Use of Biopolymer to Improve Water Quality.

Water turbidity is an important factor that controls the growth of submerged aquatic vegetation in fresh water system. Laboratory simulation study was conducted to evaluate the effectiveness of a biopolymer (chitosan) for reducing water turbidity in floc samples from stormwater treatment areas. The flocculation experiments were conducted in 1000-mL cylinders at ambient temperature with the application rates of chitosan at 0.0, 0.1, 0.5, 1.0, 2.0, 3.0 and 5.0 mg L^-1 (Control, T-1, T-2, T-3, T-4, T-5 and T-6, respectively). The initial turbidity, suspended particle concentration, pH, and electrical conductivity (EC) of the suspension samples in the cylinder were the same across all the groups. Addition of chitosan significantly reduced (P < 0.05) water turbidity in 10min of chitosan addition, and the efficiency was related to chitosan concentration and experimental time. The decrease in suspended particles was similar to water turbidity. At the application of 5 ppm chitosan, water turbidity was reduced from approximately 500 NTU to below 50 NTU (US EPA critical level for drinking water) in 10 min and to below 10 NTU in 48 h. This low water turbidity was also achieved at lower chitosan concentrations (1-4 ppm) with extended settling time (72 h). No significant differences in pH were observed among the treatments though higher EC values were measured (P < 0.05) in the various treatment groups with chitosan above 0.1 mg L^-1. The settled aggregates were stable over several months. These results indicate that this biopolymer (chitosan) may be useful for reducing or eliminating turbidity of fresh water systems.

Keywords: Biopolymer; Floc sediment; Submerged aquatic vegetation; Water turbidity;