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Looking Outwards: Isolation of Cyanobacterial Released Carbohydrate Polymers and Proteins
Published on: May 27, 2019
Understanding variability in algal solid-liquid separation process outcomes by manipulating extracellular
N R H Rao1, A M Granville2, R K Henderson3
1Algae and Organic Matter Laboratory (AOM Lab), School of Chemical Engineering, The University of New South Wales, Sydney, Australia; Centre for Advanced Macromolecular Design (CAMD), School of Chemical Engineering, The University of New South Wales, Sydney, Australia.
Modified bubbles improve microalgae separation in dissolved air flotation (DAF) by addressing extracellular organic matter (EOM) variability. Adding specific proteins and carbohydrates enhances separation efficiency, offering a more consistent and cost-effective method for water treatment.
Area of Science:
- Environmental Science
- Biotechnology
- Chemical Engineering
Background:
- Conventional dissolved air flotation (DAF) for microalgae separation faces challenges like inconsistent performance, high coagulant demand, and operational costs.
- Previous modified-bubble DAF processes showed sustainability but struggled with species-specific separation inconsistencies.
- Algal extracellular organic matter (EOM) composition, particularly proteins and carbohydrates, is hypothesized to influence separation efficiency.
Purpose of the Study:
- To investigate the impact of extracellular organic matter (EOM) protein and carbohydrate concentration and character on microalgae separation using a modified-bubble DAF process.
- To determine the optimal molecular weight (MW) and charge characteristics of protein and carbohydrate additives for enhanced algal separation.
- To elucidate the mechanisms behind improved cell separation through biomolecular interactions.
Main Methods:
- Microalgae (Chlorella vulgaris, Microcystis aeruginosa) were treated with modified cationic bubbles (poly(diallyldimethylammonium chloride)-PDADMAC).
- Extracellular organic matter (EOM) was removed, and varying concentrations of protein and carbohydrate biomolecular additives with different MW and charge were introduced.
- Flotation efficiency was assessed based on the separation percentage under different additive conditions, including simultaneous protein-carbohydrate dosing.
Main Results:
- Independent dosing of protein and carbohydrate additives increased microalgae separation from <5% to up to 62%.
- Maximum separation (up to 79%) was achieved with simultaneous dosing of high MW (>50 kDa) and high charge (>0.5 meq·g⁻¹) protein and carbohydrate additives.
- Enhanced separation correlated with the formation of protein-carbohydrate-cell suprastructures, facilitated by specific EOM characteristics (high MW >25 kDa, charge >0.2 meq·g⁻¹).
Conclusions:
- The modified-bubble DAF process's efficiency is significantly influenced by the concentration and characteristics of algal EOM proteins and carbohydrates.
- Strategic addition of specific biomolecular additives can overcome EOM-related separation inconsistencies in DAF.
- The formation of supramolecular structures involving proteins, carbohydrates, and cells is key to enhanced microalgae separation in this modified DAF system.
