EXAMENSARBETE INOM KEMITEKNIK, AVANCERAD NIVÅ, 30 HP STOCKHOLM, SVERIGE 2018 Integrating membrane filtration for water reuse in tissue mill Examiner: Mikael Lindström Supervisors: Anders Uhlin, Sverker Danielsson RISE Bioeconomy EHSAN MOSLEHI KTH SKOLAN FÖR KEMI, BIOTEKNOLOGI OCH HÄLSA Abstract Water is an essential and indispensable component is the pulp- and paper production industry. The increase in energy costs, stricter environmental regulations and water resource shortages have caused a reduction of the water footprint in the industry as well as an increase in water recycling and water circuit closure. Reducing water usage requires an understanding of where contaminants originate, as well as which streams are critical to the process and how they impact mill operation. The recirculation of water can cause contaminant accumulation; therefore mills employ technologies for water treatment in the internal water cycles, the so-called ‘kidneys’. Application of membrane technology is one such option which can improve the recycled water quality and reduce contaminant buildup. The present study was carried out on a lab-scale for the treatment of a tissue mill effluent using membrane separation. A combination of pretreatment methods and various membranes were compared with regards to separation, flux and fouling. The AlfaLaval M20 device was to treat wastewater samples sent from the mill, where the permeate was recirculated to the feed tank. COD and TOC levels are compared with regards to determining the separation efficiency. The permeate flux was measured over the two-hour filtration period, as well as flux recovery to determine fouling levels. Additionally, some economic aspects of the process are discussed. This study suggests the potential application of a combination of flocculation or centrifugation pretreatment, with reverse osmosis membranes for recycling water to replace freshwater intake. The results also indicate the possibility of using ultrafiltration as kidneys to decrease contamination buildup for further water loop closure. Keywords: Membrane separation; Paper industry; Paper mill effluent; Water reuse ; Reverse Osmosis i Acknowledgments This project has been performed at RISE Bioeconomy as the Master’s thesis for the Chemical Engineering for Energy and Environment program at the KTH Royal Institute of Technology. The project was a collaboration between ÅF and the Sofidel AB tissue plant in Kisa. I would first like to thank my thesis advisor Anders Uhlin at RISE. The door of Anders’s office was always open whenever I ran into trouble or had a question about my research and writing. He consistently allowed this project to be my own work, but steered me in the right the direction whenever he thought I needed it. I have been extremely lucky to have a supervisor who cared so much about my work, and who responded to my questions and queries so promptly. I would also like to thank Sverker Danielsson at RISE for giving me the opportunity to perform my thesis here at RISE Bioeconomy, as well as for his professional guidance and support during this project. I wish to acknowledge the help provided by Åsa Sivard at ÅF for sharing her years of experience with me, as well as providing me with her practical and valuable input. I would also like to thank my examiner, Mikael Lindström at KTH for his valuable and constructive suggestions during the planning and development of this research work. Completing this work would have been all the more difficult were it not for the support and friendship of those who provided a much-needed form of escape from my studies, they also deserve thanks for helping me keep things in perspective. So, Shayan, Alex, Dhinesh, Aida and Björk, Skål and Thank you! Finally, To my parents and my sister, Thank you for providing me with unfailing support and continuous encouragement throughout my years of study. This dissertation stands as a testament to your unconditional love and encouragement. Ehsan Moslehi ii Table of Contents Introduction .................................................................................................................... 1 Aim and Goals ................................................................................................................. 2 Theory .............................................................................................................................. 3 Membranes ................................................................................................................... 3 Membrane Materials ..................................................................................................... 6 Membrane Modules ...................................................................................................... 8 Fouling .......................................................................................................................... 9 Membrane Cleaning.................................................................................................... 10 Pretreatments for Membrane Treatment ..................................................................... 10 Literature review .......................................................................................................... 11 Water in pulp and paper industry................................................................................ 11 Paper Production ......................................................................................................... 12 Water used in pulp and paper production ................................................................... 13 Water recirculation ..................................................................................................... 15 Pulp and Paper Wastewater Treatment ....................................................................... 17 Membrane technology implementation on water circuits .......................................... 19 Industrial case studies ................................................................................................. 22 Methodology .................................................................................................................. 24 Device ......................................................................................................................... 24 Membrane Assembly .................................................................................................. 26 Membranes ................................................................................................................. 27 Water Samples ............................................................................................................ 29 Experimental Procedure .............................................................................................. 30 Pre-cleaning ................................................................................................................. 30 Filtration ...................................................................................................................... 30 Post Cleaning .............................................................................................................. 31 Cleaning efficiency ..................................................................................................... 31 iii Chemical Analysis……… ……………………………………………………………...32 COD measurement ....................................................................................................... 32 TOC measurement ....................................................................................................... 32 Conductivity ................................................................................................................ 33 Turbidity ...................................................................................................................... 33 Results………………………………………………………………………... ............ 35 Wastewater ................................................................................................................. 35 UF Experiments .......................................................................................................... 36 Pretreatment Methods ................................................................................................. 39 Microfiltration pretreatment and reverse osmosis ...................................................... 39 Screen and ultrafiltration pretreatment and reverse osmosis ...................................... 43 Centrifugation pretreatment and reverse osmosis....................................................... 45 Flocculation pretreatment and reverse osmosis .......................................................... 47 Spraywater PM-3 ........................................................................................................ 49 Process water PM-4 .................................................................................................... 51 Discussion ...................................................................................................................... 53 Membrane Comparison .............................................................................................. 53 Pretreatment Method Comparison .............................................................................. 54 Economic Calculations ................................................................................................. 55 References .....................................................................................................................