TM 55-1925-284-14&P
OPERATOR, UNIT, DIRECT SUPPORT, AND GENERAL SUPPORT MAINTENANCE
MARINE SANITATION DEVICE FOR
INLAND AND COASTAL LARGE TUG (LT)
THEORY OF OPERATION
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 toilets 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 dis-
solved, 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.
0003 00-1
