Microalgae-bacteria nexus for environmental remediation and renewable energy resources: Advances, mechanisms and biotechnological applications

Abstract

Microalgae and bacteria, known for their resilience, rapid growth, and proximate ecological partnerships, play fundamental roles in environmental and biotechnological advancements. This comprehensive review explores the synergistic interactions between microalgae and bacteria as an innovative approach to address some of the most pressing environmental issues and the demands of clean and renewable freshwater and energy sources. Studies indicated that microalgae-bacteria consortia can considerably enhance the output of biotechnological applications; for instance, various reports showed during wastewater treatment the COD removal efficiency increased by 40%-90.5 % due to microalgae-bacteria consortia, suggesting its great potential amenability in biotechnology. This review critically synthesizes research works on the microalgae and bacteria nexus applied in the advancements of renewable energy generation, with a special focus on biohydrogen, reclamation of wastewater and desalination processes. The mechanisms of underlying interactions, the environmental factors influencing consortia performance, and the challenges and benefits of employing these bio-complexes over traditional methods are also discussed in detail. This paper also evaluates the biotechnological applications of these microorganism consortia for the augmentation of biomass production and the synthesis of valuable biochemicals. Furthermore, the review sheds light on the integration of microalgae-bacteria systems in microbial fuel cells for concurrent energy production, waste treatment, and resource recovery. This review postulates microalgae-bacteria consortia as a sustainable and efficient solution for clean water and energy, providing insights into future research directions and the potential for industrial-scale applications.

Keywords: Electron transfer mechanisms; Microalgae microbial fuel cell; Microalgae-bacteria consortia; Photosynthetic electrogens; Renewable energy resources; Wastewater treatment.

Graphical abstract

Fig. 1

A diagram illustrating the light-dependent and light-independent reaction steps in the photosynthesis process. During the light-dependent reaction, the excited electron replacement and generation of hydrogen occur through the photolysis of water molecules, then ATP and NADPH are produced to be supplied to the Calvin cycle of light-independent reaction to fix carbon dioxide into sugar. The sketch was drawn based on the information provided by Marchand et al. [101].

Fig. 2

Overview of MFC processes and extracellular electron transport (EET) mechanisms. Indirect transport of electrons with shuttle transfer and direct transfer with surface contact is depicted in the left and middle sections of the figure. The electron shuttle mediates the indirect transfer of electrons back and forth between the electrode and bacterial cells. Where, Mtr (metal-reducing) conduit system comprising several multi-heme c-type cytochormes (c-Cyts) including Fcc₃-flavocytochrome c3 (tetraheme), MtrA (periplasmic, decamehe), MtrB (outer membrane-bounded), CymA- (cytoplasmic inner membrane-bounded, tetraheme), STC-small tetra heme cytochrome, MtrC (periplasmic protein, decaheme) and OmcA-outer membrane c-Cyt (decaheme). MQ and OM represent menaquinol and organic matter, respectively. The sketch was drawn based on the information provided by Zou et al. [144].

Fig. 3

Illustration of microbial fuel cell (MFC). a) conventional MFC, where bacteria are electricigens to release electrons from organic matter (OM), b) photosynthetic-MFC (PMFC), where microalgae are electricigens to release electrons from photolysis, and c) microalgae-MFC (mMFC), where microalgae are biocathode by producing oxygen to reduce electron and release water. The diagrams show electrons are transported via external circuits and protons flow through a proton exchange membrane (PEM) to the cathode chambers to react with oxygen and electrons to produce water. The sketch was drawn based on the information provided by Saratale et al. [193].

Fig. 4

Illustration of microalgae-MFC where microalgae inoculated as biocathode (a) and MCC where microalgae inoculated as biocathode and CO₂ from the anodic chamber (AC) is channeled to cathodic chamber (CC) (b). Where OM is organic matter and BM is biomass accumulated. The sketch was drawn based on the information provided by Das et al. [196].

Fig. 5

An illustration of SMFC (a) and PSMFC inoculated with microalgae (b), installed with an anode buried in sediment and a cathode hung in the surface water. Where OM is organic matter. The sketch was drawn based on the information provided by Yang and Chen [230].

Fig. 6

An illustration of MDC (a) and PMDC (b, inoculated with microalgae) installed into three chamber configurations mainly anodic chamber (AC), desalination chamber (DC) which is separated by cation exchange membrane (CEM) and anion exchange membrane (AEM), and cathodic chamber (CC). Showing the possibilities to produce HCl and NaOH, and connecting CO₂ feeding the cathode (b). Where OM is organic matter. The sketch was drawn based on the information provided by Kim and Logan [213].