[Effect of extracelluar organic matter and natural organic matter on coagulation]

Influence of EOM and NOM on removal of algae and turbidity was investigated. The result showed that EOM had both beneficial and harmful effects on coagulation, it hindered the charge neutrality of the flocculant. Zeta potential of algae decreased from -40.6 mV to -14.7 mV, only when the modified chitosan was added above 0.2 mg x L(-1). But it became a coagulant aid when it combined with flocculant. The experiment indicated that turbidity removal would reach the peak efficiency (96%) with appropriate concentration of EOM (5.18 mg x L(-1)), therefore EOM would enhance the removal efficiency. NOM had the more negative effect on coagulation, the optimum removal efficiency of algae and turbidity decreased by 11% and 18% separately. Besides, the optimum dosage of modified chitosan increased from 0.35 mg x L(-1) and 0.1 mg x L(-1) to 0.7 mg x L(-1) and 0.3 mg x L(-1) respectively. So it is the key point to take advantage of EOM and remove the NOM in practice, as a result the flocculant loading will be decreased, the removal efficiency will be improved.