PRIMA conducted a series of screening level column tests to evaluate the ability of Sulfur Modified Iron (SMI) to remove selenium from refinery wastewater. Results of the study led to the performance of pilot-scale tests at two sites.
Effluent from sour water (SW) strippers and other wastewater streams from oil refineries is often impacted with selenium at concentrations of 1 mg/L or higher. Existing removal methods include iron co-precipitation and biological removal, which may be expensive, produce large amounts of sludge, or require a large footprint. SMI (also known as SeleniumZero) is a granular media known to remove a variety of contaminants from water through physical and/or chemical means.
PRIMA conducted small scale (1″ diameter by 4″ tall) column tests on nine wastewaters from four refineries. The wastewaters were used “as received” or pre-treated. Tests ran for about 120 bed volumes with an empty bed contact time (EBCT) of 10-20 minutes. Selenium removal efficiency was highly dependent on the wastewater, ranging from poor removal to 100% removal (see Table). Based on the results of the screening level tests, field pilot tests were conducted at Site A (SW-A water) and Site B (SW-B water). Both pilot tests used 2″ diameter by 40″ tall columns, a 5 minute EBCT, and no pre-treatment. For Site A, influent selenium 0.65-1.2 mg/L, while effluent selenium was < 0.005 mg/L for the duration of the 6 month test. The resulting capacity was over 12 mg Se/g SMI. For Site B, influent selenium was 0.85 mg/L and effluent was below 0.005 mg/L for the 3 week test.
Results of this work were presented at the 11th International Conference on Remediation of Chlorinated and Recalcitrant Compounds (Battelle, 2018, Palm Springs, CA). For more information about discuss column testing, contact Cindy Schreier, PRIMA Environmental, Inc. For more information about SMI / SeleniumZero, contact Pete Santina, PE of SMI-PS, Inc. at pete@smiwater.com or 916-345-0254.
Table 1. Results of SMI Screening column Tests.