Some properties of a granular activated carbon-sequencing batch reactor (GAC-SBR) system for treatment of textile wastewater containing direct dyes

Resting (living) bio-sludge from a domestic wastewater treatment plant was used as an adsorbent of both direct dyes and organic matter in a sequencing batch reactor (SBR) system. The dye adsorption capacity of the bio-sludge was not increased by acclimatization with direct dyes. The adsorption of Direct Red 23 and Direct Blue 201 onto the bio-sludge was almost the same. The resting bio-sludge showed higher adsorption capacity than the autoclaved bio-sludge. The resting bio-sludge that was acclimatized with synthetic textile wastewater (STWW) without direct dyes showed the highest Direct Blue 201, COD, and BOD5 removal capacities of 16.1±0.4, 453±7, and 293±9 mg/g of bio-sludge, respectively. After reuse, the dye adsorption ability of deteriorated bio-sludge was recovered by washing with 0.1% sodium dodecyl sulfate (SDS) solution. The direct dyes in the STWW were also easily removed by a GAC-SBR system. The dye removal efficiencies were higher than 80%, even when the system was operated under a high organic loading of 0.36 kg BOD5/m3-d. The GAC-SBR system, however, showed a low direct dye removal efficiency of only 57±2.1% with raw textile wastewater (TWW) even though the system was operated with an organic loading of only 0.083 kg BOD5/m3-d. The dyes, COD, BOD5, and total kjeldalh nitrogen removal efficiencies increased up to 76.0±2.8%, 86.2±0.5%, 84.2±0.7%, and 68.2±2.1%, respectively, when 0.89 g/L glucose (organic loading of 0.17 kg BOD5/m3-d) was supplemented into the TWW.