## 4 Discussion
### Wastes and By-Products: Generation and Characteristics
A number of solid wastes (like brewers' spent grains, BSG's) pose no further issues for their use and treatment other than the optimization of known processes and an adequate management of the substrates, as brewers' spent grains are generated in bulk quantities and can easily deteriorate [47]. However, others such as truly and slurries can pose a problem as when treating they by themselves. Their potential as biogas production raw materials is high but some of their characteristics (fluid state with a high solid load) make their treatment difficult by conventional anaerobic treatments for liquids. Trub, furthermore, pose additional problems for their treatment as, on one hand, the cell walls of yeasts are difficult to hydrolyze [48]; and on the other, the high content in nitrogen in yeast remains may induce process inhibition due to ammonia toxicity. Besides, the antibacterial properties of compounds found in hop and which can be found in a concentrated form in truly is another factor that can hamper the anaerobic process of this substrate, so its methanogenic potential can be masked. The researchers have collected some data on site, in a well-established artisan brewery of the region, in order to assess the waste production related to the general production of the industry. In the year 2016 they had a total production of 280,000 L of beer made in 110 batches (averaging 2545 L per batch). The good sales of the production leading to an increased demand set a horizon for the year 2019 of an increased production of up to 150 batches. For each batch, an amount of 500 kg of dry malt and 15 kg of hops are used, which transforms roughly into 750 kg of wet spent brewer's grains. Fermentation of the word is initiated by the inoculation or pinching of 2 kg of yeast per batch, which become 100 L of truly at the end of the process. The amount of water used for cleansing purposes of the equipment is reduced by keeping the process as aseptic as possible and just using a limited amount of water mixed with caustic ly to create a very alkaline cleansing solution, so no more than 18,250 L of solution are used per year. The final amount of brewer's spent grains for this brewery was of 82,500 kg per year in 2016, which would be increased up to 112,500 kg in 2019. The disposal method used by the brewery is to give the wastes for free to farms, so they can be used to feed livestock. The other breweries in the region do not reach the amount of production of the one studied, with modest figures in term of both sales and waste production. The brewing process takes place throughout the whole year and so does the generation of wastes. However, artisan breweries are scattered along the region, most of them being small sized (microbreweries). This poses a difficulty for joint waste management in the shape of cooperatives and the consequential benefit of scale economy profit. The fact that a number of them are placed in rural areas with farms and agricultural exploitations, however, could provide opportunities for biogas generation of these brewery wastes as co-substrates in addition to other farm production wastes whose potential as substrates for biogas production has been proven [49]. About wine production, even though there are no data available about waste production, they could be extrapolated from data attained through the vineyard surveys performed by the Ministerio de Agricultura, Pesca y Alimentacion del Gobierno de Espana [50,51] and the production data of wines with protected geographical indication (IGP) [52] of the Spanish Ministry of Agriculture (MAPAMA). There are two geographical indications in Cantabria under which the great majority of wine produced in the region are compliant--Liebana wines and wines from the coast of Cantabria. Almost the totality of grape marc of Liebana wines is used to make _orujo_ and the data about this exhausted grape marc is treated separately in this work, so this part of the work will be focused in the coast of Cantabria wine production.