This study demonstrated that the application of filamentous co-culture could be a promising supplementary approach to further purify municipal tertiary wastewater in Nordic country. Initial screening of 25 algae strains across multiple genera revealed that Spirogyra sp. and Klebsormidium sp. were suitable for use as a coculture for phycoremediation of the tertiary effluent from a wastewater treatment plant, and this result was validated in three consecutive outdoor pilot tests at 10–15 oC. In the first two batches of pilot tests, the total prosperous and ammonium were depleted close to zero in 24 hours, while the pH in the wastewater increased from 7 to 9. In the 3rd batch, CO2 was thereby added for pH control. Macronutrients (N and P) were successfully removed from the treated wastewater. The total algae biomass increased 2 to 3 times over 7 days with average algae productivity of 1.68 g m2 d− 1. Meanwhile, the produced algae biomass accumulated notable mineral elements (Ca, Mg, K, Fe and Al) and some heavy metals at levels of g kg− 1 and mg kg− 1, respectively. In light of circular economy concept, the produced biomass could be used for different valorizations based on the analytical analysis. This study provides a new insight of phycoremediation for further purification of municipal treated wastewater, by effectively using filamentous algae coculture. Given a great potential for further optimization and improvement, this proof of concept will benefit to the green transition of wastewater treatment plants in Nordic country.