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

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/m 2 and 37 mg/m 2 of polysaccharides, respectively, remained on the membranes even after alkaline cleaning.

Analysis of membrane fouling by Brunauer-Emmett-Teller nitrogen adsorption/desorption technique

“…Based on the irreversible flux decline ratio of 80% the fouling was severe. This is in accordance to previous results observed by Thuvander et al They suggested that this was most likely caused by adsorptive fouling of polysaccharides 31 .…”

“…The reference spectra of the GR95PP and UP010 membranes can be assigned to characteristic PES membranes. The reference spectrum of the UFX5-pHt contains peaks characteristic for PSU membranes and are in accordance to Thuvander et al 31 who investigated the same membrane.…”

“…The O-H stretching area was slightly intensified for the UFX5-pHt membrane fouled with TMP process water. This intensification likely origins from fouling of polysaccharides such as hemicelluloses 31,36 . The peaks at 1014 and 1080 − cm 1 are attributed to the aliphatic C-C and aromatic -CH rocking which is assigned to polysaccharides.…”

Innovative Optical-Sensing Technology for the Online Fouling Characterization of Silicon Carbide Membranes during the Treatment of Oily Water

“…R irrev is caused by the persistent adsorption of pollutants (dissolved and colloidal material) on the membrane surface or in the entrance to membrane pores. R irrev cannot be eliminated by either moderate physical or chemical cleaning [51][52][53][54]. R f is calculated as shown in Equation (4) [51,55]:…”

“…The main foulants are organic, colloidal and mineral, which account for 50%, 30% and 20%, of fouling respectively [58]. The purpose of chemical cleaning is to reverse the loss of membrane permeability and restore flux and rejection by removing the foulants described above [54,59].…”