China's Taihu Lake sees improved water quality over past 10 years
A field trial using a two-stage nanobubble treatment system across a 3,300-square-metre section of Taihu Lake in eastern China reduced a key measure of toxic cyanobacteria by nearly 90 per cent within 20 days. Published in the journal Environmental Research and indexed on PubMed, the peer-reviewed study describes an in-situ restoration project aimed at controlling harmful algal blooms and improving water clarity in one of China's largest freshwater lakes. The treatment combined hydrodynamic cavitation with ozone nanobubbles in a semi-enclosed test area. Water quality monitoring showed that chlorophyll-a, a key indicator of cyanobacteria levels, fell by 89.8 per cent during the three-week trial. Severe cyanobacterial blooms have affected Taihu Lake for decades. Agricultural runoff, industrial discharge and urban wastewater across the Yangtze River Delta have helped drive the problem. These blooms reduce dissolved oxygen, release toxic microcystins and threaten drinking water supplies for millions of people in Jiangsu and Zhejiang provinces.
Dual-stage physical and chemical treatment
Traditional methods of treating polluted water, such as using copper sulfate or mechanically removing algae, can be difficult to use across large areas. They can also create additional chemical pollution. To address these problems, researchers used a mobile treatment platform that produces tiny gas bubbles directly in the water. Nanobubbles are less than 200 nanometres wide. Unlike larger bubbles, which quickly rise to the surface and burst, they can remain suspended in water for weeks. This allows gases to move into the water more efficiently and supports a range of physical and chemical reactions. The first stage used hydrodynamic cavitation, which creates strong forces in the water that damage cyanobacterial cells and break their gas vesicles. This causes the algae to lose buoyancy and sink. The second stage added ozone-filled nanobubbles. When these bubbles collapsed, they produced hydroxyl radicals that broke down organic pollutants and remaining algal toxins without adding synthetic chemicals.
Rapid chemical and biological recovery
Water samples collected during the 20-day trial showed major reductions in chemical pollutants and nutrients across the 3,300-square-metre treatment area. Ammonia nitrogen levels fell sharply, reducing one of the main factors that contributes to eutrophication and repeated seasonal blooms. Total phosphorus and chemical oxygen demand also decreased, while dissolved oxygen levels steadily increased as the nanobubbles carried oxygen deeper into the water. Higher oxygen levels helped stabilise bottom sediments and reduced the chance of stored nutrients being released back into the lake. Water transparency also improved significantly. Clearer water allowed more sunlight to reach the lakebed, supporting the natural recovery of submerged aquatic plants.
Scaling up ecological restoration
Taihu Lake lies between Jiangsu and Zhejiang provinces and covers more than 2,200 square kilometres. Its shallow basin makes it especially vulnerable to summer algal blooms linked to high temperatures. The problem gained international attention in 2007, when a major blue-green algae outbreak forced Wuxi to shut down parts of its municipal water supply. Since the 2007 crisis, regional authorities have spent billions of yuan on environmental restoration. Measures have included removing polluted sediment, expanding sewage networks and introducing stricter limits on industrial discharges. Nanobubble technology represents a move towards more targeted, high-tech methods of managing polluted water. The research team said the low energy use and efficient transfer of gases make two-stage nanobubble systems suitable for larger bays and tributaries. Further long-term monitoring is planned to determine how well water quality improvements continue after active nanobubble treatment is stopped.
