Abstract: To solve the problem of turbidity removal from highly turbid water, this study uses composite materials prepared by acid-modified fly ash and chitosan with different mass ratios to treat highly turbid water. The effects of amount of fly ash and chitosan composite materials, stirring time, pH, and initial turbidity on the turbidity removal performance and the combined effects of various other factors were studied through single-factor experiments and orthogonal experiments. The single-factor experiment results show that when the mass ratio of fly ash to chitosan is 6:1, the turbidity removal rate can reach 93.78%; when the composite material CWF3 dosage is 0.6 g, the turbidity removal rate can reach 73.52 %; when the stirring time is 30 min, the turbidity removal rate can reach 90.28%; when pH = 6, the turbidity removal rate can reach 84.50%; when the initial turbidity is 300 NTU, the turbidity removal rate can reach 95.67%. The orthogonal experiment results show that when the mass ratio of fly ash to chitosan is 6:1 and the optimal combination includes a dosage of 0.7 g, stirring time of 35 min, initial wastewater pH of 7, and initial wastewater turbidity of 350 NTU. Adding chitosan to acidmodified fly ash will strengthen the affinity and lower the cost. It can compensate for the shortcomings of using fly ash or chitosan alone and benefit large-scale wastewater treatment.

Key words: fly ash, chitosan, highly turbid water, turbidity removal rate, composite material