Effect of CO2 addition on treating anaerobically digested abattoir effluent (ADAE) using Chlorella sp. (Trebouxiophyceae)

Microalgae cultivation on wastewater augments the conversion of a waste stream into a profitable end-product, thus, establishing a circular economy. In this study, we successfully isolated and established the growth of a local microalga Chlorella sp. (Trebouxiophyceae) on raw anaerobically digested abattoir effluent (ADAE). The effect of CO2 addition on culture properties and the growth, photosynthesis, nutrient removal efficiency and biochemical composition of Chlorella sp. were evaluated. The addition of CO2 resulted in 28 % increase in biomass productivity when compared to the control culture with no CO2 supplementation. CO2 addition also resulted in higher ammoniacal nitrogen removal rate (95 %) when compared to the control (59 %) while no significant difference was recorded in terms of phosphate removal in both treatments. Chlorella cultures aerated with CO2 also showed a higher effective quantum yield (F-q'/ F-m') when compared to the control culture. No significant differences were observed in terms of total protein and pigment content of cultures aerated with and without CO2 while total carbohydrate content was higher in the control cultures. Based on a mass balance analysis, between 12-16 % of ammoniacal nitrogen and between 11-16 % of total phosphorus removed from the ADAE was assimilated for the formation of algal biomass in the cultures. The remaining ammoniacal nitrogen was most likely removed by ammonia volatilization through air stripping.