Extraction of galactoglucomannan from thermomechanical pulp mill process water by microfiltration and ultrafiltration-Influence of microfiltration membrane pore size on ultrafiltration performance

Galactoglucomannan is the major hemicellulose in process water from thermomechanical pulping of spruce. The recovery of hemicelluloses from this process water would both reduce the load on pulp mill water treatment plants and yield a biopolymer suitable as a raw material for renewable products. One method of recovering these hemicelluloses is two-stage filtration employing microfiltration to remove large contaminants, such as suspended matter and colloidal extractives, followed by ultrafiltration to concentrate and purify the hemicelluloses from low molecular mass contaminants. This investigation shows that a microfiltration membrane with a pore size of 0.1μm removes colloidal extractives while still maintaining a high amount of high molecular mass hemicelluloses in the microfiltration permeate. The removal of extractives resulted in an increase in the initial flux during the subsequent ultrafiltration step from 90 L/m²h to over 200 L/m²h.