Solar heterogeneous photocatalytic degradation of phenol on TiO2/quartz and TiO2/calcite: a statistical and kinetic approach on comparative efficiencies towards a TiO2/glass system.

Phenol is a widely used synthetic organic compound, which according to global estimations, is discharged into the environment at a rate of 10 tons/year through industrial waste. Phenol is a recalcitrant pollutant, and human exposure to water containing phenolic substances can lead to health issues. It has been found both in drinking water and wastewater. Solar heterogeneous photocatalytic phenol degradation, measured through chemical oxygen demand, was performed on a thin film tilted plate reactor with TiO2 immobilized onto different support materials. A full factorial experimental design (4 × 3 × 3) was carried out to statistically evaluate if the independent variables' effects were significant. Four advanced oxidation processes (photolysis, photolysis + H2O2, heterogeneous photocatalysis, and heterogeneous photocatalysis + H2O2), three support materials (quartz, calcite, and glass), and three pH levels (3, 5.4, and 9) were evaluated. Reaction kinetics were fitted to the pseudo-first-order reaction rate and data was analyzed with an ANCOVA and means test, considering solar light intensity as a covariate. Photolysis/calcite at pH 5.4 and heterogeneous photocatalysis + H2O2/glass plate at pH 3 gave the best results, with a reaction rate constant kph = 3.047 × 10-3 min-1 and kphC = 4.498 × 10-3 min-1, respectively. The three independent variables and their interactions had a significant effect in the phenol degradation (p < 0.05).

Photocatalysis for arsenic removal from water: considerations for solar photocatalytic reactors.

The following work provides a perspective on the potential application of solar heterogeneous photocatalysis, which is a nonselective advanced oxidation process considered as a sustainable technology, to assist in arsenic removal from water, which is a global threat to human health. Heterogeneous photocatalysis can oxidize trivalent arsenic to pentavalent arsenic, decreasing its toxicity and easing its removal with other technologies, such as chemical precipitation and adsorption. Several lab-scale arsenic photocatalytic oxidation and diverse solar heterogeneous photocatalytic operations carried out in different reactor designs are analyzed. It was found out that this technology has not been translated to operational pilot plant scale prototypes. General research on reactors is scarce, comprising a small percentage of the photocatalysis related scientific literature. It was possible to elucidate some operational parameters that a reactor must comply to operate efficiently. Reports on small-scale application shed light that in areas where other water purification technologies are economically and/or technically not suitable, and the solar energy is available, shed light on the fact that solar heterogeneous photocatalysis is highly promissory within a water purification process for removal of arsenic from water.

Co-occurrence, possible origin, and health-risk assessment of arsenic and fluoride in drinking water sources in Mexico: Geographical data visualization.

Arsenic and fluoride in drinking water present a significant challenge to public health worldwide. In this study, we analyze the results of one of the largest surveys of drinking water quality in Mexico: 14,058 samples from 3951 sites, collected between January and December 2017. We use these data to identify the distribution and possible origin of arsenic and fluoride in drinking water throughout the country, and to estimate the associated health burden. The highest concentrations appear in alluvial aquifers in arid northern Mexico, where high-silica volcanic rock likely releases both arsenic and fluoride to the groundwater. We find fluoride contamination to be significantly correlated with aridity (Pearson correlation = -0.45, p = 0.0105), and also find a significant difference in fluoride concentrations between arid and humid states (Welch's t-test, p = 0.004). We estimate population exposure by assigning to each town in Mexico the average concentration of any sampling sites within 5 km. Our results show that 56% of the Mexican population lives within 5 km of a sampling site, 3.05 million people are exposed to fluoride above the reference dosage of 0.06 mg/(kg ∗ day), 8.81 million people are exposed to arsenic above the limit of 10 µg/L, and an additional 13,070 lifetime cases of cancer are expected from this arsenic exposure alone. This burden of disease is concentrated in the arid states of north-central Mexico.