Centre for Bioprocess Engineering Research (CeBER), University of Cape Town, Cape Town, South Africa, 7701Tel: +27 21 650 2759 ; Fax: +27 21 650 5501; Email: CeBER@uct.ac.za; www.CeBER.uct.ac.za

IntroductionAcid rock drainage (ARD) produces water with an unsafe concentration of sulphate and heavy metals. Sulphate reducingbacteria (SRB) is being investigated as a solution to both1. This requires continuous flow reactors that will encourage the growthof dynamic cultures of SRB2. A continuous stirred tank reactor (CSTR), a laminar flow channel reactor (LFCR) and an up-flowanaerobic sludge blanket reactor (UASBR) were investigated for their mixing characteristics. The LFCR and UASBR require growthsupports (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 52Chris Molteno and Chris ZaaymanCentre 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

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(H2S)Biosulphur

(S8)Reduction Oxidation

Anaerobic SRB

Aerobic oxidation Metal sulphide

precipitates

Hypothesis 1Polyurethane foam will prove the most suitable growth support for SRB due to shearprotection, increased surface area and improved mass transfer. This hypothesis will be testedbased 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 thestudy 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

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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