Removal of Different NOM Fractions from Spent Filter Backwash Water by Polyaluminum Ferric Chloride and Ferric Chloride

Abstract

Increasing world population, water shortage and high-quality standards for drinking water lead to conduct numerous efforts in water treatment plants to reuse spent filter backwash water and improve the productivity of plants. The aims of this study were to investigate the fractional composition of the spent filter backwash water from Isfahan’s water treatment plant in Iran and to determine the coagulation performance of polyaluminum ferric chloride (PAFCl) and ferric chloride (\(\hbox {FeCl}_{3}\)) regarding different fractions of natural organic matter (NOM). Conventional jar test apparatus was used for the coagulation procedure, and the NOM was fractionated into hydrophobic, transphilic and hydrophilic fractions. Isolation was done with DAX-8 (supelite) and XAD-4 (amberlite) resins. The results showed that optimum amount of \(\hbox {FeCl}_{3}\) was 30 mg/L. At this level, turbidity, \(\hbox {UV}_{254}\) and DOC removal reached to 99.4 (±0.2), 46.9 (±4.4) and 44.3 (±2)%, respectively. Also at the optimum dose of PAFCl (13 mg/L) turbidity, UV\(_{254}\) and DOC removal reached to 99.6 (±0.1), 50 (±3.5) and 50 (±2)%, respectively. Thus, the performance of PAFCl for organic matter removal was better than \(\hbox {FeCl}_{3}\). Hydrophobic fraction was more easily removed by both of the coagulants compared to the hydrophilic and transphilic fractions. However, FeCl\(_{3}\) was more efficient than PAFCl for the removal of hydrophobic fraction and vice versa was occurred for the removal of transphilic fraction.