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Adsorption of Colour from Pulp and Paper Mill Wastewaters onto Diatomaceous Earths A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Chemistry at The University of Waikato by Shane B Carter 2007 © 2007 Shane B Carter II Abstract Production of pulp and paper from raw wood involves the washing of substantial quantities of highly coloured material from the wood pulp. Although most of this colour is trapped within the mill and the mills wastewater treatment system, discharge of coloured wastewater remains a problem of public concern. Lake Rotorua, New Zealand is filled with sediment consisting almost exclusively of diatoms. The most abundant species, Aulacoseira, has been shown to have very small pores (< 200 nm) that could be very useful for the capture and holding of large organic molecules. Lake Rotorua is situated close to the two largest pulp and paper mills in New Zealand and may have to be dredged to solve a problem of eutrophication. Wastewaters generated at the Kinleith (Tokoroa) and Tasman (Kawerau) mills in the North island of New Zealand have been used to assess the characteristics of colour removal by Lake Rotorua diatoms. Vacuum filtration through the diatoms succeeded in removing colour but proved to be impractically slow as an industrial process. Addition of diatoms to wastewater streams in stirred experiments showed that significant adsorption took place. The majority of the colour was removed within 30 seconds of mixing. The efficiency of colour removal was found to vary between wastewater streams within the mills. The pH dependency of this removal was tested and found to be most effective in a pH range of 3.6 to 5. Attempts to reuse the diatoms showed that chemical backwash regimes were more effective than calcination. This study concluded that surface silanols were likely to be the principle agent in forming coagulants with the colour material and were subsequently trapped on the diatom surfaces, but more importantly within the pores. III IV Acknowledgements I wish to acknowledge the many individuals who have contributed to this thesis. Special thanks to Chris Hendy (University of Waikato) my supervisor and to Alan Langdon (University of Waikato), who allowed himself to be dragged in as an unofficial secondary supervisor. To all the staff in the Chemistry Department at the University of Waikato, Annie Barker, Steve Cameron, Wendy Jackson, Helen Turner, Kath Dabell and Pat Greed. Thanks to staff at SCION, Trevor Stuthridge for his valued input and help, Alison Slade and Kim McGrouther. Special thanks to my industry mentor Ed Mercer (Kinleith Pulp and Paper Mill). Thanks to the Environmental Systems team from Kinleith Pulp and Paper Mill, especially Yvette Hejl who managed to answer lots of questions whilst collecting samples and Jim Newfield for fitting me in to his busy schedule. Thanks to Ian Fulton and team from Tasman Pulp and Paper Mill for their help and input and Paul Hartley for the use of his boat and other equipment. Funding for this project was provided by Technology New Zealand through a TIF grand with Kinleith Pulp and Paper Mill. Final thanks to all the other staff and students at the University of Waikato and a big thanks and hugs to my family who put up with quite a lot. V VI Table of contents Title I Abstract III Acknowledgements V Table of contents VII List of Figures X List of Tables XI List of Images XII Abbreviations XIII Chapter 1 Introduction and Literature Review 1 1.1 Introduction 1 1.2 Pulp and Paper Mill wastewaters 2 1.3 Filtration 4 1.4 Coagulation 5 1.5 Pulp wastewater colour removal technologies 7 1.6 Diatomaceous earths 8 1.7 Diatoms 10 1.8 Lake Rotorua – Diatomaceous sediment source 19 Chapter 2 Materials and Methods 25 2.1 Materials 25 2.1.1 Bleached Kraft Pulp Mill Sampling 25 2.1.2 Diatomaceous Sediment Samples 26 2.2 Equipment 27 2.3 Methods 29 2.3.1 Packed column filter 29 2.3.2 Stirred adsorption 29 2.3.3 Neutral pH wastewater 32 2.3.4 High pH wastewaters 33 VII 2.3.5 Acid wastewaters 34 2.3.6 Reclamation of Organic Surface Deposits and Diatoms 35 Chapter 3 Results and Discussions 37 3.1 Introduction 37 3.2 Packed Column Filter 37 3.3 Stirred Adsorption Studies 39 Diatom Settling Rate 40 Sample Degradation 40 Diatom effect on pH 40 Change in wastewater colour with change in pH 40 Change in wastewater pH and absorbance by addition of distilled water 41 3.3.1 Neutral pH wastewaters 42 Experiment 1a, single dose of wastewaters 42 Experiment 1b, single dose of wastewaters 43 Experiment 2, double dose of diatoms 44 Experiment 3, multiple dose of wastewater 45 3.3.2 High pH wastewaters 48 Experiment 4, single dose of diatoms 48 3.3.3 Acid wastewaters 50 Experiment 5, multiple dose of wastewaters 50 3.3.4 Rapid response adsorption studies 54 Experiment 6, rapid response 54 3.3.5 Reclamation of Organic Surface Deposits and Diatoms 57 3.3.6 Scanning Electron Microscopy/Energy Dispersive x-Ray Fluorescence 59 Diatomaceous Earth Classification 59 Adsorption Study Images 65 Chapter 4 Conclusions and implications 83 VIII References 91 Appendix 99 A. Maps 99 A-1. Rotorua Region 99 A-2. Kinleith Mill sample sites 99 A-3. Diatom sample sites 100 B. CPU standard 101 C. Absorbance and pH data 104 1. Packed column filter 104 2. Change in wastewater with change in pH 106 3. Experiment 1a: Single dose of diatoms 107 4. Experiment 1b 107 5. Experiment 2: Multiple dose of wastewater, Pond inflow 108 6. Experiment 3: Multiple dose of wastewater, Acid 109 7. Experiment 5: Acid wastewaters 110 8. Rapid response 112 9. Wastewater degradation during storage 112 IX List of Figures Figure 1.1: Relative sizes of some filter materials 4 4- Figure 1.2: SiO4 tetrahedron 16 Figure 1.3: Octahedral aluminium unit 17 Figure 1.4: Micelle, aluminium and silica in sheet 17 Figure 3.0: percentage reduction in absorbance 37 Figure 3.1: Absorbance vs. pH for the main wastewater streams 41 Figure 3.2: CPU results for Tasman pond inflows 42 Figure 3.3: Single dose of diatoms 43 Figure 3.4: Double dose of diatoms 44 Figure 3.5: Multiple dose of wastewater 46 Figure 3.6: Experiment 3 46 Figure 3.7: Kinleith caustic wastewater, absorbance vs. pH 49 Figure 3.8: Kinleith acid wastewater, experiment 5 pH 50 Figure 3.9: Kinleith acid wastewater, experiment 5 absorbance 51 Figure 3.10: Kinleith acid wastewater, experiment 5, 6 g diatoms 51 Figure 3.11: Kinleith acid wastewater, experiment 5, 10 g diatoms 52 Figure 3.12: 10 g diatoms, experiment 3 & 5 comparison 52 Figure 3.13: Kinleith acid wastewater, absorbance vs. pH (a) 53 Figure 3.14: Experiment 6: 10 minutes, absorbance vs. time 54 Figure 3.15: Experiment 6: 1 minute, absorbance vs. time 55 Figure 3.16: Kinleith acid wastewater, absorbance vs. pH (b) 55 Figure 3.17: Kinleith acid wastewater, experiment 6 ICP-MS 1minute 56 Figure 3.18: Kinleith acid wastewater, experiment 6 ICP-MS 10 minutes 56 Figure 3.19: EDS spectra of deposits in diatom pores 75 Figure 3.20: EDS & SEM of tephra (a) 77 Figure 3.21: EDS & SEM of tephra (b) 79 Figure 4.1: Changes in absorbance with pH of main wastewaters 83 Figure 4.2: Multiple dose of wastewater, Tasman inflow 84 Figure 4.3: Absorbance vs. time, Kinleith acid data compilation 85 Figure 4.3: Capture efficiency as a function of particle size 87 List of Tables Table 3.0: Packed column filter elution times 38 Table 3.1: Diatom effect on pH 40 Table 3.2: Dilution of wastewater, effect on pH 41 Table 3.3: Caustic and continuous digester absorbance vs. pH 48 Table 3.4: Kinleith acid absorbance drop due to centrifuging 56 Table 3.5: Absorbance for 6 g regenerated diatoms 58 Table 3.6: Absorbance for Calcinated diatoms 58 Table 3.7: Transect block count for aggregates 65 Table 4.1: Data points for figure 4.1 80 XI List of Images Image 1.2: Diatom valves 13 Image 1.3: Diatom hypovalve joint 13 Image 1.4: Separation valve 13 Image 1.5: Girdle band 13 Image 1.6: Hymen and thecae 13 Image 1.7: Framboid formation 21 Image 1.8: Weathering of outer hymen 21 Image 3.1: Cyclottela diatoms (a) 61 Image 3.2: Cyclottela diatoms (b) 61 Image 3.3: Cyclottela diatoms (c) 61 Image 3.4: Larger diatoms (a) 61 Image 3.5: Larger diatoms (b) 61 Image 3.6: General SEM of sediments 61 Image 3.7: Aulacoseira 61 Image 3.8: Diatom pores (a) 63 Image 3.9: Diatom pores (b) 63 Image 1.10: Hymen 63 Image 3.11: Aulacoseira inner pore structure 63 Image 3.12: Sediment parts smaller than 40 μm 67 Image 3.13: Pulp fibre 67 Image 3.14: Aggregates around pulp fibre 67 Image 3.15: Aggregates, general 69 Image 3.16: Aggregates from 48 hour stirring 69 Image 3.17: Surface deposits, outer diatom 69 Image 3.18: Hymen surface mottling and dissolution 69 Image 3.19: Diatom pore deposits (a) 71 Image 1.2: Diatom pore deposits (b) 71 Image 3.21: Diatom pore deposits (c) 73 Image 3.22: Diatom surface mottling and dissolution 73 XII Abbreviations General BSi Biogenic silica CPU Chloroplatinate Unit(s) DAF Dissolved Air Flocculation DE Diatomaceous Earth(s) et al.