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

Abstract

Abstract The performance of an anoxic-oxic membrane bioreactor electrochemically assisted (A/O-eMBR) was assessed as an alternative for azo dye (Remazol Brilhant Violet -RBV) removal from 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 performance on the decolorization process for all experimental conditions, 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. a behavior attributed to the lower biomass content under these conditions. When the exposure mode was 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, the use of electric current to exposure mode of 6 ON´/ 12´OFF resulted in lower membrane fouling propensity, with a MFR of 0.333 kPa d− 1. A more attractive cost-benefit ratio in terms of dye removal was obtained by using the exposure mode of 6´ON/30´OFF, for which the energy demand was estimated at 21.9–22.6 kWh kg dye− 1removed, 92–99% lower than that observed for the mode of 6´ON/12´OFF.