Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Immersed membrane systems hold many operational and environmental advantages in biological
treatment of wastewater. However, immersed membrane filtration have only found application in
niche markets to date because of higher capital and operating costs associated with membrane
fouling. But with capital costs on the decline as membranes become less expensive, immersed
membrane systems are increasingly considered as an attractive alternative to conventional
treatment processes. Operating costs remain high however, since energy intensive techniques
such as air-sparging are required to limit membrane fouling. Improving the air-scouring efficiency
of air-sparged immersed membranes can significantly reduce operating costs and unlock the
immersed membrane system technology to wider application.
The aim of this study was to identify factors that will improve air-scouring efficiency in order to
produce guidelines that will help in the development of an immersed microfiltration membrane
system with a resulting lower operating cost. Although, the research was done on a flat-sheet
microfiltration membrane, the guidelines obtained can be used for the development of any
immersed microfiltration membrane arrangement.
An airlift reactor set-up was chosen for this study. Six system hydrodynamic factors were
evaluated in a factorial design to determine their effects on the cross-flow velocity profile. They
were the downcomer area to riser area ratio, top clearance distance, bottom clearance distance,
aeration intensity, water depth and air sparger location. It was found that the air-scouring
efficiency was increased by generating a cross-flow velocity profile with increased magnitude and
uniformity, but absolute uniformity of the cross-flow velocity profile was found to be a prerequisite
for optimisation of air-scouring efficiency. Downcomer area to riser area ratio was found to be
99.9% significant in determining the magnitude of the cross-flow velocity profile.
Two models were developed to respectively predict the relative magnitude and uniformity of the
cross-flow velocity profile. By using these two models, a methodology was developed to design an
airlift reactor set-up that would produce system hydrodynamics with an improved air-scouring
efficiency. / AFRIKAANSE OPSOMMING: Gesonke membraanstelsels beskik oor talle bedryfs- en omgewingsvoordele in biologiese
behandeling van afvalwater. Maar weens die hoër kapitaal- en bedryfskostes wat gepaardgaan
met membraanbevuiling, kon gesonke membraanstelsels tot op hede nog net toepassing in
nismarkte vind. Maar soos kapitaalkoste daal met al hoe goedkoper membrane beskikbaar, word
gesonke membraanstelsels al hoe aanlokliker as ‘n alternatief vir konvensionele
behandelingsprosesse. Bedryfskostes bly egter hoog aangesien energie-intensiewe tegnieke soos
lugborreling benodig word om membraanbevuiling te vertraag. Deur die effektiwiteit van die
skropaksie wat lugborreling aan gesonke membrane bied te verbeter, kan ‘n beduidende besparing
in bedryfskostes teweeggebring word om sodoende die uitgebreide toepassing van gesonke
membraanstelsel tegnologie moontlik te maak.
Hierdie studie het ten doel gehad die identifisering van faktore wat lugskropaksie effektiwiteit kan
verbeter en om riglyne op te stel vir die ontwikkeling van ‘n gesonke mikrofiltrasie membraanstelsel
met gevolglik laer bedryfskostes. Alhoewel hierdie navorsing ‘n plat-blad mikrofiltrasie membraan
gebruik het, kan die riglyne steeds vir enige gesonke mikrofiltrasie membraanuitleg gebruik word.
Daar is besluit op ‘n lugligter-reaktor opstelling vir hierdie studie. Ses stelselhidrodinamika faktore
is geëvalueer in ‘n faktoriale ontwerp om hul effekte op die kruisvloei snelheidsprofiel te bepaal.
Hulle was die afvloei-area tot opvloei-area verhouding, topruimte-afstand, bodemruimte-afstand,
belugtingsintensiteit, waterdiepte en belugterligging. Daar is bevind dat die lugskropaksie
effektiwiteit verhoog word wanneer ‘n kruisvloei snelheidsprofiel geskep word met ‘n verhoogde
grootte en gelykvormigheid, maar die absolute gelykvormigheid van die kruisvloei snelheidsprofiel
is gevind om ‘n voorvereiste te wees vir optimale effektiwiteit. Afvloei-area tot opvloei-area
verhouding is gevind om 99.9% beduidend te wees in die bepaling van die snelheidsprofiel se
grootte.
Twee modelle is ontwikkel om afsonderlik die relatiewe grootte en gelykvormigheid van die
kruisvloei snelheidsprofiel te voorspel. Die modelle is in ‘n metodologie vervat vir die ontwerp van
‘n lugligter opstelling met stelselhidrodinamika wat verbeterde lugskropaksie effektiwiteit sal skep.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5206 |
| Date | 12 1900 |
| Creators | Hamann, Martin Louis |
| Contributors | Bradshaw, S. M., Jacobs, E. P., University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 155 p. : ill. |
| Rights | University of Stellenbosch |
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