Water derived from storm events in Taiwan is a critical issue because of its high turbidity, which could be larger than 100,000 Nephelometric Turbidity Units (NTU), due to the fragile geology and steep topography of the island. The high turbidity water lowers the efficiency of a water treatment plant or can even shut down the facility resulting in a loss of water supply. Commonly used coagulants, such as aluminum salt, iron salt, and polymers, have dosage limitations and application restrictions due to health concerns. This study provides a new method for turbidity reduction, which can be applied both inside and outside of a water treatment plant. This method then provides a more stable, safe, and environment-friendly water supply by using Chitosan as bio-based polymer for extremely high turbidity water. Representative samples are used to evaluate the effectiveness of Chitosan: (1) the collected sample from Chengqing Lake Reservoir in southern Taiwan; (2) Kaolin soil (or Kaolinite clay), and (3) Ottawa standard sand. The results show that the residual turbidity is directed related to (1) bio-polymer dosage, (2) initial concentration, (3) particle size, (4) mixing method, and (5) settling time. Also, the bio-polymer dosage of 0.2 mg/L can reduce the turbidity from about 50,000 to 25 NTU, which is well below the drinking water standard of 30 NTU for high turbidity periods.
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