In a simplified representation, the treatment of landfill gas to produce high-quality pipeline gaseous fuel can be split into the steps of collection, cleaning, upgrading and feed-in. Normally, in the cleaning step, hydrogen sulphide and other sulphur compounds are removed through a conventional active carbon adsorption, alone or in combination with chilling systems [44]. The next step contains the most expensive unit in this chain in which carbon dioxide is uptaken by a technology such as pressure swing absorption (PSA), pressure water wash (PWW) [45], or amino-chemical absorption [46]. In addition to carbon dioxide removal, the simultaneous elimination of ammonia take places, as well as sulphur, halogenated, and silicon compounds; in most cases, these two steps are sufficient to satisfy the most relevant gas injection requirements. Although there are differences in the cost of carbon dioxide uptake between the previously mentioned technologies, these differences intrinsically depend on utility prices, i.e. electricity, cooling water, labour, etc., and landfill gas flow to be treated. Nevertheless, for this study estimate, no differences in the upgrade technology investments and operating cost are assumed, such that a unique mathematical relation (i.e., presented in Table 3) can correlate them. Fig. 2 shows the investment data for the carbon dioxide removal units and the mathematical correlation that best fits them