Thesis (PhD)--Stellenbosch University, 2002. / Some digitised pages may appear illegible due to the condition of the original hard copy. / ENGLISH ABSTRACT: Membrane fouling is universally accepted as one of the most critical problems
limiting the wider application of membranes in liquid separations. The development
and utilization of a suitable non-invasive technique for the on-line monitoring of
fouling in industrial and laboratory applications may enable the effectiveness of
fouling remediation and cleaning strategies to be quantified.
The overall objective of this research is to develop ultrasonic time-domain
reflectometry (UTDR) and its use as an analytical tool for the real-time study of
inorganic-, organic- and protein- fouling of various types of membranes including
nylon, polysulfone (PSU) and polyethersulfone (PESU) and modules, including flatsheet
and tubular types. Different separation systems including microfiltration (MF)
and ultrafiltration (UF), flat-sheet and tubular modules, and suitable ultrasonic probes
were used in this study.
Results of this study show a good correlation between the UTDR signal response and
the development of a fouling layer on a membrane surface. UTDR effectively detected
the appearance, growth and movement of a fouling layer echo as fouling proceeded.
Cake (fouling)-layer compressibility was observed by UTDR. The structure and
compaction of an asymmetric PSU membrane could be detected by UTDR. UTDR
was also successfully used for monitoring membrane cleaning and evaluating the
cleaning effectiveness o f various cleaning methods. UTDR results corroborated the
flux measurements and SEM analyses.
The ultrasonic unit is a programmed microprocessor, and can be used to compare
reference and test signals to produce a differential signal (a fouling layer echo). A
differential signal indicates the state and progress o f a fouling layer on the membrane
surface in actual operations. Both amplitude and arrival time of differential signals as
a function of operation time provide useful quantitative information, i.e. changes in
thickness and density of a fouling layer, on the fouling processes.
A predictive modelling program, ultrasonic reflection modelling (URM), was
developed to describe the processes of ultrasonic testing related to the deposition of
fouling layers on membrane surfaces. The mathematical model could substantiate
changes in the densities of the fouling layer as well as the thickness. This is important
as deposit resistance to flow is related to both thickness and density (compressibility).
The predicted results of cake layer deposition are in good agreement with the actual
UTDR measurements obtained in MF and UF.
Furthermore, protein fouling was successfully detected in tubular UF by UTDR.
Ultrasonic frequency spectra could be used as an additional tool for fouling detection. / AFRIKAANSE OPSOMMING: Membraan-aanvuiling of -verstopping is die grootste struikelblok wat die meer
algemene aanwending van membrane vir verskillende watersuiweringsprosesse
beinvloed. Die ontwikkeling en gebruik van ‘n geskikte nie-inmengende tegniek vir
die in-lyn meting van aanvuiling van membrane in laboratorium-en
nywerheidstoepassings mag ‘n geleentheid bied vir die kwantifisering van die
verwydering van aanvuiling en skoonmaakstrategiee.
Die hoofdoel van hierdie studie was die ontwikkeling van ultrasoniese tydgebiedsweerkaatsing
(Eng: ultrasonic time-domain reflectometry, UTDR) en die
gebruik daarvan as ‘n analitiese metode vir die studie van anorganiese-, organiese- en
bio-besoedeling op verskeie tips membrane, insluitend nylon, polisufoon (PSU) en
polietersulfoon (PESU), in beide platvel- en buismodules. Verskeie skeidingsisteme,
insluitend mikrofiltrasie (MF) en ultrafiltrasie (UF) is ontwerp en gebruik in hierdie
studie.
Eksperimentele resultate het goeie ooreenstemming tussen die UTDR seinrespons en
die ontwikkeling van ‘n aanvuilingslaag op die membraanoppervlakte bewys. Die
ultrasoniese tegniek kon die vorming, groei en beweging van ‘n
bevuilingslaagterugkaartsing waarneem namate bevuiling vorder.
Aanvuilingslaagsamepersing is deur UTDR waargeneem. Die struktuur en
samepersing van ‘n asimmetriese PSU membraan is ook deur UTDR gesien. UTDR is
verder suksesvol gebruik om die skoonmaak van membrane te monitor en om die
skoonmaakgeskiktheid (cleaning effectiveness) van verskeie skoonmaakmetodes te
bepaal. UTDR resultate het permeaatvloeimetings en SEM analyses bevestig.
Die ultrasoniese eenheid is ‘n geprogrameerde mikroverwerker, en kan gebruik word
om verwysings- en toetsseine te vergelyk, en dan ‘n differensiaalsein te gee (‘n
aanvuilingslaagweerklank). ‘n Differensiaalsein dui die toestand en vordering van ‘n
aanvuilingslaag op die membraanoppervlakte gedurende gebruik aan. Beide amplitude
asook aankomstyd van differensiaalseine as funksies van gebruikstyd verskaf bruikbare kwantatiewe inligting, dws. Veranderings in die dikte en digtheid van ‘n
aanvuilingslaag, op die aanvuilingsproses.
‘n Voorspellingsmodelleringprogram - ultrasonieseweerkaatsingsmodellering (Eng:
ultrasonic reflection modeling, URM) is ontwikkel om die proses van ultrasoniese
toetsing by die deponering van aanvuilingslae op membraanoppervlaktes beter te
beskryf. Veranderings in die digtheid en dikte van die aanvuilingslaag teenvloei is
verwant aan dikte en digtheid (saampersbaarheid). Die voorspelde resultate van
aanvuilingslaagdeponering stem goed ooreen met die werklike UTDR-metings wat in
MF en UF gemaak is.
Bio-aanvuiling is suksesvol waargeneem deur UTDR in buisvormige UF membrane.
Ultrasoniese frekwensiespektra kan dus as ‘n bykomende metode gebruik word vir die
waarneming van aanvuiling op skeidingsmembrane.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53027 |
| Date | 12 1900 |
| Creators | Li, Jianxin |
| Contributors | Sanderson, R. D., Stellenbosch University. Faculty of Science. Dept. of Chemistry & Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 238 pages : illustrations |
| Rights | Stellenbosch University |
Page generated in 0.0119 seconds