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This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International licence Newcastle University ePrints -eprint.ncl.ac.uk Umar A, Caldwell GS, Lee JM. Foam flotation can remove and eradicate ciliates contaminating algae culture systems.

Microalgae and cyanobacteria have been evaluated for biological CO2 capture from flue gases for over 40 years;however, commercial open ponds and photobioreactors suffer many drawbacks including a slow rate of CO2 capture and high water usage. We evaluate an intensified 3D cell immobilisation approach with a small water demand, by coating latex binders onto defined surface area (947 m 2 m -3 ) and void space (81.78 ± 4.41%) loofah sponge scaffolds, forming porous 3D biocomposites with three microalgae species; freshwater Chlorella vulgaris, marine Dunaliella salina and Nannochloropsis oculata, and two strains of freshwater Synechococcus elongatus cyanobacteria. Binder toxicity and adhesion screening protocols were established ahead of eight weeks semi-batch and six weeks continuous CO2 fixation trials. Acrylic and polyurethane binders were effective for microalgae, and bio-based (Replebin®) binders were suited for cyanobacteria. The highest average net CO2 fixation rates from each species were 0.17±0.01, 0.25±0.01, 0.12±0.01, 0.68±0.18 and 0.93±0.30 g CO2 g -1 biomass d -1 for C. vulgaris, D. salina, N. oculata, S. elongatus PCC 7942 and S. elongatus CCAP 1479/1A respectively. This equates to predicted CO2 capture from scaled systems of up to 340.11±110 tCO2 t -1 biomass yr -1 . Analysis of the kinetics of CO2 absorbtion and SEM imaging suggests that the cells were embedded within a polymer film that covered the scaffold. Biocomposites continuously fed with 5% CO2 had high lipid contents approaching 70% dry weight. This biocomposite approach shows promise to intensify biological CO2 capture and possible application in bioenergy with carbon capture and storage (BECCS).

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