| Summary: | 碩士 === 國立屏東科技大學 === 環境工程與科學系所 === 106 === Inappropriately treated swine wastewater is usually discharged into its receiving water body to cause environmental pollution, if the three-stage system for swine wastewater treatment is not properly operated. This study investigates the feasibility of using electrochemical advanced oxidation to remove organic and ammonium nitrogen pollutants from swine wastewater. For this process, we explored thebetter operating condition of this process through testing various operating parameters (electrolyte, current density, anode material and area, COD/ammonium nitrogen load). Tetracycline (TC), one of environmental emerging contaminants and the most commonly used antibiotics in animal agriculture, is often found in livestock wastewater. Therefore, this study used the obtained better operating condition for the electro-degradation of organic and ammonium pollutants in swine wastewater and prepared solution to explore the degradation efficiencies of COD and ammonium nitrogen and reaction kinetic parameters. Liquid chromatography-mass spectrometry (LC-MS), high performance liquid chromatography (HPLC), and ion chromatography (IC) analyses were performed to identify the intermediates (products) and pathways of TC electro-degradation. Moreover, Ultraviolet-visible (UV-Vis) and fluorescence excitation-emission matrix (EEM) tests were conducted to evaluate the electro-degradation characteristics of water matrices during operations.
The results show that good COD degradation of swine wastewater was achieved by using the better operating condition ((boron-doped diamond(BDD) anode (4 cm2), Ti cathode (2 cm2), addition of sodium chloride (0.05 M), current density = 0.25 A / cm2, and temperature = 25 °C). After electro-degradation for 240 minutes, the removal rates of COD all batchs of wastewater were more than 93, while those of BOD, TOC, and NH3-N were 47%‒100%, 61%‒100%, and ~100%, respectively. Nitrite nitrogen was not detected in most of the wastewater batches; however, the concentration of nitrate nitrogen increased in the first half of the electrolysis and then decreased.
According to cyclic voltammetric analysis, an oxidation peak of TC appeared without any corresponding reduction peak on a BDD electrode, revealing that TC could be directly electro-oxidized on the surface of BDD although its electrochemical behavior is totally irreversible. The TC degradation efficiency and TOC removal rate increased with the increase of electro-degradation time. The TC spiked in swine wastewater could be degraded to the level of ND, accompanied with the removal efficiencies of COD, TOC, BOD, and NH3-N = 93%‒100%, 87%‒100%, 77%‒100%, and 84%‒100%, respectively. The absorption peaks detected in UV-vis analysis for the swine wastewater with/without TC addition and prepared TC solution exhibited decreasing intensity as the electrolysis time increased and disappeared finally. In fluorescence analysis, swine wastewater showed fluorescence peaks in region I (tyrosine-like)/region II (tryptophan-like) and region IV (soluble microbial by-product), respectively, while the prepared TC solution had a fluorescence peak across the region III (fulvic acid-like), region IV (soluble microbial by-product), and region V (humic acid-like). However, the intensity of these fluorescence peaks decreased with the increase of electrolysis time and they disappeared finally. The TC in prepared solution was electrochemically degraded to intermediates with m/z = 60, 431, 479, 95, 411, 395, 297, 450, 366, 252, 230, and 222, followed by further electro-degradation into 2-3 dioxo-succinic acid, but-2-enedioic acid, 2-oxo malonic acid, carbamic acid or oxalic acid and finally mineralization products.
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