resulted in the range 120-170€MWh-1EE, depending on fed materials and plant scale. EC had great impact on biomass supply costs and should be reduced, in favor of organic waste and residues; plant scale still heavily influences the production costs. The EU States should drive incentives in dependence of these factors, to further develop this still promising sector. © 2014 Elsevier Ltd.

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