There is increasing concern about contamination by surfactants that are used to extract organic pollutants during remediation of polluted soils and aquifers. For instance, the surfactant sodium dodecyl sulfate may produce sulfate, which is a pollutant at high concentrations. Reports suggest that when remediation involves sodium dodecyl sulfate and electrochemical treatments, SO 4 2− ions could be produced then oxidized to persulfate (S 2 O 8 2−). However, there is few knowledge on the mechanism of electrochemical production of sulfate and persulfate. Here, we tested for first time the electrochemical production of persulfate from sulfate released by oxidation of sodium dodecyl sulfate, using anodic oxidation with boron-doped diamond. Results show a high efficiency of persulfate production, reaching 2.5 μM, when 500 mg/L of surfactant in 0.05 mol/L of Na 2 SO 4 was electrolyzed at 60 mA cm −2 , by comparison with only 0.7 μM of persulfate without surfactant in solution. This efficiency is explained by electrogeneration of hydroxyl radicals and persulfate. Results also show that 97% of the surfactant is transformed by fragmentation and oxidation, as revealed by particle size measurements.
In this study, for the first time, the production of green hydrogen gas (H2) in the cathodic compartment, in concomitance with the electrochemical oxidation (EO) of an aqueous solution containing Calcon dye at the anodic compartment, was studied in a PEM-type electrochemical cell driven by a photovoltaic (PV) energy source. EO of Calcon was carried out on a Nb/BDD anode at different current densities (7.5, 15 and 30 mA cm−2), while a stainless steel (SS) cathode was used for green H2 production. The results of the analysis by UV-vis spectroscopy and total organic carbon (TOC) clearly showed that the electrochemical oxidation (EO) of the Calcon dye after 180 min of electrolysis time by applying 30 mA cm−2 reached up to 90% of degradation and 57% of TOC removal. Meanwhile, under these experimental conditions, a green H2 production greater than 0.9 L was achieved, with a Faradaic efficiency of 98%. The hybrid electrolysis strategy is particularly attractive in the context of a circular economy, as these can be coupled with the use of more complex water matrices to transform organic depollution into an energy resource to produce H2 as a chemical energy carrier.
This study is focused on a proposal of a smartphone imaging-based quantification for providing a simple and rapid method for the analysis of chemical oxygen demand (COD) and color throughout the use of the HSV and/or RGB model in digital devices. For COD, calibration curves were done based on the theoretical values of potassium biphthalate for a proper comparison between the spectrophotometer and the smartphone techniques. The smartphone camera and application attain an average accuracy higher than the analysis in the spectrophotometer (98.3 and 96.2%, respectively). In the color analysis, it was demonstrated that only the UV–vis bands measurement is not feasible to perform the real abatement of the dye in the water because the limiting concentration that allows obtaining a linear relationship in this equipment related to the dye concentration is about 10 mg L−1. Above this value, the spectrophotometer can not reach the real difference of color in the solution. Meanwhile, the smartphone method by using the camera reaches linearity until 50 mg L−1. From an environmental point of view, smartphones have been used for monitoring several organic and inorganic pollutants, however, no attempts have been published related to their use to evaluate the color and COD during wastewater treatment. Therefore, this investigation also aims to assess the utilization of these methods, for the first time, when high-colored water polluted by methylene blue (MB) was electrochemically treated by using a boron-dopped diamond (BDD) as the anode, with different current densities (j = 30, 45, 60, and 90 mA cm−2). COD and color abatement results clearly showed that different organic matter/color removal efficiencies were achieved, depending on the j used. All the results are aligned with the studies already available in the literature, with the total removal of color in 120 min of electrolysis with 60 and 90 mA cm−2, and almost 80% of COD abatement with the higher j. Moreover, samples of real effluent from beauty salons were compared, with standard deviation varying from only 3 to 40 mg O2 L−1, which is acceptable for COD values close to 2000. Finally, the methods here presented can be a great benefit for public water monitoring policies, since it is cheap and has a decentralized characteristic, given that smartphones are very common and portable devices.
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