ASSESSMENT OF ORGANIC WASTE MANAGEMENT METHODS THROUGH ENERGY BALANCE

In Italy, the Organic Fraction of Municipal Solid W aste (OFMSW) is nowadays landfilled or processed through aerobic composting. The Italian towns curre ntly support a high cost for OFMSW disposal and cau se a high environmental impact, because of long distance s travelled from towns to a few available landfills and fewer treatment places, as well as the used waste m anagement methods. An interesting option for OFMSW is Anaerobic Digestion (AD), producing biogas and “dig estate”. In this survey a theoretical biogas plant was placed near a town of Sicily Region (Italy), centra lised with reference to the area considered for pro ducing OFMSW. The distances travelled every year to transp ort OFMSW from the nine towns considered to the nearest composting plant and the biogas one were ca lculated using QGIS software. Therefore, the energy balance was computed for each of the four considere d sc narios. Within the implementation of Integrate d Solid Waste Management (ISWM) method, AD resulted i n an energy balance much higher than that of aerobi c composting. In fact, differently from composting, A D can significantly contribute to energy recovery, while retaining the nutrients in the digestate produced a nd reducing Greenhouse Gas (GHG) emissions. The use of a rational network of towns for OFMSW collection and transportation results relevant, in terms of increa sed energy balance, only in the case of composting. The refore, if AD would be implemented as OFMSW management method, by means of biogas plants, each of them placed in an area including some towns, e.g . that considered in this survey, it could highly red uce the cost and the environmental impact of waste di posal.

Moreover, the Anaerobic Digestion (AD) of the biodegradable Organic Fraction of the landfilled MSW causes several environmental problems, like odours due to Volatile Organic Compounds (VOCs) and leachate, the presence of vectors (i.e.insects, rodents and birds) determining public health hazards and plant toxicity (Thorneloe and Pacey, 1994).All these negative impacts and the long time required to stabilise raw materials (care period) are the major issues that make landfills unsustainable (Pognani et al., 2009).The Intergovernmental Panel of Climate Change (2006) reported that more than 60% of the total MSW produced in the world is landfilled: 67% in Europe, 69% in Africa, 61% in America, 63% in Asia (Dong et al., 2014) and 75% in Oceania.Within EU, Greece is the only old Member State where landfills have a share higher than 80%, while all the other EU countries having so high landfill use are new Member States (Cucchiella et al., 2014).The European Council Directive on waste landfills requires Member States to plan strategies for reducing the amount of biodegradable MSW transferred to landfills to only 35% of that produced in 1995 over a 15-year period (EU, 1999).Moreover, according to the Directive 2006/12/EC, "the use of waste as a source of energy" must be encouraged by Member States as a good manner to avoid landfill and to prevent pollution (Novarino and Zanetti, 2012).The compliance to the above Directives, as well as the fact that new landfill sites are difficult to find, because of shortage of utilisable land and opposition of people living nearby, is diverting the use of the Organic Fraction of Municipal Solid Waste (OFMSW) to other purposes (Rimaityt÷ et al., 2010;Novarino and Zanetti, 2012).The high moisture content and low calorific power of OFMSW do not allow energy reclaim by its direct combustion (Chang et al., 1995;Rimaityt÷ et al., 2010).Furthermore, as OFMSW is a biodegradable material, the alternative management methods to the disposal at landfills or incineration are biological processes, such as aerobic composting and AD (Pognani et al., 2009;2012).
Aerobic composting has been the main method for managing OFMSW and has been used increasingly over the last 10 years.
As the new EU policy aims at increasing the production of renewable energy, using also organic wastes, the AD of OFMSW has become very popular (Novarino and Zanetti, 2012;Tudisca et al., 2013).Furthermore, AD is nowadays a very interesting process in Europe, where the number of biogas plants is increasing (Pognani et al., 2009;Novarino and Zanetti, 2012;Comparetti et al., 2013a).
A high yield, in terms of biogas and high quality compost production, is generally associated with the treatment of Separately Collected (SC) or Source Sorted (SS) OFMSW, while Mechanically Sorted (MS) OFMSW gives lower biogas production and a residual material which has to be disposed at landfills or incinerated (CITEC, 2004).Two main simple technologies have been used for the rapid AD of OFMSW: sequential leach bed bio-reactor (O' Keefe and Chynoweth, 2000) and Continuous Stirred-Tank Reactor (CSTR) (Pavan et al., 2000) or Batch bioreactor (Lissens et al., 2001;Kim et al., 2002).Sustainable methods for waste treatment, aimed at recycling and feeding back nutrients to soils, will produce a high benefit for the environment (Braber, 1995;Sakai et al., 1996;Lema and Omil, 2001).
The Centralised Anaerobic Digestion (CAD) of OFMSW inside a bio-reactor, centralised with reference to the area of waste collection, allows to produce methane, determining a net energy gain and a bio-fertiliser from the process residuals (Dagnall, 1995;Hamzawi et al., 1999;Edelmann et al., 2000;Sonesson et al., 2000).The centralised or joint biogas plants are usually of large scale, with digester capacities ranging from a few hundreds of m 3 up to several thousands of m 3 .Denmark was one of the pioneer countries in developing agricultural centralised biogas plants since the early 1980 s. A joint biogas plant allows the valorisation of resources, the co-digestion of manure and other organic wastes, the nutrient recycling and redistribution.Thus, the biogas production cycle generates intertwined agricultural and environmental benefits, like renewable energy production, cheap and environmentally healthy organic waste recycling, lower greenhouse gas emission (i.e.CH 4 , N 2 O and NH 3 ), pathogen reduction through sanitation, improved fertilisation efficiency (Holm-Nielsen et al., 1997;Amon et al., 2006;Holm-Nielsen et al., 2009;Comparetti et al., 2013a;Cucchiella et al., 2014;Eriksson et al., 2014), less nuisance from odours and flies (Birkmose, 2007), economic advantages for farmers.The digested biomass is transferred to storage tanks, which are usually covered with a gas proof membrane, in order to reclaim the remaining biogas (Holm- Nielsen et al., 2009).The biogas produced, rich in methane, would be used either on-site or very near the plant.The possible uses of biogas are: transport to the natural gas distribution pipeline; upgrading into vehicle fuel (like in Sweden); Combined Heat and Power (CHP) generation, for producing hot water, to be used by the heating equipment of the consumers in the surrounding area and electricity, to be sold and transferred to the grid (Dagnall, 1995;Holm-Nielsen et al., 1997;Nielsen et al., 2002;Persson et al., 2006;Novarino and Zanetti, 2012;Comparetti et al., 2013a).Some of the thermal energy is used inside the biogas plant for process heating (Holm-Nielsen et al., 1997).These biogas plants could serve either a single large farm or several ones, typically with in a radius of 10 km ca., because of the high moisture content of the feedstock (6-10% dry matter).Instead, the feedstock having high dry matter (more than 25%), e.g.agro-industrial waste and poultry litter, could be transported for higher distances, up to 50 km (Dagnall, 1995;Bolzonella et al., 2006).The codigestion of OFMSW and sewage sludge or other substrates (agro-industrial by-products, e.g.dairy and olive oil industry residues) was developed in the recent years, in order to obtain multiple waste treatment in a plant and an increasing methane content inside biogas (Fantozzi and Buratti, 2011).
The biogas plants can be equipped with installations for separating the fibre and liquid fractions of the biomass digested ("digestate").The liquid fraction of digestate is stored inside tanks and, then, used in the farms as a pathogen free organic fertiliser (MAFF, 1986;Novarino and Zanetti, 2012).Farmers receive back only the amount of digestate which they are allowed to apply on their fields, according to the regulation on nutrient loading/ha (Holm- Nielsen et al., 2009).Thus, farmers can save money for buying inorganic fertilisers (Dagnall, 1995;Novarino and Zanetti, 2012;Eriksson et al., 2014).Although the fibre fraction of digestate has an immediate value as soil conditioner (because it increases the soil organic matter content and improves its structure), it may be further processed to produce a higher value organic compost (Dagnall, 1995).This process, called aerobic "polishing", is able to reduce odours, pathogens, moisture and carbon content in the digestate (McDougall et al., 2001;Tchobanoglous et al., 2002).
Generally OFMSW allows a high biogas yield inside bio-reactors.When OFMSW consists of a high ratio of garden waste, it has low pH, water content and nutrient concentrations (Rivard et al., 1989;1990).Instead, when OFMSW consists of a high ratio of food waste, it contains high concentrations of proteins, originating also ammonia, which can inhibit AD, especially when the digestate is recirculated in the bio-reactor (Gallert and Winter, 1997).Furthermore, OFMSW can contain considerable amounts of heavy metals and xenobiotic compounds (Braber, 1995;Hartmann and Ahring, 2003).Both "wet" and "dry" anaerobic technologies have been used as part of Mechanical-Biological Treatment (MBT) (Mata-Alvarez, 2003).There are also examples of the processing of mixed source segregated biodegradable wastes, like kitchen and garden wastes (Archer et al., 2005), but there are a few reports on AD plants entirely operating on household food waste separated at source (Banks et al., 2011).The interest in this approach is growing in Europe, due to rising energy costs associated with the processing of wet waste, the requirement to meet the targets of the EU Landfill Directive (99/31/EC) (EU, 1999) and the need to comply with regulations for the disposal of animal byproducts (EU, 2002).When AD is used to process waste separated at source, it produces not only biogas but also a high quality nutrient-rich organic fertiliser (Banks et al., 2011).According to the regulations of many European countries, whether the waste is not separated at source but the organic fraction is reclaimed through a MBT plant, the digestate produced is not allowed to be applied on land (Stretton-Maycock and Merrington, 2009).As a consequence, government and industry are strongly interested in the methods of AD process of household food waste separated at source (Banks et al., 2011).
Waste management is nowadays a worldwide problem to be solved, yet.In fact, the landfill sites have been or will be filled in with MSW very soon in Italy and elsewhere, where people don't accept the use of new sites in their municipal land, while the former landfills have to be recovered (Rimaityt÷ et al., 2010).Moreover, the measures aimed at promoting segregated waste collection were only scarcely implemented in Italy, where the environmentalist movements always fight against the building of incinerators.As a consequence, the inefficient waste management has often caused public health problems in whole cities (Naples, Palermo, etc.), from where sometimes waste has been transported abroad (Germany, etc.).
In the above perspective the aim of this survey is "to make a virtue of necessity": to valorise the Organic Fraction of MSW, instead of treating it as a not segregated waste.The motivation behind this survey is to provide towns with a criterion for selecting, among the organic waste management methods, that able to optimise the energy balance.Thus, by means of this criterion, town administrators could choice an alternative and sustainable method for OFMSW management, enabling to reduce the high cost and the environmental impact of waste disposal.

EXPERIMENTAL PROCEDURES
In this survey the energy balance of four scenarios for the management of the OFMSW produced in an area of Sicily Region (Italy) was evaluated and compared.
The mass of MSW (M MSW ) produced per year was calculated according to the number of inhabitants N inh and the waste mass produced by one person per year m inh (Equation 1): Where: The Total Solid (TS) concentration in OFMSW was determined, by drying the above sample in an oven at 105±2°C temperature for 24 h, as well as Volatile Solid (VS) concentration, by burning biomass at 500°C temperature.Total organic Carbon concentration (CT) was determined, by using an analyser TOC II, as well as Total Nitrogen concentration (NT), by using a Kjeldal apparatus.
AD tests were carried out in a laboratory scale anaerobic digester under controlled temperature (38±0.5°C).The laboratory digester consists of stainless steel vessels (having 20 litre volume) with substrate mixer (having mixing intensity of 60 min −1 ).The biogas produced was collected at the top of the digester and conveyed through the drum type flow meter to a gasholder (25 litre Tedlar® bag).Later the biogas collected was analysed by using a Schmack SSM 6000 biogas analyser.
The following four scenarios for waste management have been considered: (1) currently used method for OFMSW management, whereas this waste collected in each town is transported to the nearest composting plant (in this scenario often the trucks must travel even if they are only partially filled in with OFMSW, so that the transportation cost is not optimised); (2) method for OFMSW management using an efficient and rational network of towns for waste collection and transportation, similar to that proposed by (Menikpura et al., 2013), to the nearest composting plant, aimed at minimising its cost and fuel consumption; (3) method for OFMSW management, whereas this waste collected in each town is transported to a theoretical biogas plant placed at Marineo (Palermo); (4) method for OFMSW management, whereas this waste collected in each town is transported to a theoretical biogas plant placed at Marineo, using the above efficient and rational network of towns for waste collection and transportation.
In the considered scenarios the travelled distance for waste transportation was computed by using the plugin Road Graph for QGIS software.The selected tracks can be displayed by using Google Maps or Google Earth software.
According to the Italian law, the OFMSW produced and collected can be stored for a maximum time of 72 h, then it must be transferred to a landfill or any treatment plant.Therefore, relying on the OFMSW produced and collected in each town during a week, the truck loading capacity and the above law restriction, the number of travels needed was computed for each scenario.
The scenarios 2, 3 and 4 are hypotheses aimed at improving OFMSW management with reference to the current scenario 1.
In the scenarios 1 and 2 OFMSW is transported to two Sicilian composting plants, placed at Castelbuono (Palermo) and Sciacca (Agrigento), where it is treated for producing compost.
In the scenario 2 four groups of towns, each of them using the same truck, addressed to the nearest composting plant, were considered: • San Cipirello and San Giuseppe Jato, from where OFMSW is transported to Sciacca; • Bolognetta and Marineo, from where OFMSW is transported to Castelbuono; • Altofonte, Piana degli Albanesi and Santa Cristina Gela, from where OFMSW is transported to Sciacca; • Belmonte Mezzagno and Misilmeri, from where OFMSW is transported to Castelbuono (Fig. 1).The scenarios 3 and 4 follow the typical centralised Danish pattern, whereas OFMSW is transported from each town to a centralised biogas plant, to be built at Marineo.
In these two scenarios the biogas produced is converted in CHP, while the digestate is stored inside tanks and, then, used as fertiliser.
In the scenario 4 OFMSW is transported, by means of the same truck, from each of the four groups of towns reported in the scenario 2, to the theoretical biogas plant placed at Marineo.
In all scenarios, within the cycle of organic waste management, the energy input is needed for the steps of waste collection, pre-treatment, transportation to the processing plant and treatment process.This energy input depends on the following factors: distance from the waste production site to the processing plant, transportation type (presence or absence of a rational network of towns), design of treatment plant and processing technology.
As OFMSW can be processed into compost (in a composting plant) or biogas (in a bio-reactor), the energy input of waste treatment technology Ein (composting or AD, respectively) is the sum of the energy input for transportation E tr and that for processing technology E techn (Equation 2): (2) Where: E tr = Energy input for OFMSW transportation to the processing plant (J t −1 of treated waste); E techn = Energy input for OFMSW processing technology (J t −1 of treated waste).
In all scenarios trucks of 12 t loading capacity (15 m 3 hopper volume) were considered for OFMSW transportation.As far as the fuel consumption, it is difficult to know the effective data of used machines, both trucks and tractors (Febo and Pessina, 1995).According to EUCAR (2007) a fully loaded new truck consumes 23.5 l of diesel fuel 100 km −1 , assuming the density of the fuel 832 kg m −3 and its heating value 43.1 MJ kg −1 .Fuel consumption was calculated according to the used loading capacity of the truck.
The AD results of OFMSW were evaluated by means of the following indicators: biogas production intensity b, biogas yield from biomass BM, biogas yield from biomass TS BTS, biogas yield from biomass VS BVS, energy obtained from biomass eM, from biomass TS eTS and from biomass VS eVS.Biogas production intensity b indicates the volume of biogas produced during the time of biomass biological degradation.Biogas yield from biomass BM, from biomass TS BTS and from biomass VS BVS was calculated by means of the following Equations 3 to 5 (Navickas et al., 2003): Where: e b = Energetic value of biogas (MJ m −3 ), which depends on methane concentration in biogas (%).
The energetic value of biogas was determined by means of the following Equation 9: 0.0353 100 Where: The energy efficiency of OFMSW conversion into biogas was determined as follows (Equation 10):

RESULTS AND DISCUSSION
The surveyed towns of Palermo province produce 35.9 thousand tonnes of MSW per year (Table 1).OFMSW was supposed to be the 30% of MSW, that is equal to 10.8 thousand tonnes, of which only the 70% is collected (Sicilian Region, 2010;Comparetti et al., 2012).Therefore, 7.5 thousand tonnes of OFMSW per year are collected and available for composting or AD.
The chemical composition of OFMSW sample resulted as follows: 15.6% TS; 91.1% organic materials (in TS); 5.69% organic carbon; 0.328% total nitrogen (TS).Generally optimum C/N ratios in anaerobic digesters are in the range of 20-30 (Themelis and Verma, 2004;Ward et al., 2008).The C/N ratio of the OFMSW analysed resulted 17.4 and, therefore, optimal for AD process.Nevertheless, in a review article (Ward et al., 2008) reported that lower C/N ratios (approximately 9) are also accepted by anaerobic bacteria after an acclimation period.
During AD tests, whose duration was 12 days, the biogas yield obtained from biomass resulted 104.6 l kg −1 (Table 2 and Fig. 2).The methane concentration in biogas was 61.9%.The biogas yield from organic matter was 712.7 l kg −1 and, therefore, comparable with the results of Banks et al. (2011), i.e., 642 l kg −1 with a methane content of 62% and Bolzonella et al. (2006), i.e. 700 l kg −1 with a biogas yield from biomass of 180 l kg −1 and a methane content of 56% from sorted OFMSW.
The biogas yield from organic matter could be temporally variable, due to changing life style and consumed food composition.The results obtained by Mata-Alvarez et al. (1992), using organic waste coming from a large food market, show that biogas yield from a similar feedstock reaches 487 l kg −1 .The energy obtained from biomass (e M ) resulted 2.28 MJ kg −1 , that from dry matter (e SM ) 14.68 MJ kg −1 and that from organic matter (e SOM ) 16.13 MJ kg −1 .
In the scenario 1 the total travelled distance for OFMSW transportation per year resulted 191,748 km, while in the scenario 3 this distance decreased to 42,432 km (Table 3).
With respect to the total travelled distance per year recorded in the scenario 1, in the scenarios 2 and 4, having a rational network of towns for OFMSW transportation to the nearest composting (scenario 2) or biogas plant (scenario 4), this distance decreased to 111,146 and 28,954 km, respectively (Table 3).
In the scenario 2 the total travelled distance per year decreased by 42% with respect to the scenario 1, as well as the energy input for OFMSW transportation, reduced by 40% (Table 4).In the scenario 3 the total travelled distance per year and the energy input for waste transportation decreased by 78% with respect to the scenario 1.
In the scenario 4 the total travelled distance per year and the energy input for transportation decreased by 74% with respect to the scenario 2, even if the same rational network of towns for OFMSW collection and transportation is used in both scenarios.
Thus, the scenario 1 is the worst one, in terms of energy input for transportation, but the adoption of a rational network for this operation can significantly reduce this input, as it is shown in the scenario 2.
The energy input for OFMSW composting technology resulted 1751 GJ per year and, therefore, higher by 29% with respect to AD technology (1240 GJ per year).Furthermore, the anaerobic treatment technology produces biogas, which resulted in an energy output of 17198 GJ.
The highest total energy balance per year was recorded in the scenarios 4 and 3, 15738 and 15647 GJ, respectively (Table 4).
The scenarios 1 and 2 showed no energy production capacity but only energy usage for transportation and composting, so that they resulted in a negative total energy balance (Fig. 3).These results comply with those obtained by Corsten et al. (2013).In fact, differently from composting, AD can significantly contribute to energy recovery, while retaining the nutrients in the digestate produced and reducing Greenhouse Gas (GHG) emissions (Corsten et al., 2013).
In the four considered scenarios the energy input for waste treatment technology per inhabitant was calculated according to the number of inhabitants of each town (Fig. 4).The results showed that the town of Santa Cristina Gela has the highest energy input per inhabitant in all scenarios, as it has the lowest number of inhabitants and a high transportation distance.
The OFMSW composting technology requires energy input, which was calculated to be 232 MJ t −1 .Energy input for AD resulted 165 MJ t −1 , which can be compared to the results obtained by Bolzonella et al. (2006) during the AD of sorted MSW (72 kWh t −1 , equal to 259.2 MJ t −1 ).

CONCLUSION
Waste management is a key element contributing to a sustainable and efficient resource use, because it includes waste prevention and reuse, as well as recycling of products (Corsten et al., 2013).
The Directive 75/442/EEC defines a hierarchy of five waste management options, which must be applied by EU Member States: (1) waste prevention; (2) waste reuse; (3) waste recycling; (4) waste recovery, including the recovery of part of the energy embodied inside raw materials through AD; (5) safe waste disposal at landfills.The implementation of the above hierarchy is aimed at preventing and reducing waste production, avoiding, eliminating and preventing the causes of environmental impact, preventing GHG emissions, saving energy, protecting resources, creating new jobs and developing green energy technology (Menikpura et al., 2012;Corsten et al., 2013;Cucchiella et al., 2014).
Yet, a combination of treatment methods to manage the different waste fractions, e.g.recycling and AD, is required for a sustainable MSW management (Liamsanguan and Gheewala, 2008;Bahor et al., 2009;Tabata et al., 2011;Hoornweg and Bhada-Tata, 2012).This approach, known as Integrated Solid Waste Management (ISWM), includes the source-separation of waste made by residents, an efficient collection and transportation network (similar to the rational network of towns used in this survey), the recovery of useful materials and energy, as well as the disposal of residual waste (Kathiravale and Yunus, 2008;Menikpura et al., 2012).
OFMSW contaminates recyclable materials in combined waste collection methods and releases methane to the atmosphere when landfilled.Methane has a Global Warming Potential (GWP) 23 times higher than that of carbon dioxide over a 100-year period (Lema and Omil, 2001) and therefore, significantly contributes to climate change (Browne and Murphy, 2013).About 50% of MSW is nowadays landfilled, whereas a content of 30% ca. of OFMSW (unless paper and cardboard) is included in this waste (Tilche and Malaspina, 1998).
Among Southern Europe countries, MSW generation has recently increased in Spain, as a result of improved living standards, so that management measures are required to minimise the impact of MSW on the environment.The OFMSW produced in Spain, that is between 40 and 45% of the MSW, is suitable to be used for producing electricity through AD and CHP plants.In fact, 8.5 million tonnes ca. of biological waste were processed in Spanish treatment plants in 2006(Fernandez Rodriguez et al., 2012).
Furthermore, a very high increase of anaerobically digested OFMSW is envisaged in the next future, especially as a consequence of the GHG emission reduction agreed during Kyoto summit: a daily reduction of 180,000 tonnes of CO 2 equivalents can be estimated as contribution of AD, that is 30% ca. of the global emission reduction agreed during this summit (Tilche and Malaspina, 1998).
As a result of implementing an appropriate ISWM method, organic waste landfilling will be avoided and, therefore, the release of methane to atmosphere will be prevented, while resources such as energy and materials will be recovered and GHG emissions will be mitigated (Menikpura et al., 2013).
OFMSW is one of the largest waste fractions produced yearly in Italy, as well as in other European countries.11 million tonnes ca. of OFMSW are produced yearly in Italy but only 1% ca. is currently treated inside AD plants.A large fraction of this OFMSW, 50% w/w ca., together with other wastes, is disposed at landfills.
Even if landfills usually have biogas recovery facilities, 1700-2400 GWh ca. of potential renewable energy per year is lost (Di Maria et al., 2012).
In Sicily, in 2011, 5 millions ca. of inhabitants produce 2 million tonnes ca. of MSW per year (430 kg/person/year), of which the 37% (159 kg/person/year) can represent the organic fraction, even if the OFMSW treated is only the 3% ca. of MSW (Comparetti et al., 2013b;Cucchiella et al., 2014).
Within EU, Ireland, having a population of 4.6 millions, similar to Sicilian one, generates 3 million tonnes ca. of MSW per year (652 kg/person/year), 2/3 of which are considered biodegradable.Food waste makes up 25% ca. of domestic household waste and 42% of commercial waste.It is estimated that 820,000 t/year ca. of food waste (178 kg/person/year) are generated in Ireland, whereas the catering sector produces over 100,000 t/year of food waste (Browne and Murphy, 2013).
In the above perspective, within the implementation of ISWM method, the results of this survey, in terms of energy balance of the two considered processes of OFMSW treatment, show that AD has an energy efficiency much higher than that of aerobic composting.
Moreover, the use of a rational network of towns for OFMSW collection and transportation results relevant, in terms of increased energy balance, only in the scenarios where this waste is aerobically treated, while it did not significantly affect the scenarios where OFMSW is converted into biogas and digestate.
Furthermore, in the scenarios where OFMSW is anaerobically digested, the highly positive energy balance obtained would be increased if also the energy saved for replacing the manufactured fertilisers with the digestate produced, were included among the energy inputs.
This study contributes to solve the problem of waste disposal, by demonstrating the usefulness of a criterion, based on energy balance.This criterion enables to identify a sustainable method for OFMSW management, i.e.AD, providing both economic and environmental benefits.
In fact, based on the results of this survey, if the Italian towns, that support a high cost for OFMSW transportation to landfills or composting plants and the subsequent treatment, would implement AD, could achieve a high saving.At the same time the environmental benefits for all citizens would be the reduction of GHG emissions, as well as soil and ground water pollution by leachate.
The limitation of implementing the results of this study is "ecomafia", that is the mafia involved in environmental business and, therefore, controlling the waste management.The "criminal systems" (as defined by the judge Roberto Scarpinato) are complex illegal networks including policy makers, entrepreneurs, professionals and traditional mafia men (OALL, 2011).
Therefore, a cultural change is needed, firstly in citizens and secondly in policy makers, entrepreneurs and professionals, in order to optimise the separate waste collection and the subsequent recycling, as well as valorise OFMSW through biogas and digestate production.

Fig. 2 .Fig. 3 .Fig. 4 .
Fig. 2. Biogas yield Obtained From biomass (OFMSW) during AD tests: the histograms are the daily yield b M , while the curve is the total cumulated yield B M Number of inhabitants; m inh = Mass of MSW produced by one inhabitant per year (kg year −1 ) with assumed MSW mass of 1.2 kg produced by one person per day.A sample of OFMSW was collected in Marineo town and transported to the laboratory of the Institute of Energy and Biotechnology Engineering of Aleksandras Stulginskis University in a day of March 2012.

Table 1 .
Number of inhabitants and waste mass produced per year

Table 2 .
Results of AD tests