Microalgal biofilms: Towards a sustainable biomass production

Microalgae are an excellent source of sustainable biofuels. However, the current microalgal growth using traditional liquid-based culture is not economically viable as the price of microalgal biofuel is still higher compared to its fossil fuel counterpart. In fact, microalgal dewatering requires substantial energy and represents a major bottleneck limiting the industrial microalgal mass production. Compared to conventional planktonic microalgae growth systems, the attached growth or biofilm-based growth represents several advantages such as higher biomass content compared to liquid culture and lower capital costs, which has a great potential to help microalgal fuels reach economic viability. However, despite the many advantages of biofilm-based growth, limited work has been reported on their use to mass produce microalgal biofuels or bioproducts. This review discusses the factors affecting microalgal biofilms growth as well as the challenges that hinder their large-scale production. Several parameters such as the microalgal strain, the microalgal adhesion to the substrate, operation conditions, and physico-chemical properties of the substrate are outlined in depth. This review highlights the current challenges in microalgal biofilm development and identifies strategies to improve biofilms growth, to optimize the economics of microalgal biomass production and downstream processing, and to promote the commercial industrialization of algal biofilm. A preliminary economic assessment of Chlorella sp., Spirulina sp. and Scenedesmus sp. biofilms compared to liquid cultivation is evaluated, showing that the biomass production costs for biofilm-based cultivation system are 8-10 times lower than that of suspension-based cultivation system.