Effects of solid retention time and exposure mode to electric current on Remazol Brilliant Violet removal in an electro-membrane bioreactor

The performance of an electrochemically assisted anoxic–oxic membrane bioreactor (A/O-eMBR) was assessed as an alternative for azo dye (Remazol Brilhant Violet (RBV)) removal from simulated textile wastewater. The A/O-eMBR was operated under three experimental conditions (runs I, II, and III), in which different solids retention time (SRT) (45 and 20 d) and exposure mode to electric current (6′ON/30′OFF and 6′ON/12′OFF) were assessed. The reactor exhibited excellent decolorization performance for all runs, with average dye removal efficiency ranging from 94.3 to 98.2%. Activity batch assays showed that the dye removal rate (DRR) decreased from 16.8 to 10.2 mg RBV L −1 h −1 when the SRT was reduced from 45 to 20 d, likely attributed to the lower biomass content under lower sludge age. At the electric current exposure mode of 6′ ON/12′OFF, a more substantial decrease of DRR to 1.5 mg RBV L −1 h −1 was noticed, suggesting a possible inhibitory effect on dye removal via biodegradation. By reducing the SRT to 20 d, a worse mixed liquor filterability condition was observed, with a membrane fouling rate (MFR) of 0.979 kPa d −1 . In contrast, using the electric current exposure mode of 6′ON/12′OFF resulted in lower membrane fouling propensity, with an MFR of 0.333 kPa d −1 . A more attractive cost–benefit ratio for dye removal was obtained using the exposure mode of 6′ON/30′OFF, for which the energy demand was estimated at 21.9–22.6 kWh kg dye −1 removed, almost two times lower than that observed for the mode of 6′ON/12′OFF.