Technical Report

Spectrum Water Technology was asked to investigate methods of treating a Spent Caustic Stream at a US Refinery very heavy in Chemical Oxygen Demand (COD) and Total Recoverable Phenol (TRP). Initial testing revealed a COD concentration in excess of 350,000 mg/l, and a Phenol concentration in excess of 90,000 mg/l.

This particular waste stream was generated at a rate of 6.8 million gallons per year. The disposal contract was at a cost of $0.077 / gallon, creating a yearly expenditure of $518,918.40 for disposal.

The goal was to determine if this material could be fed to the wastewater system (Activated Sludge) at a prescribed rate.

Approach

Spectrum conducted an audit of the operating data for the previous 36 months determining the following: Influent and Effluent COD had a direct correlation, COD, Phenol, Ammonia and Sulfide removal were intermittently complete and highly dependent on influent loading, when influent Phenol loading was consistent effluent quality was consistent, and when Mixed Liquor Volatile Suspended Solids (MLVSS) was controlled to lower than 2800, more biological aggression was observed with regard to consistent effluent quality.

It was determined that this system could withstand higher affluent loading, specifically higher Phenol loading.

Recommendations were made for the control of Aeration, ortho-phosphate residuals and MLVSS concentration. A step feed program was created for the high strength spent Caustic Stream based on performance observed in historical data. Due to the then determined inconsistent Influent Phenol concentration, a specific Phenol Degrading bacterial blend (SBT 600C) was created and implemented on a daily basis. Spectrum Water's goal with the daily addition of bacteria was to compensate for the short term inhibition created each time the Phenol concentration lowered and spiked – which occurred almost daily. The inhibition was created by a continuing shift in the biological growth cycle, associated with inconsistent influent concentration.

As the program was started, the COD loading through the Equalization System increased by 27%, and the Phenol concentration increased by 120% as shown in Table 1.0.

Program Results:The COD loading to the system was increased significantly, an the Phenol loading more than doubled during the above compared periods. However, in both cases there was a reduction in the concentration of COD and Phenol in the wastewater effluent. Refer to Table 2.0 and Graph 1.0.

Summary:Through system study, manipulation, and the use of a bacterial blend created for aggressive Phenol removal, Spectrum Water Technology was successful in treating a high strength Spent Caustic Stream at a US Refinery. The cost of offsite disposal of the material prior to the Spectrum program was $0.077/gallon. The program costs allowed significant costs savings, to treatment costs of $0.019/gallon. The savings totaled $390,873.60 on a yearly basis.