Improved resistance to organic matter load by compositing a cationic flocculant into the titanium xerogel coagulant

Titanium xerogel coagulant (TXC) has been proved as a promising coagulant in water treatment. However, the turbidity removal efficiency of TXC is unsatisfactory as there is a considerable amount of dissolved organic matter (DOM). To overcome this shortage, a cationic flocculant, poly(diallyl dimethyl ammonium chloride) (PDADMAC), was composited into the TXC. With the removal of Escherichia coil (E. coli) and the residual turbidity as evaluation index, the composition of PDADMAC to TXC was proved to result in an enhanced resistance to DOM load. The resultant PDADMAC-TXC (P-T) composites had a good pH-resistance. In the pH range of 4.0-10.3, the required dose of P-T composites kept at a low level, whereas much higher doses were needed for the TXC. At pH 8.7, the minimum dose required to achieve a 90% E. coli removal from a 10 mg/L DOM solution was reduced from 70 mg/L TXC to 15 mg/L P-T composites. The improvements could be attributed to the three effects of PDADMAC in the P-T composites: strengthened charge neutralization for negatively charged E coil, enhanced adsorption bridging through the polymer chains, and weakened complexation between organic matter and titanium due to the hydrophobic interactions between the aliphatic chains of PDADMAC and the hydrophobic segments of TXC. The work here provides a useful strategy for the fabrication of DOM-resistant coagulants to meet the requirements for some special kinds of water.