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 2.2.2 SEWAGE TRANSPORT PUMPS AND DISCHARGE SYSTEMS. CHT pumps are electric-
motor-driven, non-clog marine sewage pumps, connected in parallel. Rated
capacities per pump and ship sewage discharge rates are shown in Table 2-1.
Generally, one pump will have sufficient capacity to transfer the sewage
flow arriving at the CHT tank it serves, with the other pump acting as standby.
However, in case of high flows, both pumps will operate to increase the rate
of sewage discharge. For example, ships arriving from sea duty, with sewage
in holding tanks over the 60% level, will have both pumps running during the
first transfer operation. Flow rates of about 150% of the single pump flow
rate should be expected during these operations.
Waste water pumped from CHT holding tanks flows under pressure to dis-
charge risers which are fitted with full port ball or plug valves, and the
male portion of a cam-lock, quick connect/disconnect hose coupling. The dis-
charge risers, in most cases, are conveniently located on both sides of the
ship on the weather deck. Sewage pressure pipes run athwart the ship to
interconnect the risers. Thus, most vessels are equipped to discharge sewage
from port or starboard, depending upon which is alongside of the pier. This
piping arrangement also permits nested surface ships to connect their sewage
risers together by hoses so that sewage may be pumped from outboard ships
through the piping systems of inboard ships to the pier sewer. Since several
interconnected ships can pump at the same time, rates of sewage flow coming
ashore from nested ships may at times exceed flow rates from single large
vessels.
2.2.3 MSD's. Combatant ships and service craft outfitted with MSD's will
operate in a manner similar to the CHT arrangement discussed above. By defi-
nition, an MSD is any equipment for installation on board a vessel that is
designed to receive, retain, treat, and discharge sewage. Existing systems
rely on a reduced flush process to minimize the volume of liquid to be handled,
and on a liquid incinerator to reduce the concentrated sewage to a sterile
ash. Other types of systems store the concentrated waste volumes, and period-
ically transfer them to shore for disposal. The following wastewater/waste
management systems are in service currently on board U.S. Navy vessels:
a. Collection, Holding and Transfer. This system provides no treatment.
CHT is a method of collecting and holding wastewater until it can be trans-
ferred to a suitable facility for treatment in port or discharged overboard at
sea.
b. Sewage Discharge Connection. This is a topside fitting aboard sub-
marines designed to connect holding tank discharge to a shore collection
facility.
c. Drydock Industrial Wastewater Alterations. This is a physical treat-
ment system designed to remove suspended solids from wastewater generated dur-
ing drydock operations. Settling tanks are utilized for removing sediment,
and a filtration system is used for removing suspended solids. The water is
discharged overboard or to a pier collection facility.
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