Microalgae are biological sources with an extensive range of biotechnological applications, e.g., for bioremediation of industrial and municipal wastes. Microalgae are used to monitor environmental toxicants like pesticides, heavy metals, and pharmaceuticals and in the final stage of wastewater treatment when organic pollution should be removed. CO 2 capturing is also important due to the environmental issues. Macro/microalgae cultures, depending on their growth stages and life cycles, have great poten-tial for CO 2 fixation. They are a dominant group of microorganisms for biological treatments with regards to their substantial biosorption ability to deactivate toxic heavy metals. Actual carbon biofixation can be employed in the direction of environmental sustainability and economic facility. Besides, algae are sustainable feedstock to produce a wide range of biofuels by applying thermochemical or biological conversion methods.

Microalgae Chlorella Vulgaris is enriched in vitamin B12 and cobalt ion which is positioned in the center of the vitamin molecule. This study aimed to investigate how different concentrations of cobalt chloride salt affected the vitamin B12 production by utilizing CO2 gas, to assess C. vulgaris biomass. Therefore, Bold's basal medium used as the medium and 0.5, 1.5, 2 and 2.5 μM cobalt chloride salt was added to C. vulgaris culture. Under four cobalt chloride salt treatments, the best growth rate was obtained at the 2 μM of cobalt chloride salt (0.186 + 0.07 g /L.d). CO2 gas was supplied by 5% CO2 gas cylinder and fermented milk as a novel biological CO2 gas generator (CO2,10%). Use of fermented milk is a practical approach for elimination of waste gas emission and converting CO2 into biomass. The results revealed that, in the presence of 5% CO2 gas, C. vulgaris vitamin B12 content at 2 and 2.5 μM cobalt chloride, were 166.23 ± 1.78 and 173.32 ± 4.23 μg /100 g of dry biomass (7 and 12% higher than control), respectively. However, under controlled condition (ambient air and 2 μM cobalt chloride) vitamin B12 content was 154.9 ± 1.14 μg / 100 g of dry biomass.