Microalgal/cyanobacterial biofilm formation on selected surfaces: the effects of surface physicochemical properties and culture media composition

Abstract

The increased interest in photosynthetic microorganisms for wastewater treatment processes has led to the demand for new biomass harvesting strategies. Biofilm systems have emerged as a good alternative to planktonic photosynthetic cultures. However, knowledge on the environmental aspects influencing microalgal/cyanobacterial biofilm formation is required. This study reports the influence of: (i) surface physicochemical properties of selected microorganisms (Chlorella vulgaris, Pseudokirchneriella subcapitata, Synechocystis salina, and Microcystis aeruginosa) and materials (copper—Cu; glass—G; poly(methyl methacrylate)—PMMA; polystyrene—PS; polyvinyl chloride—PVC; and AISI316 stainless steel—SS) and (ii) culture media composition (glucose-deficient and glucose-enriched media) on biofilm formation (up to 7 days), with constant temperature, light irradiation, and shaking conditions. Adhesion was assessed through thermodynamic prediction of adhesion and by in vitro adhesion assays on microtiter plates. In general, higher biofilm densities were observed after 7 days of experiment, and followed the order: SS > PS > G > PVC > PMMA> Cu. M. aeruginosa was the highest biofilm-former microorganism (2.1 × 106 CFU cm−2), while P. subcapitata has shown lack of ability to adhere. Moreover, the higher biofilm formation ability was observed when glucose-deficient medium was used. Furthermore, the present results pointed out that the thermodynamic approach failed to predict the stochasticity of microalgal/cyanobacterial adhesion. In light of these findings, others factors must be considered when using predictive tools. Therefore, fine-tuning on photosynthetic biofilm formation can be obtained by optimizing the bulk fluid composition and the type of surface. In conclusion, the results show the potential of the selected microalgae/cyanobacteria for biofilm-based technology.