Regulating colored textile wastewater by 3/31 wavelength ADMI methods in Taiwan

The wastewater from textile dyeing facilities is difficult to treat satisfactorily because of high compositional variability and high color intensity. To reduce colored effluents discharged into watercourses, the government of Taiwan adopted the Effluent True Color Standard in 1998. The true color discharge limit is 400 American Dye Manufactures Institute (ADMI) units. The adopted analytical method is the ADMI Tristimulus Filter Method (3 wavelength (WL) method), and the 31 WL ADMI method might be also adopted as an alternative for color value measurement. The refractory nature of textile dyes and the introduction of this new regulation present an environmental challenge to the Taiwanese textile industry. The main objectives of this study were to (1) evaluate the efficacy of current wastewater treatment systems for controlling the colored textile wastewater discharges, and (2) evaluate the correlations between 3 and 31 WL ADMI methods. Ten representative textile wastewater treatment facilities employing biological and chemical coagulation treatment technologies were selected to perform a 10-consecutive-day effluent sampling and analysis. Results show that a significant difference between 3 and 31 ADMI methods was observed. These two ADMI methods cannot be substituted for each other, and the discharge standard should be determined based on the selected testing method. Investigation results also suggest that the commonly used wastewater treatment technology (biological + chemical coagulation) fails to effectively remove dye from the colored textile wastewater. Sodium hypochlorite (NaOCl) addition was applied by most facilities as the temporary post-polishment step to comply with the color discharge standard.