Long-lasting biofouling formation on transparent fouling-release coatings for the construction of efficient closed photobioreactors.

In order to build an efficient closed-photobioreactor (PBR) in which biofouling formation is avoided, a non-toxic coating with high transparency is required, which can be applied to the interior surface of the PBR walls. Nowadays, amphiphilic copolymers are being used to inhibit microorganism adhesion, so poly(dimethylsiloxane)-based coatings mixed with poly(ethylene glycol)-based copolymers could be a good option. The 7 poly(dimethylsiloxane)-based coatings tested in this work contained 4% w/w of poly(ethylene glycol)-based copolymers. All were a good alternative to glass because they presented lower cell adhesion. However, the DBE-311 copolymer proved the best option due to its very low cell adhesion and high transmittance. Furthermore, XDLVO theory indicates that these coatings should have no cell adhesion at time 0 since they create a very high-energy barrier that microalgae cells cannot overcome. Nevertheless, this theory also shows that their surface properties change over time, making cell adhesion possible on all coatings after 8 months of immersion. The theory is useful in explaining the interaction forces between the surface and microalgae cells at any moment in time, but it should be complemented with models to predict the conditioning film formation and the contribution of the PBR's fluid dynamics over time.

Adsorption Analysis of Exopolymeric Substances as a Tool for the Materials Selection of Photobioreactors Manufacture.

An improved method that allows the robust characterization of surfaces is necessary to accurately predict the biofouling formation on construction materials of photobioreactors (PBR). Exopolymeric substances (EPS), such as proteins and polysaccharides, have been demonstrated to present a similar behavior to cells in terms of surface adhesion. In this work, these EPS were used to optimize parameters, such as EPS concentration or adsorption time, to evaluate accurately the adsorption capacity of surfaces and, with it, predict the biofouling formation in contact with microalgae cultures. Once the method was optimized, the characterization of seven commercial polymeric surfaces was submitted to different abrasive particles sizes, which modified the roughness of the samples, as well as protein and polysaccharide lawns, which were prepared and carried out in order to evaluate the characteristics of these substances. The characterization consisted of the determination of surface free energy, water adhesion tension, and critical tension determined from the measurement of the contact angle, roughness, surface zeta potential, and the EPS adhesion capacity of each material. This will be useful to understand the behavior of the surface in the function of its characteristics and the interaction with the solutions of EPS, concluding that the hydrophobic and smooth surfaces present good anti-biofouling characteristics.

Influence of abiotic conditions on the biofouling formation of flagellated microalgae culture.

This work analyses the adhesion of flagellated microalgae to seven surfaces that have different water adhesion tension characteristics. Chlamydomonas reinhardtii and Isochrysis galbana, were cultivated in batch and fed-batch mode at four nitrogen/phosphorus (N/P) ratios (from 1.29 to 70) and subjected to four irradiance levels (50, 100, 200 and 400 µE·s-1·m-2) at 23 °C. Cell adhesion was greater in C. reinhardtii and a higher biomass concentration was obtained for this strain, reaching 2 g·L-1 compared to 1 g·L-1 for I. galbana. The adhesion of cells and exopolymeric substances was measured upon the batch and the first fed-batch reaching the stationary growth phase, observing a direct correlation between them and inversely to biomass generation in the cultures. The protein adhesion data for the different materials are comparable to those for cell adhesion coinciding with minimums of Baier's theory and Vogler. It is observed displacements in the curves as a function of the irradiance level.