Challenge

In 2007, a large refiner contacted Siemens Water Technologies for assistance with reduction of selenium below a 12ppb discharge limit.  The refining of crude oil can result in wastewater selenium concentrations above state and federal guidelines. The customer analyzed multiple point sources within the facility and determined that the main contributor of selenium was the sour gas stripper.

Siemens was contacted to design a treatment system capable of consistent compliance with the selenium discharge requirements.

Solution

Siemens considered various technologies for both point source and total effluent treatment to achieve the goals.  Membrane treatment was evaluated but not selected due to high temperatures and organics at the unit operation.  Co-precipitation of selenium was identified as the best alternative for tertiary treatment after interfering compounds were removed by existing facility unit operations.

Siemens provided mobile clarification systems ideally suited for pilot testing. The mobile clarification system is a self-contained, trailer mounted unit which features Actiflo® technology. The patented Actiflo® technology uses microsand as a seed to enhance floc formation and increase settling rate. The microsand promotes production of higher quality effluent than other types of clarification systems, and is ideally suited for treatment of difficult raw waters. Pilot testing reduced total selenium below the permitted limits.

The treatment process recommended by Siemens was confirmed in pilot testing and the customer expanded the application to a full scale installation hat continues to meet their discharge requirements effectively and efficiently.

Results

The customer was able to try a new treatment technology on a temporary basis using Siemens’ mobile assets. This enabled actual site results to be demonstrated before the customer proceeded to contract for a full-scale system.

The customer was able to consistently and reliably meet wastewater discharge requirements, thereby avoiding liabilities from US local, state and federal authorities.

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