Case

Cleanit LC cleans a California city's well water

Höganäs conducted a pilot study to assess the treatability of a California city’s well water by the Cleanit® LC process for hexavalent chromium [Cr(VI)] removal.

The Cleanit LC pilot system operated for 280 days and treated over 47,000 bed volumes (BV). The well water quality contained concentrations of Cr(VI) of 40 ±6.7 μg/L including the presence of arsenic (As), uranium (U) and nitrate. The study was divided into two phases: (1) Phase 1, steady-state operation and (2) Phase 2, simulated disrupted operation. Performance of each phase can be summarized as follows:

Phase 1: Steady-state operation

During the 6 month, uninterrupted validation, the major operational parameters for the water treatment system were: empty bed contact time (EBCT) of 7.5 minute for each Cleanit column; regular backwash (BW) conducted every two days; and media reconditioning (MR) every three weeks. These operational parameters effectively maintained the performance of the Cleanit process in completely removing the target contaminant Cr(VI) and total Cr to below the method detection limit (MDL) of 0.05 μg/l throughout the study period. The presence and removal of co-existing contaminants such as As, U and nitrate did not have any negative impact on Cr(VI) removal performance of the system. One of the benefits of the Cleanit process is multiple contaminants removal in a single step process. This has been proven in this study by the concurrent removal of As and partial removal of U and nitrate. Complete U removal is attainable using the Cleanit process, but would require a longer EBCT.

Phase 2: Simulated disruption operation

The five planned disruption events of phase 2 included; extended shut-down, fluctuations in flow rate (0.5 – 1.5 times the designed flowrate), random shut-down events, fluctuations in pH (6 – 9 pH) and spikes of influent Cr(VI) concentration (100 and 200 μg/L). There were no negative impacts on performance of the Cleanit process for Cr(VI) removal throughout the disruptions. Lower pH conditions resulted in enhanced As and U removal.

Competing technologies my only reduce contaminants from there oxyanion state to a more reduced state only to potentially re-oxidize downstream of the process. With both reductive and adsorptive properties, the Cleanit system consistently removed Cr(VI) and total chromium (Cr) to levels of non-detect. Concentrations of other co-contaminants including As, U, and nitrate in the final effluent were also under MCL values. Leaching tests of the used Cleanit media suggested that the used media was not a Resource Conservation and Recovery Act (RCRA) hazardous waste, and could be shipped back to Höganäs facility for reuse or recycling, which confirmed the “Green” aspect of the Cleanit technology.