Climate-Resilient Microalgae-Based CO₂ Capture Systems for Sustainable Urban Environments

Abstract

Microalgae-based carbon capture has emerged as a sustainable alternative for mitigating atmospheric CO₂ emissions while simultaneously generating valuable biomass. However, the long-term performance of outdoor photobioreactors strongly depends on environmental conditions, particularly seasonal temperature fluctuations. This work evaluates the resilience of a native Scenedesmus sp. strain cultivated in a 50 L bubble-column photobioreactor designed for future integration into urban infrastructure for passive atmospheric CO₂ capture.

The photobioreactor was operated under controlled climatic conditions simulating representative spring, extreme summer, and winter environments. Temperature, light intensity, and photoperiod were reproduced using a climatic chamber, while algal growth was monitored through optical density, cell counting, dry biomass, elemental carbon analysis, and physicochemical parameters throughout long-term operation. The system was designed to operate with minimal maintenance, without pH adjustment or medium replacement, reproducing realistic outdoor operating conditions. Results demonstrated continuous cultivation for more than 60 days under spring conditions and approximately 75 days under extreme summer temperatures despite an initial thermal shock. Biomass concentrations reached 1.04 and 0.68 g L⁻¹ under spring and summer conditions, respectively, confirming the high thermal tolerance of the native strain. In contrast, temperatures below 10 °C resulted in culture failure, indicating the need for a low-energy heating strategy during winter operation.

The proposed semi-autonomous system demonstrates the feasibility of integrating native microalgae into urban CO₂ capture devices capable of operating under Mediterranean climatic conditions. These findings contribute to the development of climate-resilient nature-based solutions that combine carbon capture, biomass production, and sustainable urban infrastructure, supporting future low-carbon cities and circular economy strategies.