Electrodeposition of metal and bimetal oxides for electrolysis of chloride ions and indirect electrochemical oxidation of aquaculture ammonia nitrogen
| Autor: | Shih-Hsuan Huang, 黃士軒 |
|---|---|
| Rok vydání: | 2019 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 107 The phenomenon of algae blooms caused by excessive phosphorus and nitrogen in water resources is accompanied by the decomposition of animal and plant corpses, which consumes dissolved oxygen in water and forms a vicious cycle of water anoxia. However, molecular ammonia is highly toxic to most cultured fish species. According to the regulations of the Environmental Protection Department of the Executive Yuan, aquatic water belongs to B and C, and ammonia nitrogen content should be less than 0.3 ppm. It is known that the folding point chlorination disinfection method can oxidize ammonia nitrogen and convert it into non-toxic nitrogen release. In this study, the indirect electrochemical oxidation mechanism of chloride ions in electrolytic water was studied to investigate the efficiency of various metal oxide electrodes. Transition metal oxides (Sn, Pb, Mn, Co) were synthesized by electrodeposition and compared with commercial DSA. The electrochemical analyzer was used to evaluate the reactivity of electrodes for the formation of active chlorine by electrolytic chloride ions. The materials were identified by electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The effects of current density, chloride ion concentration and pH value on the production of free residual chlorine and the degradation of ammonia nitrogen were tested by batch experiments. SEM showed that the surface of the materials (Co, Mn, Sn metal oxides) plated by alkaline bath was nano-particles, while that of the Pb metal oxides synthesized by acidic bath was microparticles with good relative crystallinity. XRD and XPS analysis showed that the main metal oxides synthesized were CoOOH, PbO2, MnO2, SnO, and the bimetallic oxides were NiCo2O4 and ZnCo2O4. Among the tested materials, cobalt oxide is the best anode for chlorine production. Under the condition of current density of 3.33 mA/cm2 and initial chloride ion concentration of 0.05 M, 1.48 mM of active chlorine can be produced within 120 minutes, and the current efficiency can reach 65%. The bimetal has synergistic effect that cobalt-zinc bimetallic oxide can make the active chlorine concentration up to 1.92 mM, the current efficiency reaches 80%. Through electrochemical analysis and batch experiments, it was found that the cobalt-nickel bimetallic oxide anodic electrolysis oxidation with synergistic effect was the best method to treat simulated seawater containing ammonia and nitrogen ([NH4+]0 = 20 ppm) compared with other materials, and the removal rate of ammonia nitrogen was 99.98% at the current density of 3.33 mA/cm2 for three hours, and there was no obvious nitrite and nitric acid in the process. When the actual aquaculture water is treated ([NH4+]0 = 3 ppm), the ammonia nitrogen concentration can be effectively reduced to less than 0.3 ppm of the regulatory standard, and the selectivity of nitrogen conversion is higher than that of traditional chemical methods. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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