The rhodophytes or red seaweeds are an ancient group of organisms that are related to plants. Like terrestrial plants, they use secondary compounds to protect themselves from microbial infection and grazing by herbivores. However, unlike terrestrial plants, they produce mostly halogenated secondary compounds and rarely alkaloids. Osmundaria serrata (Rhodophyta) is found along the eastern South African coast and the Maldive Islands. Its descriptive common name is “red spirals” and the species is adapted to live in habitats with high wave action. Extracts from this seaweed had previously shown to have antimicrobial activity, but ecologically irrelevant microbes were used to test the extracts. In this study, ten bacteria were isolated from the surface of O. serrata and its habitat, and identified. Mostly aerobic and Gram-negative bacteria were isolated (Halomonas and Pseudomonas species) along with facultatively anaerobic forms (Vibrio spp.) and a Gram-positive (Marinococcus sp.). These were used in bioassays to compare the activity of extracts made from O. serrata and other seaweeds that occur in the same habitat. Marine bacteria are the initial colonizers in biofilm formation and subsequent fouling of surfaces in marine environments. The study of these bacteria in relation to their macroalgal hosts may help to control biofouling of surfaces that cause economic losses worldwide. A comparison was made between using agar dilution and microtitre methods for testing the antibacterial activity of an O. serrata extract. The microtitre method was found to be more sensitive than the agar dilution method. Possibly because e some of the bacteria on the petri plates (in the agar dilution method) were not in direct contact with the toxicant in the growth medium, but were in direct contact in the liquid medium of the wells in the microtitre plates. The extract from 0. serrata was the most active of the thirteen species of macroalgae collected from the same habitat and tested for antibacterial activity. Deformities in bacteria were observed in response to the 0. serrata extract. Increased capsule production and blebbing of the outer membranes were observed by transmission electron microscopy (negative staining). Lanosol diethyl ether was isolated from 0. serrata and tested for antibacterial activity. Lanosol is produced mainly by the rhodophytes, but it is also found in other macroalgae and fungi in lower concentrations. The compound inhibited the test bacteria with average MIC's of 0.27 ± 0.07 mg.mr1 (bacteriostatic) and 0.69 ± 0.15 mg.mr1 (bactericidal). Different forms of biofilm were observed by scanning electron microscopy on the thirteen species of macroalgae. These ranged from a very little biofilm covering on the calcified reds to complex communities on the other macroalgae. The treatment with OS04 vapour before fixation in glutaraldehyde preserved the biofilm structure better than no treatment and indicated that lipids are important in maintaining biofilm structure. Since a complex biofilm community was seen on the surface of 0. serrata, it is unlikely that lanosol functions as an antifouling agent. This chemical seems to multifunctional with antimicrobial and feeding deterrent activities. / Thesis (PhD (Botany))--University of Pretoria, 2006. / Plant Science / unrestricted

The goal of drinking water treatment is to produce and deliver safe water to the consumers. To achieve these objectives water treatment plants are designed based on the concept of the multibarrier approach which combines several drinking water treatment processes in order to increase the reliability of the system. The presence of pharmaceutically active compounds (PhACs), personal care products (PCPs) and endocrine disrupting compounds (EDCs) in drinking water sources is becoming a concern, because of chronic and indirect human exposure to contaminant mixtures at sub-therapeutic levels via drinking water consumption. Membrane filtration can be an efficient treatment process to remove microorganisms and/or trace organic contaminants from drinking water sources. However, membranes are confronted by a major limitation: membrane fouling. Fouled membranes suffer from a loss in performance either leading to a reduction in flux or a higher pressure requirement. Generally, membrane fouling increases the need for membrane maintenance measures such as backwashing and chemical cleaning which has a negative impact on the operating costs and membrane life time. Severe membrane fouling may even impact permeate quality and/or compromise membrane integrity. The aim of this study was to establish if biofiltration pretreatment without prior coagulation would be able to control membrane fouling in natural waters. The second objective investigated the removal of trace organic contaminants by individual treatment processes (i.e. biofiltration and membrane filtration). Parallel to this work, the presence and concentration of selected trace organic contaminants in Grand River (Ontario, Canada) were determined. The trace organic contaminants investigated included atrazine, carbamazepine, DEET, ibuprofen, naproxen, and nonylphenol. Direct biofiltration pretreatment (no coagulation) significantly reduced both reversible and irreversible fouling of ultrafiltration membranes. Results showed that the different degree of reduction of hydraulically reversible fouling was primarily attributed to the absolute concentration of a specific fraction of the dissolved organic matter (i.e. biopolymers) in the biofilter effluent (i.e. membrane feed). The study also suggests that the composition of biopolymers rather than their absolute concentration is important for the control of irreversible fouling. High pressure membranes such as nanofiltration membranes are also subjected to fouling. Results showed that biofiltration pretreatment was able to achieve fouling control but membrane characteristics (i.e. molecular weight cut off) influence the efficiency of the pretreatment. This study also showed that not only biopolymers but also humic substances and low molecular weight acids are being rejected by nanofiltration membranes. Selected trace organic contaminants were detected in Grand River water in the low ng/L range with detection frequencies between 48 to 100%. Seasonal occurrence patterns could be explained by compound use and possible degradation mechanisms. These results confirm the impact of human activities on the Grand River. This study showed that under the right conditions rapid biofiltration is capable of completely removing biodegradable emerging contaminants at ng/L concentrations. DEET, ibuprofen, and naproxen were biodegradable and therefore amenable to removal while carbamazepine and atrazine were recalcitrant. Factors such as empty bed contact time, influent concentration, and temperature influenced the biodegradation kinetics. Finally, both membrane and contaminant properties influenced the degree of rejection achieved by nanofiltration membranes. Results showed that steric hindrance and electrostatic repulsion were the major rejection mechanisms. Several benefits are associated with the use of direct biofiltration for drinking water treatment. These benefits include: the removal of easily biodegradable organic matter leading to biologically stable effluents; the removal of biodegradable trace organic contaminants contributing to the multibarrier approach; the absence of chemicals coagulation which is of advantage for operations in isolated areas; the simple operation and maintenance which is an advantage for locations with limited trained operators; and finally if used prior to membrane filtration biofiltration pretreatment can control membrane fouling.

The goal of drinking water treatment is to produce and deliver safe water to the consumers. To achieve these objectives water treatment plants are designed based on the concept of the multibarrier approach which combines several drinking water treatment processes in order to increase the reliability of the system. The presence of pharmaceutically active compounds (PhACs), personal care products (PCPs) and endocrine disrupting compounds (EDCs) in drinking water sources is becoming a concern, because of chronic and indirect human exposure to contaminant mixtures at sub-therapeutic levels via drinking water consumption. Membrane filtration can be an efficient treatment process to remove microorganisms and/or trace organic contaminants from drinking water sources. However, membranes are confronted by a major limitation: membrane fouling. Fouled membranes suffer from a loss in performance either leading to a reduction in flux or a higher pressure requirement. Generally, membrane fouling increases the need for membrane maintenance measures such as backwashing and chemical cleaning which has a negative impact on the operating costs and membrane life time. Severe membrane fouling may even impact permeate quality and/or compromise membrane integrity. The aim of this study was to establish if biofiltration pretreatment without prior coagulation would be able to control membrane fouling in natural waters. The second objective investigated the removal of trace organic contaminants by individual treatment processes (i.e. biofiltration and membrane filtration). Parallel to this work, the presence and concentration of selected trace organic contaminants in Grand River (Ontario, Canada) were determined. The trace organic contaminants investigated included atrazine, carbamazepine, DEET, ibuprofen, naproxen, and nonylphenol. Direct biofiltration pretreatment (no coagulation) significantly reduced both reversible and irreversible fouling of ultrafiltration membranes. Results showed that the different degree of reduction of hydraulically reversible fouling was primarily attributed to the absolute concentration of a specific fraction of the dissolved organic matter (i.e. biopolymers) in the biofilter effluent (i.e. membrane feed). The study also suggests that the composition of biopolymers rather than their absolute concentration is important for the control of irreversible fouling. High pressure membranes such as nanofiltration membranes are also subjected to fouling. Results showed that biofiltration pretreatment was able to achieve fouling control but membrane characteristics (i.e. molecular weight cut off) influence the efficiency of the pretreatment. This study also showed that not only biopolymers but also humic substances and low molecular weight acids are being rejected by nanofiltration membranes. Selected trace organic contaminants were detected in Grand River water in the low ng/L range with detection frequencies between 48 to 100%. Seasonal occurrence patterns could be explained by compound use and possible degradation mechanisms. These results confirm the impact of human activities on the Grand River. This study showed that under the right conditions rapid biofiltration is capable of completely removing biodegradable emerging contaminants at ng/L concentrations. DEET, ibuprofen, and naproxen were biodegradable and therefore amenable to removal while carbamazepine and atrazine were recalcitrant. Factors such as empty bed contact time, influent concentration, and temperature influenced the biodegradation kinetics. Finally, both membrane and contaminant properties influenced the degree of rejection achieved by nanofiltration membranes. Results showed that steric hindrance and electrostatic repulsion were the major rejection mechanisms. Several benefits are associated with the use of direct biofiltration for drinking water treatment. These benefits include: the removal of easily biodegradable organic matter leading to biologically stable effluents; the removal of biodegradable trace organic contaminants contributing to the multibarrier approach; the absence of chemicals coagulation which is of advantage for operations in isolated areas; the simple operation and maintenance which is an advantage for locations with limited trained operators; and finally if used prior to membrane filtration biofiltration pretreatment can control membrane fouling.

Cette thèse étudie le procédé d’ultrafiltration tangentiel assisté par ultrasons aux échellesmacro et nanométriques. Différentes dispersions colloïdales ont été filtrées (argiles, micelle decaséine, nanocristaux d’amidon et de cellulose). Les propriétés d'écoulement et les changementsinduits par les ultrasons (US) ont été caractérisés. Les organisations structurelles à proximité de lamembrane ont été mises en évidence pour la première fois aux échelles nanométriques, lors de lafiltration par diffusion de rayons X aux petits angles in-situ. L’application des US a permis uneaugmentation significative des flux de perméation d’un facteur 1,6 à 13,5, selon l'organisationstructurale des colloïdes. Trois mécanismes induits par les US ont été identifiés : une érosioncomplète, une rupture partielle ou pas de changement (nanométrique) des couches de particulesaccumulées. Grâce aux profils de concentration obtenus, une approche de modélisation a permisune prévision du flux perméation. / This thesis studies an ultrasonic assisted cross-flow ultrafiltration process from macro tonano scales. Different types of colloids were investigated: synthetic and natural clay dispersions,casein micelles (skim milk) and starch or cellulose nanocrystal suspensions. Firstly, flowproperties and the changes due to ultrasound (US) were investigated. Secondly, structuralorganizations at nanometer length scales in the vicinity of the membrane during filtration havebeen revealed for the first time by real-time in-situ Small Angle X-ray Scattering. The applied USincreased significantly the permeate flux of ultrafiltration by an enhancement factor of 1.6 to13.5, depending on the structural organization of the colloids. The applied US has led to threemain effects: a removal of accumulated particle layer, a partial disruption or no change of thenano-organization. Thirdly, thanks to the obtained concentration profiles, a modeling approachhas allowed a prediction of the permeate flux.