Integrating photochemical vapor generation with photo-oxidation trapping for effective mercury removal from polluted water and its on-line monitoring

• Photochemical vapor generation is used for mercury removal from polluted water.
• Photo-oxidation is used for trapping the removed mercury onto a quartz tube.
• An atomic fluorescence spectrometer is used for sensitive on-line monitoring.
• It could be useful in treating slightly mercury-polluted water for drinking in the field.

A new system was constructed and its performance evaluated for simultaneous mercury removal from water and on-line monitoring. The system consisted of a photochemical vapor generator (Photo-CVG, for mercury removal), a photo-oxidation trapping reactor (for collection of removed mercury) and a commercial atomic fluorescence spectrometer (AFS, for on-line monitoring). In the presence of organic acids, inorganic Hg(II) was converted by UV irradiation to mercury cold vapor in the Photo-CVG, which was then rapidly separated from the water sample in a gas-liquid separator (GLS) and transported to the photo-oxidation trapping reactor by air or argon for collection of the removed mercury and subsequent on-line monitoring by AFS for early-warning of mercury vapor leak to the environment. The factors affecting the efficiencies of cold vapor generation, transport, collection and on-line monitoring were carefully investigated. Under the optimized conditions, a limit of detection of 0.003 μg L− 1 was obtained for the proposed system by using only formic acid. Meanwhile, both the efficiencies of mercury removal and collection can be even close to 100% in the mercury concentration range of 2–100 μg L− 1. The proposed system provided a safe, green, complete, simple and fast yet inexpensive method for low concentration mercury removal and on-line monitoring.