Effect of carbon dioxide injection on photosynthetic wastewater treatment using microalgae Chlorella vulgaris and Euglena gracilis

Abstract

Photosynthetic wastewater treatment of secondary animal wastewater was investigated using two microalgae (Chlorella vulgaris and Euglena gracilis) under both control and CO2-enriched conditions. The addition of CO2 to the microalgae culture contributed to foster nutrient uptake for C. vulgaris, but E. gracilis culture was not affected much. E. gracilis culture under CO2 injected condition showed the highest cell density and C. vulgaris showed the highest specific growth rate in the CO2 enrichment experiment. C. vulgaris cells were 15-times smaller than those of E. gracilis. The noticeably distinguishable sizes affected the separation processes. E. gracilis possessed better filterability and dewaterability. The CO2 injection greatly enhanced biomass protein production in both algae, but reduced lipid and carbohydrate fraction. By adding CO2, lipid profile of C. vulgaris has changed greatly, as opposed to E. gracilis that has remained pretty much the same way.