Scale effect of anaerobic digestion tests in fed-batch and semi-continuous mode for the technical and economic feasibility of a full scale digester Barbara Ruffino a,⇑ , Silvia Fiore a , Chiara Roati a , Giuseppe Campo a , Daniel Novarino b , Mariachiara Zanetti a a DIATI, Politecnico di Torino, Corso Duca degli Abruzzi, 24, 10129 Torino, Italy b SMAT, Società Metropolitana Acque Torino, S.p.A., via Po 2, 10090 Castiglione Torinese, TO, Italy highlights  CH 4 production capacity of vegetable waste was assessed on different scales and modes.  CH 4 yield from the pilot scale test was about 80% of that from the smaller scale test.  Produced net electricity was from 30% to 50% of the food industry plant consumption.  Available thermal energy can cover from 10% to near 100% of the plant requirement. article info Article history: Received 28 November 2014 Received in revised form 2 February 2015 Accepted 7 February 2015 Available online 13 February 2015 Keywords: Mesophilic anaerobic digestion Fed-batch tests Semi-continuous tests Vegetable processing waste Cost–benefit analysis abstract Methane production capacity in mesophilic conditions of waste from two food industry plants was assessed in a semi-pilot (6 L, fed-batch) and pilot (300 L, semi-continuous) scale. This was carried out in order to evaluate the convenience of producing heat and electricity in a full scale anaerobic digester. The pilot test was performed in order to obtain more reliable results for the design of the digester. Methane yield, returned from the pilot scale test, was approximately 80% of that from the smaller scale test. This outcome was in line with those from other studies performed in different scales and modes and indicates the success of the pilot scale test. The net electricity produced from the digester accounted for 30–50% of the food industry plants’ consumption. The available thermal energy could cover from 10% to 100% of the plant requirements, depending on the energy demand of the processes performed. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Italian food industry, with a sales volume of 130 G€, is the sec- ond most important industry after the car manufacturing. The Ital- ian food industry plants buy and transform 72% of domestic agricultural raw materials. Inevitably, the processes performed in food industries generate huge amounts of agro-industrial waste. For Italy, Petruccioli et al. (2011) reported productions of 2.4 Mt/ y of grape pomace, 0.7 Mt/y of olive pomace and 0.2 Mt/y of both tomato pomace and soybean integuments. It can be estimated that the transformation of 1 t of agricultural raw materials generates from 30 to 100 kg of organic waste. Agro-industrial waste, that includes both fruit and vegetable waste, may be stabilized by the anaerobic digestion (AD) process (Khalid et al., 2011). AD is known as a more environmentally friendly and energy saving process for stabilizing high-strength organic waste, than other disposal options like landfilling, incin- eration, and composting (Hosseini Koupaie et al., 2014; Traversi et al., 2013). In addition to biogas generation, AD benefits include enhancing nutrient characteristics of the dewatered digestate used as fertilizers as well as pathogens reduction. Greenhouse emissions are also decreased because the AD process diverts organic waste from landfills, thus preventing uncontrolled methane and carbon dioxide emissions from decomposition (Xie et al., 2011). In spite of the potential advantages of the AD process for the management of agro-industrial waste, at present, in Italy, most of it is sent to composting plants. This work aims to carry out a tech- nical and economic assessment of a more sustainable way of managing waste from food industry processes, by evaluating the convenience of producing heat and electricity in an on-purpose http://dx.doi.org/10.1016/j.biortech.2015.02.021 0960-8524/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: DIATI, Department of Environment, Land and Infras- tructure Engineering, Politecnico di Torino, Corso Duca degli Abruzzi, 24, 10129 Torino, Italy. Tel.: +39 011 0907632; fax: +39 011 0907699. E-mail address: barbara.ruffino@polito.it (B. Ruffino). Bioresource Technology 182 (2015) 302–313 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech