JAE_fascicolo 2017_04.qxp_Hrev_master 04/12/17 15:29 Pagina 196 Journal of Agricultural Engineering 2017; volume XLVIII:727 Potential biogas production from agricultural by-products in Sicily. A case study of citrus pulp and olive pomace Francesca Valenti, Simona M.C. Porto, Giovanni Cascone, Claudia Arcidiacono Building and Land Engineering Section, Department of Agriculture, Food and Environment, University of Catania, Italy showed the highest production of both citrus pulp and olive Abstract pomace. Therefore, a further analysis regarded the quantification Renewable energy sources represent a suitable alternative to of olive pomace and citrus pulp at municipal level. The results of conventional fossil fuels, due to the possible advantages in terms this analysis showed that the total amount of available citrus pulp of environmental impact reduction. Anaerobic digestion of and olive pomace corresponded theoretically to about 11,102,469 3 biomasses could be considered an environmental friendly way to Nm /year biogas. Finally, the methodology adopted in this study treat and revalorise large amounts of by-products from farming made it possible to identify suitable areas for the development of industries because it ensures both pollution control and energy new biogas plants by considering both the spatial distribution of recovery. Therefore, the objective of this study was to define a the olive and citrus growing areas and the locations of the existing methodology for evaluating the potential biogas production avail- processing industries. able from citrus pulp and olive pomace, which are suitable agri- cultural by-products for biogas production. In the first phase of the study, the spatial distribution of both olive and citrus-producing only areas was analysed in Sicily, a geographical area of the Introduction Mediterranean basin highly representative of these types of culti- The production of climate-altering gases is strictly related to vation. Then, a GIS-based model, which had been previously the increasing demand for energy consumption due to several defined and utilised to evaluate the amount of citrus pulp and olive causes such asuse the rapid growth of the world’s population, the pomace production, was applied to this case study. Based on the accelerating industrialisation as well as the expanding urbanisa- results obtained for the different provinces of Sicily, the province tion. This condition arises public concern on global warming, of Catania was chosen as the study area of this work since it which is likely to grow based on the forecasts of increased emis- sions (Commission of the European Communities, 2007). Since fossil fuels used for energy production are highly responsible for greenhouse gas emissions, renewable energy technologies must be Correspondence: Simona M.C. Porto, Building and Land Engineering Section, Department of Agriculture, Food and Environment, University implemented to balance and reduce fossil energy use (De Montis, of Catania, via S. Sofia 100, 95123 Catania, Italy. 2014) and sustainably satisfy energy demand. Among many E-mail: [email protected] renewable energy alternatives (i.e., solar, wind, hydro, geother- mal, and biomass), which have been intensively studied and Key words: Olive pomace; citrus pulp; by-products; anaerobic diges- developed in the past decades, the production of biogas from tion; biogas; GIS; spatial analysis. commercialbiomass by anaerobic digestion has developed significantly worldwide in the last twenty years (Molari et al., 2014). Acknowledgements: this study was carried out within the research proj- A growing number of biogas plants have been built in Italy, ect of Dr. Eng. Francesca Valenti, PhD student of the Doctorate in which became the third world biogas producer after China and Agricultural, Food, and Environmental Science (XXX Ciclo) of the Germany, and most part of the investments in this field have been University of Catania (Advisor: Dr.Non Eng. Simona M.C. Porto, Co- made in Northern Italy (Piccinini et al., 2010; Fabbri et al., 2013; Advisor: Prof. Eng. Wei Liao). Sgroi et al., 2015). Contributions: the authors contributed equally. However, in most Italian regions, especially in North-Central Italy, the biogas is produced by using dedicated energy crops (e.g., Ethical standards: the experiment carried out in this study complied beetroot, sugar cane, sorghum, and corn and wheat), which arise with the current Italian laws. environmental, social and economic concerns related to the com- petition between food and no-food products (Boscaro et al., 2015). Received for publication: 22 May 2017. As a consequence, there is the necessity to analyse the possibility Accepted for publication: 4 July 2017. of using alternative biomass sources for the production of methane by anaerobic digestion (Thompson and Meyer, 2013). Therefore, ©Copyright F. Valenti et al., 2017 Licensee PAGEPress, Italy in more recent years, an innovative concept to produce biogas, Journal of Agricultural Engineering 2017; XLVIII:727 based on a system of sustainable intensification of crop rotation doi:10.4081/jae.2017.727 and the use of agro-industrial wastes, was developed (Dale et al., 2016). The adoption of this new system of production would This article is distributed under the terms of the Creative Commons reduce the environmental, economic and social impacts generated Attribution Noncommercial License (by-nc 4.0) which permits any non- by both the cultivation of dedicated energy crops and the presence commercial use, distribution, and reproduction in any medium, provid- of waste generated by agro-industrial activities (Dell’Antonia et ed the original author(s) and source are credited. al., 2013). [page 196] [Journal of Agricultural Engineering 2017; XLVIII:727] JAE_fascicolo 2017_04.qxp_Hrev_master 04/12/17 15:29 Pagina 197 Article To date, the development of biogas plants in Sicily is still very the structure of agriculture and animal husbandry system at a limited, despite the importance of the agricultural sector for the national, regional, and local level. island. However, this situation of delay with respect to North Italy The computed values of Scitrus_i and Solive_i were used to per- could be an advantage for the biogas sector, as the development of form GIS analyses, by using the regional technical map related to biogas production plants still has the potential to be planned the year 2008 (RTM 2008) as base map. The RTM 2008 is a according to environmental, economic and social criteria of sus- numerical map produced at a 1:10,000 nominal scale and includes tainability. the projections of the most relevant geographical features. Among On this basis, the objective of this study was to evaluate the the different layers included in the RTM 2008, the olive layer potential availability of two main by-products of the Sicilian agro- (layer G1) and citrus layer (layer G0_A), which are two of the veg- industrial sector, i.e., citrus pulp and olive pomace, obtained from etation layers (layer G) and include the polygons of olive produc- the citrus and olive oil processing industries. Since they are suit- ing areas, were chosen. This last information was compared with able agricultural by-products for biogas production, their quantifi- that coming from the 6th Agricultural Census in order to validate cation and localisation in Sicily could contribute to build an infor- the database used for the GIS-based analyses. This validation mation base suitable for multi-criteria analysis aimed at finding could be carried out also when the considered land use coverage optimal locations for biogas plants in view of increasing them in was not available in the adopted base map, by performing the auto- number. mated classification of agricultural cultivation within remote sens- ing images (Arcidiacono and Porto, 2010, 2008; Modica et al., 2016a, 2016b). Materials and methods Olive pomace and citrus pulp potential production, Op_i The GIS-based model for the computation of olive and Cp_i pomace and citrus pulp availability In order to acquire onlyinformation about the amount of citrus pulp Previous research studies (Valenti et al., 2017a, 2017b, 2017c) (Cp_i) and olive pomace (Op_i) potentially available in each munic- have demonstrated how citrus and olive crops have maintained a ipality of the study area, the model proposed by Valenti et al. decisive position for the regional economy of Sicily and have con- (2016, 2017a) was applied. The average percentage of olive firmed the Sicily’s key role in the Italian production. In fact, by pomace (Ousepav %) and citrus pulp (Cpav %), produced by the process- considering the Italian citrus production, Sicily contributes with ing industries were obtained by utilising a specific questionnaire 56% of the total, and in the Italian olive oil sector, the data analysis for surveying each company of the study area. These indices were confirms that South Italy, particularly Apulia, Calabria and Sicily used to compute Op_i and Cp_i, by applying the following relations: produce 70% of the total olive production (Inea, 2014a, 2014b). To evaluate the potential biogas production from citrus pulp (2) and olive pomace, which are the main by-products of citrus and olive oil industries, the methodology proposed by Valenti et al. (2016) and Valenti et al. (2017a, 2017b) was applied to compute the index iocp_n, which describes the level of availability of olive (3) pomace and citrus pulp for biogas production at provincial level: where Cacitrus and Caolive are the coefficients of