Thesis (PhD)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Microorganisms show a tendency to accumulate on surfaces in aqueous environments
to form biofilms. Microbial biofilms represent a significant problem in public health
microbiology as the development of these microbial communities, especially in water
distribution systems, may lead to (i) the enhanced growth of opportunistic pathogens,
(ii) the development of organoleptic problems, (iii) the reduction in the flow rate and
(iv) the regrowth of microorganisms.
In this project, biofilm monitors were installed in a large water distribution
system to study biofilm phenomena in drinking water systems, and to deduce the
biological stability and quality of the potable water. Measurements of biofilm formation
potential showed that biofilms did not reach a steady state after 100 to 150 days. The
microbial cells in these biofilms were mostly non-culturable. The contribution of the
heterotrophic colony count to active biomass, as determined with cell numbers based
on ATP measurements were often < 1%, while the ratio of heterotrophic plate counts
and direct acridine orange counts were also <1%. The ratio between cell numbers
based on ATP measurements and direct acridine orange counts were often < 100%.
Results also showed that under certain conditions, such as those investigated in the
present study, 1 pg of ATP may not be equal to approximately 104 active
bacteria/cells, as stipulated by previous investigations, and that the average ATP
content per active bacterial cell is indeed less than 10-16 - 10-15 g. It was calculated
that threshold values for assimilable, and dissolved organic carbon below -5 IJg Gil
and -0.5 mg Gil, respectively, should be target values for the control of biofilm
formation in this system. It was shown that polyethylene, polyvinylchloride, teflon,
plexiglass, copper, zinc-coated steel and aluminium provide favourable attachment
surfaces that allowed primary colonisation and subsequent biofilm formation.
Significant (p < 0.05) differences in surface colonisation on the materials were
observed, indicating that the composition of the material has a direct influence on
microbial colonisation. The two grades of stainless steel evaluated in this study were
the least favourable materials for biofilm formation. It was further demonstrated that
the nature of the surface of these materials, flow conditions and water type all had a
direct influence on biofilm formation. While modification of the attachment surface did
not result in significant differences (p > 0.05) in disinfection efficiency of two commonly
used biocides, the concentration of the biocide, as well as the material to which the
biofilm is attached, greatly influenced biocidal efficiency. The results show that biofilm
monitoring needs to be implemented at the water treatment plants in addition to
common biostability measurements. / AFRIKAANSE OPSOMMING: Mikro-organismes neig om te akkumuleer aan oppervlaktes in akwatiese omgewings
om biofilms te vorm. Mikrobiese biofilms verteenwoordig In betekenisvolle probleem
in publieke gesondheidsmikrobiologie omdat die ontwikkeling van hierdie mikrobiese
gemeenskappe in waterverspreidingsisteme mag lei tot (i) die verhoogde groei van
opportunistiese patogene, (ii) ontwikkeling van organoleptiese probleme, (iii) die
vermindering in die vloeitempo en (iv) die hergroei van mikro-organismes.
In hierdie projek was biofilm monitors geïnstalleer in In groot
waterverspreidingsisteem om biofilm fenomene in drinkwatersisteme to bestudeer, en
om die biologiese stabiliteit en kwaliteit van drinkwater af te lei. Bepalings van
biofilmvormingspotensiaal het aangetoon dat biofilms nie In stabiele stadium na 100
tot 150 dae bereik nie. Die mikrobiese selle in hierdie biofilms was meestal niekweekbaar.
Die bydrae van die heterotrofiese kolonie tellings tot aktiewe biomassa,
soos bepaal deur seltellings gebaseer op ATP metings was dikwels < 1%, terwyl die
verhouding van die heterotrofiese plaatteIIings en direkte akridien oranje tellings ook
< 1% was. Die verhouding tussen seltellings, gebaseer op ATP metings en direkte
akridien oranje tellings was dikwels < 100%. Resultate het ook aangetoon dat onder
sekere omstandighede, soos dié wat ondersoek was in die huidige studie, 1 pg ATP
nie gelyk is aan min of meer 104 aktiewe bakterieë/selle soos gestipuleer deur vorige
ondersoeke nie, en dat die gemiddelde ATP inhoud per aktiewe bakteriële sel
inderdaad minder as 10-16 tot 10-15 g is. Dit was bereken dat die drempelwaardes vir
assimileerbare en opgeloste organiese koolstof onder -51-1g C/l en -0.5 mg C/l,
onderskeidelik, teikens moet wees vir die beheer van biofilmvorming in hierdie
sisteem. Dit was aangetoon dat polyetileen, polyvinielchlroried, teflon, plexiglas,
koper, sink-bedekte staal en aluminium gunstige aanhegtings oppervlaktes voorsien
wat primêre kolonisering en daaropvolgende biofilmvorming toelaat. Betekinisvolle (p
<0.05) verskille in oppervlak kolinisering op die materiale was waargeneem, wat
aandui dat die samestelling van die materiaal In direkte invloed op mikrobiese
kolonisering het. Die twee tipes vlekvryestaal wat geëvalueer was in hierdie studie,
was die minder gunstige materiale vir biofilmvorming. Dit was verder gedemonstreer
dat die aard van die oppervlak van hierdie materiale, vloeitoestande, en water tipe
almal In direkte invloed het op biofilmvorming. Terwyl die aanpassing van
aanhegtingsoppervlak nie die ontsrnettinqsdoeltreffendheid resultaat van die twee
algemeen-gebruikte biosiede betekinisvol (p > 0.05) beïnvloed het nie, het die
konsentrasie van die biosiede
doeltreffendheid grootliks beïnvloed.
asook die aanhegtings-materiaal, biosied
Die resultate het aangetoon dat biofilm
monitering geïmplementeer moet word by waterbehandelingsaanlegte as In alternatief
vir algemene biostabiliteit metings.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/53751 |
| Date | 03 1900 |
| Creators | Khan, Wesaal |
| Contributors | Wolfaardt, G. M., Saftic, S., Rohns, H-P., Stellenbosch University. Faculty of Science. Dept. of Microbiology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 213 p. : ill. |
| Rights | Stellenbosch University |
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