A thesis submitted in fulfillment of the requirement for the Degree Master of Technology: Biotechnology, M.L. Sultan technikon, 2000. / The ever-increasing demand for a wide variety of paper products has led to the pulp and paper industry becoming one of the largest industries in the world. In 1988 the United States alone produced almost 71 million metric tonnes of paper and pulp board (Jeffries, 1992). South Africa has also become one of the major international producers of pulp and paper products. Since 1970, the production of paper and board by the South African industry achieved an average growth rate of 5.2% per annum, and in 1997 South Africa was the twelfth largest producer of pulp and 24th biggest supplier of paper and board in the world (Molony, 1999 / M

Abstract Washing during kraft pulping can be divided into two separate areas each with its own distinct features: namely brownstock washing and washing in bleaching. Research interest has so far concentrated mostly on investigating brownstock washing and factors affecting its efficiency. Pulp washing in bleaching, however, has been practically neglected. The basic phenomena are the same as in brownstock washing, but there are differences which have not been taken into consideration to a sufficient extent. This less explored area is the focus of this research. In this thesis, it is shown that brownstock washing and pulp washing between bleaching stages are distinct areas with their own specific features. They differ for example in terms of the composition and molecular size of the impurities in the pulp suspension. Various process conditions, pH, temperature and so on cause further differences between washing in bleaching and brownstock washing. The removal of specific compounds can be clearly affected by the appropriate selection of wash liquor. It is shown that the dynamic behaviour during washing is different for different compounds and depends on the properties of the wash water. The key element is to find the most harmful compounds in specific positions in bleaching and on the basis of that finding, to determine the most suitable wash liquor system. Chemical oxygen demand (COD) is a widely used method for evaluating the washing result, but as a collective measurement variable it does not describe the actual compounds that cause the "loss" of bleaching chemicals. Studies have shown that many compounds contribute to COD load but ultimately most of them have no real effect on the bleaching result. A suggestion for more precise definition of wash loss is offered than COD.

Abstract Information about interactions among metals, hydrogen peroxide and chelating agents is needed to develop environmental technology and the operating efficiency of modern elemental chlorine free and total chlorine free bleaching processes. The work presented here focused on the properties of metal chelates and corrosion of titanium in an alkaline hydrogen peroxide solution. A comparative study between three rapid analysis methods, ICP-AES, XRF and ISE, was performed in pulp matrix and error sources of ISE were investigated in detail. Sensitive and selective GC methods for chelating agents ADA and NTA in water matrices were developed. Decomposition of ADA (percentage of residual 71) was observed already at the hydrogen peroxide anion level of 400 mg/l in which DTPA was more persistent (percentage of residual 94). EDTA was stable even in the hydrogen peroxide anion level of 1200 mg/l, in which its percentage of residual was 94. DTPA, EDTA and ADA were more soluble in the presence of iron and manganese than in the absence of these metals. The chelation of iron appeared to be thermodynamically limited in hydrogen peroxide bleaching conditions. Unalloyed (Grade 2) and alloyed (Grade 5) titanium corroded at the hydrogen peroxide anion level of 200 mg/l. The presence of calcium and silica inhibitors and further iron and manganese enhanced the critical hydrogen peroxide anion levels. Grade 5 was inferior to Grade 2. During rapid uniform corrosion, the potential of unalloyed titanium was under 200 mV (SHE) and lower than that of platinum. Over 90% of manganese and many other metals could be leached into aqueous phase for ICP-AES analysis using chelation or acid hydrolysis. An XRF method for manganese, iron and copper in pulp including little or no sample treatment was developed. Measuring temperature differences and atmospheric carbon dioxide were observed to be notable error sources of the ISE technique.

Magister Scientiae Dentium - MSc(Dent) / Summary: Aim: The aim of this laboratory study is to assess the efficacy of a tooth bleaching agent by evaluating the degree of color change with the use of a spectrophotometer and not by the usual subjective, visual methods. Methodology: Twenty specimens of human teeth will be collected, polished and divided into two groups. A baseline color measurement by the CIE L* a* b* with a spectrophotometer against a white background will be taken before one group is immersed in coffee and the other in red wine for two weeks. Bleaching of the specimens will be done according to manufacturer’s instructions for two weeks. Color readings will be taken before bleaching, weekly during bleaching and 1 and 2 weeks after the bleaching treatment. Color change (ΔE) will be calculated mathematically as Δ E = [ (Δ L*)2 + (Δ a*)2 + (Δ b*)2 ]1/2. An observation of whether the baseline color reading will be regained by the bleaching process will be made. Results: Data collected will be recorded on an Excel spreadsheet. Advice from a qualified statistician will be sought to analyze the data. Results will be discussed in comparison with the existing literature on this subject. / South Africa

Objective: The aim of this pilot study is the evaluation and measurement of color stability from baseline until stabilization of color associated with bleaching and the dehydration and rehydration process of the teeth. Method: Six extracted intact human third molars were randomly selected, cleaned, and stored in artificial saliva at 370C. A custom positioning jig was fabricated for each tooth for reproducible color measurement. A baseline shade was recorded according to the Commission Internationale de l'Eclairage L*a*b* (CIE-L*a*b*) using a Minolta Chromameter CR-(200). Color measurement for all testing was taking at baseline, 15 min, 30 min, 2h, 12h and every 2 h thereafter until color stabilization occurred. Phase 1(dehydration-rehydration w/o bleaching): For dehydration, all teeth lightened and color stability occurred at 6 h. Rehydration of teeth to the baseline of color was achieved after 14 hours. Phase 2 (Effect of bleaching): An in-office bleach material (Zoom 25% HP) was applied to each tooth according to the Kwon technique (polyethylene wrap placed to cover the gel) for one hour. All comparisons were made to a Delta value of 2.6 (perceivable difference). Result: Phase 1: A mean äL*=-13.05(±15.62) was observed for tooth dehydration with no perceivable changes in chroma äa* and äb*. Phase 2: In-office bleaching produced dehydration and chroma changes when measured immediately after bleaching with a mean of äL*=-12.45(±2.4), äa*=0.31(±0.53), and äb*= 3.67(±1.76). After rehydration of bleached teeth, luminosity values (äL*) returned to normal and only chromaticity changes (äb#8727;) were observed with a mean of 4.77(%B11.91). Conclusion: Within the limits of this study, in-office bleaching produced dehydration and chroma changes, represented by äL* and äb*. Upon rehydration, the color changes were not as discernible. Further study will be conducted to determine the validity of these findings.

Corals reefs worldwide are facing many challenges due to global warming. Of these challenges, increasing sea temperatures represent a major threat. An increase of 1 °C above summer mean levels is greatly associated with coral bleaching, and massive coral bleaching is observed when accumulation of thermal-stress reaches 4 °C-weeks according to Degree Heating Weeks (DHW) measurements. The coral holobiont is an assemblage of many organisms including Symbiodiniaceae; a family of photosynthetic microalgae that form an endosymbiotic relationship with corals. Studies suggest that Symbiodiniaceae may drive the performance of the host, therefore, resilience of the coral host against thermal stress may be largely influenced by Symbiodiniaceae. The aim of this study was to compare the physiological performance under acute heat and light-stress conditions of several Symbiodiniaceae strains (clade A and B) isolated from different geographical locations with distinct thermal profiles (Red Sea, Hawaii, and North Carolina). Oxygen production, respiration rate, photosynthetic efficiency, and production of ROS were measured under conditions of acute heat and light-stress. The Red Sea strains (RS-B*, RS-B, and RS-A) exhibited a higher photosynthetic efficiency with increasing temperatures than the Hawaii and North Carolina strains (SSBO1, SSAO1, respectively). After heat-stress of 34 °C, RS-A was found to have the best thermotolerance with regard to ROS production. Oxygen production and respiration rate data showed high biological variation between culture replicates which prevented inter-strain comparisons and limited observation of consistent trends. The observed variability was largely due to the differential age of the cultures used, and the inability of the cell counting method to differentiate between live and dead cells. The results of this study indicate that Symbiodiniaceae strains originating from warmer geographic locations exhibit an overall better performance under acute heat-stress conditions. Variability in the physiological response of three samples from the same species (Breviolum minutum) exemplifies the large diversity in the family Symbiodiniaceae, and indicates the need to support genomic identification of Symbiodiniaceae isolates with physiological studies. Efforts to predict the future of coral reefs under current threats of climate change will only be productive if we have a comprehensive understanding of the complex interactions between corals and Symbiodiniaceae.

Hong Kong provides a marginal marine environment for coral growth due to its high latitude in addition to massive freshwater run-off from the Pearl River Delta. Previous studies have reported that Hong Kong waters nurture 84 species of scleractinian corals in 28 families distributed in various locations, especially the protected bays in the eastern waters. However, very little is known about the benthic composition and health of coral communities. This study aimed to 1) determine the benthic composition of local coral communities and understand the environmental determinants of coral coverage and coral community composition; 2) record coral colony size frequency distribution across these 33 sites to understand the patterns of coral recruitment in recent years; 3) quantify coral bioerosion and corallivory by the long-spined sea urchin and explore the feasibility of remediating the coral damage by a coral-associated portunid crab. Surveys were conducted at 33 sites in Hong Kong, which cover sites with the highest coral coverages that are mainly located in the north-eastern, east and south-eastern waters. A belt-transect photo quadrant method was applied. 22 hard coral genera were identified, among which the genera Porites, Platygyra and Pavona were found to be the most abundant. Most of the study sites were dominated by few genera of massive corals which led to a low diversity. Coral coverage was negatively associated with nutrient levels including nitrogen, phosphorus and organic matter deposition rates based on sediment trap data. Apart from sedimentary parameters, coral coverage was also found to be strongly negatively correlated with the density of the long-spined sea urchin Diadema setosum. Study sites were categorized into four different conservation classes with sites of higher diversity assigned a higher conservation value. These data could serve as a baseline for measuring changes in benthic composition in the future, and as a reference for management planning such as designating new marine parks. Determining the size structure can help predict how a population may change in the future and whether conservation efforts are effective in promoting the increase in numbers of individuals. To determine coral size structure in local waters, a video transect method was adopted to capture videos on the benthic substrates of the 33 study sites. In the laboratory, the video clips were analyzed to extract information on the size and growth form of all coral colonies along the transects. Size-frequency distribution plots generally showed a highly positive skewness, which indicated a dominance of small-sized (i.e. 10 - 30 cm) colonies, yet low in recruitment-sized (i.e. 5 cm) colonies. An examination of the size distribution of the most common genera showed that the distribution patterns were more genus-dependent rather than site-dependent. Also, massive corals were the most dominant growth form, while branching corals were the least common which was different from healthy tropical reefs. Apart from establishing a baseline of coral communities, coral bioerosion was further studied. Previous studies found that coral coverage and urchin density were negatively correlated in local waters. Further, severe coral bioerosion had been reported to cause community-level coral damage in several locations. Therefore, impact coral bioerosion by the sea urchin Diadema setosum and whether such impact could be remediated were further investigated in a series of controlled experiments in the field. Although sea urchins were reported to prevent shifting from coral-dominant to algae-dominate phase elsewhere, they were found to cause severe tissue loss and bioerosion at high densities in my study. Thalamita prymna, a common portunid crab in local coral communities, was found to effectively reduce coral damages including bioerosion and surface mortality. Crab predation, an overlooked relationship in coral reefs, can thus be exploited to control urchin corallivory and bioerosion. Prohibiting fish trapping in reef areas could reduce the by-catch of these crabs and protect reefs against urchin attack.

Coral reefs are in global decline due to ocean warming and ocean acidification. While these stressors are commonly studied in climate change predictions, salinity, although being an important environmental factor, is not well understood. The response of the coral holobiont (the association of the coral host, its algal endosymbiont and a suit of other microbes) to changes in salinity and the contribution of each holobiont compartment underlying the necessary osmoadaptation remain especially elusive. Interestingly, we find some of the most thermotolerant corals in some of the most saline seas, e.g. the Red Sea and the Persian Arabian Gulf. This observation sparked the hypothesis of a link between osmoadaptation and coral thermotolerance. Here, we set out to elucidate the putative effects of high salinity on conveying thermotolerance and thereby a possible link to bleaching in the context of the coral holobiont. For this, we conducted a series of heat stress experiments at different salinities in the coral model Aiptasia and subsequently validated our findings in corals from the central Red Sea. We confirm a role of osmoadaptation in increased thermotolerance and reduced bleaching in Aiptasia and Red Sea corals. This salinity-conveyed thermotolerance was characterized by a reduction in algal endosymbiont loss, photosystem damage and leakage of damaging reactive oxygen species (ROS) in high salinity. Further analysis of the osmoadaptation response using targeted GC-MS uncovered high levels of the sugar floridoside at high salinity only in holobionts that show the salinity-conveyed thermotolerance. The increase of floridoside, an osmolyte capable of scavenging ROS, and the concurrent reduction of ROS argues for a mechanistic link of increased thermotolerance and reduced bleaching in high salinities. In addition, the restructuring of the microbiome at high salinity that aligned with the difference in thermotolerance in Aiptasia may be indicative of a microbial contribution towards a more beneficial holobiont composition. Hence, emphasizing the potential cumulative contribution of each holobiont compartment during stress-resilience, as well as highlighting the overall role of osmoadaptation in the thermotolerance of corals.

Objective: The purpose of this ex vivo study was to assess the changes in tooth color and existing orthodontic bracket bonding when exposed to a bleaching agent. Methods: 120 freshly extracted human premolars were equally divided into 4 groups: a negative-control group, a positive-control bleaching group, a bracket-bonded group, and a bracket bonded-bleached group. The bleaching protocol was carried out as recommended by the manufacturer of Opalescence Go® – 30 minutes each day for 10 consecutive days. The color value of each tooth was measured daily by spectrophotometry for the negative-control group and the positive-control bleaching group in 6 different locations: central, occlusal, left, right, gingival, and lingual. The color values of the bracket-bonded group and bracket-bonded bleached group were measured initially at day 1 and after the debond test and removal of remaining composite at day 11. At the end of bleaching, the changes in existing bracket bonding were assessed by measuring shear bond strength (SBS), adhesive remnant index (ARI), and the number of tooth fractures during debond testing. Results: This orthodontic-specific bleaching system bleached teeth with no brackets bonded, comparing color values of the negative-control group and the positive-control bleaching group. However, it did not show an added whitening effect on teeth with existing brackets at the central, occlusal, and gingival sites, comparing the color values of the bracket-bonded group and the bracket-bonded bleached group. There were no statistically significant differences noted on SBS and ARI between the bracket-bonded group and the bracket bonded-bleached group. To our surprise, the bracket-bonded bleached group showed a statistically significant increase in the rate of tooth fracture during debond (33%), compared to the bracket-bonded group (10%). Conclusions: Using this bleaching protocol on teeth with existing bonded brackets did not have an added whitening effect at central, occlusal, and gingival sites. The added whitening effect was only noted at left, right, and lingual sites. Especially with no significant difference in the color values at the central sites, which were underneath the bonded brackets, there was no added bleaching effect with the use of this bleaching system on the teeth with existing bonded brackets. The bleaching did not show a significant effect on bracket bonding SBS or ARI. However, it may compromise the tooth structure and lead to an increase in enamel fractures during debond.

No description available.