CH2M HILL conducted a recent study with a refinery in Southern Europe to identify main sources of selenium in the process waste streams sewer system. The study helped determine which treatment technology effectively reduces selenium below target levels to meet regulatory standards.

By: Mauro Marinetti, Ph.D., P.E., CH2M HILL and Kar Munirathinam Ph.D., Principal Technologist, CH2M HILL

Mauro Marinetti’s paper “Selenium Removal from a Refinery Wastewater: Integrated Approach from Source Control to Wastewater Treatment” will be presented by co-author Kar Munirathinam,CH2M HILL, on Tuesday, October 8 at 10:30 a.m. in TS303, during the Water Environment Federation Technical Exhibition and Conference (WEFTEC), in Chicago, Illinois. Learn more about CH2M HILL’s WEFTEC 2013 participation and technical sessions.

Many of the activities involved with oil refining and mining release selenium, a naturally occurring element present in organic-rich marine sedimentary rocks as well as fossil fuels such as coal and oil. To comply with environmental regulations, refineries must properly treat wastewater to remove selenium and other hazardous chemicals before treated water is drained into nearby aquatic environments.

Interested in identifying alternatives for treating wastewater, a refinery located in Southern Europe initiated a study to review its existing wastewater treatment system to determine immediate, mid, and long term actions to improve operations at its existing wastewater treatment system (WWTS).

The study evaluated the existing WWTP, composed of three main components:

  • a sour water stripper column treating the sour water followed by an ozone contact column oxidizing the sour water stripper bottoms to eliminate phenols
  • two API separators treating the main refinery waste streams
  • two Induced Air Flotation units treating all the wastewater before the discharge

After assessing these components, selenium was identified as one of the primary roadblocks for complying with regulatory standards. Selenium occurs in wastewater discharges in various oxidation states and chemical forms. Each chemical form varies in terms of its treatability characteristics, toxicity and bioaccumulation potential. To adequately treat refinery wastewater, a good understanding of the speciation of selenium is critical.

Given the refinery’s process sewer system, CH2M HILL proposed not to follow the “end of pipe” philosophy for the selenium removal, but rather to explore the possibility of treating at the source with low flow and high selenium concentration. This process requires a rigorous step-by-step methodology and gradual evaluation approach, involving the following steps:

1)      An initial analytical campaign to identify waste streams, which contributes most to the total selenium load. These results (total selenium only) provided insight to perform an overall mass balance of the entire WWTS of the refinery and to run simulations to identify the best treatment strategy.

2)      Experimental phase to characterize the speciation pattern of the high selenium content waste streams, to identify feasible treatment technology and achievable removal efficiencies.

3)      Conceptual design and development of the Front End Engineering Design (FEED) of the selected technology, verify the technology in parallel with appropriate capacity pilot scale testing with the objective of improving the quality of the WWTS final effluent during the period of confirmation testing (i.e. immediate solution to the problem while optimizing the operation of the treatment technology at pilot scale).

Overall, the pilot plant study helped the refinery identify ways to optimize its operating conditions by developing an integrated approach to effectively remove selenium from its wastewater. Study results allowed for design of a plant treating 1/5 of the “end of pipe” flow rate (reducing therefore the size of the plant) and helped the refinery to develop a design parameter for the full - scale treatment plant, taking into consideration optimal chemical doses, operating pH, chemicals consumption rate, and sludge production to improve selenium removal.

Dr. Mauro Marinetti has 12 years of experience in water and wastewater treatment, both for municipal and industrial application.  He is the Process Leader of CH2M HILL’s Milan office and the water sustainability coordinator for the Europe Region. Marinetti has a doctorate in Environmental Engineering from Politecnico di Milano, Italy and is a Registered Associate Italian Engineer.

Dr. Munirathinam, a CH2M HILL Principal Technologist, has more than 30 years of experience in treatability studies, process designs and coordination of detailed design of biological and physical/chemical treatment systems for treating waters and wastewaters laden with conventional and priority pollutants. He also specializes in start-up and commissioning of treatment plants providing process oversight and trouble shooting. He has his Ph.D. in Environmental Engineering from Oklahoma State University as well as two master’s degrees. Dr. Munirathinam also has experience as an associate and adjunct professor.