Ultrafiltration of Desizing Wastewater Containing PVA in Bench Scale Test

Abstract

Ultrafiltration (UF) of desizing wastewater containing PVA (MW=10 000–70 000), which is a synthetic and non-biodegradable sizing agent, was investigated to develop the technology for size recovery from textile effluents. Using bench-scale UF system with polysulfone hollow fiber membranes (MWCO= 10 000 and 30 000), membrane performance, i.e. permeate flux and rejection rate, was examined with the variation of operating parameters such as PVA concentration, transmembrane pressure, temperature, pH, cross-flow velocity, and prefilter sizes. From the experimental results, it was confirmed that the ultrafiltration of desizing wastewater through polysulfone membranes is controlled by the well-known phenomena of concentration polarization caused by gel-layer formation. The permeate flux exhibited asymptotic behavior beyond a certain transmembrane pressure, 2.0 kg cm−2, and the rejection rate was over 99 %. However, the flux at high concentration ranges (> 3.0 wt % of PVA) did not satisfy a linear semi-logarithmic relationship predicted by the gel-layer model, that is, upward limiting flux was observed. Prefilter treatment before UF process considerably reduced the suspended solids in the feed (about 70–80 %), and it appears to better control the ultrafiltration of desizing wastewater. In basic conditions (pH=9–10), the permeate flux was increased almost two times at the expense of a slight decrease of rejection rate. With respect to membrane MWCO, there was distinct difference in permeate flux between MWCO=10 000 and 30 000.