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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Microbial Phosphorus Removal in Waste Stabilisation Pond Wastewater Treatment Systems

Mbwele, Lydia Ambakisye January 2006 (has links)
<p>Waste Stabilisation Ponds (WSPs) are characterised by low phosphorus (P) removal capacity. Heterotrophic bacteria are principal microbial agents in WSPs in addition to algae. As treatment proceeds in WSPs, algal growth increases and pH rises, this has lead to believe that P removal is mainly through sedimentation as organic P algal biomass and precipitation as inorganic P. In activated sludge treatment plants (AS), microbial P removal has been improved and is termed as enhanced biological phosphorus removal. There was a need to establish whether it was possible to enhance P removal in WSPs. A performance assessment of pond system at the University of Dare s Salaam (UDSM), Tanzania, has shown that 90% of the P removed was in the primary pond (facultative) and the rest in the maturation pond (aerobic).</p><p>In these studies, a pure strain A. hydrophyla was isolated from an activated sludge wastewater treatment plant in Sweden. This plant has a train that functions with enhanced biological phosphorus removal. The strain was tested for P uptake in minimal media supplemented with glucose, succinate or acetate, grown aerobically and anaerobically/aerobically. This strain was able to take up P without having been subjected to the anaerobic phase. It was observed that P uptake was enhanced after the anaerobic phase with media supplemented with glucose, but not with succinate or acetate. Phosphorus uptake repeatedly followed the bacterial growth pattern with correlation coefficients of more than 95%. Therefore P removal has a direct correlation with bacterial growth.</p><p>Two isolates Acinetobacter sp. (isolated from the primary facultative pond) and E .coli (isolated from the maturation pond) were obtained from a tropical WSP treatment system at the UDSM. They were subjected to aerobic P uptake experiment similar to those of A.hydrophyla. The uptake per unit absorbance of bacterial growth was found to be comparable to that of A.hydrophyla, isolated from AS. These results showed that heterotrophic activity is important in WSPs. It is possible to enhance P removal in these systems by designing the primary ponds for maximum heterotrophic activity and probably enrichment.</p>
2

Development of Computational Fluid Dynamic Models for the Design of Waste Stabilisation Ponds

Wood, Matthew Unknown Date (has links)
Waste stabilisation ponds (WSP) are a popular form of wastewater treatment worldwide, especially for rural-based manufacturing plants and small community sewage treatment. Ponds offer a robust and operationally simple technology, which are inexpensive where land is available, and have the potential to provide a considerable degree of treatment. However the continued use of WSP is being undermined by their inconsistent performance relative to current discharge requirements, particularly with respect to suspended solids, pathogen and nutrient removal. In a climate of increased public awareness of pollution, and the ever more stringent environmental protection regulations, novel pond designs need to be developed, and existing ponds retro-fitted, to improve their performance. This dissertation investigated the hydraulic modelling of non-mechanically mixed ponds, and produced a modelling framework from which improved pond designs could be evaluated. Computational fluid dynamics (CFD) simulations were used to develop models which were able to predict the hydraulics of arbitrarily shaped, non-mechanically mixed ponds under controlled conditions. The models represent an important departure from traditional pond modelling techniques, which are based on either historical experience or simple hydraulic and reaction models. The CFD approach overcomes the main limitation of these models, as it accounts for spatial variations of parameters within a pond such as fluid velocity, or pollutant concentration. This allows for the prediction of pond hydraulics based on the pond geometry (such as inlet configuration, pond shape or baffle placement), pond inlet boundary conditions and the fluid properties. Thus CFD models allow the rapid investigation of the effect of design modifications on pond performance. The WSP models were designed using a two stage process. The first stage, a steady state simulation, calculated the velocity and turbulence fields for the pond; the second stage, a transient numerical tracer, utilised the underlying steady state results to calculate the advection and diffusion of a tracer species. The species concentration at the outlet was then integrated to produce residence time distributions (RTD) and other quantities which were used to characterise the pond hydraulics, and quantitatively compare the models with experimental results to assess the pond¡¦s performance. These techniques could be applied to any numerical pond flow model, and are a discerning test of the model¡¦s consistency. RTD generated from two-dimensional (2-D) CFD simulations were compared to experimental RTD derived by Mangelson and Watters (1972). In one of the three geometries simulated, the 2-D CFD model successfully predicted the experimental RTD. However, the flow patterns in the other two geometries were not well described, due to the difficulty of representing a three dimensional (3-D) inlet in the 2-D CFD model. As no general relationship could be found for approximating a 2-D inlet in 3-D, full 3-D simulations were used to model the unsuccessful cases. The 3 D simulations provided much improved results, predicting all the major features of the RTD over the first residence time, and matching exponential decay of the RTD after this period. Due to the uncertainty in the exact experimental inlet dimensions, a range of inlet depths were simulated. This showed that the CFD model was sensitive to changes in the inlet configuration, and using the appropriate inlet depth, the simulated RTD matched the experimental results well. A sensitivity analysis of the effect of the inlet turbulent boundary conditions and tracer molecular diffusivity for the k-ƒÕ turbulent model, showed the RTD was insensitive to these properties, thereby confirming similar results in related systems (Benelmouffok, 1989; De Vantier and Larock, 1987). This is significant for future pond modelling, as these properties are difficult to measure experimentally or predict reliably. Tracer studies were performed in this dissertation on five full-scale pond systems. In Tasmania three identical sewage ponds with different inlet and baffle configurations were investigated. However wind conditions in this locality masked any effect of these modifications. Tracer studies were also performed on sugar mill ponds near Mackay. While the models predicted qualitative consistent RTD results, they did not match the experimentally measured RTD due to uncontrolled environmental mixing factors and the long residence times of these ponds. A preliminary investigation of the effect of wind mixing was undertaken by imposing a velocity to the top surface of the model. These results confirmed the strong influence of even small wind velocities due to the large surface area of the ponds. Practical experience has indicated that the pond hydraulics are often the limiting factor in pond performance. Both experimental and simulation results have confirmed this through the presence of short circuiting and dead zones within the pond. Three baffle designs were assessed, all of which improved the pond hydraulics by either dispersing the inlet jet, or utilising the jet to generate specific pond mixing. Finally the work in this thesis has highlighted a number of other areas for future investigation. These include reservations over the use of RTD to characterise full-scale pond hydraulics, and considerations regarding the most efficient use of the inlet mixing in ponds. The hydraulic models developed in this dissertation can be extended to include solids, stratification and reaction models, which would enable the direct validation of the model based on physical or chemical parameters. In addition, a coupled flow and reaction model would provide a tool that could be used to truly optimise pond performance. This offers the possibility of tailoring the design of ponds for specific reactions, such as improved biological nutrient removal.
3

Microbial Phosphorus Removal in Waste Stabilisation Pond Wastewater Treatment Systems

Mbwele, Lydia Ambakisye January 2006 (has links)
Waste Stabilisation Ponds (WSPs) are characterised by low phosphorus (P) removal capacity. Heterotrophic bacteria are principal microbial agents in WSPs in addition to algae. As treatment proceeds in WSPs, algal growth increases and pH rises, this has lead to believe that P removal is mainly through sedimentation as organic P algal biomass and precipitation as inorganic P. In activated sludge treatment plants (AS), microbial P removal has been improved and is termed as enhanced biological phosphorus removal. There was a need to establish whether it was possible to enhance P removal in WSPs. A performance assessment of pond system at the University of Dare s Salaam (UDSM), Tanzania, has shown that 90% of the P removed was in the primary pond (facultative) and the rest in the maturation pond (aerobic). In these studies, a pure strain A. hydrophyla was isolated from an activated sludge wastewater treatment plant in Sweden. This plant has a train that functions with enhanced biological phosphorus removal. The strain was tested for P uptake in minimal media supplemented with glucose, succinate or acetate, grown aerobically and anaerobically/aerobically. This strain was able to take up P without having been subjected to the anaerobic phase. It was observed that P uptake was enhanced after the anaerobic phase with media supplemented with glucose, but not with succinate or acetate. Phosphorus uptake repeatedly followed the bacterial growth pattern with correlation coefficients of more than 95%. Therefore P removal has a direct correlation with bacterial growth. Two isolates Acinetobacter sp. (isolated from the primary facultative pond) and E .coli (isolated from the maturation pond) were obtained from a tropical WSP treatment system at the UDSM. They were subjected to aerobic P uptake experiment similar to those of A.hydrophyla. The uptake per unit absorbance of bacterial growth was found to be comparable to that of A.hydrophyla, isolated from AS. These results showed that heterotrophic activity is important in WSPs. It is possible to enhance P removal in these systems by designing the primary ponds for maximum heterotrophic activity and probably enrichment. / QC 20101119
4

Sustainability assessment of potential wastewater treatment techniques in Tupiza, Bolivia / Hållbarhetsanalys av potentiella lösningar för avloppsrening i Tupiza, Bolivia

Burström, Johanna January 2020 (has links)
Aiming for sustainable sanitation systems can provide benefits among a vast range of Sustainable Development Goals. In this study the sustainability of potential options for renovating or upgrading thewastewater treatment plant in Tupiza, a rapidly growing city in theSouthern highlands of Bolivia, was evaluated. The local context was characterized by increasing issues of flooding which in recent years has destroyed important wastewater treatment infrastructure and polluted sources of water for several downstream communities. Three system options consisting of different treatment technologies were evaluated against four criteria of sustainability; health,technical, environmental and financial and institutional. A "conventional" option consisting of waste stabilization ponds was compared against two more options with added steps of treatment, such as constructed wetlands, anaerobic reactors and alkaline and ammonia treatment of sludge. Social acceptance and demand of reuse of treated wastewater and sludge in agriculture was evaluated using qualitative research analysis. Results indicate that the systems with added treatment steps could help improve several areas of sustainability such as risks of disease transmission, space efficiency, treatment capacity and efficiency as well as enable safe reuse of sludge and wastewater in agriculture. Implementation of funding mechanisms covering the entire sanitation service chain as well as flood mitigation measures resulted essential in ensuring the long-term functionality of such improvements. This project was intended as a pre-study and identified several areas of future research including additional evaluation of nutrient content in effluent, investigation of a possible certification process for recycled byproducts from the wastewater treatment plant, risk assessment of floods of different magnitudes, evaluation of the long-term economic impact of having improved systems and evaluationof local institutional capacity surrounding the sanitation service chain in Tupiza. / Hållbara sanitetssystem för med sig många fördelar som kan främja majoriteten av de globala hållbarhetsmålen. I denna studie utreds hållbarheten i potentiella alternativ för renovering eller uppgradering av ett avloppsreningsverk i Tupiza, en snabbt växande stad i södra Bolivias högland. Den lokala kontexten präglades av en tilltagande översvämmningsproblematik som de senaste åren bidragit till förstörelse av central infrastruktur for avloppsvattenrening samt påföljande vattenföroreningar i samhällen nedströms reningsverket. Tre systemalternativ beståendes av olika reningstekniker utreddes utefter fyra hållbarhetskategorier; hälsa, teknologi, miljö samt finansiell/institutionell. Ett konventionellt alternativ som utgjordes av stabiliseringsdammar jämfördes mot två mer avancerade alternativ med ytterligare reningssteg såsom anlagd våtmark, anaerobiska reaktorer samt alkali- och ammoniakbehandling av slam. Social acceptans och efterfrågan för återanvändning av behandlat avloppsvatten och slam inom lantbruket utreddes i en kvalitativ forskningsstudie. Resultaten tyder på att system med fler reningssteg kan främja flera hållbarhetsområden såsom risk för överföring av sjukdomar, yteffektivitet, reningskapacitet och effektivitet samt möjliggöra säkert återanvändande av slam och avloppsvatten i jordbruket. Implementering av mekanismer för finansiering som täcker hela sanitetskedjan samt åtgärder mor översvämningar visade sig vara centrala för att säkerställa långsiktig funktion av sådana förbättringar. \\\\Det här projektet var menat som en förstudie och identifierade flertalet områden för vidare forskning såsom ytterligare utvärdering av näringsinnehåll i utgående vatten, utredning av möjlig certifieringsprocess för återvunna produkter från avloppsreningsverket, analys av översvämningsrisker av olika magnituder, utvärdering av den indirekta ekonomiska effekten av att ha system med fler reningssteg samt utvärdering av lokal institutionell kapacitet för hela servicekedjan för sanitet i Tupiza. / En este estudio se evaluó la sostenibilidad de opciones potenciales para renovar o mejorar la planta de tratamiento de aguas residuales de Tupiza, una ciudad de rápido crecimiento en las tierras altas del sur de Bolivia. En los últimos años, el contexto local se ha caracterizado por la ocurrencia de lluvias de mayor intensidad. Estas ocasionaron inundaciones que en efecto causaron daños importantes en la infraestructura de la planta de tratamiento de aguas residuales (PTAR). El deterioro de la infraestructura provocó el derrame de aguas residuales al río y la contaminación del agua en las comunidades ubicadas en la cuenca baja. Trés opciones de sistemas de tecnologías de tratamiento de aguas residuales para la renovación y/o mejoro de la planta de Tupiza fueron evaluadas considerando cuatro criterios de sostenibilidad: Salud, tecnolgía, ambiental y financiera/institucional. Por otra parte la aceptación social y demanda de reúso de aguas residuales y lodos tratados en la agricultura se evaluaron mediante un análisis de investigación cualitativa. La opción convencional que consiste en estanques de estabilización de desechos, se comparó con dos otras alternativas que incluyen pasos adicionales de tratamiento, como son humedales artificiales, reactores anaeróbicos y tratamiento de lodos con urea y cal. Los resultados indican que los sistemas de pasos adicionales de tratamiento podrían ayudar a mejorar diferentes aspectos de sostenibilidad, como los riesgos de transmisión de enfermedades, la eficiencia espacial,  la capacidad y eficiencia de tratamiento y la posibilidad de reutilización segura de lodos y aguas residuales en la agricultura. La implementación de mecanismos de financiación que cubren toda la cadena de servicios de saneamiento, así como las medidas de mitigacióin de inundaciones se mostraron esenciales para garantizar la funcionalidad a largo plazo de tales mejoras. La tesis es un estudio preliminar e identificó varias áreas de investigación futuras, la evaluación adicional del contenido de nutrientes en el efluente, la investigación de un posible proceso de certificación de subproductos reciclados de la PTAR, la evaluación de riesgos de inundaciones de diferentes magnitudes, la evaluación del impacto económico a largo plazo de la implementación de sistemas con pasos adicionales de tratamiento y la evaluación  de capacidad institucional local a lo largo de la cadena de servicios de sanemiento.

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