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Cocco D.,University of Cagliari | Petrollese M.,University of Cagliari | Asquer C.,Biofuels and Biomass Laboratory | Pistis A.,Biofuels and Biomass Laboratory | And 3 more authors.
Proceedings of the 27th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, ECOS 2014 | Year: 2014

The main aim of the study presented in this paper was to evaluate the energy performance of anaerobic digestion of fruit and vegetable wastes (FVW) on a pilot scale in mesophilic conditions (35 °C), without the addition of any other kind of co-substrate. The anaerobic digestion experiment was carried out in a semi-continuous tubular horizontal reactor (1.13 m3) and lasted 6 months to take into account all the possible changes in feedstock composition during different periods of the year. Throughout the experiment the feedstock was characterized by measuring the total solid content, volatile solid content and higher heating value. The composition and energy contents of the biogas produced and the residue sludge were also evaluated. The results of the study demonstrate that fruit and vegetable wastes lead to high biogas yields and high methane contents. In particular, an average biogas yield of 0.80 Nm3 /kgvs and a specific methane yield of 0.45 Nm3 /kgvs were obtained. Since biogas is mainly used for energy production, a cumulative calculation of the energy content of feedstock, biogas and digestate during the whole experiment was carried out. At the end of the experimental period the energy content of the biogas produced was about 60% of the feedstock energy input, the residual energy content of the digestate was 15%, while the remaining 25% was the energy content of the biomass contained within the reactor. Energy conversion efficiency increases to about 80% by taking into account the biogas that would be produced by the biomass contained within the reactor. It is very interesting to note that the energy content of the reactor remains almost constant when the steady state is completely reached. Source

Scano E.A.,Biofuels and Biomass Laboratory | Scano E.A.,University of Cagliari | Asquer C.,Biofuels and Biomass Laboratory | Pistis A.,Biofuels and Biomass Laboratory | And 3 more authors.
Energy Conversion and Management | Year: 2014

This paper presents the experimental results obtained through an anaerobic digestion pilot plant by using fruit and vegetable wastes as single substrate. The substrate materials were sampled from the wastes produced by the Fruit and Vegetable Wholesale Market of Sardinia (Italy). The experimental study was carried out over a period of about 6 months to evaluate the most suitable operating parameters of the process depending on the availability of different kinds of fruit and vegetable wastes over the different periods of the year. Overall, the optimum daily loading rate of wastes was 35 kg/d, with a corresponding hydraulic residence time of 27 days. The optimum organic loading rate ranged from 2.5 to 3.0 kgVS/m3 d and the average specific biogas production was about 0.78 Nm3/kgVS, with a specific methane yield of about 0.43 Nm3/kgVS. The results of the experimental investigation were used for a preliminary performance evaluation of a full-scale anaerobic digestion power plant for treating all the fruit and vegetable wastes produced by the Wholesale Market of Sardinia (9 t/d). The estimate of daily methane production (290 Nm 3/d) leads to a CHP unit with a power output of about 42 kW and an annual electrical production of about 300 MW h/year (about 25% of the wholesale market electrical consumption). The AD power plant also shows interesting economic features, since its energy production cost (about 150 €/MW h) is slightly lower than the energy purchase cost of the wholesale market (about 200 €/MW h) and a Pay-Back Time of about 7.25 years can be achieved in the case of dispatching the electrical energy to the national grid. The PBT decreases to about 5.4 years if 50% of the available thermal energy is used to substitute heat production from fossil fuel boilers. © 2013 Elsevier Ltd. All rights reserved. Source

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