Biofilm formation of benthic diatoms on commercial polyvinylidene fluoride membrane

Abstract

Marine benthic microalgae always have their own ubiquitous nature to adhere to diverse submerged substrates. Immobilized submerged biofilm system offers huge reduction of liquid culture volume, high biomass production and ease of harvesting of biomass. The studies on the biofilm formation and properties towards membrane surfaces are rare therefore the objectives of this paper were to investigate the relationships between the algal attachment rate onto membranes via biofilm and the compositional changes of the extracellular polymeric substances in the biofilm. To delve further into the biofilm-forming capacity of three benthic diatoms (Amphora coffeaeformis, Cylindrotheca fusiformis and Navicula incerta) onto polyvinylidene fluoride membrane (PVDF), a simple adhesion test was run for 96 h under controlled temperature and light conditions. Attached biomass was carefully scraped for cell count and extracellular polymeric substances (EPS) were extracted for characterization in terms of its biochemical compositions. As a result, A. coffeaeformis and N. incerta were found to adhere well with membrane substrate with equal cell attachment (3 × 108 cells/m2) at the end of the experiment while the lowest was observed for C. fusiformis (1.33 × 108 cells/m2). Biofilm of three diatoms was observed to form as soon as 2 h after inoculation and its development was aided by the high accumulation of TEP amount at 96th hour ranging from 91 mg X eq/m2to 170.61 mg X eq/m2. EPS excreted was found to re-accumulate after 48 h with polysaccharides as major component (>59.87%) for N. incerta and C. fusiformis except A. coffeaeformis which was mainly composed of proteins (>50%). The biofilm formed by A. coffeaeformis was considered the most robust because of its hydrophobic-hydrophobic interaction between the cells and the membrane. Understanding of biofilm physiology will pave the way for describing biofilm systems and membrane-based wastewater treatment systems.