The client contacted Steward for support to meet their target for effluent mercury concentration levels of 1.3 ppt. The client had an existing water treatment system that reduced their mercury concentration to single ppt levels but it could not achieve their target level of 1.3 ppt or lower.

To properly address the problem Steward had to utilize EPA test method 1631: Measurement of Mercury in Water by Oxidation, Purge and Trap, and Cold Vapor Atomic Fluorescence Spectrometry. This test method allows measurements down to 0.5 ppt. Steward’s Cold Vapor Atomic Fluorescence (CVAF) unit from Tekran was used for this test method. The validity of analysis data was confirmed based on the good MS% (matrix spike recovery %) and RPD% (relative percentage difference). However, when the client samples were measured by Steward, they were higher than reported by the client. The client reported mercury concentration of 2.8 ppt but the Steward measurements were 4.5 ppt. This difference may be due to the relative long period of storage in an unpreserved and non-fluoropolymer or glass bottles. The samples were sent in HDPE bottles.

The pH of the sample was measured as 6.7. No pH modification was necessary since the pH was well within the working range of SAMMS. To test for SAMMS treatment the liquid to solid ratio was 200:1. After the 6 minute general kinetics test, the mercury concentration was reduced to 0.7 ppt as shown in Figure 1.

FIGURE 1. Mercury Concentration

Based on the success of the bench scale testing Steward has proposed to conduct a field test at the client’s facility using our contactor tank system and membranes for SAMMS retention. The systems have been effectively utilized in other field tests. Further testing with this client can prove the effectiveness of SAMMS and the contactor tank systems for mercury reduction to ultra low concentration levels.