Advanced ultrafiltration technology for lignocelluloses recovery and purification from thermomechanical pulp (TMP) mills process waters

Abstract

Process waters of thermomechanical pulp (TMP) mills contain a large valuable quantity of lignocellulosic materials that end up in the wastewater for biological treatment. In recent years, interest in utilizing such compounds has increased, and plenty of applications have been proposed. Thus, the recovery of hemicelluloses and lignin from these process waters as value-added chemicals would be beneficial for TMP mills not only to increase their profitability and competitiveness but also to reduce the organic loading to the wastewater treatment facility. However, this implies adoption of different types of appropriate separation technologies. Among the proposed separation methods, membrane technologies have been studied in a wider range of perspectives, and have been shown to play a key role in products recovery and purification in biorefining processes. In this study, the feasibility of the advanced UF technology for hemicellulose recovery and concentration from thermomechanical pulp (TMP) mill process waters was evaluated. In particular, the influence of ultrafiltration membrane cut-offs and volume reduction factors on membrane flux, and recovery and purity of hemicelluloses were investigated. Based on this study, the three tested membranes had shown different ability to recover hemicelluloses from the TMP process water. 5KDa membranes achieved the highest percent recovery of hemicellulose (95.7%), followed by 10KDa membranes 89.2% for the volume reduction (VR) of 95%. 30KDa membranes had the lowest percent recovery of 52% for VR value of 95%. Compared to 5kDa membranes, a cut-off of 10kDa seems to be feasible for the separation of lignin from hemicelluloses; it retained hemicelluloses while allowing the lignin to pass through it. Retentions of lignin were markedly low with the tested 10kDa membranes, compared with hemicelluloses retention. Volume reduction had a significant influence on the amount of hemicelluloses and lignin held back by the membrane. In this study also the characteristics of permeates and concentrates of UF membrane with different cut-offs were studied.