| Carbon dioxide (CO2) emitted from facilities such as incinerators in wastewater treatment plants (WWTPs) is an essential carbon source for indigenous microalgae, and cultivation with the CO2 is a promising energy production system for the WWTPs. In this study, CO2 addition was controlled by pH in cultures, and indoor experiments, including three reactors with the addition (pH at 7, 8, 9) and one reactor without the addition (at 10.8), were conducted to reveal suitable additional conditions for the cultivation with treated effluent. Six-month outdoor experiments were performed to investigate its effectiveness. The indoor experiments verified that not only an increase of suspended solids concentrations but also that of higher heating values to which high carbon and hydrogen content contributed were achieved by CO2 addition, represented as 170?mg/L and 21.0?kJ/g at pH 8 and 50?mg/L and 11.6?kJ/g at 10.8. The suitability of the addition at pH 8 is suggested. The outdoor experiment revealed that Scenedesmaceae and Dictyosphaeriaceae dominated with the addition at pH 8 and without the addition, respectively. Addition of CO2 at pH 8 enhanced energy production efficiency approximately from 110 to 150 kJ/(m2?d), and its effectiveness on the outdoor cultivation was verified. |
