Xu Jiajie, Bian Bin, Angenent Largus T, Saikaly Pascal E
Biological and Environmental Science and Engineering (BESE) Division, Water Desalination and Reuse Center (WDRC), King Abdullah University of Science and Technology, Thuwal, Saudi Arabia.
Environmental Biotechnology Group, Center for Applied Geosciences, University of Tübingen, Tübingen, Germany.
Front Bioeng Biotechnol. 2021 Aug 13;9:726946. doi: 10.3389/fbioe.2021.726946. eCollection 2021.
Medium-chain carboxylic acids (MCCAs), which can be generated from organic waste and agro-industrial side streams through microbial chain elongation, are valuable chemicals with numerous industrial applications. Membrane-based liquid-liquid extraction (pertraction) as a downstream separation process to extract MCCAs has been applied successfully. Here, a novel pertraction system with submerged hollow-fiber membranes in the fermentation bioreactor was applied to increase the MCCA extraction rate and reduce the footprint. The highest average surface-corrected MCCA extraction rate of 655.2 ± 86.4 mmol C m d was obtained, which was higher than any other previous reports, albeit the relatively small surface area removed only 11.6% of the introduced carbon pertraction. This submerged extraction system was able to continuously extract MCCAs with a high extraction rate for more than 8 months. The average extraction rate of MCCA by internal membrane was 3.0- to 4.7-fold higher than the external pertraction (traditional pertraction) in the same bioreactor. A broth upflow velocity of 7.6 m h was more efficient to extract MCCAs when compared to periodic biogas recirculation operation as a means to prevent membrane fouling. An even higher broth upflow velocity of 40.5 m h resulted in a significant increase in methane production, losing more than 30% of carbon conversion to methane due to a loss of H, and a subsequent drop in the H partial pressure. This resulted in the shift from a microbial community with chain elongators as the key functional group to methanogens, because the drop in H partial pressure led to thermodynamic conditions that oxidizes ethanol and carboxylic acids to acetate and H with methanogens as the syntrophic partner. Thus, operators of chain elongating systems should monitor the H partial pressure when changes in operating conditions are made.
中链羧酸（MCCAs）可通过微生物链延长从有机废物和农业工业副产品中产生，是具有众多工业应用价值的化学品。基于膜的液液萃取（渗透萃取）作为一种用于萃取MCCAs的下游分离工艺已成功应用。在此，一种在发酵生物反应器中采用浸没式中空纤维膜的新型渗透萃取系统被用于提高MCCA萃取率并减少占地面积。获得了最高平均表面校正MCCA萃取率为655.2±86.4 mmol C m⁻² d⁻¹，这高于以往任何其他报道，尽管相对较小的表面积仅去除了引入碳的11.6%用于渗透萃取。这种浸没式萃取系统能够以高萃取率连续萃取MCCAs超过8个月。在同一生物反应器中，内膜对MCCA的平均萃取率比外部渗透萃取（传统渗透萃取）高3.0至4.7倍。与作为防止膜污染手段的周期性沼气再循环操作相比，7.6 m h⁻¹的料液上流速度在萃取MCCAs方面更高效。40.5 m h⁻¹的更高料液上流速度导致甲烷产量显著增加，由于氢气损失，超过30%的碳转化为甲烷，随后氢气分压下降。这导致从以链延长菌为关键功能组的微生物群落转变为产甲烷菌，因为氢气分压的下降导致了热力学条件，使得产甲烷菌作为共生伙伴将乙醇和羧酸氧化为乙酸盐和氢气。因此，链延长系统的操作人员在改变操作条件时应监测氢气分压。
