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Theses and dissertations (Applied Sciences)

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End date: 2009Subject: search.filters.subject.Sewage

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    Development and assessment of a membrane bioreactor for wastewater treatment
    (2001) Osifo, Peter Ogbemudia; Bux, Faizal
    A woven fibre membrane unit was developed locally and used for this study. The membrane unit was submerged in the aerobic tank of an anoxic-aerobic biological treatment process to treat dairy effluent. Another unit similar to the process above was also set up but with a gravity settling tank replacing the membrane unit. Kinetic studies were done on both processes and their results compared. Effluent characteristics of both processes were also compared. For the membrane bioreactor, the effectiveness of two backflush methods ie air and water, were tested. In this study it was discovered that air backflush could remove the clogging formed at external and internal pores of the membrane better than water backflush measured in terms of rate of pressure recovery and energy consumption. The effluent quality of the membrane bioreactor (MBR) in terms of COD, nitrogen, suspended solids and turbidity was excellent under all conditions tested and was better than conventional activated sludge system. The COD removed based on the average value in MBR was 96.02 % compared to 94 % conventional system. A mass balance of the processes showed that 79 % in the form of nitrogen fed into both the MBR and conventional systems was denitrified. The effluent suspended solids from the MBR was not determinable while that of conventional system was 2.09 mglL. Maximum specific nitrification rate determined graphically was 3.0 d-I and 2.10 d-I in conventional and MBR respectively. The smaller value of nitrification rate in MBR could be attributed to large number of nitrifier volatile suspended solids in the system. The estimated true yield and decay rate coefficients of conventional system is 0.204 kgVSS/kgCOD and 0.013 d-I respectively. The flux obtained from this study is between 22 and 92 L/m2.h. However, the average flux value is 57 L/m2.h for the whole period of operation. Regular flux decline observed during operation was improved through regular backwash with air and chemical cleaning. The transmembrane pressure did not as whole increase more than 55 kPa due to frequent cleaning of the membrane surface.
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    Identification of polyphosphate accumulating bacteria from pilot- and full scale nutrient removal activated sludges
    (1999) Atkinson, Blaise William; Bux, Faizal
    General removal of phosphorus (P) from wastewater was introduced in Scandanavia in the late 1960's. At that time it was believed that P alone was limiting to algal growth and that the sole removal of P would solve the problem of eutrophication. However, we now know that both P and nitrogen (N) contribute to this deleterious effect and as such, much research has been conducted concerned with both the biological and chemical removal of these nutrients from sewage effluents. Enhanced biological phosphorus removal (EBPR), which is basically the biological accumulation of soluble P (as polyphosphate or poly-P) from the bulk liquid in excess of normal metabolic requirements, still tends to be sensitive to many external parameters and, as such, is subject to fluctuations. This makes it extremely difficult for wastewater treatment installations to achieve and maintain full compliance with strict discharge regulations. A more comprehensive understanding of the microbial community within the mixed liquor of a wastewater treatment system is therefore required which will ultimately assist in improving system design and performance. Chemical and civil engineers, when designing biological wastewater treatment systems, consider only the processes (biological or chemical) taking place within the reactor/s with little or no regard for the individual microbial species or the entire microbial community involved. Process design appears to be tackled empirically from a 'black box' approach; biological reactions or processes occurring within a system such as wastewater treatment are all lumped together and attributed to a single surrogate organism ie., the response of the surrogate to certain stimuli accounts for the total system response. This is similar to an analogy which Professor George Ekama (Dept of Civil Engineering, UCT), a leading scientist in wastewater treatment and process design, refers to where engineers, if, for example, are confronted with modelling the dynamics of carbon dioxide utilisation ofa forest, would recognise the accumulative system response and not give cognisance to each individual tree's contribution. It is true that if one had to consider every microbial species present in a highly organised community such as activated sludge, process models, designed to make quantitative and qualitative predictions as to the expected effluent quality from a particular design, would become increasingly complex and superfluous. It is evident from the countless accomplishments that engineers have succeeded, to a certain degree, in modelling wastewater treatment systems. One only has to consider the tremendous success of biological P (bio-P) removal and nitrification/denitrification processes at full-scale. However, there are limitations to this empirical approach and EBPR processes occasionally deteriorate in phosphate removal efficiency. In order to further optimise biological processes, whether they be organics oxidation, bio-P removal, nitrification or denitrification, biological community analyses will have to play a more significant role in design. The better microbial community structure and function is understood, the better the control and management of the system. With the advent of improved microbial identification and enumeration (to a certain extent) techniques (in situ), it was considered significant to investigate the mechanism ofbio-P removal and to elucidate which bacteria are actively responsible for this process. To this end, experimental work was conducted in two phases: \xAE laboratory, where samples of mixed liquor were obtained from a full-scale wastewater treatment facility exhibiting biological nutrient removal (BNR) characteristics and @ pilot plant, where an enhanced culture ofpolyphosphate accumulating organisms (PAO's) was developed and probed using molecular identification and enumeration techniques (as well as a cultivation-dependent approach). During phase \xAE of experimentat
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    Extraction, characterisation and metal biosorption of extracellular polysaccharides from activated sludge
    (1998) Zondo, Raynold Mduduzi; Swalaha, Feroz Mahomed
    Waste activated sludge is a biological adsorbent whose potential to remove metals from solution and effluent has been demonstrated. Extracellular polysaccharides (EPS) as components of activated sludge are thought to contribute to activated sludge metal biosorption. During the present study characterisation and determination of the metal biosorptive capabilities of domestic and industrial extracellular polysaccharides (EPS) revealed similarities both in terms of chemical composition and metal adsorption potential. Extracellular polysaccharides were extracted from activated sludge, obtained from domestic and industrial sludge treatment plants, using chemical techniques which involved sodium hydroxide extraction and solvent precipitation. A purification technique, which involved precipitation of protein with chloroform and removal of nucleic acids was developed. To assess the efficiency of the purification method, the ratio of extracted polysaccharide to the amount of protein present was determined. This provided an indication of the magnitude of EPS extracted in relation to the degree of cellular disruption. The type of activated sludge being treated was shown to be of particular importance. The quantity of EPS present in the original sample was found to be higher in domestic sludge than in industrial sludge. Purified EPS was fractionated in a column of DEAE-Sepharose CL-6B using stepwise pH gradient elution. Molecular weight distribution was conducted on a column of Sepharose CL-4B. Component monosaccharides were identified by paper chromatography. Monomers identified were glucose, fructose, glucuronic acid and galactosamine. Ion-exchange chromatography results demonstrated the presence of a number of different polysaccharide fractions while gel filtration results indicated a wide molecular weight distribution range of EPS from both domestic and industrial activated sludge. This indicated potential for variety in the EPS content of the activated sludge. Metal adsorption studies were conducted to determine the capabilities of EPS to adsorb metals
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    Evaluation of anaerobic sludges as metal biosorbents and development of a biotechnological process for metal ion removal from selected wastewater
    (1997) Bux, Faizal; Kasan, Hamanth C.
    As a result of rapid expansion of the industrial sector and increasing population, the environment has been under phenomenal stress. The volume of sewage and other effluents has increased tremendously in the last century. Globally, approximately .12 million tonnes of dry sludge biomass is produced and discarded of by landspreading, landfilling, incineration or dumping in lagoons and oceans. The discharge of industrial effluents into receiving waters has been documented to be the cause of severe environmental contamination. Heavy metals have been the cause of particular environmental concern. Their toxic and carcinogenic potentials at low concentrations, as well as the large quantities disposed to the environment, have prioritised them as leading contaminants. Current technologies of remediating heavy metal containing effluents are expensive and, in most cases, ineffective. Locally, most industries are merely diluting their effluents, thus resulting in the loss of valuable water resources. Waste sludges have shown the ability to adsorb heavy metals from their aqueous environment. Therefore, the current study attempted firstly, to compare biosorptive capacities of various waste sludges for a range of heavy metal ions, and secondly, to establish a relationship, if any, between biosorptive capacity and sludge surface charge. Finally, a laboratory scale biosorption process, encompassing desorption and recovery of metal ions from sludge surfaces, would have to be developed. Effluents used included pure, metal solutions of divalent zinc, cadmium, copper, nickel, trivalent and hexavalent chromium. In addition, synthetic effluents comprising a cocktail of the above-mentioned metal ions as well as an industrial effluent from a metal plating company were used. Five waste digested sludges were prepared and challenged against pure metal solutions to determine and compare their respective biosorptive capacities. Mechanisms of biosorption were elucidated using the Langmuir adsorption isotherm model. Sludge surface charge was determined using the millivolt quantification method. Upscaling of bioreactor trials to fully mixed laboratory scale was also investigated. These experiments encompassed the use of three sludges showing the greatest potential for biosorption and desorption using the selected mineral acid, H2S04, In addition, a simultaneous fully mixed biosorption and desorption process was designed and optimised. Subsequent trials involved comparing the latter process with a packed bed configuration whereby biomass was immobilised using poly sulfone resin. The overall comparative adsorptive capacities of the sludges (SI-SS) for metal ions in single solutions was S3 > S2 > S4 > SS > SI. Surface charge determination showed S3 to contain the most electronegative charge, with other sludges following in the same descending order as mentioned above. These findings supported the theory of a direct correlation between sludge surface charge and biosorptive potential. The affinity series of the sludges for metal ions followed the descending order of Cd2+ > Cu2+ > Ni2+ > Zn2+ > Cr6+ > Cr3+. Fully mixed studies, using mixed synthetic effluents, resulted in lower biosorptive capacities being recorded by the three selected sludges ie., S2, S3 and S4, as compared to single solution experiments. Biosorption studies with industrial effluent, containing Zn2+ as the most prevalent metal at 119.4 mg.F'. resulted in S3 biosorbing a maximum of 4.5 mg.g' of the cation. Sulphuric acid (H2S04) at O.2N, hydrochloric acid (HCI) at O.2N and acetic acid (CH3COOH) at O.4N were tested for their desorptive efficiencies. Sulphuric acid proved to be the most effective desorbing agent. Using S3 as biosorbent and O.2N H2S04 as desorbent, the manipulation and operation of a simultaneous process proved to be successful since both biosorption and desorption occurred concurrently, thus reducing time required for successful remediation considerably. Immobilised biomass, in a packed bed configuration, produced acceptable final effluent regarding standards as stipulated by the Durban Municipality for trade effluents. However, biosorption capacity of the sludge was compromised, with subsequent reductions in desorption being recorded, when the process was compared to fully mixed trials. Affinity series determined for the packed bed process wasC~+ >Cd2+>Zn2+>Cu2+>Cr6+ >Ni2+. Waste digested sludge has shown potential as metal biosorbent on an industrial scale. The present findings have succeeded in demonstrating a novel laboratory scale biotechnological process for the remediation of metal laden industrial effluents.
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    Molecular analyses of pure cultures of filamentous bacteria isolated from activated sludge
    (2005) Naidoo, Dashika
    The activated sludge process is the mostl used biological treatment process. Engineers and microbiologists are constantly seeking ways to improve process efficiency, which can be attributed to the increasing demand for fresh water supplies and proper environmental management. Since the inception of the activated sludge process, bulking and foaming have been major problems affecting its efficiency. Filamentous bacteria have been identified as the primary cause of bulking and foaming. Numerous attempts have been made to resolve this problem. Some of these attempts were effective as interim measures but failed as long term control strategies. The identification of filamentous bacteria and the study of their physiology have been hampered by the unreliability of conventional microbiological techniques. This is largely due to their morphological variations and inconsistent characteristics within different environments. To fully understand their role in promoting bulking and foaming, filamentous bacteria need to be characterized on a molecular level. The aim of this study was, therefore, to identify filamentous bacteria in pure culture with the purpose of validating these findings to the physiological traits of the pure cultures when they were isolated. Fourteen different filamentous cultures were used for this study. The cultures were identified using specific oligonucleotide probes via fluorescent in situ hybridisation and nucleotide sequencing. Prior to sequencing, an agarose gel and a denaturing gradient gel Electrophoresis profile were determined for each isolate. The various techniques were optimised specifically for the filamentous isolates. The isolates were identified as Gordonia amarae, Haliscomenobacter hydrossis, Acinetobacter sp./Type 1863, Type 021N, Thiothrix nivea, Sphaerotilus natans and Nocardioform organisms.
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    Elucidation of the microbial community structure within a laboratory scale activated sludge process using molecular techniques
    (2006) Padayachee, Pamela; Bux, Faizal
    The microbial community present in a laboratory-scale modified Ludzack-Ettinger activated sludge system was investigated using a combination of novel molecular techniques. The parent system was investigated for a duration of one year and samples were taken at regular intervals to determine the profile and structure of the microbial community present within the anoxic and aerobic zones of the MLE system. The combination of molecular techniques included fluorescent in situ hybridisation (FISH) and denaturing gradient gel electrophoresis (DGGE). FISH was performed using oligonucleotide probes, which were complementary to conserved regions of the rRNA for the alpha, beta and gamma subclasses of the gram negative family Proteobacteria as well as a group-specific HGC oligonucleotide probe as a representative of the gram positive actinomycetes branch. The total eubacteria present was determined using the EUB oligonucleotide probes, EUB388, EUB388-II and EUB388-III. The DGGE analysis of PCR-amplified 16S rDNA gene segments was used to examine the microbial community profile in the anoxic and aerobic zones. The profile for each of the zones revealed a number of consistent bands throughout the duration of the laboratory-scale process. However, the profiles obtained suggested that a diverse microbial community existed within the aerobic and anoxic zones. The bands also indicated the presence of dominant and less dominant species of bacteria. Hybridisations obtained from the FISH analyses indicated that the alpha and gamma subclasses were predominant within the anoxic zone and the aerobic zone showed a dominance of the beta subclass of Proteobacteria. The steady state behaviour of the MLE system was confirmed with the results obtained from COD, TKN, nitrates and OUR analytical tests. COD and nitrogen mass balances were conducted to confirm the acceptance of the results obtained for each batch as an indication of the system performance for the MLE model. Nitrogen mass balances indicated an upset in the nitrogen levels for batches two and seven.
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    Characterisation of the microbial communities present in an anaerobic baffled reactor utilising molecular techniques
    (2005) Lalbahadur, Tharnija; Bux, Faizal
    The provision of safe and sanitary water is a constitutional right and above all, a necessity of life. As a result of the rapid urbanisation and the past policies of apartheid, a large population of South Africa dwell in informal settlements, where there is very little hope of development, as the government does not possess the resources that are necessary for a full-scale sanitation programme. Therefore, on-site treatments have been considered to provide sanitation in these dense peri-urban areas. The anaerobic baffled reactor (ABR) is one such sanitation system. This reactor utilises the phenomenon of anaerobic digestion to degrade substrates. One of the major disadvantages of any anaerobic treatment processes is the extreme sensitivity of the bacterial communities, thus inducing slow recovery rates following toxic shocks. Therefore, an understanding of these microbial consortia is essential to effectively control, operate and optimise the anaerobic reactor. Fluorescence in situ hybridization, 4’,6-diamidino-2-phenylindole (DAPI) staining and DNA sequencing techniques were applied to determine the microbial consortium, as well as their reactions to daily operating conditions. With an understanding of these populations and their responses to perturbations within the system, it is possible to construct an anaerobic system that is successful in its treatment of domestic wastewater. In situ hybridizations were conducted for three operating periods, each characterised by specific flow rates. Results showed Eubacterial population dominance over the Archaeal population throughout both of the operating periods investigated. However, these cells cumulatively consisted of 50% of the total biomass fraction, as determined by DAPI staining. Group-probes utilised revealed a high concentration of fermentative acidogenic bacteria, which lead to a decrease in the pH values. It was noted that the ABR did not separate the acidogenic and methanogenic phases, as expected. Therefore, the decrease in pH further inhibited the proliferation of Archaeal acetoclastic methanogens, which were not present in the second operating period. DNA sequencing results revealed the occurrence of the hydrogenotrophic Methanobacterium and Methanococcus genera and confirmed the presence of Methanosarcina. Sequencing of the bacterial DNA confirmed the presence of the low G+ C Gram Positives (Streptococcus), the high G+C Gram Positives (Propionibacterium) and the sulfate reducing bacteria (Desulfovibrio vulgaris). However, justifications were highly subjective due to a lack of supportive analytical data, such as acetate, volatile fatty acids and methane concentrations. Despite this, findings served to add valuable information, providing details on the specific microbial groups associated with ABR treatment processes.
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    Microbial degradation of polychlorinated biphenyls
    (2007) Mustapha, Shubnum
    The aromatic compounds Polychlorinated Biphenyls (PCBs) are one of the largest groups of environmental pollutants. The greatest concern is the release of PCBs in the water systems by industrial effluent, accidental spillages or leaks. PCBs are able to bioaccumulate in the fatty tissues of animals, fish and humans. The impact on human health due to PCBs has prompted interest in their degradation. The application of microbial degradation of PCBs can transform many PCB metabolites. There are a wide variety of microorganisms that can degrade PCBs or utilise them as sole carbon sources. This study focused on isolating microrganisms from industrial wastewater capable of aerobic degradation of PCBs. The degradation potential of the selected isolates were investigated by using different analytical techniques viz. ultra violet or visible spectrophotometer (UV/Vis), thin layer chromatography (TLC) and gas chromatography electron capture detector (GC-ECD).