278 2.3. Autonomous Solar Water Treatment Plant A large-scale, fully autonomous solar water treatment plant was designed and implemented for field operation. The system design integrated local water quality parameters and solar radiation data. This plant can treat up to 9 m3 of water per day, operating on an automated 8-hour filtration and disinfection cycle. 2.4. Photocatalytic Activity Evaluation 2.4.1. Chemical Degradation Studies Phenol was selected as the model organic contaminant to evaluate the oxidative capacity of the synthesized photocatalytic films. Experiments were conducted under controlled solar irradiation, monitoring the degradation rate in both the flat-plate and concentrating reactor configurations. 2.4.2. Bacterial Disinfection Studies Disinfection efficacy was evaluated using commercial Escherichia coli (ATCC® 11229) and wild bacterial consortia collected from urban wastewater were used as challenge organisms. For experiments involving E. coli in groundwater, the initial bacterial load was adjusted to approximately 1.6 107 CFU/100. Dark control experiments were performed simultaneously to ensure that bacterial inactivation was due to photocatalytic and photolytic mechanisms rather than natural die-off; these controls maintained constant bacterial counts throughout the assay duration. 3. OUTCOMES Several treatment pilots were developed and evaluated under controlled laboratory conditions as well as in real-world settings (Figures 1–4), each one tackle an specific challenge in water purification needed. For instance, water decontamination systems based on titanium dioxide supported on glass tubes have been developed, employing concentrating solar optics such as parabolic troughs [6] and compound parabolic collectors [7–10], as well as electrochemical approaches [11,12]. For the first one, Figure 1(a) shows the detail of the parabolic concentrator for 5 cm diameter glass/catalyst tubes containing contaminated water [6]. Its efficiency for the photocatalytic decontamination of water polluted with phenol was evaluated on different catalyst [6] and presented in Fig. 1(b). The developed system was evaluated over long periods of use; the reduction in its efficiency after 250 hours is due to the accumulation of calcium carbonate from bacteria. The accumulation of calcium carbonate was removed using a citric acid solution (lemon juice), which acidified the surface and dissolved the carbonate scale, restoring 99% efficiency [7] as it is shown in Figure 1(c). Figure 1(d) illustrates the disinfection of water in an autonomous recirculating cylindric parabolic compound (CPC) system, for which in the inset is presented the reflective CPC geometry, used catalyst were based on cellulose/TiO₂ and ruthenium, which was evaluated in Cusco city [8]. The photocatalytic disinfection of E. coli bacteria, based on the number of catalysts uses at specified treatment times, was evaluated and is presented in Figure 1(e) [8] and in Figure 1(f) the CPC system based on Cobalt ferrites [9,10], for which disinfection was observed even in the dark as it is seen in Figure 1(g) [9], addressing a great opportunity to avoid bacteria regrowing under dark conditions. On the other hand, regarding the second topic, Figure 1(h) shows the capacitive water desalination (CDI) prototype [11,12] and the developed characterization system, with its deionization dynamics shown in Figure 1(i) [11], this technology has shown to need just half of the energy than reverse osmosis to do the same work [11]. Composite materials combining adsorbents and photocatalysts (e.g., activated carbon with titanium dioxide) were also explored [13], along with photocatalysts supported on polymers [14]. These efforts led to an innovative prototype for disinfection and decontamination designed for disaster zones [15] Figure 2, which can be easily deployed and, using solar energy, convert unsafe water into drinking water. The nonrecirculating photocatalytic water decontamination system is shown in Figure 2(a), using a PET bottle with contaminated water and pellets [13]. A cross section of the activated carbon and TiO₂ pellet is shown in Figure 2(b), the efficiency for photocatalytic decontamination of phenol-contaminated water using solar energy [13] over two consecutive days is shown in Figure 2(c). Figures 2(d) and 2(he) illustrate a householdscale procedure for arsenic removal from water: Figure 2(d) shows the state before treatment, and Figure
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