T.S. Patriot State Engineering Manual

Patriot State was the training ship of the Massachusetts Maritime Academy from 1986 to 1998.

Marine Sanitation Device

The training ship is equipped with a Marine Sanitation Device (MSD) in in order to treat sewage and waste water before it is discharged overboard.

Fixed activated sludge treatment (FAST) biologically oxidizes the organic matter in sewage and produces a clear odorless effluent. This effluent is disinfected by chlorine and is automatically pumped overboard. No chemicals or additives are required.

Raw sewage enters the media tank through the inlet; biological treatment takes place in the media tank. The water level in the media tank is constant. As sewage enters, an equal volume of clear effluent discharges through the spillover into the wet well. The spillover utilizes a water seal to isolate the wet well from the media tank. Chlorine is injected in the wet well by the chlorine pump. Treated and disinfected water flows overboard.

Detailed Description

The basic unit is set-up for gravity flow operation using an external air supply. The unit incorporates a liquid chlorinator, air pressure regulator and orifice plate. The air pressure regulator is adjusted to regulate air from the external space to 3.5 psi.

Biological oxidation takes place in the media tank. The bacteria naturally attach themselves to the large surface area provided by the media. The air lifts circulate the sewage to the bacteria and transfer oxygen into the water. The water level is constant. At the top of the tank is an air gap of 9" or more.

The media is assembled into blocks by corrugated sheets of PVC, which provide flow channels and a large surface area for microbial growth.

Air lifts are vertical pipes which extend from below the media to above the waterline. Compressed air is injected near the bottom of each air lift, which act as high volume pumps within the media tank. The air bubbles transfer oxygen into the water as does the splashing action above the water line. This aeration is critical to the process. The turbulent flow from the air lifts also throws foreign objects to the sides and ends of the media tank and prevents foreign objects from clogging or interfering in the process.

At the bottom of the media tank is a PVC hose assembly with holes drilled on the underside at regular intervals. When compressed air is routed to the air scours, the air bubbles break up the accumulated sludge permitting removal of the sludge from the tank.

A standpipe gravity spillover is installed in the media tank to feed the wet well. As sewage enters the media tank, an equal volume of treated water is displaced through the spillover gravity connection to the wet well. The spillover is equipped with a water seal to prevent venting of the media tank air through the wet well vent, which is located at the top of the well and vents directly to the spacing. The wet well is an independent tank. Clear and odorless water flows from the media tank through the spillover pipe into the wet well. The wet well is a retention tank, sized for adequate disinfection time during peak flow periods. The wet well vent is open to the immediate spacing. The wet well is discharged by duplex discharge pumps. Each is rated for 100% duty, ergo one pump is selected as the "duty" pump and the the other as "standby." If the duty pump malfunctions, the water level in the well reaches the "high level" float switch, automatically starting the standby, which will pump until the wet well level reaches the "pump off" float switch which turns the standby pump off.

The liquid chlorinator is a separate unit which consists of the pump, chlorine tank and associated suction and discharge hoses and fittings. The discharge from the chlorine pump is injected in the wet well tank. The pump is cycled on and off by the discharge pump auxiliary contacts. Whenever the discharge pump runs the chlorinator pump runs. The chlorination feed rate is adjustable from 10% to 100% of the chlorine's pumps open discharge rating via the calibrated knob found on the side of the chlorine pump housing.

D-8 Marine Sanitation Device Specifications
     Manufacturer:                Marine Systems Division of St. Louis Ship
     Average Capacity:            12,180 G.P.D.
     Peak Capacity:               15,225 G.P.D.
     Max. angle of Pitch:         15°
     Max. angle of Roll:          15°
     Date Passed by Coast Guard:  March 28, 1984


MSD Start-Up

  1. Close all air and water valves
  2. Fill media tank with water (use the same water source, if possible, as used for sanitary) fill media tank until water spills into wet well and reaches a level one half way up the wet well sight glass
  3. Set-up for normal operation as specified above
  4. Start compressed air supply
  5. Bleed air out of centrifugal pump casing
  6. Gradually add more water to media tank and check for proper cycling of pump(s)
  7. Set chlorine pump on automatic and check for proper cycling, fill chlorine storage tank with liquid disinfectant and prime chlorine pump with water
  8. Open sewage valve to media tank

MSD shut down

If the system will be inactive for more than two weeks, long term lay-up is needed, for less than two weeks leave the system on line.

MSD long term lay-up

  1. Secure all flow into the media tank
  2. Secure chlorine metering pump, drain chlorine pump and holding tank
  3. Flush media tank
  4. Isolate wet well, pump contents in wet well overboard
  5. Air scour media tank for two hours and pump contents into suitable receiving facility
  6. Refill media tank with water, air scour for 30 minutes and pump overboard
  7. Add anti-freeze to media tank if water must be left in the tank
  8. Secure electrical power
  9. Drain all piping, fitting and traps containing water

Direct comments to William Haynes whaynes@maritime.edu
Mon, Jul 1, 1996
TSPS Engineering Manual ©1995 Massachusetts Maritime Academy