Living microalgae-textile and cyanobacteria-loofah biocomposites for intensified carbon capture, utilisation and storage

Abstract

Microalgae and cyanobacteria have been intensively studied as biological routes for carbon capture. Conventionally, they are cultivated in suspension within open ponds or enclosed photobioreactors (PBR); however, these systems suffer from many drawbacks including large land and water consumption, slow mass transfer rates, and high risk of contamination. This thesis presents a biocomposite culture system to overcome these disadvantages by immobilising cells onto solid supports (textiles and loofah sponge) using non-toxic hydrogel and latex-based binders. The performance of Chlorella vulgaris (a eukaryote microalga) textile-based hydrogel top coated biocomposites were tested in semi-batch CO2 absorption tests, resulting in enhanced CO2 capture. The highest CO2 absorption rate was 1.82 ± 0.10 g CO2 g-1 biomass d-1 from coated cotton biocomposites, followed by 1.55 ± 0.27 g CO2 g-1 biomass d-1 from uncoated cotton biocomposites. There was some degradation of the cotton, which could limit operational lifetime of the biocomposites. Loofah-based Synechococcus elongatus (prokaryote cyanobacterium) latex-based biocomposites had CO2 absorption rates of 0.68 ± 0.18 and 0.93 ± 0.30 g CO2 g-1 biomass d-1 for S. elongatus strain PCC 7942 (PCC) and CCAP 1479/1A (CCAP) respectively; however, cell outgrowth occurred midway through the trials. The formulations of synthetic latex binders were adjusted using different styrene/butyl acrylate blends and a coalescence agent (i.e. TexanolTM), increasing CO2 uptake rates by 14-20 and 3-8 fold for CCAP and PCC relative to their suspension controls. The CCAP biocomposites lasted in excess of 12 weeks whereas the PCC biocomposites experienced cell leaching after four weeks. A simplified techno-economic analysis was conducted, revealing that water and energy consumption were significantly reduced compared to raceway ponds, flat plate PBRs and biofilm-based PBRs.