Effect of dye aggregation and salting-out on membrane fouling and control measures during nanofiltration of saline dye wastewater

Abstract

In the nanofiltration (NF) treatment of saline dye wastewater, whether dye aggregation and salting-out occur in membrane elements is still not well understood. In this study, a reactive turquoise blue KN-G (RTB), which is easy to aggregate and salt-out, was selected for experimental study. Firstly, the effects of dye and salt concentrations on the aggregation and salting-out rate of RTB were investigated by beaker experiments. Then NF experiments and scanning electron microscope (SEM) observation were carried out to investigate the membrane fouling caused by dye aggregation and salting-out. Finally, based on the mechanical analysis of dye particles in cross-flow filtration system, two membrane fouling control measures of increasing cross-flow velocity and ultrasonic irradiation of feed water were investigated. The results showed that the aggregation degree and the salting-out rate of RTB were positively correlated with the salt concentration. SEM showed that the fouling on the membrane surface had particle characteristics. During NF experiment, the normalized flux (J/J0) decreased from 0.96 to 0.42 when the added salt concentration increased from 0.0 g·L−1 to 5.0 g·L−1. However, the attenuation of J/J0 was significantly reduced by increasing cross-flow velocity or ultrasonic irradiation of feed water. Therefore, in the process of NF treatment of saline dye wastewater, salting-out in membrane elements could occur and increase membrane fouling, and increasing cross-flow velocity or applying ultrafiltration can effectively reduce the membrane fouling caused by dye aggregation and salting-out.