Succinic acid-producing biofilms of Actinobacillus succinogenes: reproducibility,stability and productivity |
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Authors: | K. Maharaj M. F. A. Bradfield W. Nicol |
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Affiliation: | 1. Department of Chemical Engineering, University of Pretoria, Lynnwood Road, Private Bag X20, Hatfield, 0002, Pretoria, South Africa
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Abstract: | Continuous anaerobic fermentations were performed in a biofilm reactor packed with Poraver® beads. Dilution rates (D) varied between 0.054 and 0.72 h?1, and d-glucose and CO2 gas were used as carbon substrates. Steady-state conditions were shown to be repeatable and independent of the operational history. Production stability was achieved over periods exceeding 80 h at values of D below 0.32 h?1. In these situations, steady-state variation (expressed as fluctuations in NaOH neutralisation flow rates) exhibited a standard deviation of less than 5 % while no indication of biofilm deactivation was detected. The total biomass amount was found to be independent of the dilution rate with an average dry concentration of 23.8?±?2.9 g L?1 obtained for all runs. This suggests that the attachment area controls the extent of biofilm accumulation. Specific succinic acid (SA) productivities, based on the total biomass amount, exhibited a substantial decrease with decreasing D. An SA volumetric productivity of 10.8 g L?1 h?1 was obtained at D?=?0.7 h?1—the highest value reported to date in Actinobacillus succinogenes fermentations. SA yields on glucose increased with decreasing D, with a yield of 0.90?±?0.01 g g?1 obtained at a D of 0.054 h?1. Production of formic acid approached zero with decreasing D, while the succinic to acetic acid ratio increased with decreasing D, resulting in an increasing SA yield on glucose. |
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