Process optimization and mechanism revealing of KMnO4 pre-oxidation coupled powdered activated carbon adsorption for 2-MIB removal

Abstract

Taste and odor compounds such as 2-Methylisoborneol (2-MIB) have been a long-term challenge in drinking water treatment plants (DWTPs) and become increasingly concerning due to the implementation of stricter water quality regulations. The addition of powdered activated carbon (PAC) is one of the most effective approaches to control 2-MIB during cyanobacterial blooms. In this study, the process optimization of PAC adsorption and potassium permanganate (KMnO4) pre-oxidation was investigated and the mechanisms of the observed results were revealed. When the raw water was firstly pre-oxidized and subsequently treated by PAC, the adsorption of 2-MIB was not affected by the pre-oxidation, no matter whether the KMnO4 was depleted or remained. Even though the molecular weight distribution of the natural organic matter (NOM) was altered by the pre-oxidation, the trend of the NOM removal by pre-KMnO4/post-PAC was similar to that of the KMnO4 pre-oxidation, indicating that the KMnO4 did not affect the following PAC adsorption. When the raw water was added with PAC and KMnO4 simultaneously, the adsorption of 2-MIB decreased with the increase of KMnO4 dosage. The adsorption efficiency of NOM with smaller molecular weights (<3 kDa) decreased and that of NOM with larger molecular weights (>3 kDa) increased. It was found that the shrink of the micropore volume (but not surface functional groups) resulted in the negative effect on PAC by KMnO4. Therefore, the general recommendation to the DWTPs is that try to dose KMnO4 as early as possible so the remaining KMnO4 will not pose a negative effect on PAC for 2-MIB removal. Our study provides both practical guidance and theoretical fundamentals on the operation of DWTPs with KMnO4 pre-oxidation and PAC for 2-MIB removal.