Publication: Microalgal adhesion and biofilm development: role of algal organic matter and substratum properties
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Date
2021-12-01
Authors
Cheah, Yi Tong
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Abstract
Microalgal biofilms benefit biofilm cultivation systems to mitigate the limitations by microalgal suspension culture systems. Numerous works regarding the modulation of extrinsic factors in biofilm adhesion studies were found but they lack insight in the ubiquitous cells-substrates interactions governing the cell adhesion in response to surroundings. Thus, this thesis intends to elucidate the microalgal biofilm development on different porous surfaces varying in pore size, surface roughness, surface wettability and surface biocoatings. Three benthic microalgae namely Amphora coffeaeformis, Cylindrotheca fusiformis and Navicula incerta were cultivated in a self-designed flow lane incubator to investigate the extent of surface properties towards microalgal attachment and growth. Various colloidal approaches were utilized to represent the cornerstone of cell-substratum interactions while
COMSOL Multiphysics was employed for the simulation of computational fluid dynamics analysis. Findings depicted that cell adhesion varied significantly with substrata type (p<0.05). The maximum accumulated cell density was achieved by C. fusiformis around 47.64±4.03×109 cells m-2 onto hydrophobic polyethersulfone (PES) membranes (contact angle 79.29 ° ) and the least by N. incerta around 6.40±0.49×109 cells m-2 onto hydrophilic PES (contact angle 47.56°). Extended Derjaguin, Landau, Vervey, and Overbeek model stated that the biofilm adhesion was mostly controlled by Lewis acid-base interactions (hydrophobic) in high-ionic strength solution while the hydrokinetic present in the cultivation system drew the importance of substrates’ pore size and surface roughness. Similarly, rougher 30 kDa PES enabled higher cell attachment for C. fusiformis, followed by A. coffeaeformis and N. incerta. Retention of the algal cells was promoted by the asperities and hydrodynamic stagnant zones on rougher surfaces. Both soluble extracellular
polymeric substances (sEPS) and bounded EPS (bEPS) contributed towards the formation of adhesive gel layer onto the porous surfaces. bEPS gathered were relatively higher than sEPS while bEPS accumulated at least 10% higher on both hydrophilic PES and smooth 1 kDa PES. The abundant hydrophilic polysaccharides extracted contributed the most to biofilm development for all substrata tested while hydrophobic proteins analyzed managed to retain biofilm structure though in a much smaller fraction (as small as 5.46%). Moreover, optimized EPS pre-coating (7.20 pH, 30 mL cell suspension volume and 50 mL EPS volume) substantially improved the attached N. incerta density by as high as 271% than pristine polyvinylidene fluoride membrane due to rougher surface and presence of sticky exopolymer particles with data variation less than 1%. Outcomes from this present work would pave a way towards large-scale biofilm-based photobioreactors designs especially in supporting materials selection.