Objective
In this project, microbial degradation of sodium dodecyl sulfate was successfully demonstrated as a new potential method to provide an environmentally-safe, cost and energy savings methodology for reducing surfactant emulsions while improving oil-water partitioning. Surfactant concentrations tested at 1000 parts per million were reduced over time and degradation rates were calculated. Pseudomonas aeruginosa was a successful bacterial candidate for sodium dodecyl sulfate degradation but not Pseudomonas putida, Bacillus subtilis, or Bacillus cereus. Pseudomonas aeruginosa was capable of efficiently degrading sodium dodecyl sulfate but not sodium dodecylbenzenesulfonate nor nonyl phenoxypolyethoxylethanol, in culture or in agar plate challenges.
Technical Approach
To accurately measure the degradation rates of sodium dodecyl sulfate by Pseudomonas aeruginosa, a consistent sampling and analytical technique was required. A final, repeatable sampling method was developed where sample removal, centrifugation, supernatant removal, and a heat-kill step of the supernatant was used to completely eliminate all remaining Pseudomonas aeruginosa. Sodium dodecyl sulfate biodegradation concentrations were analytically measured by liquid chromatography-mass spectrometry. These methods overcame surfactant solubility issues associated with freeze-thaw analysis, filtration, and centrifugation, which are standard methods to isolate microorganisms from analytical samples.
Results
The pH and media effects of sodium dodecyl sulfate bio-degradation by Pseudomonas aeruginosa at pH 6.1, 7.1, 8.1, and 9.1 resulted in a general trend of increasing sodium dodecyl sulfate (SDS) degradation rates with increasing pH. Results show a pH dependent relationship where the degradation rates of sodium dodecyl sulfate by pseudomonas aeruginosa vary from 4–7 parts per millions of surfactant per hour. Additionally, a color change was noted for each culture likely due to a change in the chromophore expression or redox environment at elevated pH and 1000 parts per million SDS. Additional experiments regarding chromophore expression or redox activity are warranted.
Benefits
Future experiments will include continued bacterial de-emulsification of a simulated bilge water as well as “real” bilge water. For these experiments, the project team will identify and analyze any temperature and salinity effects associated with bilge water de-emulsification. Additionally, the project team plans to isolate and identify microorganisms currently surviving in on-ship bilge water that have seemingly adapted to the emulsion environment.