| Microalgae cultivation and energy recovery technologies have attracted much attention, specifically cultivation with wastewater originated nutrients. In this study, in order to develop low cost and low energy microalgae cultivation system in WWTP, influences by addition of CO2, which are generated from anaerobic digesters and/or incinerators, on microalgae growth and energy content are discussed. Two raceway reactors (surface area, effective height and effective volume: 1.52 m2, 0.25 m and 380 L) were set outside, and continuous microalgae cultivations with secondary effluent were conducted from May to November 2014. When culture pH reached to 8, CO2 was added to a reactor (reactor 1) to provide carbon source for microalgae. The other was operated with no CO2 addition (reactor 2). Inorganic carbon in reactor 2 was 5.1 mgC/L and lower than that in reactor 1 (21 mgC/L). The CO2 addition enhanced microalgae concentrations from 138 to 155 mgSS/L, and dominant microalgae species in the reactors were different: Scenedesmaceae in reactor 1 and Dictyosphaeriaceae in reactor 2. The higher heating value in microalgae from reactor 1 (16 kJ/g-SS) was 1.1 times higher than that in reactor 2 (14 kJ/g-SS). Regarding enhancement of energy production of cultivated microalgae, effectiveness of CO2 addition was suggested. |
