1. Centre for Bioprocess Engineering Research (CeBER), University of Cape Town, Cape Town, South Africa, 7701
Tel: +27 21 650 2759 ; Fax: +27 21 650 5501; Email: CeBER@uct.ac.za; www.CeBER.uct.ac.za
Introduction
Acid rock drainage (ARD) produces water with an unsafe concentration of sulphate and heavy metals. Sulphate reducing
bacteria (SRB) is being investigated as a solution to both1. This requires continuous flow reactors that will encourage the growth
of dynamic cultures of SRB2. A continuous stirred tank reactor (CSTR), a laminar flow channel reactor (LFCR) and an up-flow
anaerobic sludge blanket reactor (UASBR) were investigated for their mixing characteristics. The LFCR and UASBR require growth
supports (matrices or beads) to protect and encourage the growth of SRB and these were investigated in batch reactors.
ASSESSING BACTERIAL SUPPORT STRUCTURES AND REACTOR
PERFORMANCE ACROSS THREE BIOREACTORS: PROJECT 52
Chris Molteno and Chris Zaayman
Centre for Bioprocess Engineering Research (CeBER), Department of Chemical
Engineering, University of Cape Town, South Africa.
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• PVA was shown to be unsuitable for SRB colonization.
• Sodium alginate beads showed growth potential and feasibility of fluidisation in the UASBR
but the beads degraded over time.
• Foam showed successful growth of SRB and evidence of colonization and is therefore
recommended for use as a growth support in the UASBR.
• High concentration lactate based feed encourages fermentative activity whereas an acetate
based feed does not and consequently acetate is recommended for batch reactors.
• The UASBR with recycle and packing showed results indicative of an intermediate between a
dynamic and stable reactor system.
• Perform mixing studies for ½, 1day, 2day etc. to further determine mixing characteristics.
• Employ a shorter and wider UASBR to avoid plug flow and to prevent matrices from clogging.
• Consider using the UASB reactor as a packed bed reactor.
Sulphate
(SO4
2-)
Sulphide
(H2S)
Biosulphur
(S8)
Reduction Oxidation
Anaerobic
SRB
Aerobic
oxidation Metal sulphide
precipitates
Hypothesis 1
Polyurethane foam will prove the most suitable growth support for SRB due to shear
protection, increased surface area and improved mass transfer. This hypothesis will be tested
based on the SRB’s ability to reduce sulphate.
• What is the best bacteria support structure for colonisation and sulphate reduction?
• How feasible is the use of different growth matrices and hydrogels in continuous reactors
The Up-Flow Anaerobic Sludge Blanket Reactor (UASBR) will prove the ideal reactor for the
study of SRB due to favourable hydrodynamics.
• What are the mixing characteristics of the three reactor types UASBR, LFCR and a CSTR?
• Which of the three reactors provides conditions for a suitable intermediate between a
highly dynamic and a stable system?
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Conductivity study and residence time response for a CSTR using a 5 min residence time Phenolphthalein indicator study (visual study) of a CSTR (with impeller on) to determine the mixing characteristics within this reactor at 50 second intervalsCSTR Schematic
Laminar Flow Channel Reactor (LFCR) Schematic Conductivity study and residence time response for a LFCR using a 6 hour residence time Phenolphthalein indicator study of a LFCR to determine the mixing characteristics at 45 min intervals
UASBR
Schematic
Phenolphthalein indicator study of the Up-flow Anaerobic Sludge Blanket Reactor (UASBR) to determine the mixing
characteristics within this reactor at 45 min intervals
Conductivity study and residence time (RT) response for the UASBR with no recycle or packing (A) showing the characteristic
‘S-Shape’ synonymous of plug flow and the RT response for a UASBR with recycle and packing (B) showing improved mixing
A B
Sulphate
Reduction
Time
Sulphate
A range of growth supports were grown in
individual anaerobic batch reactors
These were compared
according to cellular
growth on the matrices
Reduction of sulphate
and production of
sulphide was analysed
Growth supports tested: Polyurethane
foam, saddles, wedges, carbon pellets,
carbon fibre, PVA hydrogel beads and
sodium alginate hydrogel beads
Growth supports are
investigated for use in
continuous reactors
Sulphate and sulphide concentrations of SRB cultures grown with and without growth support Redox and pH readings of SRB cultures to show suitability of growth conditions for SRB VFA analysis results of an SRB culture grown on polyurethane foam
References: 1(Garcia et al., 2001), 2(Oyekola et al., 2008), 4(Moosa et al., 2005),
3(Levenspiel, 1999)
Acknowledgements: Dr Robert Huddy, Prof Sue Harrison, Dr Mariette Smart, Mr
Tynan Marais and Miss Jennifer Couperthwaite