Textile dye removal by membrane technology and biological oxidation

The objective of this research was to evaluate the effectiveness of two methods for dyestuff removal from a textile waste stream. In the first step, different types of dyes used in textile industries were studied in order to determine the types with highest usage rates. In this regard, basic, reactive, disperse and acidic dyes were selected. In the second step, dye biodegradability was studied through Zahn-Wellens method (ISO-9888 1999). Results showed final chemical oxygen demand (COD) and dye rejection coefficients (R%) of (61%, 57%), (73%, 76%), (25%, 14%), (32%, 8%) for acidic, basic, reactive and disperse dyes, respectively. In the third step, spiral-wound membrane modules nanofilter (NF) with a molecular weight cut off (MWCO) of 300 and 600 dalton (Da) and reverse osmosis (RO) of 50 Da were used. The operating conditions in phase 3 were adjusted as: temperature 30 to 35degreesC, pressure 4 bar for NF membranes and 7.5 bar for RO, flow rate of 10 L/min, and dye concentration of 0.01%. Results showed that COD and dye rejection coefficients for NF with 300 Da and for acidic, basic, reactive and disperse samples of dyes were (6%, 55%), (44%, 70%), (33%, 36%) and (71%, 93%), respectively. These results for NF with 600 Da were (7%, 54%), (64%, 76%), (33%, 29%), (59%, 92%) and for RO were (95%, 99%), (96%, 98%), (45%, 99.6%). Results clearly showed higher removal efficiency for the membrane treatment than for biodegradability studies.