Simultaneous CO۲ Bio-fixation and Wastewater Treatment by Microalgae

BACKGROUND AND OBJECTIVESUsing photosynthetic microorganisms for carbon dioxide (CO۲) bio-fixation is one of the ways to prevent releasing it into nature and reduce the effects of greenhouse gases and global warming. Microalgae, found in freshwater and saltwater, are capable of producing oxygen and biomass with sunlight, water and CO۲. The produced biomass can eventually be used for food, medicine, cosmetics and as source of biofuel. Ayatollahi et al. (۲۰۲۱) prepared experiments with five CO۲ concentrations (air-۵-۱۰-۱۵-۲۰ %), synthetic municipal wastewater and C.vulgaris cultivation on it. The results revealed that the best growth rate of microalgae achieved at ۵% of CO۲ concentration with a C/N ratio of ۴, of the wastewater.MATERIALS AND METHODSIn this research, Chlorella vulgaris microalgae was used for CO۲ bio-fixation. In order to reduce costs and also save water consumption, the wastewater of the Tuna processing factory was used as a cultivation medium. Three concentrations of CO۲ (۵%-۱۰%-۱۵% in N۲) at different dilutions of wastewater in distilled water (۱:۴, ۲:۴, ۳:۴ and ۴:۴) were investigated to determine the best conditions for C. vulgaris growth. Cultivation was carried out at room temperature. Lighting was cyclic (۱۲-۱۲ h), at intensity of ۶۰۰۰ lux. Cultivation was done in two systems, batch (serum bottles) and semi-continuous (airlift photobioreactor). In both systems, wastewater analyzed at the beginning and the end of the experiments to determine the COD, total phosphorus, nitrate and ammonium removals. CO۲ consumption also detected by GC to give an insight into the simultaneous gas consumption, biomass production and wastewater treatment.RESULTS AND DISCUSSIONThe results showed microalgae٬s ability to grow in all concentrations of CO۲ in both systems.In semi-continuous photobioreactor after ۲۳ h, (at ۵% gas) the CO۲ stabilization and the effluent analysis of ۱:۴ dilution, both showed more than ۵۰% of gas bio-fixation and nitrate removal, respectively.CONCLUSIONThe results were promising showing the ability of the system for simultaneous CO۲ bio-fixation and wastewater treatment.

کلیدواژه ها:

Microalgae ، CO۲ Bio-fixation ، Tuna processing wastewater.