# Design of a Device Based on an LED Matrix for Water Sterilization
## 4 Discussion  
The aim of the present study was to design a flexible, low-cost, and easily integrated device that incorporates UV LED technology within polymers capable of direct contact with water for sterilization purposes. To achieve this, polymers such as ETFE and EVA were chosen for their suitable properties as encapsulants for UV LEDs. ETFE was selected for its lightweight and flexible nature, which does not degrade or yellow under UV radiation. On the other hand, EVA was chosen for its transparency and high adhesion properties. The ability to easily configure an array of LEDs to match the required dimensions and geometry for specific applications represents an advantage over traditional standard UV disinfection systems. Initially, different encapsulated LEDs obtained from various manufacturers were tested to identify the best candidate for the application. Since the goal was to measure the antibacterial properties of UV rather than heat-induced death, the heating produced by the different devices was determined. It is known that non-sporulating bacteria die above 50 \({}^{\circ}\)C, whereas spore-forming bacteria require at least 100 \({}^{\circ}\)C [8]. The results showed that the LEDs used did not generate sufficient heat to produce a sterilizing effect. Several studies have analyzed the removal of viable microorganisms caused by UV light [9; 10]. LED devices have also been described as more cost-effective than other options, such as the use of mercury lamps [5; 11]. To study the sterilizing capacity of LEDs, _E. coli_  
Figure 9: Effect of LED array prototype on microorganism viability in 5 L of river water. (**A,C**) Effect on anaerobic microorganisms. (**B,D**) Effect on aerobic microorganisms. (**A,B**) Trials conducted under static conditions. (**C,D**) Trials conducted under stirring. In all cases, exposure times (from left to right and top to bottom) were: control, 5, 10, 15, 20, 40, 60, 90, and 120 min. suspensions were employed, as this microorganism serves as an indicator of pathogenic bacteria and fecal contamination, making it a good measure of water quality [12]. The assays conducted in this work demonstrated that all the LEDs used could produce total microorganism death, although there were notable differences in their respective efficiencies. LEDs 6, 8, and 2, under agitation conditions, yielded the best results, with the first two capable of completely eliminating viable bacteria in less than 1 min and the third in less than 2 min. In the absence of agitation, the times required for sample sterilization increased significantly. The decrease in bacteria survival capacity under agitation conditions has been described [13] and has been attributed to the homogenization of the average irradiation distances achieved under these conditions [14]. The price per unit of LED 2 was EUR 2.22, while those of LED 9 and LED 6 were 530% and 918% more expensive, respectively (EUR 11.78 and EUR 20.39). This efficiency-price ratio led to the selection of LED 2 as the best candidate for the project. To study in detail the effect of UV radiation from LED 2 on bacterial viability, three basic parameters were evaluated: time, concentration, and sample volume. Sanitary criteria to ensure the safety of drinking water for human consumption determine the analysis of certain microbiological parameters, including the viability of _E. coli_, _Enterococcus_, and _C. perfringens_, the latter including both vegetative forms and resistance spores [15]. This study also included two pathogens, _S. enterica_ and _K. pneumoniae_. In all cases, LED 2 was able to affect bacterial viability, although the time needed to achieve this effect depended on each species, with _C. perfringens_ being the most resistant, while _K. pneumoniae_ and _E. faecalis_ were easily eliminated. These results are consistent with previous descriptions that established the influence of time, concentration, and volume on microorganism viability [4; 16]. _C.