The BOWTS shore-side systems have successfully operated at Naval Shipyard Long Beach, Naval Air Station Alameda, California; Fleet Industrial Support Center Oakland, California; Naval Station Pearl Harbor, Hawaii; Naval Station Guantanamo Bay, Cuba; Naval Station Guam; Naval Station San Diego, California; Submarine Base San Diego, California; Naval Construction Battalion Center, Port Hueneme, California; and the Naval Station Roosevelt Roads, Puerto Rico. Mobile systems also were shipped to Yokosuka and Sasebo Japan in September 1999.

The ship's bilge water is transferred to a large load equalization tank, equipped with a skimmer for removal of bulk free product. After sufficient residence time, the water fraction is selectively removed and fed through a plate coalescer for mechanical removal of free oil. The water then passes through mixing chambers where chemical treatment is performed.

Three chemical metering pumps feed a reverse emulsion breaker, sodium hydroxide, and anionic polymer into the mixing chambers to breakdown the emulsion, precipitate the heavy metals, and floc the solids. The effluent is then pumped into an induced-air flotation unit, where all the solids generated by the process are removed. Two slop oil tanks are provided for collecting the free oil separated in the load equalization tank and the oil/water separator, and a sludge tank is provided for holding the sludges collected in the oil/water separator and the induced-air flotation device. The water fraction leaving the system will be of sufficient quality to be discharged directly into the sanitary sewer.

Although the pollutants found in ships' bilges and other oily wastewaters vary from ship to ship, NFESC applied a strategy to categorize and quantify the principal pollutants. The data collected were used in designing the basic BOWTS. Additional process units could be added where local discharge requirements indicate the need for more rigorous treatment than is available from the basic system design.

The compliance benefits listed here are only meant to be used as general guidelines and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g., the amount of workload involved.

Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing this technology.

• BOWTS can recover oil for recycling.
• BOWTS is a proven off-the-shelf technology.
• The system is sufficiently flexible to accommodate a wide range of concentrations and flow ranges; each system can be tailored to site-specific requirements (e.g., configuration and modifications).
• The BOWTS requires only one or two people to operate and monitor the process.

• Not an economical alternative for activities generating less than one million gallons of ship’s bilge and oily wastewater annually.

Assumptions:

• The system processes 15 million gallons of wastewater annually.
• Traditional methods require transport of large volumes of oily wastewater for treatment/disposal at a cost of $0.24/gallon.
• Cost figures for the BOWTS system are actual budgetary allocations for each activity provided by Naval Station San Diego.

Table 1. Cost Comparison for BOWTS System vs. a Traditional Disposal System

Economic Analysis Summary:

• Annual Savings for BOWTS: $3,060,000
  
• Capital Cost for Diversion Equipment/Process: $1,400,000
  
• Payback Period for Investment in Equipment/Process: < 6 months

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