Assessing the effectiveness and environmental impacts of using natural flocculants to manage turbidity

Graduation date: 2006The objective of this research was to determine the feasibility of using chitosan\ud as a natural flocculant to control turbidity during in-stream construction work. A\ud series of field tests in Oak Creek, Corvallis, OR were conducted in order to test the\ud effectiveness for turbidity control and the environmental impacts of applying chitosan\ud directly into a stream environment. No significant removal was obtained with\ud chitosan doses up to 0.5 mg/L under the conditions tested, mostly due to high pH of\ud the creek and other unfavorable water quality parameters. Water quality analysis for\ud total organic carbon, total phosphorus, total Kjeldahl nitrogen, and biochemical\ud oxygen demand showed that chitosan does not adversely impact the aquatic\ud environment at low doses.\ud Due to the inconclusiveness of the field test data, a series of bench-scale tests\ud were conducted to evaluate the effectiveness of chitosan under controlled conditions,\ud as well as its responses to different test conditions, e.g. pH, initial turbidity, chitosan\ud dose and sediment type. The bench scale tests were conducted using water collected\ud from Oak Creek and a standard jar tester. It was found that flocculation efficiency\ud depends strongly on sediment type. However, the most critical factor that determines\ud the effectiveness of chitosan seems to be an unidentified water quality parameter,\ud which is likely related to the organic matter in the stream