Photocatalytic decomposition of nonbiodegradable substances in wastewater from an acrylic fibre manufacturing process

Abstract

The testing samples in this experiment were obtained from an acrylic fibre manufacturing companys industrial wastewater. The water was the waste of the acrylic polymerization process. The company is located in Ulsan, Korea. The concentration of acrylonitrile (AN) in the wastewater was about 25-35 mg/L. Concentrations of 3-10 mg/L of methyl acrylate (M-35) were also found. The samples were treated by the TiO2/UV system and were analyzed to determine the values of COD ammonia, nitrite nitrogen, and nitrate nitrogen by using an Auto Analyzer (Bran+ Luebbe, Germany) and a TOC (Tekmar Dohrmann, USA). Various reaction parameters, such as TiO2 content, light intensity and wavelength, and the number of UV lamps were varied and their effects or decomposition efficiency were analyzed. The adsorption onto TiO2 surfaces by organic materials in the wastewater was negligible. The reaction-rate constant was also calculated. The reaction rate constant for the G36T6L lamp at both 185 rim. and 256 nm was 0.0661 hr(-1) which is 1.3 times higher than that of the TUV36T5 lamp at 256 nm. While the reaction rate was increased by increasing the surface area of the photocatalyst, the excess photocatalyst blocked the light sources, causing a photo-enclosure effect. The stability of the treated wastewater was greatly increased because the elimination of the concentration of nitrite was followed by an increase in the concentration of nitrate. Generally, the ratio of BOD5/CODcr is used as the criterion for determining biodegradability. A ratio of 0.3 is needed for biological degradation. The ratio of the treated wastewater increased to 0.5 after 12 hours of reaction. The ratio increased to 0.8 after 20 hours.