## 3 Results and Discussion
### Discussion  
Several conclusions can be extracted after the experimentation process. First, the importance of having a well-adapted and strong inoculum can never be underestimated. BSGs have resulted in a good feedstock for anaerobic digestion processes. While the usual way to dispose of both brewers' and distillers' spent grains is to use them as feed for livestock [29; 30] (with the limitations for DSGs of copper toxicity, especially for ovine and caprine livestock) or even for human consumption [31], a lot of interest has arisen lately for their use in biogas production [32; 33], with a good final biomethane production and, as a by-product, a digestate with a good volumetric reduction and which could still be useful in agriculture as a fertilizer or as an organic amendment for soils [34]. This fact has lead to the appearance of several studies and works focused on its use. In this experimental process, the results attained were fairly good. The only objection could be the long time needed throughout the experiment to attain good results with a good amount of final biogas production. In that sense, it should be commented that, after the first experiences and failures with the other substrate, the experimentation was performed on a very cautious side. The values of VFA's COD accumulated in the percolate tank never reached levels which, after the experience, could be considered dangerous for the process. Thus, the general process could be accelerated using a more intense recirculation in terms of volume and frequency (always bearing in mind it should be a progressive process). Further studies would be needed to adjust and optimize the operational actions in order to speed up the process while keeping it on the safe side to avoid process failure. On the other side, DGSBs have resulted in a problematic feedstock. This could be the product of the substrate nature in itself. As commented in the introduction, juniper berries are a mandatory ingredient for distilled gin by definition, according to the EU regulations for alcoholic beverages [21]. Juniper galbuli (berries) essential oils have a complex composition with a large number of chemical compounds [35] and have shown anti-microbial and anti-fungal effects [35; 36]. While it could be objected that other distilled gin producers could use different recipes and mixes of botanicals, affecting the repeatability of similar experiments, the obligatory nature of the use of a high proportion of juniper berries in the botanicals mixture allows one to think that results similar to ours would be attained, unless an unusually high inoculum-to-substrate ratio (normally not feasible in real-scale dry batch anaerobic digestion reactors) were used. Other frequent distilled gin ingredients, suchas angelica roots and seeds or cinnamon bark, have also shown anti-microbial effects [37; 38]. As a first measure to deal with the treatment of these products, procedural changes in the distillation process could be adopted. The use of \"infusers\"(mesh containers made of an inert material which don't transmit unexpected flavors to the distillate while allowing free contact between botanicals and the liquid phase of water and ethanol) for each ingredient, for example, could make easier to separatethe different species and fractions of botanicals after distillation is completed. This way, the different types of waste could be treated accordingly to their own characteristics, enabling the extraction of valuable chemicals from the separate fractions and using the less problematic products to be used in anaerobic digestion. After these experiments, it could be supported that DGSBs are not suited for dry batch anaerobic digestion, as it is usually performed in current standard appliances; and its addition as a co-substrate, whileitshould be analyzed on a case-to-case basis, could result in process problems, especially in the initial phases.