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 TM 55-1925-273-10-1
OPERATOR'S MANUAL
INLAND AND COASTAL LARGE TUG (LT)
THEORY OF OPERATION
MARINE SANITATION DEVICE
GENERAL
The Marine Sanitation Device (MSD) receives, treats, and discharges all sewage generated aboard the LT. The system is
comprised of a vented media tank, chlorinator, wet well, discharge pump, and blower.
SYSTEM
All raw sewage from the water closets on the main deck and 01 level flows to the media tank (figure 1, item 1). Potable water
for flushing carries waste from the toilets to the media tank using 4" drain lines and 1 " vents.
The water level in the media tank is maintained at a constant level. As raw sewage enters the media tank via the 4" inlet
(figure 1, item 2), an equal volume of treated clear effluent is displaced into the spillover pipe (figure 1, item 3). This
effluent passes through the tablet chlorinator (figure 1, item 4), where it is disinfected.
As the water passes through the tablet chlorinator (figure 1, item 4), calcium hypochlorite tablets are dissolved,
releasing chlorine into the effluent. The amount of chlorine released is proportional to flow. A full feed tube (figure 1,
item 5) holds 20 five-ounce tablets, equaling 6.25 lb (2.83 kg). Expected tablet consumption is determined by water usage.
Leaking fixtures will greatly increase water usage and tablet consumption.
Clear and odorless water flows from the media tank (figure 1, item 1) through the spillover pipe (figure 1, item 3) and trap into
the wet well (figure 1, item 6). The wet well is a retention tank sized for adequate disinfection time during peak flow periods.
The wet well vent (figure 1, item 7) is open to the immediate environment. The disinfected water is discharged overboard by
the discharge pump (figure 1, item 8).
The discharge pump (figure 1, item 8) handles the peak flows expected for the system. The pump assembly includes a pump,
isolation valve, discharge pressure gauge, float switch for automatic operation, motor, and a motor starter. As the water level
in the wet well rises, the "pump on" float switch automatically starts the discharge pump, which discharges the water
overboard. When sufficient effluent is discharged from the wet well, the float switch stops the discharge pump.
A separate sewage holding tank holds sewage during maintenance or transfer of sewage or graywater to a shore connection.
Piping is provided to bypass the Marine Sanitation Device (MSD), sending sewage and graywater (wastewater system)
directly to the holding tank. Two pumps are provided for the sewage holding tank (SEWAGE DISCHARGE PUMP NO. 1 and
SEWAGE DISCHARGE PUMP NO. 2) so that the tank contents can be pumped overboard or to shore. A connection is also
provided between the MSD media tank and the sewage holding tank, allowing the contents of the media tank to be drained
by gravity to the sewage holding tank for maintenance.
0030 00-1
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