Chitosan has various applications in the treatment of urban drinking water. It can effectively remove suspended materials, algae, bacteria, and residual aluminum, providing a safer and cleaner water supply.
1. Removal of Suspended Materials: Chitosan, as a long-chain cationic polymer, can neutralize the negative charge of suspended substances in water. It acts as a coagulant and adsorption bridging agent, resulting in a strong coagulation effect. Compared to traditional flocculants like alum and polyacrylamide, chitosan demonstrates better clarification capabilities. The optimal pH range for turbidity removal is found to be 7.0-7.5, with a chitosan dosage of 1mg/L. Within this range, chitosan forms effective aggregates with particles, resulting in thick flocs and fast sedimentation. However, the efficiency decreases when the pH deviates from this range. Adding bentonite as a coagulant can enhance the aggregation of chitosan on particles, especially when turbid water contains particles similar to kaolin.
2. Removal of Algae and Bacteria: Chitosan has shown promising results in adsorbing and flocculating biological colloidal systems such as algae and bacteria. It effectively removes freshwater algae like spirulina, oscillating algae, chlorella, and blue-green algae. The optimal pH for freshwater algae removal is 7, while for marine algae, it is lower. The dosage of chitosan depends on the algae concentration, with higher concentrations requiring more chitosan. Increased chitosan dosage accelerates flocculation and sedimentation. Turbidity measurements indicate the removal of algae, with 5mg/L chitosan at pH 7 capable of removing 90% of turbidity. The flocs formed are coarser, leading to better sedimentation performance. Microscopic examination reveals that the flocculated and settled algae remain in an active state. Chitosan does not negatively impact water species, allowing the treated water to be used for freshwater aquaculture. The removal mechanism of chitosan for bacteria is complex, involving unbalanced bridging and hydrogen bonding.
3. Removal of Residual Aluminum: Chitosan is an effective alternative to aluminum salts and polymeric aluminum flocculants used in tap water treatment. These aluminum-based flocculants can increase the aluminum content in drinking water, posing health risks