An in-depth study of the biodeterioration of the Hulett Aluminium hot roll mill emulsion,
Prosol, was conducted. Samples of the emulsion in use at the hot roll mill were taken from
various areas of the emulsion reticulation system in order to identify regions of highest
microbial contamination. Standard plate count techniques and diagnostic procedures were
employed to quantify and identify the microorganisms in these samples. In some of the highly
contaminated areas of the emulsion reticulation system, microorganisms exceeded
lxlO'CFUml'1 emulsion. A range of bacteria was identified which included members of the
genera: Bacillus; Pseudomonas; Escherichia; Enterobacter; Sporosarcina; Micrococcus; Aeromonas;
Chromobacterium and Desulfovibrio. Various fungi, including several yeasts, were also isolated
and some of the filamentous spore-forming types were identified zsAspergillus spp.; Penicillium
spp. and a Cladosporium sp.
A visual scale was developed to assess the growth rate of the isolated microorganisms on a range
of specific media containing various emulsion components as carbon and energy source.
Although the results obtained by using this scale were not conclusive, a few biodegradable
components were nonetheless identified. It was found that mixed cultures of the above
microorganisms had a greater biodeteriorative effect on the emulsion than did any of the pure
cultures when applied separately. This suggested complex microbial interactions were involved
in the breakdown of the emulsion.
A laboratory-scale model system representative of the Hulett Aluminium hot roll mill was
designed and constructed to carry out a series of tests on unprotected and biocide-treated
emulsions. A range of biocide concentrations were tested from which the minimum biocide
inhibitory concentration was calculated. It was shown that microorganisms exposed to sublethal
doses of the biocide Busan (active component glutaraldehyde) over a prolonged period
of time, exhibited greater levels of tolerance and resistance to the biocide than did those
microorganisms not previously exposed. It was deduced that less frequent, shock doses of
biocide are more effective in the control and eradication of emulsion degrading
microorganisms than are frequent, low level doses of the same biocide. In addition to the biocide studies, three imported so-called 'biostable' emulsions were evaluated as possible
replacements for the susceptible Prosol. Of these three imported emulsions, two viz. HRF3
and Houghton Biostable were shown to be more resistant than Prosol to biodeterioration.
After assessing the current hot roll mill management practices, a number of recommendations
were made, including: the improvement of plant hygiene; education of the mill workers;
improvement of emulsion monitoring; improvement of down-time management and
improvement of biocide dosing regimes. Recommendations are also made for minimizing
potential microbial growth in the new hot roll mill currently under construction at the Hulett
Aluminium processing plant at Pietermaritzburg, South Africa. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1998.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/5410 |
| Date | January 1998 |
| Creators | Ramsden, Peter John. |
| Contributors | Wallis, Frederick Malcolm. |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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