## 1 Introduction
Currently, there is literature available about anaerobic treatment and valorization in general for waste of almost any kind of alcoholic beverage, from beer or wine production [13; 14; 15], whisky and other grain distillates [16; 17], to even requila and other agaye-based beverages [18; 19]. However, there's a void in studies dealing with the wasteof gin production. The making process of distilled gin as defined in the European legislation involves the mixing of botanicals and aromatics with ethyl alcohol of agricultural origin and water [20] and the distillation of that mixture. The botanicals used may be a mixture ofdifferent components in different proportions according to the producer's recipe (which is almost always a company secret) but the use of juniper berries (_Juuiperus communis_ L.) is mandatory, as its taste must be predominant by definition [21]. Other common flavoring agents that may be used or not are angelica (_Angelica archangelica_ L.) roots, cinnamon (_Cinnumnumum verum P._) bark, caraway (_Carum carvi_ L.) and coriander (_Coriandrum sativum_ L.) seeds, and orris root (the rhizomes of _Iris germanica L._ and/or _Iris pallida Lam._). The distillation product is mixed with water to achieve the desired alcoholic strength by volume, which has to be a 37.5% minimum. A minimum of two flows of wastes can be identified in the making process. One of solid matter, consisting of the spent botanicals and aromatics, which will be wet and impregnated with a certain amount of alcohols, and another of liquids. At first sight, it appears as a mass of mixed items, which can be distinguished under close inspection, showing their nature. The liquid waste can consist of the heads and tails of the distillation process as well as the filtered remains in the pot still and spent wash. Process and cleaning waters can be added to this flow, increasing its volume. Through the course of their research career, the authors have had previous experience with distilled gin waste, having dealt with the liquid waste of distilled gin production [22]. However, and knowing the working system of a gin distillery, there's no knowledge available on the treatment of the solid waste flow of distilled gin spent botanicals (DGSBs). Thus, it can be considered necessary to add research for the possible treatment and energetic valorization of these wastes to achieve a total overview of the ways to deal with them. Experience with distilled gin liquid waste showed the possible need for a co-substrate for anaerobic digestion treatment, as the biological process can be hampered by the nature and characteristics of the substrate. The use of brewer's spent grains (BSGs) resulted in an obvious choice for several reasons. The gin distillery was planning to expand their business, creating their own grain alcohols from malls (and thus, reducing their dependence from external sources of ethyl alcohol of agricultural origin), and the characteristics and composition of distiller's spent grains (DSGs) are very similar to those of BSGs, if not identical. As the authors had previously proven the feasibility of anaerobic digestion treatment for distilled gin liquid waste, it was decided to try anaerobic digestion for solid wastein box-type reactors for both substrates, alone and in co-digestion. Some other research lines showed the influence of the use of a conductive material in the biochemical methane potential for some substrates from alcoholic beverage production [23], so it was decided to use granulated activated charcoal in some experiments.