On-line and in-situ kinetics studies of biofilm formation on solid marine submerged substrata by contact angle wettability and microscopic techniques

Abstract

The characterization of wetting properties (by contact angles CA) of several undersea artificial (glass plates) and natural(stones, sand layers, soft-bottom structures, aquatic macrophytes, sediments) solid substrata in the Baltic Sea brackish water (Gulf of Gdansk) were performed. The apparent surface free energy γ_SV and other interfacial interaction parameters: 2D film pressure Π, workof adhesion W_A, and of spreading W_S; dispersive term γ_SV^d of γ_SV were derived from CAH approach developed by Chibowski (2003)with only three measurable quantities: surface tension of the probe liquid γ_LV and its advancing □_A and receding □_R contact anglehysteresis (CAH = □_A - □_R). The most useful technique to measure in situ CAs giving reproducible and accurate values turned out acaptive bubble method, for fully hydrated interfacial layers of highly hydrophilic and porous nature met at seabed. Since the outermostsurface of the submerged substrate is sensed with the presented CA captive bubble technique (captive bubble syringe set-up + USBmicroscope system was assigned to field work), surface evolution of the formed biofilm structure can be monitored on-line and in-situ atdifferent stages of its formation from seconds (conditioning film) to weeks (macrofouling). In addition to surface free energy, otherfactors, including surface charge, surface roughness, temperature, contact time and fluid shear flow velocity turned out to havesignificant influence on the adhesion of biofouling. Views of the glass biofouled slides taken with confocal scanning laser microscopyallowed 3D biofilm architecture on glass to be visualized and quantified. The evolution of the wettability parameters allowed toindentify the particular biofilm states: best release properties, maximum organic matter accumulation, mature film dispersion. Thepresence of adsorbed organic matter layer lead to the surface hydrophobization (CA ↑, γ_SV ↓, W_A ↓, W_S more negative).