Utilization of renewable resources is becoming increasingly important, and only sustainable processes that convert such resources into useful products can achieve environmentally beneficial economic growth. Wastewater from the pulp and paper industry is an unutilized resource offering the potential to recover valuable products such as lignin, pigments, and water [1]. The recovery of lignin is particularly important because it has many applications, and membrane technology has been investigated as the basis of innovative recovery solutions. The concentration of lignin can be increased from 62 to 285 g∙L−1 using membranes and the recovered lignin is extremely pure. Membrane technology is also scalable and adaptable to different waste liquors from the pulp and paper industry.

Spent sulfite liquor is an abundant but currently less used wastewater stream from the pulp and paper industry. The recovery of lignin from this resource would provide an inexpensive raw material for the manufacture of fuels and fine chemicals. Here we investigated the suitability of ceramic hollow-fiber membranes for the concentration of spent sulfite liquor as an alternative to common membrane technologies. We tested three ceramic hollow-fiber membranes (3, 8, and 30 nm) in different membrane processes (fed-batch and total recycle mode) and compared their performance with the widely-used tubular membrane geometry. We also evaluated backflushing as a strategy to reduce membrane fouling during filtration. The juxtaposition of the two membrane geometries revealed that wall shear stress is the most important process parameter for the assessment of membrane performance according to permeate flux. The higher the wall shear stress, the higher the permeate flux. Due to the smaller inner diameter of the hollow-fiber membranes, higher wall shear stress can be achieved more easily. Backflushing had no effect on the permeate flux during the concentration experiments.

Im Rahmen dieser Forschungsarbeit wurde ein effizientes membranbasiertes Verfahren zur Rückgewinnung von gereinigtem Ligninsulfonat (LS) aus der Dünnlauge des chemischen Holzaufschlusses mithilfe von keramischen Ultrafiltrationsmembranen entwickelt. Das Ziel dabei war, die Ligninsulfonate von niedermolekularen organischen Verunreinigungen (Zucker, Carbonsäuren etc.) und Prozesschemikalien abzutrennen, sie aufzukonzentrieren und sie für eine gezielte Weiterverwertung bereitzustellen. Ein weiterer Aspekt des Projektes war die Separation der Produkte (Zielmoleküle) der Lignosulfonatspaltung mittels keramischer Membrantechnologie.