Microbial Interactions for Wastewater Treatment Focusing on Microalgae-Based Systems

There is a considerable variety of research on microalgae-based wastewater treatment systems (MWWTS). This chapter discusses the diverse microbial associations that have been applied to MWWTS as well as the role of other biological players, such as zooplankton and viruses. Although microalgal-bacterial associations are widely studied, others such as microalgal-fungal are now receiving increasing attention. The metabolisms of photosynthetic microalgae and aerobic bacteria complement each other, increasing the overall efficiency of MWWTS. Statistical meta-analyses of the literature data indicate that microalgal-bacterial and microalgae-only wastewater treatment systems remove significantly different percentages of COD (paired t-test, t21 = 4.138, P < 0.001), TN (paired t-test, t10 = 3.61, P = 0.004), and TP (paired t-test, t15 = 2.37, P = 0.031). Meanwhile, microalgae and fungi are readily pelletized and accumulate large amounts of lipids, which can be used for biofuel production. On the other hand, zooplankton and viruses can also be present in MWWTS, interacting with the implemented consortia. The presence of zooplankton communities can compromise MWWTS; however, several zooplankton control techniques have been studied and are effective at optimizing the MWWTS process. Regarding aquatic viruses in MWWTS, more research should be conducted given the roles of virioplankton and their interactions with microalgae in naturally occurring water bodies. Independently of the important roles of different organisms (aerobic-anaerobic) on wastewater treatment, the presence of other microorganisms such as microalgae improves different wastewater treatment processes. Thus, more research is needed on the use of different microalgae, bacteria and fungi species to enhance the removal of different pollutants (including toxic and persistent compounds) and micronutrients, while providing oxygen to the system and consuming CO2, reducing the need for mechanical aeration and fixing CO2 from the environment.