Assessment of nanoclay-sludge ratios in sequencing batch membrane bioreactors: Azo dye removal and fouling alleviation

Abstract

This study characterized the Sequencing Batch Membrane Bioreactors (SB-MBR) system containing nanoclay in the treatment of Acid Red 18 (AR 18) azo dye in two steps. The first step compared SB-MBRs operations containing six different concentrations of Cloisite® 20A as nanoclay. A Hydraulic Retention Time (HRT) of 24 h was considered to remove a high initial concentration of 500 mg/L of dye at a sludge retention time of 45 d. In the first step, the Transmembrane Pressure (TMP) changes was reduced 74 % by 10 g/L cumulative nanoclay Cloisite® 20A concentration (0.22 g/L.d), but no improvement in dye removal was observed. The TMP rate reduction was due to Extracellular Polymeric Substances (EPS) decreasing from 370 mg/L to 330 mg/L for SB-MBR1 to SB-MBR6. Change in the morphology via reduced particle sizes and floc stability was another main factor of fouling alleviation following the addition of nanoclay. Floc stability reduction can also be confirmed by changing Tightly Bound EPS (TB-EPS) (≈330−160 mg/L) to Loosely Bound EPS (LB-EPS) (≈40−170 mg/L) in SB-MBR1 to SB-MBR6, respectively. In the second step, some parameters were changed to obtain the optimum values and improve obtained ≈30 % dye removal efficiency in the first step for all the reactors. The HRT and fresh daily nanoclay were increased to 48 h and 1.5−4 g/L.d, respectively. Consequently, dye removal improved to about 80 %.