Chitosan/Sodium Alginate, a Complex Flocculating Agent for Sewage Water Treatment

The effectiveness of the treatment to sewage water by using chitosan, sodium alginate and their complex as flocculating agent was investigated. It was discovered that parameters, such as pH value, temperature, speed and time of stirring, and setting time had direct relations with flocculants. Color/turbidity removing rate could be up to 90% with 15mgL-1 chitosan solution, while sodium alginate alone cannot act as flocculant since no floccules can be observed. Chitosan/sodium alginate complex flocculating agent was found to be an excellent coagulant which made a compliment with each other. The optimum dosage was 15mg L-1 chitosan plus 7.5mg L-1 sodium alginate for complex agent. The results of the orthogonal experiment showed that the optimum conditions to treating sewage water were 70°C for temperature, pH=5.5, fast stirring（600r/min or 900r/min） for 2min, plus slow stirring（100r/min or 300r/min） for 8min, and setting time 2.5h. In this case the chitosan/sodium alginate complex agent could achieve 100% color/turbidity removing rate and approximately 90.01% COD reducing rate.