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Theses and dissertations (Applied Sciences)

Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/6

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Subject: search.filters.subject.Sewage--Microbiology

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Now showing 1 - 6 of 6
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    Physiological and biochemical evaluation of pure cultures of problematic filamentous bacteria isolated from activated sludge
    (2004) Ramothokang, Tshireletso R.; Bux, Faizal
    Since the development of the activated sludge process, bulking and foaming have been a major problem affecting treatment efficiency. Filamentous bacteria have long been known to be the primary cause of bulking and foaming problems in activated sludge wastewater treatment systems. Attempts to cure filamentous bulking and foaming have thus far not shown great success in effective long-term control measures due to a lack of understanding of these organisms. Chemical methods such as chlorination and the use of hydrogen peroxide are still used to cure bulking but are only effective as interim measures. This could be due to the main factors stimulating filamentous bacterial growth not being changed by these methods for curing bulking and also, a lack of in-depth understanding of filamentous bacteria by scientists. It is therefore important to gain a proper understanding of these bacteria on the basis of their physiological, biochemical and growth characteristics. For all this to be successfully attained, filamentous bacteria need to be studied in pure culture so as to facilitate a better understanding of bulking and foaming and the control thereof during wastewater treatment. The aim of this study was therefore, to isolate and cultivate problematic filamentous bacteria and determine the physiological, biochemical and morphological traits of these organisms in pure culture, with the purpose of being able to integrate these findings to in situ analysis. Using four different isolation techniques, a total of 14 isolates from 7 different wastewater systems were obtained and evaluated for a range of physical, chemical, redox and substrate conditions. Results of the study indicate that filamentous survival and proliferation in BNR systems is largely due to varied phosphate uptake capacities and widespread ability to denitrify both nitrate and nitrite. Lipid hydrolysis is also a major component of filamentous bacterial metabolism with hydrolysis of other large compounds, as revealed by Biolog, such as starch, dextrin, proteins/peptides, Tween 40, Tween 80 and nucleosides indicating an affinity for larger slowly biodegradable substrates. They also strive on a variety of amino acids and sugars. The results obtained in this study revealed that filamentous bacteria are more diverse and complex in their biochemistry and physiology hence the difficulty in achieving long- term optimal control of filamentous bulking in activated sludge. It was concluded that filamentous bacteria have the ability to survive during times of starvation where growth factors are limiting and, this may be attributed to their ability to store storage compounds such as PHB, glycogen and polyP. The filaments' ability to store storage compounds and denitrify, suggests that they may in fact play significant roles in denitrification and EBPR. It is also concluded from this study that the filamentous bacteria under study are sensitive to aromatic compounds and that they have an affinity for slowly biodegradable polymers such as lipids, nucleosides, proteins/ peptides, dextrin and starch. Also concluded is that, the use of Biolog for biochemical profiling! fingerprinting of filamentous bacteria is useful, however, due to the possibility that some organisms may in fact, not grow and! or may give negative results on some and! or all substrates, other strategies. for biochemical profiling be established and used in this regard. Identification and evaluation of filamentous bacteria based on morphological traits is limiting and requires development and optimization of in situ techniques, such as DNAIRNA based probes and micro autoradiography. Bulking and BNR are elaborate and still not fully understood. The filaments' ability to take up phosphates and denitrify means that an advanced understanding of the roles they play in BNR systems and AA- bulking (Anoxic- Aerobic) is still required. Physiological and biochemical fingerprinting of pure cultures of filamentous bacteria is an important basis to understanding these organisms, and establishing potential bulking and foaming criteria for in situ evaluation and verification. It is from a study such as this that the main goal of curing bulking and gaining an enhanced understanding of BNR may be achieved.
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    Optimisation of food to microorganism ratios during activated sludge respirometric batch assays
    (2003) Ismail, Arshad Abdool Hak; Bux, Faizal
    The measured kinetics of a bacterial culture degrading a single organic compound as a sole carbon source in a batch reactor depends on the history of the culture, the identifiability of the parameters, and the manner in which the experiment to measure them is run. The initial substrate to biomass ratio (So/Xo) used in the experiment is particularly important because it influences both parameter identifiability and the expression of the culture history.
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    Biodiversity of anaerobic cellulolytic bacteria in landfill sites
    (2001) Goldstone, Loren; Tivchev, G. N.
    Landfills play an important role in the removal of waste from the surroundings. There is a limit to the types of waste that can be recycled and the landfill becomes the final method of waste disposal. Because waste constitutes a wide variety of materials, the microbial consortia that develop within a landfill will be equally varied, depending on the type of waste deposited, the temperature of the landfill and moisture content of the waste. The metabolism of these microbial consortia can result in products that are either harmful or beneficial. In order to increase the pool of knowledge on landfill microbiology, it is important to study the various consortia that inhabit the landfill to determine the various microbial interactions that occur and subsequently to manipulate these interactions to enhance the benefits of a landfill site and reduce the harmful effects. In this research, an attempt was made to isolate anaerobic cellulolytic bacteria from a landfill site. Six waste samples, varying in age were obtained over a period of two years. Samples were excavated from a maximum depth of 4m. Samples are processed in anaerobic, phosphate buffer and cultivated in various pre-reduced anaerobic media and incubated under anaerobic conditions. Samples were also collected from other potential anaerobic sites namely, anaerobic sludge, decomposing bagasse, compost, manure, rumen and pond sediment. Results of degradation of the cellulose source (Whatman No. 1 filter paper) indicated that it was possible to cultivate cellulose-degrading microorganisms from the landfill. Zones of clearing around colonies, which would be indicative of cellulose degradation on solid media, were not obtained. Samples from the anaerobic sludge, compost and rumen showed degradation of cellulose in liquid media but not on solid media. It is concluded that the solid media used was unsuitable for the cultivation of anaerobic, cellulolytic bacteria or that the anaerobic conditions employed were not adequate to initiate the growth of the anaerobic cellulolytic bacteria.
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    Determination of the heterotrophic and autotrophic active biomass during activated sludge respirometric batch assays using molecular techniques
    (2008) Ismail, Arshad
    Activated sludge models now in use worldwide for the design and operation of treatment systems use hypothetical concentrations of active organisms. In order to validate and calibrate model outputs, concentrations and activities of organisms responsible for nitrification and denitrification need to be reflected by actual measurements. This research has been initiated by the observation of an increasing gap of suitable techniques that exist in the direct measurement and separation of active biomass components, responsible for COD removal and denitrification.
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    Functional characterisation of heterotrophic denitrifying bacteria in wastewater treatment systems
    (2005) Ramdhani, Nishani; Bux, Faizal
    Atmospheric nitrogen pollution is on the increase and human activities are directly or indirectly responsible for the generation of the various nitrogen polluting compounds. This can lead to the two major problems of eutrophication and groundwater pollution. Therefore, the removal of nutrients such as nitrogen and phosphorus from wastewater is important. Nitrogen removal from wastewater is achieved by a combination of nitrification and denitrification. Thus, there is a need to identify and characterise heterotrophic denitrifying bacteria involved in denitrification in wastewater treatment systems. The aim of this study, therefore, was to characterise heterotrophic denitrifying bacteria through detailed biochemical and molecular analysis, to facilitate the understanding of their functional role in wastewater treatment systems. Drysdale (2001) isolated heterotrophic denitrifiers to obtain a culture collection of 179 isolates. This culture collection was used to screen for nitrate and nitrite reduction using the colorimetric biochemical nitrate reduction test. The isolates were thereafter Gram stained to assess their gram reaction, cellular and colonial morphology. Based on these results identical isolates were discarded and a culture collection of approximately 129 isolates remained. The genetic diversity of the culture collection was investigated by the analysis of polymerase chain reaction (PCR)-amplified 16S ribosomal DNA (rDNA) fragments on polyacrylamide gels using denaturing gradient gel electrophoresis (DGGE). Thus DNA fragments of the same length but different nucleotide sequences were effectively separated and microbial community profiles of eight predominant isolates were created. Batch experiments were conducted on these eight isolates, the results of which ultimately confirmed their characterisation and placed them into their four functional groups i.e. 3 isolates were incomplete denitrifiers, 2 isolates were true denitrifiers, 2 isolates were sequential denitrifiers and 1 isolate was an exclusive nitrite reducer.
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    Molecular characterization of filamentous bacteria isolated from full-scale activated sludge processes
    (2007) Marrengane, Zinhle
    Activated sludge flocs are responsible for flocculation, settling and dewaterability. It is important to maintain the growth off loc-forming bacteria for efficient sludge settleability and compaction for good quality effluent. Filamentous bacteria on the other hand are believed to provide rigid support network or backbone upon which floc-forming bacteria adhere to form stable activated sludge flocs (Wilderer et al., 2002; Ramothokang et al., 2003). Filamentous bacteria can also be detrimental to the process when they outgrow floc-forming bacteria. Morphologically filamentous bacteria are at an advantage as they have higher outward growth velocity and can extend freely to bulk liquid substrate. Proliferation of filamentous bacteria causes foaming and bulking (Martins et al., 2004). Although chemical alleviation measures to circumvent bulking are present, they are symptomatic (Chang et al., 2004). Eikelboom (1975) developed the first identification keys for the classification of filamentous bacteria that is primarily based on morphological characteristics and microscopic examination. Although very useful, this type of identification has its limitations. For instance some filamentous bacteria can change morphology in response to changes in the environment and although some of them can be morphologically similar they may vary considerably in their physiology and taxonomy (Martins et al., 2004). A vast number of filamentous bacteria are still very poorly understood which could be due to the problems of cultivation due to their slow growing nature and maintenance of cultures (Rossetti et al., 2006). This limitation necessitates a molecular approach to resolve the taxonomy of filamentous bacteria as it is a culture-independent technique which is highly accurate. This project was undertaken to verify the identity of pure cultures of filamentous bacteria isolated previously through the application of molecular techniques. The 16S rDNA are conserved regions in bacterial cells and they can be extracted and specific nucleic acid fragments amplified. Denaturation gradient gel electrophoresis enabled the separation of fragments of identical length but different size and served as an indication of purity (Muyzer et al., 1993).