Low-energy high-rate flotation technology for reduction of organic matter and disinfection by-products formation potential: A pilot-scale study.

Abstract

Despite operating complexity and high energy costs associated with its operation and maintenance, dissolved air flotation (DAF) is widely used in drinking water treatment processes. Recently, the focus has shifted to designing and developing DAF with high surface loading rates. This research compares the performance of pilot-scale high-rate DAF and low-energy high-rate flash-pressurized flotation (FPF) based on the removal behavior of natural organic matter, different molecular weight size fractions, and the formation potential of disinfection by-products. For a surface-loading rate of 30m/h, the residual dissolved organic matter (DOC) concentrations in treated samples from high-rate DAF and FPF were 1.35±0.02 (30.25±0.15% removal) mg/L and 1.37±0.03 (29.12±1.72% removal) mg/L, respectively. In contrast, the removal of high-molecular-weight fractions, i.e., biopolymers and humic substances, showed similar removal performance for both treatment processes but not for building blocks. The removal rates were 27.10% and 6.64% for high-rate DAF and FPF, respectively. The formation potential of trihalomethanes/DOC for high-rate DAF with reaction times of 1, 3, 6, and 9 days 14.12±0.18, 17.84±0.22, 23.04±0.29, and 29.73±0.37μg/mg C, respectively, and 16.83±0.34, 22.69±0.46, 27.08±0.55, and 28.54±0.58 for high-rate FPF. In the case of haloacetonitriles/dissolved organic nitrogen-humic substances and chloral hydrate/DOC, there were no significant differences. Thus, low-energy high-rate FPF with a reduction of energy of 55% provides an alternative to high-rate DAF.