Oily wastewater generated during various maintenance and operational activities of Navy and other ships cannot be discharged at sea without reducing the oil content to less than 15 parts per million (ppm) to meet the International Maritime Organizations Marine Pollution Convention (MARPOL) oil discharge provision. This causes the ship to hold these oily wastes until they can be off-loaded in port.
The overall objective of this project was to demonstrate a low maintenance, biological process for onboard treatment of bilge water to meet the 15 ppm MARPOL oil discharge provision in which the oil contaminants are completely degraded to carbon dioxide and water.
A new technique, forced molecular evolution, was used to cultivate enhanced optimized microorganisms needed for a robust, high throughput, biological process with performance, size, and maintenance characteristics suitable for shipboard deployment. The method included: (1) a whole-cell, mutagenic selection technique to rapidly cultivate broadly non-specific bacterial strains tailored to the pressures imposed by the wastewater and (2) a genetic enhancement technique to further optimize and tailor the degradation capability of the selected bacterial strains. The project also developed a new bioreactor to treat the bilge water to meet the MARPOL discharge requirements by retrofitting existing oil/water separators (OWS) to achieve the high oxygen rates and reduce the costs of implementation.
This project focused on the development of kinetically-enhanced, optimized microorganisms that were tailored for the onboard treatment of bilge water. The consortia of these organisms were developed using the techniques of forced molecular evolution that involved mutagenesis selection and genetic enhancement to tailor the degradation capability of the selected bacterial strains. The selection studies were carried out using both batch and continuous culture. A portion of the inoculum for continuous culture was comprised of mutagen-treated microorganisms. The selection pressures were sequentially increased in a bioreactor to the maximum levels expected in bilge water. For genetic enhancement, the Nah genes were shuffled. As much as 97 percent of the oil contaminants in simulated bilge water containing 3 percent oil were biodegraded at a residence time of 20 hours. The goal of reaching a discharge oil concentration of 15 ppm was not achieved, although a further increase in the degradation rate could be accomplished by the introduction of different catabolic plasmids. This project was completed in FY 2001.
Microbial consortia are now available for the treatment of bilge water and for wash rack and wash down waters from Department of Defense (DoD) maintenance facilities. In addition, a small pilot plant bioreactor system is available to evaluate various wastewaters. The potential savings to the DoD for the long term are about $25 million annually, with about 10 percent related to a reduction in maintenance costs and 90 percent related to a reduction in the costs of disposing of the separated oil.