The UVB-induced photocatalytic degradation of Methyl Red and Methyl Orange (azo dyes used in the textile industry) containing solutions was carried out by the use of a laboratory-scale pilot plant where the catalyst, TiO2 (anatase), was immobilized at the bottom of a channel through which the liquid was recirculated under UVB irradiation. The plant was preliminarily characterized hydrodynamically, i.e., flow-rate, hydraulic gradients, and residence time. Photodegradation kinetics were followed by UV−vis absorption measurements of the residual dye concentration in the liquid-phase, and the synergistic effects of the catalyst and radiation in promoting the abatement of dyes was demonstrated in the concentration range 0.3−5.0 mg/L. Kinetic data were correlated by the use of first-order (or pseudo-first-order) models up to the concentration range 0.7 mg/ L; at higher concentrations, zero-order models (pure catalytic control) better correlated the experimental data. Photocatalytic degradation of Methyl Red was faster than Methyl Orange, possibly due to the Coulomb repulsion of the negatively charged sulfonate functionalities present on this latter compound. A better hydrodynamic of the liquid recirculating in the channel, i.e., higher flow rate (lower contact time), associated with an improved surface catalyst renovation and a higher frequency of exposition of the substrate to the UVB radiation, together with an improved oxygen dissolution in the liquid-phase, played a positive role in the overall kinetic performance.

An innovative laboratory scale unit was used to carry out UV photoinduced catalytic degradation of methyl 9 orange. For this purpose, the experimental system was made of a bottom and an upper reservoir (∼120 L each) which were connected by an inclined channel through which water was recirculated. TiO2 (Anatase) was deposited (∼10−2 mg/cm2) at the bottom of the connecting channel while the Methyl Orange solution was exposed to the UVB radiation (λ ≈ 300 nm) during its recirculation through the connecting channel. The unit was first characterized from both the hydrodynamic and the hydraulic points of view. Photodegradation kinetics were followed by UV−vis absorption measurements of the residual methyl orange solution concentration along time, and the synergic effect of the catalyst and the intensity of the UV radiation in promoting degradation of the substrate was demonstrated. The abatement efficiency of the UV/TiO2 system toward methyl orange was evaluated in the concentration range 0.3−8.5 mg/L. Kinetic patterns were described by first (or pseudofirst) order theoretical models up to the concentration of 0.7 mg/L, whereas at higher concentrations kinetic trends were better described by zero-order models independently from the substrate concentration in the liquid-phase. The proposed solution, after an upscale field investigation, may represent a valuable alternative to the methods conventionally used for the abatement of textile dyes from wastewater, that is, water clarification, reverse osmosis, activated carbon sorption, and biosorption.

Il lavoro presenta i dati preliminari della reazione di degradazione di composti organici bio-persistenti mediante l'uso di un impianto pilota in scala laboratorio

Xenobiotic persistent organic pollutants are ubiquitous in the environment (air, water, soil, biota), and this is the origin of the rising concern about their potential impact. Recent advances in chemical analysis at trace levels and a lack of knowledge about the fate and transport of reference compounds lead to a strong research demand in this area. In this context, special attention is focused on control technologies in water and wastewater involving the application of advanced technologies to minimize their environmental release. After presenting the environmental and sanitary impacts associated with the main classes of persistent xenobiotic compounds, this article focuses on endocrine-disrupting compounds (EDCs), a class of chemicals interfering with the endocrine systems of mammals and lower animals. In the second part of this article, the basic principles of the advanced technologies used for EDC control in water and wastewater are critically discussed with specific reference to their engineering aspects.

Heavy metals retention [Pb2+; Cd2+; Ni2+ and Cr(VI)] on recycled waste porous glass (RWPG) from solid wastes sorting operations was carried-out. To the purpose metals containing solutions in the concentration range 2-4 mg/L, reproducing the average concentration present in, e.g., solid waste leachate from landfills or industrial effluents, were percolated onto columns loaded with RWPG beads with particle size in the range 0.35-1.0 mm, and flow-rates between 0.23 and 0.75 L/h. Metals retention mechanism was associated with ion exchange with overall capacities in the order: Pb+2 >Cd+2> Ni+2 >Cr(VI) in consideration of the hydrated ion radius and free energy of hydration of the metal ions. The rate controlling step was identified with the ions inter-diffusion in the Nernst liquid film around particles. The metals exhausted beads were embedded into cement conglomerates as inert materials thus minimizing metals release in the environment. The prepared mortar specimen showed improved thermal properties as compared to conventional (sand containing) composites.