## 4 Discussion  
### Wastes and By-Products: Generation and Characteristics  
The usage of wastes and by-products of the different industrial premises of alcoholic beverage production for biogas production should be assessed by multi-criteria analysis. [PERSON] and [PERSON] [38; 39]  
Figure 2: Total specific methane production of by-products from the alcoholic beverage production in L\({}_{\rm N}\) CH\({}_{4}\) kg\({}^{-1}\) fresh sample from the BMP tests (SD for each substrate: PA, 0.7; T, 1.7; CSW, 1.9; GSB, 5.1; BSG, 4.6; GM, 4.2; EGM, 1.5). propose a complete methodology for this analysis, though the total number of parameters used by them are not available for this study given its limitations; nevertheless and based in the set of parameters obtained and applicable to the methodology, the feasibility of the process is proven. Also, [PERSON] et al. [40] have developed a decision support system providing more managerial insights for the establishing and implementing of units of alternative biowaste treatment, showing the benefits and promotion of local bioeconnies. An important factor in waste management is the spatial distribution of the waste sources and their mode of production. This may be a clustered one with production points with concentrated productions of waste with a high pollutant potential; or a scattered one with diffuse productions of waste over extended areas. In Figure 3, we can see the spatial distribution of a number of production centers of alcoholic beverages (and thus, of the wastes associated to the specific production) throughout the region. It could be noticed that there is a trend of these centers to be gathered, in a certain proximity. This may be an advantage for join waste management when the production of waste or by-products from individual companies show low critical mass levels; in these cases the individual investment for the company for such installations and premises needed for their treatment could be profitable. Even though there is a good potential for a conjoined treatment of these wastes, they will be treated individually in this work to determine their specific characteristics and potential as substrates to undergo anaerobic treatment and their specific potential biomethanogenic production. Grape marc has, for a long time, been subject to research, both as a waste and as a potential source of energy. Both the marc \"as is,\" as a by-product of wine production and the \"exhausted one\" after fermentation and distillation as a by-product of grape marc spirit making, have the characteristic of being seasonal products, as both wine and marc spirit are items made at a certain time of the year. Wine grape marc appears shortly after grape harvest and their crushing to obtain grape musts and the only treatment it might receive is just a drying, usually under the sun in natural conditions. Then it might be pressed and, either be used to produce grape marc spirit, as livestock feed or simply be dumped at a garbage disposal facility. In Cantabria, exhausted grape marc used to produce _orujo_ is simply disposed of. Grape marc as a potential source of biogas has been subject of research [41], attaining values of up to 28 Nm3t-1. It produces a high yield of biogas on the first days (as could be expected by the high  
Figure 3: Location of the main by-product associated to the alcoholic beverage production generation areas in the region of Cantabria (Spain). Breweries and municipalities with vineyards and _orujo_ distilleries. presence of sugars in the dry matter) which later decreases as sugars become depleted and the main source of biogas is the fibrous matter in grape waste. Throughout this period, biogas production rate becomes quite stable until eventually the total depletion of food resources for the microorganisms responsible of the process arrives. It has also been found that the presence of grape seeds is beneficial for the process.