Characterization of Irreversible Fouling after Ultrafiltration of Thermomechanical Pulp Mill Process Water

Johan Thuvander,Agata Zarebska,Claus Hélix-Nielsen,Ann-Sofi Jönsson

doi:10.1080/02773813.2018.1454962

Abstract

Large volumes of wastewater with dissolved wood components are treated in wastewater treatment plants at thermomechanical pulp mills. It has been shown previously that hemicelluloses in these wastewater streams can be recovered by membrane filtration. A serious obstacle when treating lignocellulose process streams is fouling of the membranes. Fouling not only increases operating costs but also reduces the operating time of the membrane plant. When optimizing the membrane cleaning method, it is important to know which compounds cause the fouling. In this work fouling of an ultrafiltration membrane was studied. The fouling propensity of untreated process water and microfiltrated process water was compared. Fouled membranes were analyzed using scanning electron microscopy and attenuated total reflection Fourier transform infrared spectrometry. Acid hydrolysis of membranes exposed to untreated process water and microfiltration permeate revealed that 508 mg/m2 and 37 mg/m2 of polysaccharides, respectively, remained on the membranes even after alkaline cleaning.

Highlights

Valuable high molecular mass components, such as hemicelluloses, can be recovered from biomass extracts[1,2] and pulp mill process streams[3,4] using ultrafiltration (UF)
The concentration of hemicelluloses was slightly lower in the MF permeate, while the turbidity was markedly lower
It has been shown that the turbidity of pulp mill process water after the removal of suspended material is correlated with the concentration of wood resins in the water.[20,21]

Summary

Introduction

Valuable high molecular mass components, such as hemicelluloses, can be recovered from biomass extracts[1,2] and pulp mill process streams[3,4] using ultrafiltration (UF). For successful operation of membrane-based applications, it is important to minimize membrane fouling.[5] membrane fouling is a common problem when filtering solutions containing hemicelluloses, such as pulp mill process water[6,7,8] and wood hydrolysates.[9,10]. A common strategy for reducing fouling is to use hydrophilic membranes, for which the fouling substances have a lower affinity.[6,9,11] Other methods include pretreatment of the hemicellulose solution to remove as much of the fouling substances as possible prior to UF. Pretreatment methods include adsorption,[10,11] coagulation,[3] oxidation[12], and microfiltration (MF).[4]

Methods

Results

Conclusion