# Understanding Oxygen Concentrator Failures in Low Resource Settings: The Role of Dust and Humidity
## 4 Conclusions  
Exhausted zeolite samples used in OCs from Uganda, Ethiopia, and South Africa were collected and analyzed, with the results compared to those of a commercial sample not employed in OCs. The XRD analysis revealed the nature of all the samples, confirming that they all presented a low silicon X-type framework. An additional crystalline faujasite-X phase was detected in samples E-2 and SA, while an additional LTA phase occurred in samples U-1, U-2, and C-X. The presence of counterbalancing Li\({}^{+}\) ions was also deduced in sample SA from the observed contraction of its unit cell. The WDXRF highlighted the relative abundance of K\({}^{+}\) ions in sample C-X and highlighted the presence of Mg, Ca, and Fe in all the samples. Additional elements such as Zr, Ti, and Mn, considered to be dust markers, were detected only at low levels in every sample analyzed, including the \"virgin\" C-X. Hence, there was clearly no evidence of the presence of dust on the samples. On the other hand, the TGA-MS results highlighted the predominant occurrence of water in all the samples, with its release observed at the maximum mass loss rate. A positive correlation was found between the amount of water adsorbed and the efficiency of the investigated OCs leading us to conclude that humidity is the main cause of OC failure in LRSs. This outcome is particularly important because it is independent of the region of origin of the zeolite samples. Therefore, while additional data should be collected in future studies from other geographical areas, the knowledge generated by this work holds general significance. Furthermore, this study stands out for its novelty as it analyzed zeolite samples adopted in commercial OCs that operated in harsh, uncontrolled environmental conditions (unlike the controlled conditions typically found in scientific laboratories). This underscores the significance of our findings in understanding the performance of OCs in LRSs. Thus, this paper serves as a valuable guide for engineers, directing their efforts toward modifying OCs to prevent zeolite moisture poisoning. An additional layer on the inlet filter specifically designed for water removal could be a promising route. Additionally, thermal regeneration should be promoted to restore the zeolites' adsorption properties once saturated with moisture, thereby increasing the OCs' lifetime. Toward this goal, OCs should be designed to easily remove the canisters, facilitating the regeneration process. For this purpose, sustainable and frugal ways of regenerating existing exhausted zeolites to allow for their reuse should be investigated. Figure 7: Performance of OCs in terms of the oxygen concentration emitted from the instrument during zeolite sampling versus the amount of adsorbed moisture. The acronym of each sample is provided and the oxygen concentration in air is also highlighted. **Supplementary Materials:** The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app15084311/s1](https://www.mdpi.com/article/10.3390/app15084311/s1)]([https://www.mdpi.com/article/10.3390/app15084311/s1](https://www.mdpi.com/article/10.3390/app15084311/s1)), Figure S1: Weight percentages of Si, Al, and Na for each zeolite sample used in this study. **Author Contributions:** Conceptualization, D.P. and R.I.W. ; methodology, L.M., D.P. and R.I.W. ; investigation, L.M., K.S.P. and J.A.O. ; data curation, L.M. ; writing--original draft preparation, L.M., N.H.I. and E.B. ; writing--review and editing, D.P. and R.I.W. ; supervision, V.P. and L.P.; project administration, D.P. and R.I.W. ; funding acquisition, D.P. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was funded in whole by the EPSRC, via the University of Warwick's Impact Acceleration Account (EP/X525844/1). Some of the analytical equipment used in this work was provided by the University of Warwick's Research Technology Platforms.