Substrate dependent microalgal biofilm cultivation system for the blue and green economy: formation, mechanism, and applications in environmental engineering and biotechnology

Microalgae and cyanobacteria biofilm have simple physiology, fast photosynthetic growth using wastewater (WW) (primary nutrients removal, N, P), and can provide feedstock for microalgae-based biorefinery attempts. Suspended or planktonic cultures of photosynthetic algae have been widely developed for producing industrial biochemical by improving metabolic engineering via synthetic biology. Planktonic cultures can experience low algal biomass productivity, high operating costs and energy consumption when cultivating both indoor and outdoor cultivations. Algal biofilm or immobilized cells have drawn a lot of attention recently due to their prospective to improve the sustainability of livestock production, implications for carbon sequestration and climate change resilience, value-added products, and blue and green economies. Microalgal biofilm (MAB) or attached growth can be beneficial for effective removal and degradation of micropollutants, heavy metals, and hazardous chemicals, reducing harvesting costs, and transforming bioactive compounds and livestock for downstream operation. Non-axenic MABs are a smart choice for energy-alternative animal, municipal, and mining WW treatment (WWT), but they have not yet been developed as industrial options for deployment in sewage water. Besides, numerous aspects of MAB including biofilm formation mechanisms, stability, and bioreactor design, cell-cell interaction, extracellular polymeric substances (EPS), signaling molecules, and renewable products deserve deeper investigation. This article's goal is to provide a thorough review of MAB communities, their presence in the biosphere, their expansion in industrialized uses and the bio-based economy.