The release of inadequately treated urban wastewater is the main cause of environmental pollution of aquatic ecosystems. Among efficient and environmentally friendly technologies to improve the remediation process, those based on microalgae represent an attractive alternative due to the potential of microalgae to remove nitrogen (N) and phosphorus (P) from wastewaters. In this work, microalgae were isolated from the centrate stream of an urban wastewater treatment plant and a native Chlorella-like species was selected for studies on nutrient removal from centrate streams. Comparative experiments were set up using 100% centrate and BG11 synthetic medium, modified with the same N and P as the effluent. Since microalgal growth in 100% effluent was inhibited, cultivation of microalgae was performed by mixing tap-freshwater with centrate at increasing percentages (50%, 60%, 70%, and 80%). While algal biomass and nutrient removal was little affected by the differently diluted effluent, morpho-physiological parameters (F_V/F_M ratio, carotenoids, chloroplast ultrastructure) showed that cell stress increased with increasing amounts of centrate. However, the production of an algal biomass enriched in carotenoids and P, together with N and P abatement in the effluent, supports promising microalgae applications that combine centrate remediation with the production of compounds of biotechnological interest; for example, for organic agriculture.

The global population increase during the last century has significantly amplified freshwater demand, leading to higher wastewater (WW) production. European regulations necessitate treating WW before environmental. Microalgae have gained attention for wastewater treatment (WWT) due to their efficiency in remediating nutrients and pollutants, alongside producing valuable biomass. This study investigates the phycoremediation potential of a Chlorella-like strain isolated from urban WW in a 600L-scale system under winter conditions. Experiments in December 2021 and February 2022 tested the strain’s adaptability to varying environmental conditions, particularly temperatures (min-max temperature range: from −3.69 to 10.61 °C in December and −3.96 to 17.61 °C in February), and its ability to meet legal discharge limits. In December, low temperatures algal growth. Nitrates showed an RE of about 92%, while ammonia slightly decreased (RE, about 32%), and phosphorous remained unchanged. In February, mild temperatures increased algal density (33.3 × 10⁶ cell mL⁻¹) and, at the end of experiment, all nutrients were below legal limits with very high RE % (NH₄⁺, 91.43; PO₄³⁻ 97.32). Both trials showed an E. coli RE, % = 99%. The study highlights the potential of microalgae for WWT and the importance of considering seasonal variations when implementing these systems.

Microalgae are gaining increasing attention for wastewater (WW) depuration thanks to their ability to remove pollutants from WW. As environmental conditions change widely geographically and throughout the year, also reaching growth-limiting temperatures during the cold season, sites and seasons specific tests are needed to assess the actual implementation of microalgae phytoremediation. In this paper, two site-specific prototype-scale experiments were performed to test the ability of an autochthonous microalga to depurate urban WW efficiently during winter. Two setups were tested: one indoor and one outdoor. We evaluated dry biomass production, photosynthetic stress, and nitrogen (N) and phosphorus (P) removals from WW. In addition, Escherichia coli concentration was monitored on the effluent. Despite the limited growth in both conditions, N was largely removed from the medium, with the highest result recorded outdoors (almost 70%). No P removal was recorded, although P content in biomass increased both indoors and outdoors, meaning that multiple processes could occur at the same time. Moreover, a huge decrease in E. coli content was recorded in both conditions, suggesting potential for effluent disinfection.