Kim Dong-Hoon, Lee Mo-Kwon, Hwang Yuhoon, Im Wan-Taek, Yun Yeo-Myeong, Park Chul, Kim Mi-Sun
Department of Civil Engineering, Inha University, 100 Inharo, Nam-gu, Incheon, 402-751, Republic of Korea.
Biomass and Waste Energy Laboratory, Korea Institute of Energy Research, 152 Gajeong-ro, Yuseong-gu, Daejeon, 305-343, Republic of Korea.
Biotechnol Bioeng. 2016 Jan;113(1):101-11. doi: 10.1002/bit.25540. Epub 2015 May 5.
This work investigated the formation of microbial granules to boost the productivity of lactic acid (LA). The flocculated form of LA-producing microbial consortium, dominated by Lactobacillus sp. (91.5% of total sequence), was initially obtained in a continuous stirred-tank reactor (CSTR), which was fed with 2% glucose and operated at a hydraulic retention time (HRT) of 12 h and pH 5.0 ± 0.1 under a thermophilic condition (50°C). The mixed liquor in the CSTR was then transferred to an up-flow anaerobic sludge blanket reactor (UASB). The fermentation performance and granulation process were monitored with a gradual decrease of HRT from 8.0 to 0.17 h, corresponding to an increase in the substrate loading from 60 to 2,880 g glucose L(-1) d(-1) . As the operation continued, the accumulation of biomass in the UASB was clearly observed, which changed from flocculent to granular form with decrease in HRT. Up to the HRT decrease to 0.5 h, the LA concentration was maintained at 19-20 g L(-1) with over 90% of substrate removal efficiency. However, further decrease of HRT resulted in a decrease of LA concentration with increase in residual glucose. Nevertheless, the volumetric LA productivity continuously increased, reaching 67 g L-fermenter (-1) h(-1) at HRT 0.17 h. The size of LA-producing granules and hydrophobicity gradually increased with decrease in HRT, reaching 6.0 mm and 60%, respectively. These biogranules were also found to have high settling velocities and low porosities, ranging 2.69-4.73 cm s(-1) and 0.39-0.92, respectively.
本研究旨在探究通过形成微生物颗粒来提高乳酸（LA）的产量。最初在连续搅拌釜式反应器（CSTR）中获得了以乳酸杆菌属（占总序列的91.5%）为主导的产乳酸微生物聚集体的絮凝形式，该反应器以2%的葡萄糖为进料，在嗜热条件（50°C）下，水力停留时间（HRT）为12 h，pH值为5.0±0.1的条件下运行。然后将CSTR中的混合液转移到上流式厌氧污泥床反应器（UASB）中。随着HRT从8.0 h逐渐降至0.17 h（对应底物负荷从60 g葡萄糖L⁻¹ d⁻¹增加到2880 g葡萄糖L⁻¹ d⁻¹），对发酵性能和颗粒化过程进行了监测。随着运行的持续进行，明显观察到UASB中生物质的积累，其形态从絮凝状转变为颗粒状，且随着HRT的降低而变化。直至HRT降至0.5 h时，LA浓度维持在19 - 20 g L⁻¹，底物去除效率超过90%。然而，HRT的进一步降低导致LA浓度下降，残余葡萄糖增加。尽管如此，LA的体积生产率持续提高，在HRT为0.17 h时达到67 g L⁻¹发酵罐⁻¹ h⁻¹。产LA颗粒的尺寸和疏水性随着HRT的降低而逐渐增加，分别达到6.0 mm和60%。还发现这些生物颗粒具有较高的沉降速度和较低的孔隙率，沉降速度范围为2.69 - 4.73 cm s⁻¹，孔隙率范围为0.39 - 0.92。
