## 3 Advantages and Disadvantages of AWCSs  
The advantages of such systems can be found for different stakeholders [22]. For users, the service is available 24 h per day, 365 days per year; inlets for waste deposition are safe, ergonomic, and accessible; there is easy access for users with physical limitations; and there is an improvement in public hygiene conditions. For the city, they allow selective collection at the source since waste can be separated and disposed of in different fractions; they are clean and environmentally friendly, albeit with odour; the city creates an image of responsibility and compromises with the environment; and since waste collection trucks are taken out of the city, the noise disappears, and air pollution due to CO\({}_{2}\) emissions is drastically reduced. For the economy, there is a reduction in waste collection operational costs, there is a reduced number of personnel needed for operation, there are savings in urban cleaning costs, and there are flexible payback options.  
When one studies more thoroughly the ecological impact of AWCSs, energy clearly stands out as the biggest contributor to this impact [23]. This does not come as a surprise for a system that, for its operation, relies on creating fast air currents using a large pipe installation for significant periods of time, several times a day, all days of the week, all weeks of the year. Beyond its significant ecological fingerprint, energy is also an expensive resource, becoming the greatest expense when operating such systems, well beyond other running costs such as salaries. As most of these plants are either operated as a public service (i.e., by city corporations) or by companies under contract with such public institutions, a cost reduction can only be achieved via reducing energy bills (reducing personnel operating costs is very difficult for a plant that requires just token personnel to run).  
As the hardware that uses all this energy is not very complex (large fans creating air currents), there is not much margin for optimising energy usage on this front. However, for the operations schedule, that is, the schedule determining when and what waste is collected from the network, there is a wide range of options for optimisation. Surprisingly, this aspect of the operation, albeit being the subject of some researchers' attentions [24; 25], is not a really well-explored problem, while truck routing for surface waste collection, conversely, has been the subject of more detailed research [26; 27; 28], some of which dates way back [29]. On the contrary, as the existence of several patents such as [18; 19; 30] seems to suggest, that lack of research in the field does not translate to a lack of interest by the industry.  
One of the disadvantages of AWCSs is pipeline failures due to the extreme working conditions of such systems. The pipes are in direct contact with the waste transported at high velocities, where the waste may have all types of geometries and dimensions and may contain improper components of the recollected fractions, such as glass and other ceramic  
Figure 9: Multiple correspondence analysis method extracted from the database between 2009 and 2022 using R-studio software and bibliometrix library.  
materials of high hardness; this causes the attrition of the pipes. [PERSON] et al. [31] studied the origin of pipe failure in two different AWCSs, to understand the failure's primary cause and to help prevent common issues related to attrition. The results showed that 93% of failures were due to abrasive at attrition, mainly in the elbows and connections and in pipefittings. Moreover, the presence of glass in the transported waste was the main cause of attrition.