Fractionation of extracellular polymeric substances by mild techniques

The environmental impact of petrochemicals highlights the need for renewable carbon sources like recycled materials, biomass, and CO2. While recycling polymers is crucial, it can’t fully replace fossil fuels, so biopolymers are needed for a circular economy. Biopolymers, derived from animals, plants, and microorganisms, include proteins, nucleic acids, polysaccharides, polyesters, and polyphenols. Microbial production of biopolymers is efficient, scalable, and independent of geographical or seasonal factors, with extracellular polymeric substances (EPS) being a key type produced by bacteria, fungi, and algae. EPS production can use single or mixed cultures, with mixed cultures being more cost-effective and yielding higher EPS concentration due to microbial symbiosis. However, commercial-scale EPS production by mixed cultures faces challenges in downstream processing due to the broth’s complexity and low concentration.

This research explores various separation approaches for biopolymer mixtures, focusing on mild liquid-liquid extraction systems. Chapter 2 investigates water-immiscible and water-miscible ionic liquids (ILs) for fractionating model EPS (alginate and BSA), obtaining promising results with water-miscible imidazolium ILs in aqueous two-phase systems (ATPS). Chapter 3 extends the scope of mild techniques to three-phase partitioning systems (TPPS) for separating model EPS, achieving optimal separation with PEG and ethanol-based TPPS. Chapter 4 applies TPPS to real EPS samples, finding ethanol and potassium citrate effective in separating polysaccharides and proteins fractions. Chapter 5 develops a synthesis route for flavylium-modified PEG polymer with pH and photo-responsiveness, laying the groundwork for future photo-switchable systems. Finally, chapter 6 proposes a conceptual EPS fractionation process using TPPS, membrane processes, and crystallization, emphasizing the need to reduce energy consumption for economic viability.

In summary, this research advances EPS fractionation using TPP systems, focusing on recyclability and energy efficiency, contributing to scalable, sustainable biopolymer separation techniques.