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  • Comparison of the degradation of multiple amine-containing pharmaceuticals during electroindirect oxidation and electrochlorination processes in continuous system WATER RESEARCH Liu, Y., Hu, C., Lo, S. 2021; 203: 117517

    Abstract

    The degradation of pharmaceuticals by electrochemical oxidation (EO) in simulated wastewater containing multiple pharmaceuticals was compared between batch and continuous reactors. Despite the excellent efficiencies achieved in batch experiments, the practical/large-scale applications of EO-degrading amine-containing pharmaceuticals has not yet been accomplished. This paper presents the results of continuous experiments with one of the most promising electrochemical configurations of Pt/Ti electrodes before proceeding to application. In the continuous electrooxidation system (without chloride), direct oxidation on the electrode surface and oxidation by hydroxyl radicals were the main pathways. Due to their short lifespans, the radicals could not be transferred to the bulk solution, and the removal of pharmaceuticals followed the order of sulfamethoxazole (SMX) > paracetamol (PAR) > diclofenac (DIC). In the electrochlorination system (with chloride), oxidation by residual chlorine was the main pathway. The removal of pharmaceuticals followed the order of sulfamethoxazole (SMX) > diclofenac (DIC) > paracetamol (PAR). High SMX removal was realized because of the high reaction rate of SMX with free chlorine. Among the pharmaceuticals, PAR had the lowest removal because it is a neutral species with a low mass transfer rate without the attraction of electrostatic force. These results are consistent with the predictions from our previous batch-scale study, which showed that the reaction rate of dissociated compounds could be increased by the addition of electrostatic force. Furthermore, multiple coexisting pharmaceuticals, such as SMX and PAR or DIC, may form dimers that can be transferred to complex structures and cause higher toxicity.

    View details for DOI 10.1016/j.watres.2021.117517

    View details for Web of Science ID 000697761300010

    View details for PubMedID 34391021

  • Perfluorooctanoic acid (PFOA) removal by flotation with cationic surfactants CHEMOSPHERE Li, Y., Chien, W., Liu, Y., Lee, Y., Lo, S., Hu, C. 2021; 266: 128949

    Abstract

    Perfluorooctanoic acid (PFOA) was separated and recovered using a foam flotation process aided by cationic surfactants. The PFOA removal efficiency was in the following decreasing order: OTAB (C8TAB) > DTAB (C10TAB) > CTAB (C16TAB) > TBAB, which indicates that cationic surfactants with an alkyl chain that had a similar length to that of PFOA had higher affinities to PFOA. PFOA removal slightly decreased with increasing ionic strength of the surfactant but did not change with the pH. PFOA could be completely removed in 20 min with 1.25 mM of OTAB in actual wastewater. The energy yield value of foam flotation with a cationic surfactant was much higher than those of other methods, which means that using foam flotation with a cationic surfactant as the collector is a simple, fast, and energy-efficient method to separate and recover PFOA from dilute water solutions.

    View details for DOI 10.1016/j.chemosphere.2020.128949

    View details for Web of Science ID 000674624300022

    View details for PubMedID 33280843

  • pH-Dependent mechanisms and kinetics of the removal of acetaminophen by manganese dioxide JOURNAL OF ENVIRONMENTAL CHEMICAL ENGINEERING Hu, C., Kuan, W., Lee, I., Liu, Y. 2021; 9 (1)
  • pH-Dependent Degradation of Diclofenac by a Tunnel-Structured Manganese Oxide WATER Hu, C., Liu, Y., Kuan, W. 2020; 12 (8)

    View details for DOI 10.3390/w12082203

    View details for Web of Science ID 000564896200001

  • Removal of Ketoprofen from Water by Sono-Activated Persulfate Oxidation WATER AIR AND SOIL POLLUTION Liu, Y., He, B., Hu, C., Lo, S. 2020; 231 (7)
  • Effects of Surfactants on the Degradation of Diclofenac by Manganese Oxide INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH Kuan, W., Liu, Y., Hu, C. 2020; 17 (12)

    Abstract

    Amine-containing pharmaceuticals are the most often detected pharmaceuticals in wastewater and ambient aquatic environments. They can usually be degraded by manganese oxide (MnO2), which is a common natural oxidant in soils. Surfactants often coexist with pharmaceuticals in wastewater. Some amine-containing pharmaceuticals, such as diclofenac (DIC), are acidic and are thus ionic compounds in neutral conditions. These compounds, therefore, have similar properties to surfactants. Surfactants, thus, may influence the adsorption and degradation processes of DIC by MnO2. The effect of the type of surfactant on the degradation of DIC by MnO2 was investigated in this study with the addition of two common biodegradable surfactants (cetyltrimethyl-ammonium bromide (CTAB) and sodium dodecylsulfate (SDS)). The results indicated that the cationic surfactant (CTAB) significantly increased the degradation rate in neutral and alkaline conditions. On the other hand, the anionic surfactant (SDS) slightly increased the DIC removal rate in an acidic condition but significantly decreased the removal in neutral and alkaline conditions. Coexisting cationic surfactants not only influenced the kinetics but also altered the transformation mechanism of DIC by MnO2. Decarboxylation is the main transformation mechanism of DIC in the presence of CTAB, while both decarboxylation and hydroxylation are the main transformation mechanisms in the absence of CTAB.

    View details for DOI 10.3390/ijerph17124513

    View details for Web of Science ID 000549294300001

    View details for PubMedID 32585957

    View details for PubMedCentralID PMC7345797

  • Simultaneous aqueous chlorination of amine-containing pharmaceuticals WATER RESEARCH Liu, Y., Liu, H., Hu, C., Lo, S. 2019; 155: 56-65

    Abstract

    Amine-containing pharmaceuticals such as acetaminophen, diclofenac, and sulfamethoxazole are the most often detected pharmaceuticals in wastewater and other aquatic environments. Amine-containing pharmaceuticals can be effectively removed by chlorination. These drugs, however, may coexist in wastewater. Thus, they may compete with each other, and their chlorinated products may react with each other to form new products. In this study, competitive effects of the above three amine-containing pharmaceuticals by chlorination and their products were investigated. The priority of chlorination of these compounds was dependent upon the pH of the solution, due to the dissociation of the compounds and hypochlorite. It followed the order of sulfamethoxazole > diclofenac > acetaminophen in an acidic condition, the order of sulfamethoxazole > acetaminophen > diclofenac in a neutral condition, and the order of sulfamethoxazole ≈ acetaminophen > diclofenac in an alkaline condition. Some of the chlorinated products in single- and multiple-compound systems were the same. Dimers of sulfamethoxazole and its chlorinated products, however, were not found, but dimers of sulfamethoxazole and acetaminophen or diclofenac were found in multiple-compound systems. This finding is important because it means that new products may be produced if different amine-containing pharmaceuticals react with free chlorine simultaneously.

    View details for DOI 10.1016/j.watres.2019.01.061

    View details for Web of Science ID 000464488500005

    View details for PubMedID 30831424

  • Direct and indirect electrochemical oxidation of amine-containing pharmaceuticals using graphite electrodes JOURNAL OF HAZARDOUS MATERIALS Liu, Y., Hu, C., Lo, S. 2019; 366: 592-605

    Abstract

    This study investigated the direct and indirect electro-oxidation of amine-containing pharmaceuticals (acetaminophen (ACT), diclofenac (DIC), and sulfamethoxazole (SMX)) by using graphite electrodes, and to compare the influence by using different electrolytes (Na2SO4 and NaCl). Under the optimum conditions of current (I) at 0.5 A, in direct system, 74.3%, 90.0%, 81.6% of ACT, DIC, and SMX were respectively removed after 60 min (k = 0.023, 0.037, 0.027 min-1), 48.9%, 85.9%, 68.2% of TOC respectively removed after reaction time. In contrast, at the same current intensity, in indirect system, ACT, DIC, and SMX were eliminated within 30 min (k = 0.117, 0.307, 0.170 min-1), 89.6%, 92.6%, 99.6% of TOC respectively removed after reaction time. The results indicated that the dissociated compounds were attracted to the anode due to electrostatic forces and had higher mass transformation rates in the direct electro-oxidation process. According to the cyclic voltammogram, indirect oxidation occurred when active chlorine species were generated from chloride ions anodically to destroy pollutants. Based on intermediates detected during electro-oxidation treatment by ultra performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS), only oxidized intermediates were found in the direct oxidation system, while both oxidized and chlorinated intermediates were found in the indirect oxidation system.

    View details for DOI 10.1016/j.jhazmat.2018.12.037

    View details for Web of Science ID 000460709500066

    View details for PubMedID 30576998

  • Removal of nonsteroidal anti-inflammatory drugs (NSAIDs) by electrocoagulation-flotation with a cationic surfactant SEPARATION AND PURIFICATION TECHNOLOGY Liu, Y., Lo, S., Liou, Y., Hu, C. 2015; 152: 148-154