ENV-15-106 Novel Approach for Removing Selenium from Phillips 66 Ponca City, OK Refinery Effluent

Description:

The Phillips 66 Ponca City, OK Refinery (PCR) developed and implemented a novel, low-cost means of removing selenium (Se) from wastewater in order to meet new OPDES permit limits. It is well-known that Se, which is a component of the organic molecules in crude oil, is isomorphous with sulfur, is released in process units such as cokers, hydrotreaters, and fluid catalytic crackers, and hence is a constituent in refinery wastewater. After liberation from crude oil, Se accompanies the sour gas to the Sour Water Stripper (SWS), where it partitions and remains with the stripped sour water (SSW). Nearly all of the Se in a refinery wastewater is contained in the bottoms from the SWS. Because of new environmental permit requirements, PCR evaluated a number of candidate technologies for Se removal and selected co-precipitation for testing. The novelty of the approach is using co-precipitation in an existing, operating Activated Sludge Unit (ASU). Se from the SWS is oxidized in the ASU to selenite which sorbs onto the iron hydroxide created by adding (poly) ferric sulfate. Jar tests, short-term step tests, and two longer-term plant demonstration tests were conducted to determine the required dosage of ferric and poly ferric sulfate (PFS). Once sorbed onto the iron floc, the Se can be separated and managed with the biosludge. When iron sulfate is used as a coagulant aid, it improves the operation of the ASU by increasing the settleability of the sludge. The full-scale system was started up to meet a compliance date of Aug 1, 2014, and has now successfully operated below the new permit limits for more than a year.