Application of Chitosan Composite Flocculant in Tap Water Treatment

Abstract

The chitosan is a good flocculant for tap water treatment because of its properties such as faster deposition rate and higher removal efficiency for COD (organic matter), SS (suspended solids), and metal ions. However, its high price limits the use in tap water treatment. In this paper, in order to reduce costs, chitosan (CTS), polyaluminum chloride (CF-PAC), and modified rectorite (Al(OH)3 + HCl) were combined to prepare the flocculant for tap water treatment. In order to get the optimal composite flocculant formula, first, we combined these flocculants in two-by-two schema and then we combined all the three flocculants together with various dosing amounts. Through comparison between different combination schemas, the best formula of the composite chitosan flocculant was found to be CTS (ml) : CF-PAC (ml) : modified rectorite (Al(OH)3 + HCl) (ml) = 1 : 30 : 5, with a turbidity removal rate of 96.38% and a removal rate of aluminum up to 80.1%, while the treatment cost is the lowest. In addition, we have designed a cost-effective method for the treatment cost evaluation. As raw water, we used water from the Han River, which is used as raw water at Zonguan Waterworks. In order to show the effectiveness of our optimal composite chitosan formula, we have compared our treatment results to those of the aluminum polyaluminum chloride flocculant currently used in Zonguan’s water treatment plants.