Thesis (MSc)--Stellenbosch University, 2000. / ENGLISH ABSTRACT: The "classical" propionibacteria are used in a variety of natural dairy fermentations
where they produce natural preservatives (propionic and acetic acids and
bacteriocins) and large amounts of vitamin B12. The extracellular polysaccharide
(ECP) producing ability of these bacteria also make them of special interest to the
food and waste water management industries as the ECP has been illustrated to
playa role in the initial granule formation in upflow anaerobic bioreactor systems.
There is little known on the ECP production by propionibacteria and in this
study different environmental conditions that influence ECP production were studied.
Nineteen different Propionibacterium strains were examined in terms of ECP
production and Propionibacterium strain 278 was identified as the best ECP
producer. Further studies were only done on this strain because of its high ECP
production and because it was originally isolated from an anaerobic digester. The
influence of temperature, pH and sucrose concentration was determined through the
measurement of ECP production and medium viscosity. It was found that more ECP
was produced at temperatures lower than the optimum for growth with the optimum
being between 22° and 25°C. Lower initial pH conditions of the growth medium
(below pH 7.0) were found to inhibit ECP production and the influence when the
initial pH values were between 7.0 and 8.5, was not significant. A higher carbon:
nitrogen ratio, when 8% sucrose was added, was also found to enhance the ECP
production.
The upflow anaerobic sludge bed (UASB) bioreactor process depends on the
upward movement of soluble matter through a blanket of active methanogenic
granular sludge. The long start-up times as a result of the slow granulation process,
as well as the need for a speedy replacement of granules once they have been
washed out of the system, are limitations that restrict the general application of this
excellent waste water treatment technology. Full exploitation of this biomass
immobilisation technique can thus not be realised until the granule formation
conditions are defined and optimised. The precise nature of the mechanisms
involved in the formation of granules and the reason for their stability, is still not fully
understood. It was hypothised by Britz et al. in 1999 that, through the
implementation of environmental 'stress' conditions, a shift in the population dynamics of the anaerobic community can be obtained. This results in a concurrent
increase in ECP formation that appears to enhance aggregate formation.
In the second study it was found that, when 'stress' conditions were applied to
already formed granules, the Gram-positive lactate-utilising acidogenic population
gained an advantage and more propionic acid producing bacteria were present. The
propionic and acetic acid concentrations were also found to increase, and
concurrently, a decrease in the growth medium pH occurred. This confirms part of
the granulation hypothesis that, when granules are 'stressed', the acidogenic
population dynamics change and the lactate-utilising population responds to the
gradual decrease in pH and the more acid-tolerant propionic acid producing bacteria
gain a competitive advantage resulting in the increase in the propionic acid
concentration.
When propionibacteria were added to raw sludge during the granule
production process, the granules were found to be more active than when nopropionibacteria
had been added. This was probably due to the ECP formation by
the propionibacteria that enhances the aggregation of the granules. Enhanced
granulation was thus found in the batch systems with the fatty acids formed in
correlation with the model for granulation. A good correlation was evident between
the hypothesis and the experimental data and the hypothesis was partially verified in
this study. / AFRIKAANSE OPSOMMING: Die "klassieke" propionibakterieë word in 'n verskeidenheid van natuurlike suiwel
fermantasies gebruik waarin hulle verantwoordelik in vir die produksie van natuurlike
voedsel preserveermiddels (propioonsuur, asynsuur en bakteriosiene) en groot
hoeveelhede vitamiene B12. Die Ekstra Sellulêre Pollisakkaried (ESP) produserende
eienskap van hierdie groep bakterieë maak hulle ook van belang in die voedsel en
afvoerwater beheer industrieë, aangesien gevind is dat ESP 'n rol speel in die
aanvanklike granule formasie in anaerobiese bioreaktor sisteme.
Daar is nog baie min bekend oor die ESP produksie van propionibakterieë en
in hierdie studie is verskeie omgewings faktore wat die ESP produksie beïnvloed,
bestudeer. Negentien verskillende Propionibakterium stamme was bestudeer in
terme van ESP produksie en Propionibakterium stam 278 was geïdentifiseer as die
stam wat die meeste ESP produseer. Verdere studies was op hierdie stam gedoen
na aanleiding van sy hoë ESP produksie en omdat dit oorspronklik uit 'n anaerobiese
verteerder geisoleer is. Die invloed van termperatuur, pH en sukrose konsentrasie
was bepaal deur die meting van die ESP produksie en die medium viskositeit. Dit
was gevind dat meer ESP geproduseer was by temperature laer as die optimum vir
groei, met die optimum temperatuur tussen 22° en 25°C. Dit is ook gevind dat laer
aanvangs groei-medium pH (laer as pH 7.0), ESP produksie inhibeer. Die invloed
van die aanvangs groei-medium pH tussen 7.0 en 8.5 was egter nie betekenisvol
nie. Dit is ook gevind dat 'n hoër koolstof tot stikstof verhouding, verkry deur die
byvoeging van 8% sukrose, die ESP produksie verhoog.
Die "upflow anaerobic sludge blanket" (UASB) proses vind plaas as gevolg
van die opwaarste beweging van opgeloste organiese materiaal deur 'n granule bed
van aktiewe metanogeniese granulêre slyk. Die lang 'start-up' tye as gevolg van die
stadige granulasie proses, en die nodigheid om 'n vinnige verplasing van granules te
hê nadat dit uit die sisteem gewas is, is beperkings wat die algemene toepassing
van hierdie fantastiese afvoerwater tegnologie, strem. Volle implementering van
hierdie biomassa immobilisereings tegniek kan dus nie plaasvind voordat die granule
formasie gedefinieer en geoptimiseer is nie. Die presiese eienskappe van die
meganismes betrokke en die formasie van die granules en die rede vir hul stabiliteit
word egter nog nie ten volle verstaan nie. Volgens 'n hipotese deur Britz et al. (1999), vind 'n verskuiwing in die populasie dinamika van die anaerobiese
gemeenskap plaas tydens die implementasie van omgewings 'stress' toestande. Die
resultaat is 'n verhoging in ESP produksie en 'n gevolglike verbetering in die
granulasie proses.
In die tweede studie was dit gevind dat, wanneer 'stress' toestande op die
reeds gevormde granulasie toegepas word, die Gram-positiewe laktaat-benuttende
asetogeniese populasie voordeel geniet en meer propioonsuur produserende
bakterieë was teenwoordig. Die propioonsuur en asynsuur konsentrasies het ook
verhoog en met 'n gevolglike daling in die groei-medium se pH. Dit bevestig 'n
gedeelte van die hipotese dat, wanneer die granules onder 'stress' geplaas word, die
asetogeniese populasie dinamika verander en die laktaat-benuttende populasie
reageer tot die gedeeltelike afname in pH. Die meer suur-tolerante propioonsuur
produserende bakterieë verkry 'n kompeterende voordeel en gevolglik is daar 'n
verhoging in propioonsuur konsentrasie.
Propionibakterieë was gevoeg by die onbehandelde slyk gedurende die
granule produksie proses, en daar is gevind dat meer aktiewe granules gevorm word
as andersins. Dit is moontlik as gevolg van die die ESP produksie van
propionibakterieë wat die granulasie versnel het. Verbeterde granulasie was dus
verkry in die sisteme waar propionibakterieë bygevoeg is. Vetsuur analises het
gedui dat die gevormde vetsure ook in korrelasie was met die model van granulasie.
Goeie korrelasie was dus verkry tussen die hipotese en die eksperimentele data en
die hipotese is gedeeltelik bewys in hierdie studie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51866 |
| Date | 12 1900 |
| Creators | Joubert, Hannarine |
| Contributors | Britz, T. J., Stellenbosch University. Faculty of AgriSciences . Dept. of Food Science . |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 135 p. : ill. |
| Rights | Stellenbosch University |
Page generated in 0.0082 seconds