High-performance fermentation by integration with membrane technologies: a case study on biosuccinic acid

Research output: Book/ReportPh.D. thesis

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Abstract

The primary focus of this research is on improving and intensifying bioprocesses to produce essential building block products, specifically succinic acid. This is pursued through process intensification, incorporating membrane technology, electrochemical cells, and fermentation. Succinic acid is precursor to 30 commercially valuable products, including food additives, green solvents, plastics, and pharmaceutical intermediates. Traditionally sourced from petroleum refineries, there has been a significant shift toward production through biomass fermentation, fulfilling approximately half of the market demand. Presently, despite covering a substantial portion of the market, bio-succinic acid remains a niche product due to higher production costs. Exploring novel hybrid techniques and optimizing production processes have emerged as viable strategies to enhance its economic competitiveness and environmental sustainability. In this regard, membrane electrolysis has been identified to be a promising technology in both the production and separation stages of fermentation processes. Membrane electrolysis involves continuous circulation of fermentation broth between a fermenter and the cathode chamber of an electrolytic cell. The succinate anion produced in the fermenter is selectively driven to the anode chamber via an anion exchange membrane upon voltage application. This process results in the electrolysis of water, producing molecular hydrogen and hydroxide anion in the cathode compartment, as well as molecular oxygen and hydrogen cation in the anode chamber. The primary advantage of this method lies in enabling continuous product extraction, potentially  eliminating product inhibition in the fermenter. Furthermore, hydroxide ions generated during electrolysis can reduce the need for alkaline substances in the fermenter, offering economic and environmental advantages. From a downstream perspective, the electrolytic cell can reduce the number of unit operations required. The membrane is impermeable to microbial cells and solids, enabling succinate extraction and concentration in a single operation. Protons generated during electrolysis at the anode can protonate the succinate anion to succinic acid, minimizing the need for downstream acidification.
 
Despite promising results in integrating membrane electrolysis with the fermenter, there is a literature gap regarding the tuning of the electrolytic cell for such applications. The initial phase of this research focuses on experimentally characterizing the performance of an electrolytic cell with an anion exchange membrane for succinic acid extraction. Various parameters are investigated, including applied current, initial ions concentration, ions distribution, nature of ions, solution complexity, membrane area, and batch versus continuous mode. Results indicate that the extraction rate increases with applied voltage, solution complexity, ions` concentration, and anion species charge.

Having established the feasibility and advantages of the electrolytic cell, the subsequent step involves simulating a bio-succinic acid production plant with an integrated fermenter-electrolytic cell. Economic comparisons are made with a plant-based on batch fermentation. The economic advantages of in-situ extraction serve as a foundation for a systematic phenomena-based process intensification approach. This approach generates intensified unit operations, such as an electromembrane reactor and a membrane crystallizer. A total of 114 intensified process flowsheet alternatives are developed and ranked based on an enthalpy index. The top-ranked alternatives show improved economic performance and reduced environmental impact, with a minimum selling price below that of petroleum-based succinic acid.

Finally, the fermentation stage for bio-succinic acid production is investigated experimentally before integration with the electrolytic cell. Utilizing glucose, carbon dioxide, and defined media as substrates, batch experiments revealed inhibitory succinic acid levels at 20 g/L. Abiotic experiments emphasized the significance of applied voltage and recirculation rate. The integrated system in batch mode showed potential advantages respect with to the simple batch mainly in terms of overcoming product inhibition and buffer addition. Further experiments, especially in continuous mode, are essential to enhance productivity and concentration.

Even though this study focused on succinic acid, the proposed methodology can possibly be extrapolated to other carboxylic acids produced by fermentation, such as acetic acid and lactic acid, and potentially to other products that can be electrically charged such as proteins.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages158
Publication statusPublished - 2023

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