Maharaj K, Bradfield M F A, Nicol W
Department of Chemical Engineering, University of Pretoria, Lynnwood Road, Private Bag X20, Hatfield, 0002, Pretoria, South Africa,
Appl Microbiol Biotechnol. 2014 Sep;98(17):7379-86. doi: 10.1007/s00253-014-5779-3. Epub 2014 May 10.
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.
在填充有Poraver®珠子的生物膜反应器中进行连续厌氧发酵。稀释率（D）在0.054至0.72 h⁻¹之间变化，使用D - 葡萄糖和CO₂气体作为碳底物。结果表明稳态条件是可重复的，且与操作历史无关。在D值低于0.32 h⁻¹时，超过80小时的时间段内实现了生产稳定性。在这些情况下，稳态变化（以NaOH中和流速的波动表示）的标准偏差小于5%，同时未检测到生物膜失活的迹象。发现总生物量与稀释率无关，所有运行的平均干浓度为23.8±2.9 g L⁻¹。这表明附着面积控制生物膜积累的程度。基于总生物量的特定琥珀酸（SA）生产率随着D的降低而显著下降。在D = 0.7 h⁻¹时获得了10.8 g L⁻¹ h⁻¹的SA体积生产率，这是迄今为止在产琥珀酸放线杆菌发酵中报道的最高值。SA对葡萄糖的产率随着D的降低而增加，在D为0.054 h⁻¹时产率为0.90±0.01 g g⁻¹。随着D的降低，甲酸产量接近零，而琥珀酸与乙酸的比例随着D的降低而增加，导致SA对葡萄糖的产率增加。
