composite pellets of Activated Carbon (AC) and TiO2. The bottles were sealed and exposed directly to solar radiation to evaluate the synergistic effect of adsorption and photocatalysis. Additionally, variants containing Fe3+ and citric acid were employed for arsenic removal assays. 2.2.2. Solar Concentrating Reactors (Parabolic and CPC) To evaluate higher-intensity irradiation, concentrating solar reactors were employed using borosilicate glass tubes as the receiver elements. The setup consisted of cylindrical Compound Parabolic Collectors (CPC) and parabolic troughs. Catalyst Support: TiO2 was immobilized via sol-gel deposition onto frosted glass cylinders (30 mm diameter, 250 mm length) positioned along the longitudinal axis of the reactor tubes (97 mL useful photoreactor volume). Alternatively, modified catalysts such as cellulose-supported TiO2 and Ruthenium complexes on silicone strips were tested. The pilot setup consisted of three independent systems driven by 12 W electrical pumps with a recirculation rate of 12 L/min. Two systems operated with a two-tube configuration (treating 12 L), used to test the supported TiO2 and Ru-complex catalysts. The third system operated with a single tube (treating 10 L) and served as a photolysis control (solar radiation without catalyst). 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
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