In this work we have developed a novel method for determination of iron redox species by the use of diffusive gradients in thin-film (DGT) technique coupled to photothermal beam deflection spectroscopy (BDS). The combination of both methods achieved low limit of detection (LOD) of 0.14 μM for Fe (II) ions. The total Fe concentration determined in the Vrtojbica river sediment (Slovenia, Rožna Dolina, 5000 Nova Gorica) was 49.3 µgL-1. The Fe (II) and Fe (III) concentration amounted to 12.8 µgL-1 and 39.9 µgL-1 , respectively. Such an approach opens new opportunities for monitoring the content of iron species in natural waters and sediments and provides highly sensitive chemical analysis and an accurate qualitative and quantitative characteristic of the materials under study.
Advanced oxidation processes (AOPs) have been introduced to deal with different types of water pollution. They cause effective chemical destruction of pollutants, yet leading to a mixture of transformation by-products, rather than complete mineralization. Therefore, the aim of our study was to understand complex degradation processes induced by different AOPs from chemical and ecotoxicological point of view. Phenol, 2,4-dichlorophenol, and pentachlorophenol were used as model pollutants since they are still common industrial chemicals and thus encountered in the aquatic environment. A comprehensive study of efficiency of several AOPs was undertaken by using instrumental analyses along with ecotoxicological assessment. Four approaches were compared: ozonation, photocatalytic oxidation with immobilized nitrogen-doped TiO2 thin films, the sequence of both, as well as electrooxidation on boron-doped diamond (BDD) and mixed metal oxide (MMO) anodes. The monitored parameters were: removal of target phenols, dechlorination, transformation products, and ecotoxicological impact. Therefore, HPLC–DAD, GC–MS, UHPLC–MS/MS, ion chromatography, and 48 h inhibition tests on Daphnia magna were applied. In addition, pH and total organic carbon (TOC) were measured. Results show that ozonation provides by far the most suitable pattern of degradation accompanied by rapid detoxification. In contrast, photocatalysis was found to be slow and mild, marked by the accumulation of aromatic products. Preozonation reinforces the photocatalytic process. Regarding the electrooxidations, BDD is more effective than MMO, while the degradation pattern and transformation products formed depend on supporting electrolyte.
Phenolic pollutants raise health and environmental concerns due to their widespread occurrence in industrial wastewaters. Electrooxidation was studied for phenol degradation in different supporting electrolytes: NaCl, Na2SO4, H2SO4. Experiments were performed at constant current density 20 mA/cm2. Two anode materials were tested, boron-doped diamond (BDD) and mixed-metal oxide (MMO). Degradation process and its impact was investigated from technological, analytical, and ecotoxicological viewpoints. Removal efficiency was monitored by phenol index spectrophotometric method and phenol removal quantified with HPLC-DAD. Additionally, transformation by-products were tracked with GC-MS and LC-MS, as well as ion chromatography. Finally, ecotoxicity was investigated using Daphnia magna. Electrooxidation was efficient and had low energy consumption. The use of BDD anode led to higher removal efficiencies and induced more progressive degradation to simple organic acids, compared to MMO. Selection of electrolyte affected degradation pathways and detoxification pattern. Treatment by BDD in NaCl led to complete phenol removal in 30 min, but undesired chlorinated aromatic by-products were formed. Treatment in sulphate medium led to slower processes irrespective of pH, but less problematic by-products with minimal ecotoxicological impact emerged. By using multi-aspect methodology, this study reevaluates phenol electrooxidative degradation and contributes to better understanding of electrooxidation performance in water treatment.
Phenolic compounds are widespread in wastewater from various industries. Since the phenols are potentially carcinogenic for humans and hazardous for the environment, their presence in wastewater raises concerns. In this paper electrooxidation process was used for treatment of synthetical prepared wastewater containing phenol. Initial phenol concentration in wastewater was 50 mg/L with addition of different supporting electrolytes (NaCl, Na2SO4, H2SO4). The treatment was performed in a batch electrochemical reactor at constant current density of 20 mA/cm2. Boron doped diamond (BDD) and mixed metal oxide (MMO) anode materials were examined, and stainless steel was used as cathode. Phenol concentration before and after treatment was determined by standard spectrophotometric method with 4-aminoantipyrine, while transformation products were identified by different chromatographic methods. Experiments have shown that the treatment is very efficient and with low energy consumption, wherein the phenol removal efficiency mostly depends on the duration of treatment and the type of supporting electrolyte.
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