## 4 Discussion
### Practical Application of the Results of the BMP Tests  
The methane yield for the accumulated amounts of different by-products varies with their nature. For exhausted grape marc, we could give a figure of 6842 cubic meters of biomethane per year just taking into account the material used for _orujo_ under the IGP label, which increases to 9003 cubic meters adding up the waste from the distillation of marcs originating from other zones than Liebana. While these figures are modest, it must be considered that other wastes associated to wine and _orujo_ production could be added to the process (like grape stalks from destemming, whose methanogenic potential in the fork of 98 L\({}_{\text{N}}\) CH\({}_{4}\) kg VS\({}^{-1}\)[33] to 140.25 L\({}_{\text{N}}\) CH\({}_{4}\) kg VS\({}^{-1}\)[35] could supplement and add to that obtained from grape marc; or vine trimmings) which could increase the total methane yield. From wine production in the coastal region, the potential biomethane production which was of 17,025 cubic meters in 2009 and had increased up to 31,348 in 2017, could be an interesting way of waste management and resource exploitation, bearing in mind that a significant number of hectares of vineyards have been planted but are not yet in production. When this happens, the biomethane yield could increase up to double the current figures. It should be also taken in account that, in the previous figures, grape stalks, vine trimmings or wine lees (withmethanogenic potentials ranging from 370 L\({}_{\text{N}}\) CH\({}_{4}\) kg VS\({}^{-1}\) according to [PERSON] et al. [36] to 513 L\({}_{\text{N}}\) CH\({}_{4}\) kg VS\({}^{-1}\) according to [PERSON] et al. [53] and amounting to between 2% and 6% of the total wine production according to [PERSON] et al. [54]) have been kept out as material susceptible to undergo anaerobic treatment. Generally speaking, the potential energy content of the residual biomass produced from a hectare of grapevine has been evaluated in about 19 GJ of gross energy [55]. About brewer's grains, the geographical dispersion of breweries and their scarce volume of production make anaerobic treatment of the by-products and wastes impractical in most cases. On the other hand, the fact that a number of these microbreweries are placed in rural areas where other co-substrates suited for anaerobic treatment are readily available, could increase the feasibility of the implementation of anaerobic treatment systems which could be used in these cases [56]. No data about final products and waste generation of all breweries in Cantabria are available. There is only one case on which the evolution of production and subsequent wastes have increased a potential biomethane yield from 6438 cubic meters in 2016 to 8800 in 2019 from brewer's grains only (excluding trub and other wastes). This makes anaerobic treatment a prospective interesting option for self-consumption for the brewing processes in the company facilities. The added potential biomethane production of the rest of the breweries in the region could be estimated in an amount equal to the one of the aforementioned brewery, as could be concluded by adding up the fragmentary and scattered information about beer production of the companies obtained by different sources. Pot ale, gin spent wash and solid aromatics waste from gin production are wastes that have appeared either as the result of traditional _orujo_ distilleries diversification of their production or as the consequence of the appearance of new distilleries in the region, producing spirits other than those traditional in local production. As these are by-products originating from the appearance of new lines of production in a development phase and not yet consolidated, their volume is unknown and their importance in the total potential biogas production is yet to be assessed.