Indoor and outdoor cultivation of Chlorella vulgaris and its application in wastewater treatment in a tropical city—Bangkok, Thailand

Abstract

This study was carried out to assess the effectiveness of algal growth cultivated in photobioreactors (PBRs) in different conditions in a tropical environment, i.e., indoor and outdoor conditions with wastewater in Bangkok. The PBRs were inoculated with pure Chlorella vulgaris, and the cultivation was conducted in housing state wastewater. The productivity of C. vulgaris was found to be 0.0960 g/l/d in a pH-controlled outdoor PBR with pH in between 7.0 and 8.0, 0.0618 g/l/d in outdoor PBR with no control, and 0.0131 g/l/d in indoor pH-controlled PBR (with a fixed pH of 7.5). Chlorella vulgaris did not show growth in indoor PBR with no pH control. Indoor PBRs consumed 232 to 270 times more energy and needed 25 to 57 times more capital cost, and 3.8 to 16.8 times more operating cost than that of outdoor PBRs. Outdoor PBRs showed better nutrient removal efficiency of housing state wastewater than that of the wastewater treatment plant, i.e., 100% removal of biological oxygen demand, chemical oxygen demand, total phosphorus and more than 96% removal of total nitrogen; However, required time and energy consumption were more in outdoor PBRs. The possibility of improving the process performance by controlling pH, by supplying CO2 from additional source, and by supplying continuous aeration appears as an attractive option. Although precautions should be taken for CO2 supply, high concentration CO2 caused a significant drop in pH and an increase of total dissolved solids. Light transmission efficiency of PBR material polyethylene terephthalate material was 85.45% to 92.08%, and efficiency decreased with the increase in light intensity.