Biosludge from a wastewater treatment plant was able to adsorb colourants, particularly vat dyes, from textile wastewater. Autoclaved and resting biosludge showed different adsorption abilities with different types of vat dyes. The adsorption ability of the biosludge increased with an increase in sludge age (solid retention time; SRT). Autoclaved biosludge showed the highest adsorption ability under acidic conditions (pH 3) while the resting biosludge showed the highest adsorption ability under neutral or weak alkaline conditions. The maximum colourant (Vat Black 25) adsorption capacities of autoclaved and resting biosludge with a sludge age of 24 days were 85.54 ± 0.5 and 37.59 ± 0.6 mg/g biosludge, respectively. Using a sequencing batch reactor (SBR) system, the biosludge was able to remove both organic matter and colourants from both textile and synthetic textile wastewaters. The removal efficiencies of the system increased with an increase in SRT of the system. The removal efficiency of the system with textile wastewater was lower than with synthetic textile wastewater. The BOD5 and colourant removal efficiency of the SBR system with textile and synthetic textile industrial wastewaters under a BOD5 loading of 0.13 kg BOD/m3-d were 70.1 ± 4.4% and 84.9 ± 2.0%, and 98.1 ± 1.5% and 87.5 ± 5.1%, respectively.

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