Assessment of a photobioreactor-coupled modified Robbins device to compare the adhesion of Nannochloropsis gaditana on different materials

Abstract

The prevention of biofouling in the inner walls of closed photobioreactors (PBRs) becomes a critical step in improving the performance of photosynthetic microalgae bioprocesses. Selection of antifouling materials implies approaches at laboratory scale. This work reports the use of a flow cell of the modified Robbins device (MRD) type coupled to a PBR, operated in both batch and continuous modes with the model marine microalgae Nannochloropsis gaditana to study the biofouling formation on diverse materials. The fluid-dynamics within the MRD was studied via CFD-aided simulations. At separation distances lower than the cells' diffusion layer thickness, a diffusion-controlled transport of the cells to the material surface was postulated. Results suggested that the flow density of cells in the MRD (Jz), governed by cell concentration gradients, is a significant factor in the adhesion intensity (B) when the PBR is operated in batch mode; not in the continuous mode where the differences observed in B between materials were mainly attributed to the type of material. Polyvinylchloride (PVC) was clearly the best anti-biofouling material compared to polycarbonate, polystyrene, borosilicate glass and stainless steel. The B maximum occurred at the end of the stationary phase in batch culture mode. Continuous culture operation seemed to be preferable since once steady state is achieved, the B value remained low and constant, indicating equilibrium between the number of adhered cells per surface unit and the cell concentration in the culture broth – this was because the adhered cells did not grow on the surface due to phosphate limitation. The PBR-coupled MRD has demonstrated to be well-suited for the screening of antifouling materials under fluid-dynamic conditions relevant in PBRs.