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Characterisation and improvement of a microbiological anaerobic bioreactor to remediate acidic and metalliferous titanium processing leachates


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Dann, Alison Louise 2009 , 'Characterisation and improvement of a microbiological anaerobic bioreactor to remediate acidic and metalliferous titanium processing leachates', PhD thesis, University of Tasmania.

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Wastewaters and leachates from mining and mineral processing are often
characterised by low pH and high metal and sulfate concentrations. These can
affect water catchment ecosystems and impact food webs deleteriously. In northwest
Tasmania a titanium-processing plant operated between 1948 and 1996 on
the Blythe River catchment. The sulfate extraction process was used to
manufacture titanium dioxide pigment. This produced large quantities of acidic
(pH 3 - 5), metalliferous (Fe 800 - 1200mg L -1 , Mn 15 - 45mg L-1 ) and sulfurous
(SO42- 500 - 1700mg L-1 ) wastewater. The wastewater was pumped into sludge
dams, which leaked into the local catchment, and eventually Bass Strait. This
resulted in elevated metal concentrations and a highly visible red plume along the
coastline, locally suppressing the marine benthic biota and altering biodiversity.

A novel in situ bioremediation system was built in 2001 and managed
subsequently by ESD (Environmental Services and Design) Pty. Ltd. The system
comprised anaerobic processing sections that incorporated waste agricultural
products; including potatoes, spent mushroom compost and straw, to remove the
metals and increase the pH. A subsequent artificial wetland system was utilised to
reduce effluent BOD (Biological Oxygen Demand) and COD (Chemical Oxygen
Demand) to drinking water quality levels.
Using 16S rRNA gene based approaches microbial diversity and community
structure was determined over 18 months from different stages of the treatment
system. This included untreated sludge dam leachate, pre-treated effluent from an
anoxic potato-containing section intended to increase alkalinity and prevent iron
precipitation; and effluent from a series of mushroom compost and straw-based iron-reduction cells. 16S rRNA gene clone libraries revealed a community shift
from a mixed iron- and sulfide-oxidising and iron- sulfate-reducing community in
the sludge dam leachate to a community dominated by Acidithiobacillus spp. and
anaerobic fermenters (related to the genera Bacteroides and Paludibacter) in the
potato cell effluent. The reduction cell effluents proved to have higher microbial
diversity and greater heterogeneity, including iron-and sulfate reducers, ironoxidisers,
anaerobic fermenters and in one sampled effluent a high proportion of
clones clustering with previously uncultured organisms of candidate division 0P3.
Multivariate statistical analysis of 16S rRNA gene-based TRFLP (Terminal
Restriction Fragment Length Polymorphism) data revealed community
differences had occurred between treated/post-treated samples and untreated/pretreated
samples. TRFLP analysis also indicated temporal shifts in the bacterial
community composition occurred in the reduction cells. Although after 11 months
of treatment, microbial communities in three of four reduction cells showed
evidence of stabilisation probably due to exhaustion of an available carbon source
and layered design of the system. There was no evidence of a seasonal effect on
the microbial community.
A series of laboratory-scale microcosm experiments were conducted to evaluate
temperature, bicarbonate and various carbon amendments (ethanol, molasses and
vegetable oil emulsion) for bioremediation of an acidic, metal- and sulfate-rich
titanium processing leachate with the goal of optimising an existing field-based
system (described above). In all microcosms pH increased from 4 to 6.5-8 for the
length of the experiment due to the high organic matter input but had no effect on
other geochemical processes which was similar to the field-scale reduction cells
in their first year of operation. The oxidation-reduction potential decreased in all
microcosms but was most stable in the oil emulsion microcosms. Alkalinity
production was more substantial in the ethanol, molasses and oil emulsion
microcosms (-2500mg L-I ) compared to the temperature and bicarbonate
- microcosms (-600 - 1800mg L-1 ). The addition of bicarbonate did not increase pH
or alkalinity. Iron and sulfate were initially removed but the effect could not be
sustained in the unamended and bicarbonate microcosms. Liquid amendments
such as ethanol, molasses and vegetable oil emulsion were found to support
greater iron removal. However, sulfate removal only reached a maximum of 80%
removal and was found to have a lag phase of approximately 80 days, and hence
an acclimatisation stage may be needed for enhanced sulfate removal in fieldscale
bioremediation systems. 16S rRNA gene sequence-based TRFLP profiles
revealed all the microcosms had similar bacterial communities but the amended
microcosms were more successful in promoting the growth of a select bacterial
consortia needed for enhanced sulfate and iron removal. This included a
combination of anaerobic fermenters, iron- and sulfate-reducers as well as
iron/sulfur/sulfide oxidisers.
Based on the experimental data and the literature a number of recommendations
were developed to improve the operational efficiency and longevity of the field-based
leachate remediation system.

Item Type: Thesis - PhD
Authors/Creators:Dann, Alison Louise
Copyright Holders: The Author
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Copyright 2009 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
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