Catalytic Ozonation with MnOx-CeOx/ γ-Al2O3 for Wastewater Treatment of Textile Effluent

Sammanfattning: In China, the textile industry is important for the economy. However, the industry contributes to emissions of organic material and other pollutants. This affects the environment and the quality of life for people and animals. All over the world, water scarcity is becoming an increasing problem, which is why the UN has water purification as one of the goals for sustainable development. To achieve these goals and the regulations in countries, wastewater is purified in water treatment plants before it is discharged. One of the methods that can be used to purify water is catalytic ozonation, an oxidation process in which ozone is used as an oxidant to break down organic material. Catalysts, usually metal oxides, are used to increase the selectivity and the reaction rate. However, this is a relatively unexplored area in water purification and several details within the process are unknown, such as optimal conditions for various catalysts and the exact reaction mechanism. In this work, catalytic ozonation treatment with the metal oxide MnOx-CeOx/γ-Al2O3 has been investigated. Firstly, a literature study was carried out to find earlier research in the field. Then experiments were conducted, varying four different factors and the impact these factors had on the catalytic ozonation was analyzed. The factors examined were contact time, ozone dosage, gas flow and amount of catalyst. All factors had three different levels. COD and UV254 were analyzed to find the conditions that gave the highest reduction of organic matter. The highest reduction of COD was 67 % which gave a COD concentration of 23 mg/L and UV254 90 %. Since the regulations on COD emissions in China are 30 mg/L, the catalytic ozonation gave a satisfying result. The result showed that the highest yield was achieved at the highest level for contact time (40 min), ozone dosage (0.3 mg/L) and amount of catalyst (100 % filled reactor), but the second highest for the gas flow (0.3 L/min). However, the contact time was calculated to be the only significant factor for reducing COD in water. The other factors did not have a significant effect on the reduction of COD or UV254. Furthermore, the conditions that were calculated to give the greatest reduction were used to analyse the reduction of impurities in the wastewater with three dimensional fluorescence. Three dimensional fluorescence showed that the wastewater contained organic compounds, mainly aromatic proteins, soluble microbial by-products and humic acids. All of these compounds were reduced during the catalytic ozonation with MnOx-CeOx/ γ-Al2O3. The residual amount of ozone was analyzed in effluent gas flow was measured with different incoming gas flows. The residual ozone after the ozone treatment was approximately 45 % of the ingoing gas flow.