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A novel experimental procedure was developed to measure oxygen mass transfer during the oxygenation of water in a thin film of a rotating disk photocatalytic reactor (RDPR). The increase in dissolved oxygen (DO) of initially deaerated water was monitored with time in the reactor vessel at different disk angular velocities after exposure of the reactor to the atmosphere. Oxygenation was predominantly achieved by oxygen mass transport through the thin liquid film carried by the disk and to a much lesser extent by direct oxygenation of the water in the reactor vessel via a surface renewal mechanism. A mathematical model was developed to simulate the phenomenon considering both cases of presence and absence of oxygen mass transport limitations. In the latter case, the model considered that the amount of liquid carried by the disk was saturated with oxygen when returning to the reactor vessel. On the basis of the model and the experimental data, it was proven that mass-transfer limitations existed until the water in the reactor vessel became saturated with oxygen. Results obtained from the model were validated by an alternative analysis using dimensionless groups characteristic to the system. The study revealed that the mass-transfer coefficient increased linearly with disk angular velocity and thus disk Reynolds number. The results showed that oxygen mass-transfer limitations decreased with increasing disk angular velocity, mainly due to an increase in the overall mass-transfer coefficient. In the presence of UV radiation, the influence of oxygen on the photocatalytic oxidation of 4-chlorobenzoic acid was investigated in the RDPR operated in batch and continuous mode. The photocatalytic reactions occurred in a thin film of liquid carried by the disk in the presence of UV radiation and ST-B01 composite spherical ceramic (SiO2/Al2O3) balls coated with anatase TiO2 catalyst. It was found that the initial degradation rate followed Langmuir kinetics with respect to oxygen concentration in the gas phase. When the oxygen concentration in the gas phase surpassed that in air, the degradation rates did not improve significantly, suggesting that operation with air instead of oxygen is most probably a more realistic practical choice. Measurements of DO during the presence and absence of UV radiation suggested that the photocatalytic reactions were mainly oxygen concentration-limited rather than oxygen mass-transfer-limited.

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A worldwide survey was conducted to obtain up‐to‐date data on full‐scale reverse osmosis (RO) and nanofiltration (NF) water treatment plants using seawater, brackish water, or reclaimed wastewater as feedwater. Participation in the online survey was limited to facilities with capacities greater than or equal to 1 mgd and dates of startup or retrofitting later than 1990. Survey results highlighted trends in pretreatment and posttreatment, membrane characteristics, operation, costs, residuals management, and regulations. Comments by respondents directly involved in RO/NF plant operations reflected the lessons learned from day‐to‐day experience. Using the information summarized here, the industry can identify the main constraints to the advance of RO/NF technology, i.e., residuals disposals and management, operations and maintenance costs, and focus efforts on developing solutions. Facilities interested in incorporating RO/NF in their treatment process can use this study as a starting point to plan new projects or as a reference against which to compare their own experience.

In previous laboratory experiments Fenton's Reagent (FR) was successfully used as the source of hydroxyl radicals (OH*) for chemical treatment of low concentrations of methyl tert-butyl ether (MTBE) in water. Although under certain conditions MTBE degradation levels as high as 99.99% were achieved, none of these experiments resulted in complete MTBE mineralization. In all cases, these experiments applied FR as an equimolar concentration of ferrous iron (Fe2+) and hydrogen peroxide (H2O2). The present study investigates the effect of H2O2/Fe2+ molar ratio on the extent of degradation of MTBE and intermediate products in water at pH = 3.0. The initial concentration of MTBE studied was 0.0227 mM (approximately 2 mg/L). Initially, the dose of Fe2+ was kept constant at a Fe2+/MTBE molar ratio of 10:1 and the dose of H2O2 was varied to achieve different H2O2/Fe2+ molar ratios. The results revealed that higher degradation efficiency was achieved when FR was used as an equimolar mixture (H2O2/Fe2+ molar ratio = 1.0). The extent of MTBE degradation decreased when the H2O2/Fe2+ molar ratio was changed to values higher or lower than 1.0. These results suggest that a stoichiometric relationship (1:1) between the FR components optimizes the degradation process for this reactant system. It is hypothesized that an excess of H2O2 enhances the effect of reactions that scavenge OH*, while a decreased amount of H2O2 would be a limiting factor for the Fenton Reaction.