Water pollution by organic contaminants and other anthropogenic substances is one of the major global problems nowadays. The aquatic contaminants include pesticides, pharmaceuticals and personal care products (PPCPs), steroid hormones and synthetic dyes. Traditional processes such as UV irradiation at disinfection doses, coagulation, flocculation, precipitation, microfiltration and ultrafiltration are ineffective for the complete removal of organic contaminants in water, whereas the so called advanced oxidation processes (AOPs) are very effective in the oxidation of numerous organic compounds. The most widely used AOPs include heterogeneous photocatalysis based on near UV or solar visible irradiation, electrolysis, the Fenton's reaction, ozonation, ultrasound and wet air oxidation. AOPs are based on the generation of highly reactive hydroxyl radicals (oOH), which will attack the organic pollutants. However, the lifetimes of these radicals are so short to utilize them effectively. Therefore, the direct radical generations by non-thermal plasmas are widely researched. Three different types of plasma discharges (Dielectric Barrier Discharge, DBD, Gliding Arc Discharge, GAD, and Electrohydraulic Spark Discharge, ESD) were applied to investigate the degradation kinetics of the target pollutants in water. Firstly, the degradation of atrazine, verapamil and hydrocortisone was conducted successfully in the DBD reactor. After 90 min DBD treatment all the target pollutants were almost completely removed. Presence of the intermediates was confirmed by HPLC/UV analysis. The efficiency of dielectric barrier discharge on the degradation of atrazine and hydrocortisone was investigated. Atrazine was almost completely degraded after 90 min DBD treatment. The rate constant of this process was 0.029 min-1 and the corresponding half-life time was 24 min. After 90 min treatment time 54% of the atrazine was converted to CO2. Hydrocortisone was also completely degraded after 90 min DBD treatment. The rate constant of this process was 0.050 min-1 and the corresponding half-life time was 14 min. After five hours of treatment 21% of the hydrocortisone was converted to CO2. Structure of the intermediates was identified by HPLC/MS analysis. Plausible mechanisms for the degradation of target pollutants were also proposed. Degradation kinetics and degradation mechanism of verapamil in water under GAD was investigated. In the final part, the degradation kinetics of verapamil and atrazine by using electrohydraulic spark discharge and ozonation was investigated. During spark discharge, 87% of verapamil and 83% of atrazine were degraded within 40 min. The rate constants of the degradation processes were 0.065 min-1 and 0.094 min-1 for verapamil and atrazine respectively. The power introduced in the discharge was 60 W and is very low compared to the power of GAD. As a result, relatively high energy yields 5.1 × 10-2 g/kWh and 2.3 × 10-2 g/kWh were achieved for verapamil and atrazine respectively. Verapamil was completely removed by ozonation within 1.5 min., while atrazine was almost completely removed within 4 min. The rate constants of the degradation processes were 2.56 min-1 and 0.769 min-1 for verapamil and atrazine respectively. The power applied during ozonation was very low (20 W), compared to plasma discharges, leading to high energy yields 9.4 g/kWh and 1.6 g/kWh for verapamil and atrazine respectively. The degradation kinetics of verapamil and atrazine in water under DBD, GAD, ESD and ozonation were compared. The shortest half-lives of verapamil and atrazine were observed during ozonation. So, we can say that among our AOP systems, ozonation is the most efficient in degrading verapamil and atrazine in water.
| Identifer | oai:union.ndltd.org:nusl.cz/oai:invenio.nusl.cz:364449 |
| Date | January 2017 |
| Creators | BALAKRISHNAN, Syam Krishna |
| Source Sets | Czech ETDs |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis |
| Rights | info:eu-repo/semantics/restrictedAccess |
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