Removal efficiency and mechanism of geosmin by modified micro-nano bubbles in drinking water treatment process

Abstract

The problem of odor and taste caused by geosmin had been widely discussed globally. While existing water treatment processes were difficult to remove geosmin cleanly and efficiently, and the traditional aeration method of micro-nano bubbles (MNBs) led to low removal efficiency due to the low probability of collision between the bubbles and the contaminants. In this study, micro-nano bubble modification technique was used to improve the removal efficiency. Three surface modifiers, hexadecyl trimethyl ammonium bromide (CTAB), chitosan (CTS), and poly dimethyl diallyl ammonium chloride (PDADMAC), were selected for this study. The effects of the surface modifiers on the properties of MNBs and the effects of these changes on the removal efficiency of GSM were explored. The experimental results showed that when all three modifiers were dosed at 5 mg/L, the PDADMAC-modified MNBs had the best GSM removal effect of 70.9 %, while the Zeta potential of the effluent was lower at 4.17 mV, which had less influence on the downstream process, and was an ideal modifier. The contribution of various removal pathways to GSM removal was also explored through intermediate product analysis combined with variable control experiments. The experimental results showed that the enhanced removal of GSM was attributed to the enhanced capture of GSM by PDADMAC-modified MNBs and the enhanced oxidation of GSM by PDADMAC-modified MNBs. At the same time, the removal efficiency of this process in natural waters decreased by <5 % only. This study could provide data and theoretical support for the enhanced removal of olfactory compounds by modified MNBs for application in practical engineering.