Simultaneous CO2 Bio-fixation and Tuna Processing Factory Wastewater Treatment via Microalgae

Photosynthetic microorganisms such as Chlorella vulgaris can be used for carbon dioxide (CO2) biofixation to reduce greenhouse gas emissions and combat global warming. In this study, the potential of using wastewater from a tuna processing factory as a cultivation medium for C. vulgaris was investigated with the aim of reducing cultivation costs and water consumption while treating the wastewater. Different CO2 concentrations (5%, 10% and 15% in N2) and wastewater dilutions (1:4, 2:4, 3:4 and 4:4) were tested at ambient temperature, controlled pH and cyclic illumination (12h light-12h dark) at 6000 lux, using both batch and semi-continuous cultures. In the batch system, 100% CO2 biofixation was achieved at an effluent dilution of 1:4 and 5% CO2, with biomass concentration doubling after one week. High removal rates of COD (94%), total phosphorus (99%), nitrate (98%) and ammonium (99%) were observed. The semi-continuous photobioreactor showed a CO2 stabilization of more than 50% (at 5% CO2) and a 40% biomass increase, with over 50% nitrate removal in a 1:4 dilution effluent. These promising results demonstrate the potential of the system for simultaneous CO2 biofixation and wastewater treatment and underline the effectiveness of this circular economy approach to reduce greenhouse gas emissions and treat industrial wastewater.