To improve water environments, create eco-friendly environments, increase dissolved oxygen in waters, and strengthen the self-purification ability of water bodies, the EPA subsidized the Tainan City Government to carry out a pilot project to increase the oxygen levels in hypoxic river sections. Nanobubble aerators from the Industrial Technology Research Institute (ITRI) and oxygenation facilities from the Hydraulics Laboratory of the National Cheng Kung University were used in combination with intelligent controls and real-time monitoring to increase the dissolved oxygen levels in rivers and serve as fish shelters to create suitable water habitats to reduce fish deaths. 

On 13 October 2021, the EPA demonstrated river water quality improvement through a physical model and online video connection. In addition to displaying nanobubble aerator modules on-site, the EPA used an online video connection to illustrate the on-site operation of the aeration system in Tainan Canal. The aeration facility started operating automatically when  the dissolved oxygen (DO) level in the water body fell below 2 mg/L. When the DO level reached 6.5 mg/L, it automatically shut off to save energy. Through innovative and automation devices, low-DO levels in water bodies can be improved immediately with their self-purification abilities strengthened. Relevant technologies can be certified and used to enhance the oxygen-dissolving efficiency of river water substantially. In the future, it is hoped that this system can continue to be promoted and applied to river sections with low levels of DO to improve river water quality effectively.

According to the EPA, some sections of the Tainan Canal and San Ye River under the jurisdiction of Tainan City have low levels of DO. A "blind section" of the Tainan Canal between the Shinlin’an Bridge and Jinhua Bridge, affected by the rising tides on both sides, is often stagnant and has poor water quality with low DO levels with periodic occurrence of dead fish incidents over the years. According to the monitoring conducted by the pilot project at this “blind section," due to factors such as seasons, temperature, and algae activities, the DO level at night sometimes dropped to below 2 mg/L, which threatened fish life. Analysis shows that the phenomenon might be caused by respiration of algae in the river at night. In response, the EPA and the Tainan City Government (Water Resources Bureau) jointly launched the pilot project and purchased 30 aerators to operate in different areas to increase the DO in sections of Tainan Canal with low-DO levels with the prospect of revitalizing the ecological environment of the water body and improving the river’s water quality.  

The operation of the ITRI nanobubble aerator is mainly based on flow adjustment between liquid phase fluid and gas-phase medium. Under a certain pressure, the fluid and medium collide and mix to produce fine bubbles that are injected into a water body. Due to advantages such as longer residence time and larger bubble contact areas, the aerator can quickly increase and stabilize the DO level of water bodies.

According to the EPA, the number of dead fish was reduced by about 40% in Tainan Canal during the aeration pilot project. The aeration attracted fish to gather, and the facilities provided a favorable habitat for organisms in the water and a sheltering environment for fish. 

Excerpt from Major Environmental Policies, November 2021