Two-stage membrane concentration of poly(vinyl alcohol) in desizing wastewater by membrane distillation and ultrafiltration

In order to promote the recovery rate of sizing agents in the dyeing industry, a two-stage membrane treatment system composed of membrane distillation and ultrafiltration processes was developed to concentrate the poly(vinyl alcohol). The concentration performance of two-stage membrane process was investigated at different pollutant loading, flow rates and temperatures. Meanwhile, the membrane fouling models were fitted, scanning electron microscope and water contact angle device were applied to quantify the fouling of ultrafiltration membranes in poly(vinyl alcohol) concentration. According to the results, for membrane distillation stage, membrane of 0.22 μm PTFE, crossflow velocity of 0.34 m/s and temperature of 70 ℃ of feed side, crossflow velocity of 0.25 m/s and a temperature of 20 ℃ of permeate side are the optimal working conditions. In addition, the results show that the best fitting to experimental data corresponded to the complete blocking model followed by the blocking model for all the experimental conditions tested, suggesting the pore size of membrane is the key factor for ultrafiltration. Thus, for ultrafiltration stage, membrane of PVDF (molecular weight cut off size of 100 000), pressure of 0.4 MPa and temperature of 70 ℃ are the optimal working conditions. Under these optimal conditions of two-stage membrane process, the chemical oxygen demand removal rate of the desizing wastewater achieves more than 95% and the concentration rate of poly(vinyl alcohol) in desizing wastewater is more than 7 times, which facilitates the further resource utilization. Copyright No content may be reproduced or abridged without authorization.