Rhizosphere microbial dynamics in response to Desmondesmus sp. ZM-3 and carbon footprint analysis in constructed wetland

As an emerging bioremediation process for sewage treatment, microalgae-based constructed wetlands (CWs) have received attention. However, few studies have explored the specific links between rhizosphere microorganisms and microalgae in depth, and few studies have considered the combined role of these two types of organisms in carbon emissions. In this study, Desmondesmus sp. ZM-3 and coupled CW systems were set up to explore microalgae and nitrogen-related microbial interactions and greenhouse gas (GHG) emission effects. The results indicated that the removal efficiencies of TN and NH4+-N in the coupled systems were significantly higher (13.07% and 9.31%, respectively) than those of the CWs. The ATP and electron transport system activity (ETSA) of rhizosphere microorganisms and the activities of enzymes involved in the nitrogen removal process were enhanced after dosing with ZM-3. Microbial community succession analysis showed that ZM-3 addition also promoted the growth of denitrifying bacteria, which became key taxa in the CW. Thus, microalgae and denitrifying bacteria could mutually contribute to the nitrogen transformation process. Furthermore, according to life cycle assessment (LCA), the CO2 emission equivalent was decreased by 4.6 CO2 eq./m3 in the coupled systems. Clean energy usage for power generation and a reduction in light duration are improvement strategies that could further minimize GHG emissions. These findings offer new insights into microalgae-based CWs for wastewater treatment.