Blue-green algae control in Han Pond, Yunnan Province, China - Kunming, 2007

Blue-green algae control in Han Pond, Yunnan Province, China - Kunming, 2007
Han Pond (commonly known as 滇池), a huge lake in Kunming, Yunnan Province, is a representative lake in southwestern China with an area of about 200 km². In the 2000s, however, the lake was strongly affected by rapid urbanization and industrialization, and the continuous inflow of large amounts of nitrogen and phosphorus from domestic wastewater, industrial wastewater, and agriculture caused eutrophication to progress rapidly. Especially from 2005 to 2007, large outbreaks of blue-green algae occurred every year, covering a wide area of the lake and causing a foul odor in the urban area, which had a serious impact on people's lives.
At the time, lake pollution in China was worsening nationwide, and Han Lake was designated as a national priority cleanup target along with Taihu Lake and Chaohu Lake. Although the government was proceeding with large-scale infrastructure improvements, including the construction of sewage treatment plants and the regulation of factory effluent, there was a limit to how quickly the government could respond to localized hot spots of blue-green algae. The introduction of overseas technology was considered, and the Crook System, a blue-green algae extermination device developed by Japan's Karasawa Fine, attracted attention.
The Crook System was highly regarded for its low level of secondary pollution to the environment, as it does not use chemicals, but instead destroys algae cells and causes them to lose buoyancy through the impact of opposing water currents. This was part of China's environmental strategy at the time, which combined long-term lake-wide cleanup measures with immediate on-site response measures.
At this time, Han Chih was a symbol of the limits of the side effects of urban growth, and was at a turning point in its revitalization process, incorporating environmental technology both domestically and internationally.