A laboratory investigation into foam separation processes, as applied to kraft pulping and bleaching effluents is described. Two methods, foam fractionation and ion flotation were tested in the laboratory. The procedures developed concentrated primarily on the removal of effluent colour because this property lent itself most readily to the available analytical methods, and because effluent colour removal presents one of the greatest waste water treatment problems facing the industry today. The foam fractionation technique was not successful. Substantial colour removals were obtained, but it was subsequently shown that the mechanism of removal was really an ion flotation. Positive results were obtained with the use of the ion flotation process for removal of effluent colour. At optimum conditions, the recovery of flotable material and the corresponding removal of effluent colour were in excess of 95 per cent. Variation of surfactant dosage showed that below a critical level no colour was removed. As concentrations increased above this value the amount of colour removed increased rapidly, reaching a high removal level beyond which increases in surfactant concentration were of little value. The rate of flotation recovery was found to be significantly affected by the air sparge rate and the sparger pore size, both parameters which would determine the area available for adsorption. The pH of the flotation cell solution had a marked effect on the system. Optimum pH was clearly defined as 5.1. Removal of material other than just the chromophoric fraction was apparent. Biological oxygen demand data, while not extensive, demonstrate a significant reduction in the bio-degradable portion of the effluent. The possible future development of the process into a viable candidate for industrial application is discussed. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

No description available.

by Chung Wai Ki. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references (leaves 110-120). / Acknowledgments --- p.i / Abstract --- p.ii / Table of Content --- p.iii / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Sewage Treatment --- p.1 / Chapter 1.1.1 --- Overview --- p.1 / Chapter 1.1.2 --- Types of Treatment --- p.2 / Chapter 1.2 --- Activated Sludge Process --- p.3 / Chapter 1.2.1 --- Overview --- p.3 / Chapter 1.2.2 --- Biology of Activated Sludge --- p.3 / Chapter 1.2.3 --- Operation of the Activated Sludge Process --- p.4 / Chapter 1.2.4 --- Floe Formation in Activated Sludge Process --- p.10 / Chapter 1.2.5 --- Operational Problems Associated with the Activated Sludge Process --- p.12 / Chapter 1.2.5.1 --- Bulking --- p.12 / Chapter 1.2.5.2 --- Foaming --- p.14 / Chapter 1.3 --- Foaming in Activated Sludge Process --- p.15 / Chapter 1.3.1 --- Overview --- p.15 / Chapter 1.3.2 --- Causes of Foaming --- p.16 / Chapter 1.3.2.1 --- Biology of Nocardia --- p.18 / Chapter 1.3.2.2 --- Growth Strategy of Nocardia --- p.18 / Chapter 1.3.2.3 --- Metabolic Specialization of Nocardia amarae --- p.19 / Chapter 1.3.3 --- Controls of Foaming --- p.20 / Chapter 1.4 --- Microbial Lipid and Bacterial Foaming --- p.23 / Chapter 1.4.1 --- Overview --- p.23 / Chapter 1.4.2 --- Fatty Acids in Bacteria --- p.24 / Chapter 1.4.3 --- Analytical Techniques --- p.25 / Chapter 1.4.3.1 --- Chromatography --- p.25 / Chapter 1.4.3.2 --- Gas Chromatography - Mass Spectrometry (GC-MS) --- p.26 / Chapter 1.4.4 --- Significance of Fatty Acids to Foaming --- p.27 / Chapter 1.5 --- Disinfection --- p.29 / Chapter 1.5.1 --- Overview --- p.29 / Chapter 1.5.2 --- Types of Disinfectants --- p.30 / Chapter 1.5.3 --- Mechanism of Disinfection --- p.31 / Chapter 1.5.4 --- Disinfection with Chlorine and Hypochlorite --- p.31 / Chapter 1.5.5 --- Chemistry of Chlorine Disinfection --- p.32 / Chapter 2. --- Objectives of Study --- p.35 / Chapter 3. --- Materials and Methods --- p.37 / Chapter 3.1 --- Sample Collection: --- p.37 / Chapter 3.2 --- Biological Studies of Activated Sludge Samples --- p.37 / Chapter 3.2.1 --- Microscopic Examination --- p.37 / Chapter 3.2.2 --- Isolation of Foam-Causing Filamentous Bacteria --- p.38 / Chapter 3.3 --- Physiology Studies of Nocardia amarae --- p.39 / Chapter 3.3.1 --- Growth Kinetics --- p.40 / Chapter 3.3.2 --- Effects of Fatty Acids on Nocardia amarae --- p.40 / Chapter 3.3.2.1 --- Fatty Acids as Sole Carbon Source --- p.41 / Chapter 3.3.2.2 --- Growth Stimulation --- p.42 / Chapter 3.3.2.3 --- Foam Test --- p.43 / Chapter 3.4 --- Fatty Acids Analysis --- p.43 / Chapter 3.4.1 --- Fatty Acid Extraction --- p.43 / Chapter 3.4.2 --- GC Analysis --- p.45 / Chapter 3.4.3 --- GC-MS Analysis --- p.46 / Chapter 3.5 --- Laboratory-Scale Activated Sludge Unit --- p.46 / Chapter 3.5.1 --- Set Up --- p.46 / Chapter 3.5.2 --- Performance Assessment of Laboratory-Scale Unit --- p.52 / Chapter 3.5.2.1 --- Physical Parameters --- p.52 / Chapter 3.5.2.2 --- Chemical Parameters --- p.54 / Chapter 3.5.2.3 --- Biological Parameters --- p.55 / Chapter 3.5.3 --- Anoxic Condition --- p.56 / Chapter 3.6 --- Toxicity Studies --- p.56 / Chapter 3.6.1 --- Comparative Toxicity Studies in Pure Culture --- p.56 / Chapter 3.6.2 --- Chlorination Studies of the Laboratory-Scale Unit --- p.58 / Chapter 3.6.3 --- Residual Chlorine Measurement --- p.58 / Chapter 3.7 --- Scanning Electron Microscopy --- p.60 / Chapter 4. --- Results --- p.61 / Chapter 4.1 --- Biological Studies of Activated Sludge --- p.61 / Chapter 4.1.1 --- Microscopic Examination --- p.61 / Chapter 4.1.2 --- Isolation of Foam-Causing Filamentous Bacteria --- p.61 / Chapter 4.2 --- Physiological Studies of Nocardia amarae --- p.65 / Chapter 4.2.1 --- Growth Kinetics --- p.65 / Chapter 4.2.2 --- Effects of Fatty Acids on Nocardia amarae --- p.69 / Chapter 4.2.2.1 --- Fatty Acids as Sole Carbon Source --- p.69 / Chapter 4.2.2.2 --- Growth Stimulation --- p.69 / Chapter 4.2.2.3 --- Foam Test --- p.69 / Chapter 4.3 --- Fatty Acids Analysis --- p.75 / Chapter 4.4 --- Laboratory-Scale Activated Sludge Unit --- p.80 / Chapter 4.4.1 --- Assessment of Performance of the Laboratory-Scale Unit --- p.80 / Chapter 4.4.2 --- Under Anoxic Condition --- p.80 / Chapter 4.5 --- Toxicity Studies --- p.85 / Chapter 4.5.1 --- Comparative Toxicity Studies in Pure Culture --- p.85 / Chapter 4.5.2 --- Chlorination Studies of Laboratory-Scale Unit --- p.85 / Chapter 4.5.3 --- Residual Chlorine Measurement --- p.91 / Chapter 5. --- Discussion --- p.94 / Chapter 5.1 --- Biological Studies of Activated Sludge Samples --- p.94 / Chapter 5.1.1 --- Microscopic Examination --- p.94 / Chapter 5.1.2 --- Isolation of Foam-Causing Filamentous Bacteria --- p.95 / Chapter 5.2 --- Physiological Studies of Nocardia amarae --- p.96 / Chapter 5.2.1 --- Growth Kinetics --- p.96 / Chapter 5.2.2 --- Effects of Fatty Acids on Nocardia amarae --- p.96 / Chapter 5.2.2.1 --- Fatty Acids as Sole Carbon Source --- p.96 / Chapter 5.2.2.2 --- Growth Stimulation --- p.97 / Chapter 5.2.2.3 --- Foam Test --- p.98 / Chapter 5.3 --- Fatty Acids Analysis --- p.99 / Chapter 5.4 --- Laboratory-Scale Activated Sludge Unit --- p.101 / Chapter 5.4.1 --- Assessment of Performance of the Laboratory-Scale Unit --- p.102 / Chapter 5.4.2 --- Under Anoxic Condition --- p.103 / Chapter 5.5 --- Toxicity Studies --- p.103 / Chapter 5.5.1 --- Comparative Toxicity Studies in Pure Culture --- p.103 / Chapter 5.5.2 --- Chlorination Studies of the Laboratory-Scale Unit --- p.105 / Chapter 6. --- Conclusion --- p.107 / Chapter 7. --- Summary --- p.108 / Chapter 8. --- References --- p.110

by Sonia, Tze Yan Lo. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 132-147). / Abstracts in English and Chinese. / Acknowledgments --- p.i / Abstract --- p.ii / Table of Content --- p.iii / List of Figures --- p.ix / List of Tables --- p.xiii / List of Abbreviations --- p.xv / Terminology --- p.xvii / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Objectives of sewage treatment process --- p.1 / Chapter 1.1.1 --- Types of treatment --- p.1 / Chapter 1.1.2 --- Activated sludge process --- p.2 / Chapter 1.1.3 --- Functioning of activated sludge process --- p.2 / Chapter 1.2 --- Common microbially mediated solid separation problems --- p.4 / Chapter 1.3 --- Bacterial foaming --- p.4 / Chapter 1.4 --- Factors enhancing foam production --- p.5 / Chapter 1.4.1 --- Substrates present in sewage --- p.6 / Chapter 1.4.2 --- Operating conditions --- p.8 / Chapter 1.4.3 --- Overpopulation of foaming bacteria --- p.8 / Chapter 1.5 --- Bacteria reported for foaming --- p.9 / Chapter 1.5.1 --- Foaming bacteria reported in different countries --- p.9 / Chapter 1.5.2 --- Nocardia Biology --- p.10 / Chapter 1.6 --- Metaboilsm of hydrophobic substances in sewage --- p.11 / Chapter 1.6.1 --- Metabolism of alkanes --- p.11 / Chapter 1.6.2 --- Metabolism of grease and oils --- p.11 / Chapter 1.6.3 --- Functions of lipids in the formation of bacterial foam --- p.11 / Chapter 1.7 --- Competition between floc-formers and foam-formers --- p.12 / Chapter 1.7.1 --- Interactions between microbial populations in activated sludge process --- p.12 / Chapter 1.7.2 --- Monod relationship and kinetic selection --- p.15 / Chapter 1.7.3 --- Effects of grease and oils in dominance of foaming bacteria --- p.17 / Chapter 1.8 --- Suggested mechanisms for bacterial foaming --- p.18 / Chapter 1.8.1 --- Mechanism suggested in early stage --- p.18 / Chapter 1.8.2 --- Froth flotation theory --- p.18 / Chapter 1.9 --- Problems from foaming --- p.21 / Chapter 1.10 --- Control of filamentous bacterial foaming --- p.22 / Chapter 2. --- Objectives of the study --- p.26 / Chapter 3. --- Materials and Methods --- p.27 / Chapter 3.1 --- Sample collection --- p.27 / Chapter 3.2 --- Isolation of major foaming and non-foaming bacteria --- p.27 / Chapter 3.2.1 --- Isolation of foaming bacteria --- p.27 / Chapter 3.2.2 --- Isolation of non-foaming bacteria --- p.30 / Chapter 3.3 --- "Physiological studies on type strain Nocardia amarae ATCC 27810, isolated major foaming bacterium, Nocardia sp. CU-2 and non- foaming bacterium, Aeromonas sp. CU-1" --- p.31 / Chapter 3.4 --- Effects of fatty acids on growth kinetics of Nocardia sp. CU-2 and Aeromonas sp. CU-1 in pure culture --- p.32 / Chapter 3.5 --- Effects of fatty acids on growth yields of Nocardia sp. CU-2 and Aeromonas sp. CU-1 in pure culture --- p.34 / Chapter 3.6 --- Effects of fatty acids on growth yields of Nocardia sp. CU-2 and Aeromonas sp. CU-1 in mixed culture --- p.37 / Chapter 3.7 --- Effect of fatty acids on the propensity of foam formation of Nocardia sp. CU-2 growing with different fatty acids --- p.38 / Chapter 3.8 --- Effects of fatty acids on hydrocarbon affinity (HA) of Nocardia sp CU-2 --- p.39 / Chapter 3.9 --- "Effects of fatty acids on the filamentous growth, nocardial growth, foaming abilities and settling abilities of activated sludge in batch cultures of foaming and non-foaming samples" --- p.43 / Chapter 4. --- Results --- p.48 / Chapter 4.1 --- Isolation of foaming and non-foaming bacteria --- p.48 / Chapter 4.1.1 --- Isolation of foaming bacteria --- p.48 / Chapter 4.1.2 --- Isolation of non-foaming bacteria --- p.48 / Chapter 4.2 --- "Physiological studies on type strain Nocardia amarae ATCC 27810, isolated major foaming bacterium, Nocardia sp. CU-2 and non- foaming bacterium, Aeromonas sp. CU-1" --- p.56 / Chapter 4.3 --- Effects of fatty acids on growth kinetics of Nocardia sp. CU-2 and Aeromonas sp. CU-1 in pure culture --- p.56 / Chapter 4.4 --- Effects of fatty acids on growth yields of Nocardia sp. CU-2 and Aeromonas sp. CU-1 in pure culture --- p.60 / Chapter 4.4.1 --- Effects of fatty acids on Nocardia sp. CU-2 --- p.77 / Chapter 4.4.2 --- Effects of fatty acids on Aeromonas sp. CU-1 --- p.77 / Chapter 4.5 --- Effects of fatty acids on growth yields of Nocardia sp. CU-2 and Aeromonas sp. CU-1 in mixed culture --- p.78 / Chapter 4.6 --- Effect of fatty acids on the propensity of foam formation of Nocardia sp. CU-2 growing with different fatty acids --- p.78 / Chapter 4.7 --- Effects of fatty acids on hydrocarbon affinity (HA) of Nocardia sp CU-2 --- p.83 / Chapter 4.8 --- "Effects of fatty acids on the filamentous growth, nocardial growth, foaming abilities and settling abilities of activated sludge in batch cultures of foaming and non-foaming samples" --- p.103 / Chapter 4.8.1 --- The filamentous growth of activated sludge --- p.103 / Chapter 4.8.2 --- Nocardial count --- p.103 / Chapter 4.8.3 --- Foam ratings --- p.107 / Chapter 4.8.4 --- Sludge settling ability --- p.107 / Chapter 5. --- Discussion --- p.114 / Chapter 5.1 --- "Physiological studies on type strain Nocardia amarae ATCC 27810, isolated major foaming bacterium, Nocardia sp. CU-2 and non- foaming bacterium, Aeromonas sp. CU-1" --- p.114 / Chapter 5.2 --- Effects of fatty acids on growth kinetics of Nocardia sp. CU-2 and Aeromonas sp. CU-1 in pure culture --- p.114 / Chapter 5.2.1 --- Inhibition effects of MC fatty acids on growth of Nocardia sp. CU-2 --- p.115 / Chapter 5.2.2 --- Effects of fatty acids on specific growth rates --- p.115 / Chapter 5.2.3 --- Length of lag phase --- p.115 / Chapter 5.2.4 --- Kinetic selection of Nocardia sp. CU-2 and Aeromonas sp. CU-1 --- p.116 / Chapter 5.3 --- Effects of fatty acids on growth yields of Nocardia sp. CU-2 and Aeromonas sp. CU-1 in pure culture --- p.117 / Chapter 5.3.1 --- Growth of Nocardia sp. CU-2 and Aeromonas sp. CU-1 in different media --- p.117 / Chapter 5.3.2 --- "Effects of fatty acids on Nocardia sp, CU-2" --- p.118 / Chapter 5.3.3 --- Effects of fatty acids on Aeromonas sp. CU-1 --- p.119 / Chapter 5.4 --- Effects of fatty acids on growth yields of Nocardia sp. CU-2 and Aeromonas sp. CU-1 in mixed culture --- p.119 / Chapter 5.4.1 --- Effects of fatty acids in NB --- p.119 / Chapter 5.4.2 --- Effects of fatty acids in MM --- p.120 / Chapter 5.4.3 --- Effects of fatty acids in SS --- p.121 / Chapter 5.5 --- Effect of fatty acids on the propensity of foam formation of Nocardia sp. CU-2 growing with different fatty acids --- p.122 / Chapter 5.6 --- Effects of fatty acids on hydrocarbon affinity (HA) of Nocardia sp CU-2 --- p.122 / Chapter 5.6.1 --- Differences in HA of Nocardia sp. CU-2 among three hydrocarbons --- p.122 / Chapter 5.6.2 --- Differences in HA of Nocardia sp. CU-2 among three different media --- p.123 / Chapter 5.6.3 --- Effects of fatty acids on HA of Nocardia sp. CU-2 --- p.123 / Chapter 5.7 --- "Effects of fatty acids on the filamentous growth, nocardial growth, foaming and settling abilities of activated sludge in batch cultures" --- p.124 / Chapter 5.7.1 --- Abundance of filamentous microorganisms in activated sludge --- p.124 / Chapter 5.7.2 --- Nocardial count --- p.124 / Chapter 5.7.3 --- Foam ratings --- p.125 / Chapter 5.7.4 --- Sludge settling ability --- p.126 / Chapter 6. --- Conclusion --- p.127 / Chapter 7. --- Summary --- p.129 / Chapter 8. --- References --- p.132

Biosurfactants are naturally occurring surface active compounds with unique properties such as biodegradability, low toxicity and tolerance to extreme conditions. These unique properties promote their use as alternatives to traditional petrochemical and oleochemical surfactants, as they satisfy requirements for environmentally friendly manufacturing processes. However, the cost of biosurfactants is still significantly higher than chemical surfactants which hinders their large-scale commercialisation. This work presents an investigation into the production of surfactin, a lipopeptide biosurfactant, exploiting its foamability characteristics for the design and implementation of a recirculating continuous foam fractionation column operated in parallel with a bioreactor. Surfactin is a powerful amphiphilic compound produced by Bacillus subtilis. It is a plant-elicitor with antimicrobial properties offering a huge potential in the food and agricultural industries. However, surfactin has extreme foamability even at low concentrations. This foamability can lead to production problems such as large volumes of uncontrolled overflowing foam with significant product and biomass losses. Here, it is demonstrated that this overflow can be controlled, or eliminated, by integrating a foam fractionation system to the bioreactor in a recirculating loop. A dual production and separation process was engineered and enabled reaching high surfactin productivity in a controlled manner. After elucidating the surface properties of surfactin-rich broth, a foam fractionation column was designed for bench-scale production. Operation of the recirculating column in parallel with the bioreactor enabled air flow to be independently controlled for each unit. Surfactin solutions of various concentrations were tested to relate foamability to concentration over a range of bubble sizes. The sintered glass pore size was revealed to be the main factor influencing the enrichment, with a positive correlation with increasing pore size. Characterisation of the fermentation production rate enabled fractionation column air flow rate to be controlled to ensure sufficient foam surface area for product adsorption. The airflow rate was identified as the main factor impacting on the surfactin recovery rate. This characterisation enabled broth feed flow rate to be controlled to balance the removal rate with the production rate. Two processes were created coupling the newly designed fractionation column with the bioreactor operated either in aerated or non-aerated conditions. Under aerated settings, controlled surfactin production was successfully achieved at a productivity of 0.0019 g L-1 h-1 whilst simultaneously recovering 91% of the product at a maximum enrichment of 79 and 116 through the column and overflow routes, respectively. Under non-aerated settings, overflowing foam was fully avoided and 90% of the product was recovered solely through the fractionation column at an enrichment ratio of 40 under non-optimised settings. Additionally, up to 14% (g/g) increase in surfactin production was observed with the coupling of the fractionation column demonstrating a further benefit as a bioprocess intensifying device for surfactin production. This work provides a benchmark for a robust system for surfactin production, substantially improving the productivity at bench scale, potentially leading the way to more productive and less costly industrial processes for surface active compounds in a wide range of industrials fields.

Foam fractionation is an economical and environmentally friendly separation method for surface active material using a rising column of foam. The system of foam fractionation column with reflux is selected since such a system can improve the enrichment of the product collected from the top of the column. Due to the reflux, it is assumed that there is more surface active material (surfactant and/or protein) in the Plateau border than that in the foam lamella, so that the Plateau border acts as a surfactant/protein reservoir. The aim of this thesis is to investigate the adsorption and transport of surface active material such as surfactant and/or protein onto the surface of a lamella in a foam fractionation column with reflux using mathematical simulation. There are two steps involved in adsorption of surface active material onto a bubble surface within foam, which are diffusion from the bulk solution into the subsurface, a layer next to the interface, followed by adsorption of that material from the subsurface onto the interface. The diffusion follows the Fick's second law, while the adsorption may follow the Henry, Langmuir or Frumkin isotherms, depending on the properties of the surface active material. The adsorption of mixed protein-surfactant follows the Frumkin isotherm. When there is a competition between protein and surfactant, the protein arrives onto the interface at a later time due to a slower diffusion rate and it displaces the surfactant molecules already on the surface since protein has a higher affinity for that surface than surfactant. The surfactant transport from a Plateau border onto a foam lamella is determined by the interaction of forces applied on the lamella surface, such as film drainage, due to the pressure gradient between the lamella and the Plateau border, the Marangoni effect, due to the gradient of surface tension, and surface viscosity, as a reaction to surface motion. In this thesis, there are two different models of film drainage. One approach uses assumption of a film with a mobile interface and the other model assumes a film with a rigid interface. In the absence of surface viscosity, the Marangoni effect dominates the film drainage resulting in accumulation of surfactant on the surface of the foam lamella in the case of a lamella with a rigid interface. In the case of a film with a mobile interface, the film drainage dominates the Marangoni effect and surfactant is washed away from the surface of the lamella. When the drainage is very fast, such as that which is achieved by a film with a mobile interface, the film could be predicted to attain the thickness of a common black film, well within the residence time in a foam fractionation column, at which point the film stops draining and surfactant starts to accumulate on the lamella surface. The desirable condition in operation of a foam fractionation column however is when the Marangoni effect dominates the film drainage and surfactant accumulates on the surface of a foam lamella such as the one achieved by a film with a rigid interface. In the presence of surface viscosity and the absence of film drainage, the surface viscous forces oppose the Marangoni effect and reduce the amount of surfactant transport onto the foam lamella. A larger surface viscosity results in less surfactant transport onto the foam lamella. In addition, the characteristic time scale required for surfactant transport is shorter with a shorter film length.

The activated sludge process comprises a complex and enriched culture of a mixture of generalist and specialist organisms. The lack of knowledge on species diversity of microbial communities is due to the simplicity of bacterial morphology and the phenotypic characters, and the unculturable portion of microbial cells in natural habitats. Although a wide range of bacteria can be isolated using conventional microbiological techniques of sample dilution and spread plate inoculation, many well-known activated sludge bacteria can not be isolated using them. The individual microbial cells in activated sludge grow in aggregates that consist of floc-forming organisms together with filamentous microorganisms that form the backbone of the activated sludge floes. Overgrowth of these filamentous microorganisms often causes settling problems called bulking and foaming. These problems consist of slow settling, poor compaction of solids and foam overflow into the effluent. Although methods for the isolation of filamentous bacteria from mixed liquor samples have been investigated, the attempts have been largely unsuccessful. In this study we investigated bulking and foaming activated sludge to identify the dominant filamentous organisms using microscopy and molecular techniques. Using microscopy, the dominant filament associated with the foaming sample was "Microthrix parvicella" and in the bulking sample was Nocardia spp. The foaming sample was investigated using molecular techniques that involved 165 rDNA sequencing. Although some of the clones isolated from the sludge foam were associated with filamentous bacteria causing foam, no positive identification could be made. In the part of the study that was conducted in Australia, a rRNA-targeted oligonucleotide probe was designed for the identification of a filamentous organism occurring in activated sludge foam. This organism resembled Eikelboom Type 0041 and was classified in the candidate bacterial division TM7. The discrepancy that the sequence data did not indicate the dominant filamentous organisms observed by microscopy, highlights the fact that natural microbial communities need to be studied using a combination of techniques since none of the techniques available are sufficient to determine the complete community structure of complex communities such as activated sludge. / Dissertation (MSc (Microbiology))--University of Pretoria, 2005. / Microbiology and Plant Pathology / unrestricted

L'objectif de ce travail était d'étudier les trois fonctions d'une colonne airlift sous dépression qui sont le pompage, les transferts gaz-liquide et l'extraction de matières particulaires par moussage-écumage. Le champ d'application ciblé concernait principalement le traitement des eaux aquacoles incluant l'extraction et la concentration de microalgues naturelles ou de culture. Chacune des fonctions a été étudiée séparément afin d'évaluer les capacités de l'airlift dans différentes conditions. L'étude de la fonction pompage a montré l'importance de la nature de l'eau, du type de diffuseur d'air, du débit gazeux injecté et du niveau de dépression appliqué. En eau douce, une forte coalescence des bulles est observée. Elle a pour conséquence une rétention gazeuse plus faible qu'en eau de mer. Le débit d'eau fourni par la colonne apparaît ainsi supérieur en eau douce (30 à 35 m3.h-1 contre seulement 10 à 20 m3.h-1 en eau de mer pour 5 m3.h-1 d'air injecté). A l'inverse, la hauteur de refoulement disponible est plus élevée en eau de mer (jusqu'à 0.8 m) qu'en eau douce (0.6 m maximum). Pour des circuits d'aquaculture où la perte de charge est faible, l'airlift est un système de pompage économique qui permet de réduire d'environ 40 % la consommation d'énergie par rapport à celle de pompes centrifuges. La colonne airlift présente également des capacités de transferts de matière comparables à celles de systèmes conventionnels. Les valeurs de KLa calculées pour la désorption du CO2 et comprises entre 0.002 et 0.01 s-1, sont environ quatre fois inférieures à celles obtenues pour le transfert d'oxygène par aération dans des conditions comparables. Les efficacités de transfert sont comprises entre 0.02 et 0.023 Kg.KW.h-1 pour le CO2 et entre 1.52 et 1.8 Kg.KW.h-1 pour l'O2. Les vitesses de transfert dépendent significativement du débit d'air, de la température, de la taille moyenne des bulles et de la présence d'aliments dans le bassin d'élevage. Elles sont peu affectées par la salinité, le niveau de dépression, la longueur du tube interne d'échange et le débit d'eau. Enfin, les capacités de séparation par moussage-écumage évoluent de façon positive quand le débit d'air et la taille des bulles sont réduits. L'efficacité globale d'extraction diminue avec l'augmentation de la concentration des produits extraits qui peut atteindre 130 fois la concentration initiale. La colonne à dépression apparaît ainsi comme un système multifonctionnel performant, même si l'efficacité maximale, pour chacune des fonctions, correspond à des conditions opératoires différentes. Ce procédé ouvre des perspectives de développement intéressantes dans des secteurs variés (de l'aquaculture au traitement des eaux industrielles). / The aim of this work was to study the three functions of a vacuum airlift, which are water pumping, mass transfer and foam fractionation. The investigations mainly focused on the treatment of fish culture water and on phytoplancton harvesting. Each function was studied separately, in order to assess the performance of the vacuum airlift with specific operating conditions. By studying the airlift pump, the effects of water and diffuser types, air injection conditions and depression level were shown. In fresh water, bubble coalescence was observed, which reduced gas holdup compared to sea water. Consequently, the water flow of the vacuum airlift appeared higher in fresh water than in sea water (30 to 35 m3.h-1 against 10 to 20 m3.h-1) for the same air flow rate (5 m3.h-1). Conversely, the available lift height was higher in sea water (up to 0.8 m) than in fresh water (0.6 m maximum). For low head aquaculture systems, the vacuum airlift may be an economical pumping system which allows a 40 % energy saving compared to centrifugal pumps. The vacuum airlift had a mass transfer efficiency similar to other gas transfer systems. The KLa values calculated for CO2 desorption ranged between 0.002 and 0.01 s-1. They were four times lower than those obtained for oxygen transfer in similar conditions. Mass transfer efficiencies ranged between 0.02 and 0.023 Kg.KW.h-1 for CO2 and between 1.52 and 1.8 Kg.KW.h-1 for O2. Mass transfer velocities significantly depended on air flow rate, water temperature, average bubble size and the presence of feed in the rearing tank. They are weakly depending on salinity, depression level, inner tube length or water flow. At last, foam fractionation increased when air flow and bubble size were reduced. The extraction efficiency decreased when the concentration of the extracted product increased (maximal concentration factor around130). The vacuum airlift appeared to be as a high-performance multifunctional system, even if the maximal efficiency for each of the functions corresponds to different operating conditions. This process could be used in a large scope of fields ranging from aquaculture to industrial water treatment.

Foam fractionation is an adsorptive bubble separation technology that has shown potential as a replacement to the more costly and non-sustainable traditional downstream processing methods such as solvent extraction and chromatography for biological systems. However biological systems mostly tend to be a mixture of surface active species that complicates the foam fractionation separation. In this thesis a detailed experimental study on the application of foam fractionation to separate a well-defined surfactant-protein mixture was performed with emphasis on the competitive adsorption behaviour and transport processes of surfactant-protein mixtures in a foam fractionation process. Surface tension and nuclear magnetic resonance (NMR) measurements showed that nonionic surfactant Triton X−100 maximum surface pressure, surface affinity and diffusivity were a factor of 2.05, 67.0 and 19.6 respectively greater than that of BSA. Thus Triton X−100 dominated the surface adsorption at an air-water surface by diffusing to the surface and adsorbing at the surface faster than BSA. This competitive adsorption behaviour was observed in foam fractionation experiments performed for Triton X−100/BSA mixtures for different feed concentration ratios and air flow rates. The recovery and enrichment of Triton X−100 were found to increase and decrease respectively with increasing air flow rate for all foam fractionation experiments as expected for a single component system. However the recovery and enrichment of BSA were both found to increase with increasing air flow rate for high feed concentrations of Triton X−100.Bubble size measurements of the foamate produced from foam fractionation experiments showed that at steady state conditions the bubbles rising from the liquid pool were stabilised by BSA. However at the top of the column the recovery of Triton X−100 in the foamate (75% to 100%) was always greater than the recovery of BSA (13% to 76%) for all foam fractionation experiments. In addition, for high feed concentrations of both components and at low air flow rates, the enrichment of BSA remained at almost unity for most experiments and only increased when the recovery of Triton X−100 reached 100%. Thus it was concluded that Triton X-100 displaced the adsorbed BSA from the surface. The foam drainage properties of Triton X−100/BSA mixtures were characterised using two methods; forced foam drainage and from pressure profiles of steady state foam fractionation experiments (pressure method). The drainage data from the forced foam drainage was found not to be compatible with experimental foam fractionation results, by indicating that stable foam was not produced during the foam fractionation experiments. However stable foam was repeatedly produced during foam fractionation experiments. The drainage data from the pressure method was found to be in close agreement to experimental foam fractionation experiments. The work in this thesis takes a significant step beyond the literature experimental foam fractionation studies for multicomponent systems. In addition to investigating the effect of foam fractionation process parameters on the separation of mixed systems, the results from the characterisation studies of surface adsorption and foam properties provided insight and deeper understanding of the competitive adsorption behaviour of surfactants and proteins in a foam fractionation process.

Biosurfactants are naturally occurring amphiphiles with potential for use as alternatives to traditional petrochemical and oleochemical surfactants. The unique properties of biosurfactants, including their biodegradability and tolerance of a wide range of temperature and pH, make their use in a range of novel applications attractive. Currently the wider ultilisation of biosurfactants is hindered by a lack of economically viable production routes, with downstream processing presenting a significant challenge. This thesis presents an investigation into the production of HFBII, a hydrophobin protein, using an adsorptive bubble separation technique called foam fractionation for in situ recovery of the biosurfactant. The effects of foaming on the production of HFBII by fermentation were investigated at two different scales. Foaming behaviour was characterised in standard terms of the product enrichment and recovery achieved. Additional specific attention was given to the rate at which foam, product and biomass overflowed from the fermentation system in order to assess the utility of foam fractionation for HFBII recovery. HFBII was expressed as an extracellular product during fed batch fermentations with a genetically modified strain of Saccharomyces cerevisiae, which were carried out with and without antifoam. In the presence of antifoam HFBII production is shown to be largely unaffected by process scale, with similar yields of HFBII on dry matter obtained. More variation in HFBII yield was observed between fermentations without antifoam. In fermentations without antifoam a maximum HFBII enrichment in the foam phase of 94.7 was measured with an overall enrichment of 54.6 at a recovery of 98.1%, leaving a residual HFBII concentration of 5.3 mg L-1 in the fermenter. It is also shown that uncontrolled foaming reduced the concentration of biomass in the fermenter vessel, affecting total production. This series of fermentation experiments illustrates the potential for the application of foam fractionation for efficient in situ recovery of HFBII, through simultaneous high enrichment and recovery which are greater than those reported for similar systems. After the suitability of foam fractionation was demonstrated a novel apparatus design was developed for continuously recovering extracellular biosurfactants from fermenters. The design allows for the operating conditions of the foam fractionation process, feed rate and airflow rate, to be chosen independently of the fermentation parameters. Optimal conditions can then be established for each process, such as the aeration rate required to meet the biological oxygen demand of the cell population. The recirculating foam fractionation process was tested on HFBII producing fermentations. It is shown that by using foam fractionation to strip HFBII from fermentation broth in situ the amount of uncontrolled overflowing from the fermenter was greatly reduced from 770.0 g to 44.8 g, compared to fermentations without foam fractionation. Through optimisation of the foam column operating conditions the proportion of dry matter retained in the fermenter was increased from 88% to 95%, in contrast to a dry matter retention of 66% for fermentation without the new design. With the integrated foam fractionation process a HFBII recovery of 70% was achieved at an enrichment of 6.6. This work demonstrates the utility of integrated foam fractionation in minimising uncontrolled foaming in fermenters whilst recovering an enriched product. This integrated production and separation process has the potential to facilitate improved biosurfactant production, currently a major barrier to their wider use.