Complex wastewater matrices present a major environmental concern. Besides the biodegradable organics, they may contain a great variety of toxic chemicals, heavy metals, and other xenobiotics. The electrochemically activated persulfate process, an efficient way to generate sulfate radicals, has been widely applied to the degradation of such complex effluents with very good results. This review presents the fundamentals of the electro-persulfate processes, highlighting the advantages and limitations, followed by an exhaustive evaluation on the application of this process for the treatment of complex industrial effluents. An overview of the main relevant experimental parameters/details and their influence on the organic load removal is presented and discussed, having in mind the application of these technologies at an industrial scale. Finally, the future perspectives for the application of the electro-persulfate processes in the treatment of complex wastewater matrices is outlined.
Purification; Removal; Acid Abstract: Nanofiltration process for the treatment/valorisation of cork processing wastewaters was studied. A DS-5 DK 20/40 (GE Water Technologies) nanofiltration membrane/module was used, having 2.09 m(2) of surface area. Hydraulic permeability was determined with pure water and the result was 5.2 L.h(-1).m(-2).bar(-1). The membrane presents a rejection of 51% and 99% for NaCl and MgSO4 salts, respectively. Two different types of regimes were used in the wastewaters filtration process, total recycling mode and concentration mode. The first filtration regime showed that the most favourable working transmembrane pressure was 7 bar working at 25 degrees C. For the concentration mode experiments it was observed a 30% decline of the permeate fluxes when a volumetric concentration factor of 5 was reached. The permeate COD, BOD5, colour and TOC rejection values remained well above the 90% value, which allows, therefore, the concentration of organic matter (namely the tannin fraction) in the concentrate stream that can be further used by other industries. The permeate characterization showed that it cannot be directly discharged to the environment as it does not fulfil the values of the Portuguese discharge legislation. However, the permeate stream can be recycled to the process (boiling tanks) as it presents no colour and low TOC (< 60 ppm) or if wastewater discharge is envisaged we have observed that the permeate biodegradability is higher than 0.5, which renders conventional wastewater treatments feasible.
The Sr La TiO (0 ≤ x ≤ 0.4) and Sr Bi TiO (0 ≤ x ≤ 0.3) perovskites were prepared via solid state reaction by partially replacing the Sr ions in the SrTiO structure by La or Bi ions, characterized and utilized as photocatalysts immobilized in Ni-foam substrate in the degradation of the azo dye Acid Orange 7 (AO7). For both perovskite families, the XRD data reveal the existence of a predominant well-crystallized phase, belonging to a cubic perovskite in a Pm3m space group, with the presence of other minority phases. The characteristic dimension and the volume of the cell decrease with the introduction in the SrTiO lattice of the La or Bi ions. The grain size of the Sr La TiO samples is around 100 nm and slightly lower for the Sr Bi TiO samples. Regarding the utilization of the prepared perovskite powders deposited over the Ni-foam substrates as catalysts in the photodegradation of AO7 solutions, the results show an improvement in the performance of the films of the substituted perovskite when compared to the SrTiO perovskite, being the best results obtained with SrBiTiO.
In this study, Bi-doped SrTiO3 perovskites (Sr1−xBixTiO3, x = 0, 0.03, 0.05, 0.07 and 0.1) were synthesized using the solid-state method, characterized, and tested as photocatalysts in the degradation of the azo dye acid orange 7 (AO7) under visible light. The perovskites were successfully synthesized, and XRD data showed a predominant, well-crystallized phase, belonging to the cubic perovskite symmetry. For the doped samples, a minority phase, identified as bismuth titanate, was detected. All doped samples exhibited improved photocatalytic activity under visible light, on the degradation of AO7 (10 mg L−1), when compared with the undoped SrTiO3, with an increase in relative Abs484 nm decay from 3.7% to ≥67.8% after 1 h, for a powder suspension of 0.2 g L−1. The best photocatalytic activity was exhibited by the Sr0.95Bi0.05TiO3 perovskite. Reusability studies showed no significant loss in photocatalytic activity under visible light. The final solutions showed no toxicity towards D. magna, proving the efficiency of Sr0.95Bi0.05TiO3 as a visible-light-driven photocatalyst to degrade both the AO7 dye as well as its toxic by-products. A degradation mechanism is proposed.
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