Wastewater treatment and valorization coupled with cyanobacterium Synechococcus elongatus PCC 7942 cultivation

Abstract

Environmental conservation and climate change mitigation impose the need to investigate new routes for the treatment of wastewaters towards their valorization and mitigation of CO2 emissions. Wastewater streams contain valuable resources, such as water and nutrients, which are expected to become increasingly scarce for the foreseeable future. Due to their composition, wastewaters can be used as substrate for the cultivation of cyanobacteria, a sustainable feedstock for the production of biofuels and added value products. Cyanobacteria present higher photosynthetic activity than terrestrial plants and can remove/recover nitrogen and phosphorous from wastewater via assimilation into biomass, while fixating significant quantities of CO2 from atmospheric air or flue gases. This creates the opportunity for the development of processes that can offer tertiary wastewater treatment (nutrients removal) and CO2 emissions mitigation, while the generated biomass can be utilized in downstream valorization processes (Figure 1). From the plethora of cyanobacteria species that can be potentially used for wastewater treatment and valorization, this work focuses on the cultivation of freshwater cyanobacterium Synechococcus elongatus PCC 7942 monocultures in various nutrientrich wastewater media. Synechococcus elongatus PCC 7942 is a cyanobacterium that does not produce cyanotoxins and can be used as a more sustainable feedstock alternative for the production of fuels, food and chemicals. Furthermore, Synechococcus elongatus PCC 7942 can increase its intracellular sucrose synthesis when exposed to saline conditions present in some wastewater streams, hence it can be manipulated to produce added value biomass. The synthesized sucrose is a considered a valuable resource, as it can be utilized in various industrial applications, including bioethanol production. Moreover, sucrose can also be metabolically transformed by Synechococcus elongatus PCC 7942 to biohydrogen via anaerobic dark fermentation...