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Liquid Waste (Gray Water) Disposal

Graywater is wastewater from drainage from dishwashers, sinks, baths, showers, laundry, and food preparation areas. It may include contaminants such as bleach, nitrates, oil and grease, sodium, suspended solids, bacteria, organic matter, be turbid, have a high pH, high water temperature, and have both a high chemical oxygen demand and biological oxygen demand. It is estimated that the amount of graywater produced is an average of 67 gallons per day per person (different studies give different estimated averages of graywater produced on cruise ships). This was originally potable water (drinking water quality) that has been used for the purposes identified above. Graywater does not include any drainage from toilets, urinals, hospitals, or animal spaces. The graywater goes through special pipes to holding tanks for different sources of the liquid. It may go through gross particle filters or grease traps prior to the holding tanks, depending on the ship, and may be discharged without treatment into the surrounding waters or it may be treated before discharge. The holding capacity aboard ship varies considerably from as little as 5 hours to as much as 90 hours. Except in Alaska, treatment of graywater is not required before discharge. However, it should not be discharged in port or within 12 nautical miles of shore. Untreated graywater from ships may contaminate the surrounding waters.

Best Practices in Controlling Contamination of Surrounding Waters by Graywater Discharge

  • • Establish Best Practices for the design, operation, and maintenance of systems for the treatment of graywater aboard ship before discharge.
  • • Establish or revise existing standards for the discharge of graywater to require: effluent that meets federal water quality criteria at the point of discharge and the mixing zone, and those required as secondary treatment standards by publicly owned treatment works; effluent standards that are attainable by use of the best available technology economically achievable; and effluent standards that eliminate pollutants of special concern.
  • • Require the use of advanced wastewater treatment systems aboard ship.
  • • Require periodic sampling and testing of effluent discharges by onboard ship monitors.
  • • Require that there be no discharge of untreated graywater within 12 nautical miles of shore or other potentially sensitive areas.
  • • Prohibit any non-compliant vessels or their sister ships from using port facilities under US jurisdiction.
 
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