The objective of this study was to investigate the use of microalgal biomass from wastewater treatment for biogas production. The research found that the biogas production potential is not significantly affected by the season or the time the system operates. However, the biogas production from this specific biomass was lower compared to purposefully cultivated microalgae. This lower production is likely due to the natural microalgal consortia’s lower biodegradability. Still, implementing this system could reduce energy consumption in wastewater treatment by 20% and create an energy surplus of 2.8%, contributing to EU decarbonization goals. To fully realize its potential, further technical and sustainability studies are needed, with a focus on scaling up the system. Despite the challenges, leveraging microalgae-based systems for wastewater treatment could be crucial for addressing climate change.