Evolution of low molecular weight organic compounds during ultrapure water production process: A pilot-scale study

This study evaluated the evolution of low molecular weight organic compounds in ultrapure water (UPW) production using a pilot-scale UPW production system and an ultrafiltration–reverse osmosis (UF–RO) system. During UPW production, a dissolved organic carbon (DOC) removal efficiency of 99.4% was achieved with a feedwater DOC level of 1.42 mg/L. The pretreatment, make-up, and polishing stages accounted for 85.3%, 13.7%, and 0.4% of DOC removal, respectively. Urea, trichloromethane, and dibromochloromethane persisted throughout UPW production process, contributing 24.7%, 9.2%, and 22.6%, respectively, to the final effluent DOC level of 8.1 μg/L. The pretreatment and make-up stages of the UPW production process could remove N-nitrosodimethylamine, chloral hydrate, dichloroacetonitrile, and tribromomethane. The UF–RO system could remove approximately 90% of DOC. However, the proportion of halogenated disinfection by-products (DBPs) in the DOC increased by 1.4–4.5 times in the RO effluents. RO could completely reject haloacetaldehydes. However, RO could not completely remove trichloromethane, tribromomethane, bromodichloromethane, and dibromoacetonitrile, which remained the main halogenated DBPs in the RO effluents. [Display omitted] •Revealed evolution of low molecular weight organic compounds in ultrapure water (UPW) production using a pilot-scale system.•Evaluated the removal efficiency of the main units towards typical organic compounds in UPW production.•Determined contribution of urea and halogenated disinfection by-products to dissolved organic carbon in UPW production.•Illustrated removal characteristics of reverse osmosis towards typical organic compounds in UPW production.