2. Materials and methods2.1. Experimental setupThe methodology is illustrated in Fig. 1. This study is to simulatethe ecological function of algae in water body such as a river or laketo fix the greenhouse gas CO2. Looking through the current technol-ogy, HRP is the simplest symbiosis system, meets the requirementof ecological engineering concepts (Oswald, 1995) and is the bestchoice to imitate nature system in lab. Two bench scale HRPs wereset up in the Sustainable Resources and Sustainable Engineeringresearch lab (SRSE-LAB), the department of soil and water conser-vation, National Chung-Hsing University, Taichung, Taiwan. Bothreactors were operated at 10 days detention time under the roomtemperature and other operational factors including the light inten-sity were listed in Table 1.