Characteristics and mechanism of chitosan in flocculation for water coagulation in the Yellow River diversion reservoir

•Water from the Yellow River reservoir was treated with Polyaluminum chloride and a PAC/chitosan compositel.•Compared with the use of PAC only, the addition of a small quantity of CTS improved the removal effect of each index indicators by 8.7 %-46.83 %.•Under the same conditions, the size of the floc formed by the composite coagulant containing CTS increased by 36.67%.•When long-chain bridging is dominant, It's more conducive to rapid formation of structured and dense flocs.•When electrical neutralization is dominant, the flocs have better regeneration abilities.