SMALL FLOW WASTEWATER TREATMENT TECHNOLOGY FOR DOMESTIC AND SPECIAL APPLICATIONS 1089
and may reach beaches, commercial fisheries, shell-fish
growing areas and may seriously contaminate the waters,
thereby rendering them dangerous for public water supplies
and water contact sports. Contamination may also seriously
affect the commercial fisheries and the shellfish industry.
The discharge in territorial waters of the United States
is regulated by the Clean Water Act.^40 This Act also speci-
fies allowable types of marine sanitation devices (MSD), and
mandates, that the US Coast Guard test the various types of
MSD and certify them for use aboard water craft. These tests
are found in 33CFR 159, page 492, 500 and 501. 41,42 Type
I MSD utilize macerator and disinfection. Both commercial
disinfectants and onsite electrochemical devices are included.
Type II MSD include biological treatment or fiber filtration
(microscreening). Type III MSD consists of storage tank.
Sewage equipment for use aboard watercraft is already
available in the form of (1) maceration-disinfection devices,
(2) holding tanks and recirculating toilets, (3) incinerator
devices, and (4) chemical and biological treatment facili-
ties. A brief discussion of these systems is given below. For
details on manufacturers, cost and unit variations, readers
are referred to several sources in the literature. 43 – 49Maceration-Disinfection DevicesMaceration-disinfection devices utilize a mechanical macera-
tor to grind the human fecal wastes, mix a disinfecting chemi-
cal (usually hypochlorite) and retain the disinfected sewage
mixture for a brief period before discharging it into the water.
A number of companies manufacture such units for installation
aboard virtually every type of watercraft. Such units are small,
lightweight, and relatively easy to install. However, their per-
formance in terms of BOD and suspended solids reduction,
and degree of disinfection achieved may be questionable.Holding Tanks and Recirculating ToiletA holding tank is a closed container for retaining sewage
onboard a watercraft until it can be properly emptied, usu-
ally into an onshore sewage receiving facility. Holding tanks
include chemical toilets, recirculating flush toilets, classic
holding tanks, and any variation which simply retains the
sewage for later disposal at an appropriate site.
One potentially useful variation of the holding tank is
the recirculating flush toilet. This device requires a small
amount of precharge of chemically treated water in the reten-
tion tank integrated into the toilet design. Waste deposited in
this toilet accumulates in the retention tank. For subsequent
flushing, an internal separation mechanism recovers a frac-
tion of this precharge/waste mixture for continued reuse as
flushing fluid. The tank retains sewage from 80 to 100 toilet
usages before it must be emptied. It uses minimum space
and requires no water for flushing.
Although holding tanks completely prevent the discharge
of sewage from watercraft, they require extensive shore sup-
port facilities for emptying and cleaning. Low flush and
vacuum flush toilets are desirable because they minimize
storage and treatment requirement.^34Incinerator DevicesAs described earlier, several types of incinerating toilets have
been developed to reduce human waste to a small amount of
ash. The most common problems encountered with incinera-
tor devices with watercraft include the difficulty of supplying
electrical power as most small craft do not have the generat-
ing equipment required. If gas or oil burner type incinerators
are used, space is also required. Such burners also provide
fire hazards if improperly designed. Regardless of the type
of fuel used, however, burning of human wastes may result
in emission of odor from the venting stack.Chemical and Biological Treatment PlantsWastewater treatment plants similar to those frequently used
for land-base sewage treatment have been adopted for vessel
use. The mot successful of the biological treatment systems
are the extended aeration activated sludge process.^48 Attempts
have been made also to adapt thermally heated aeration sys-
tems for increased biological activity. Trickling filter-type
biological treatment systems with forced air aeration have
also been adopted to shipboard applications.^18 These sys-
tems, which provide treatment to all waste streams gener-
ated aboard the watercraft, are relatively large and heavy,
and easily upset due to change in salinity of flush water.
Among the chemical systems, an electrochemical floata-
tion plant for shipboard waste treatment was designed and
built. 49,50 This system utilized chlorine gas for disinfection,
and partial oxidation and flotation of organic matter. Another
chemical process oriented system utilized a comprehensive
approach to the management of wastewater on board ship
and is concerned not only with an improved treatment but
also with an innovation and improved collection system.
The system employs two main elements: (1) a recirculating
chemical toilet, and (2) an evaporation system for solid/liquid
separation. 31,51 – 53 Condensed liquid is discharged overboard
after chlorination. Concentrated sludge is stored for subse-
quent disposal to shore facility or into unrestricted waters.COMMERCIAL AIRCRAFTUntil about 1940, waste management problems aboard air-
craft were considered minor; human wastes were simply dis-
charged overboard. In January of 1943, the US Public Health
Service published the “Sanitation Manual for Land and Air
Conveyance Operating in Interstate Traffic,” which formu-
lated policy regarding “Discharge of Wastes from Conveyance
En Route.”^54 Following this publication, the International
Sanitary Convention for Aerial Navigation issued a publica-
tion in February, 1945, forbidding aircraft to throw or let fall
matter capable of producing an outbreak of infectious dis-
eases.^55 Federal laws and regulations now prohibit air-planes
indiscriminately discharging untreated human wastes.^56
Early waste management practices for aircraft included
carry-out pail methods of waste collection within aircraft
and hand-carrying them to the ground servicing facilities.C019_002_r03.indd 1089C019_002_r03.indd 1089 11/18/2005 11:06:46 AM11/18/2005 11:06:46 AM