Note: Descriptions are shown in the official language in which they were submitted.
CA 02538635 2006-03-02
SEWAGE TREATMENT SYSTEM FOR USE IN MARINE TOILET AND
OTHER REMOTE TOILETS
BACKGROUND OF THE INVENTION
1. Field of the Invention.
The present invention relates to a compact, unattended and cost-effective
sewage treatment system (STS) adapted to be installed and used aboard boats
and
in other remote toilet facilities where a conventional sewer system is not
available.
The system attains 100% microbial inactivation rate without the use of
chemicals,
salts, electric heaters, ultraviolet radiation or incineration. Unlike prior
art systems,
the system of the present invention operates totally unattended and
automatically,
doesn't require any mechanical maintenance or cleaning other than periodic
replacement of a phosphate filter and refilling of a denitrifying dispenser.
The system
also incorporates a full array of fault detection and diagnostic display. In
case of a
critical component failure, the system of the present invention will identify
the failed
component and will automatically shut down to prevent overboard discharge of
untreated sewage into the waters surrounding the vessel. Likewise, when the
phosphate filter media becomes saturated or the denitrifying dispenser is
empty, the
sewage treatment system will automatically shut down to prevent overboard
discharge of untreated sewage. During shut down the toilet will continue to
operate
and discharge into the boat's holding tank which will have to be emptied into
a
conventional pump-out station until the STS is serviced.
2. Description of the Related Art.
Marine Sanitation Devices (MSD) for boats have been developed to either (A)
disinfect the sewage while it is contained within a holding tank or (B) to
disinfect the
sewage flushed out of a toilet before it is pumped overboard. Some type "A"
MSDs
require the manual loading of chemicals like formaldehyde, or waste-digesting
enzymes, or biological additives or disinfectants like chlorine. Those using
waste-
digesting enzymes require a long digestion period to achieve a meaningful
reduction
CA 02538635 2006-03-02
2
of bacteria levels. Effectiveness of type "A" MSDs requiring human
intervention are
unpredictable and unreliable because they depend on the timely and accurate
loading
of specific additives into the sewage and accurately awaiting the proper
digestion
period before discharging overboard the contents of the holding tank. The
effectiveness of type "B" MSDs are also unreliable and unpredictable, because
their
effectiveness depends on periodic mechanical maintenance tasks, such as
cleaning
or replacing electrolyzing electrodes, or cleaning or replacing ultraviolet
light bulbs. If
these maintenance tasks are not carried out in a timely and professional
fashion, an
ineffective sewage treatment system may go unnoticed for long periods of time
allowing dangerous levels of live bacterial and viral organisms to be
discharged
overboard. In summary, prior marine MSDs share some of the disadvantages
described above. The long term effectiveness of some of the prior art MSDs is
compromised by either (1) their need for periodic and professional maintenance
and
cleaning, (2) because they lack the capability of automatic unattended
operation, or
(3) because they lack systems monitoring, fault diagnostic and automatic shut
down
capabilities.
For example, U. S. Patent No. 4,16, 281 to McPherson, et al. describes a
type B treatment system where final disinfection is carried out in a
chlorination tank,
thereby requiring human intervention to fill the chlorine tank.
U.S. Patent No. 6,207,047 to Gotheaux, describes a type B treatment system
where the raw sewage comes in contact with porous media inoculated with
nitrifying
aerobic bacteria which requires human intervention to replenish the
disinfecting
media.
U.S. Patent No. 5,433,842 to Morris, et al. describes a type a sewage
treatment system where the sewage in a holding tank is heated above the level
at
which coliform bacteria can't survive. A water conduit supplies heated water
from the
vessel's engine through the holding tank to heat the sewage. An electrically
operated
heating element is also mounted in the tank to be used when the engine is off.
This
system is very inefficient because after the sewage reaches the inactivation
temperature and presumably all bacteria has been killed, if a fresh charge of
raw
sewage material is received before the disinfected material is discharged
overboard,
CA 02538635 2006-03-02
3
the entire tank contents becomes contaminated and cooled again, requiring
additional
power to again disinfect the tank contents.
U.S. Patent No. 4,009,104 to Behrendt, et al. describes a type B sewage
treatment system comprising an electrolytic cell which converts the sodium
chloride to
form sodium hypochlorite by passing an electric current between a set of
electrodes.
There are two main disadvantages to this system: (1) the electrodes need to be
cleaned periodically or they will loose their effectiveness and worse, the
system
doesn't make the user aware when the electrodes need cleaning, and (2) the
sodium
hypochlorite contents of the disinfected sewage overboard discharge is toxic
to sea
organism within close proximity to the vessel.
A11 prior art MSDs including the ones referenced above can create a false
sense of security. The EPA standard for the best performing MSD (a Type It)
allows
a discharge of 200 fecal coliform per 100 ml, and the worst performing MSD (a
Type I)
allows a discharge of 1,000 fecal coliform per 100 ml. Furthermore, the EPA
requirements for MSDs doesn't include standards for other, more harmful
pathogens
found in natural abundance in human feces, such as Enterococcus and E. Coli.
Coliform bacteria do not usually cause disease. However, their presence
indicates
that pathogenic (disease-causing) organisms could be present such as
Enterococcus
and E. Coli. For health safety reasons, the effluent standard for all marine
sanitation
devices (MSD} should be changed from testing for Coliform to testing for E.
Coli or
Heterococcus.
Furthermore, these prior art MSDs only achieve partial disinfection of the
human waste prior to overboard discharging into the sea, rivers and lakes, and
do
nothing to eliminate or reduce other critical pollutants normally found in
human waste,
such as nitrates and phosphates. If these pollutants find their way into our
groundwater supply of drinking water they can be very harmful to humans.
Nitrates
are an unstable form of nitrogen formed during the decomposition of waste
materials,
such as human sewage. If infants less than six months of age drink water (or
formula
made with water} that contains more than 10 mg/L nitrate nitrogen, they are
susceptible to methemoglobinemia or blue baby syndrome. This disease
interferes
with the blood's ability to carry oxygen. Recent studies also suggest that
high nitrate
CA 02538635 2006-03-02
4
water may be linked to birth defects and miscarriages, so pregnant women
should
avoid drinking high nitrate water.
In aquatic ecosystems such as coral reefs, nitrates and phosphates are
nutrients that can cause diverse problems such as toxic alga( blooms and a
corresponding loss of oxygen, resulting in fish kills, loss of biodiversity
(including
species important for commerce and recreation), and damage to sea grass beds
and
reef habitats.
Obviously, treatment and disposal of sewage effluent into the environment is a
major problem today. In the marine environment, federal laws prohibiting
overboard
discharge of raw sewage inside a three mite coastal limit are often
disregarded by
boaters. Still today, a large number of U. S. marinas (private and municipal)
have no
pump-out facilities. Many boaters are unwilling to untie their boat from the
marina
slip, mooring or anchor and travel three miles just to empty their holding
tanks.
Sometimes unsettled weather prevents them from making this trip and with a
full
holding tank, they have no choice but to discharge overboard the contents of
their
holding tank. The U. S. Coast Guard, Marine Patrol and Harbor Police have
inadequate manpower to enforce antidumping laws inside the three mile limit,
and
even when they try, it is very difficult to determine which boat in the marina
or harbor
is the offending one. The result is that pollution of the waters in our
harbors,
anchorages and marinas continues to increase at an exponential rate. Due to
the
poor performance of prior art marine sanitation devices (MSD) which still
discharge a
significant count of Coliform (between 200 and 1,000 Coliform per 100 ml),
many
states have designated large bodies of water, both fresh and salt water, a Ono
discharge zone" (NDZ) in which overboard discharging is not allowed even when
the
boat's sewage was treated with a U. S. Coast Guard approved Type I or Type ll
MSD. Boats navigating a no discharge zone are required to retain sewage in
their
holding tanks until they are able to transfer the sewage to a Land based pump-
out
station. However, evidence shows that no discharge zones don't protect the
environment because there aren't enough operating pump-out systems to satisfy
the
need of the boating public. Because the boating public finds it is impossible
to
comply, most boaters navigating a NDZ simply ignore the law and discharge raw
CA 02538635 2006-03-02
sewage overboard. For example, the effectiveness of Rhode Island's NDZ was
tested
by Cruising World magazine and reported in their May 2001 issue. In September
1997 Rhode Island declared all of its waters -more than 244 square miles- a no
discharge zone. Cruising World investigators navigating these waters in the
spring of
2001 were totally unable to have the sewage in their holding tank -a week's
worth of
sewage- pumped-out at any shore side facility. Similar stories can be heard
regarding
other NDZ at other states across the nation.
Therefore, there is an obvious need for an onboard, compact, unattended
and cost effective marine sewage treatment system producing a discharge
effluent
which meets or exceeds the drinking water standards set by the U. S.
Environmental
Protection Agency (EPA) for Coliform, E. Coli, Enterococcus, Nitrates,
Nitrites, and
Phosphates, and that also meets or exceeds the effluent standards set by the
EPA
for a modem, municipal sewage treatment plant for biochemical oxygen demand
(BODS) and total suspended solids (TSS).
White the use of microwave energy in a device for sterilizing food products or
medical biological waste has been proposed, direct treatment of marine or
municipal
sewage with microwave energy to disinfect same has not heretofore been
proposed.
BRIEF SUMMARY OF THE DISCLOSED EMBODIMENT
The efficient, unattended and cost-effective marine sewage treatment system
of the present invention overcomes the disadvantages of the prior systems
described
above by providing a system that does not require a periodic mechanical
maintenance/cleaning schedule, by providing a system for detecting and
identifying
malfunctioning components within the system, by providing a system capable of
100
bacterial deactivation, by reducing nitrates and phosphates to levels below
EPA
standards for drinking water, and by producing an effluent having a BOD5 that
is close
to zero and a TSS that is half of the best Type II MDS. In other words, in
terms of
contents of bacteria, nitrates and phosphates, the effluent discharged by the
system
of the present invention will have the same environmental impact on the sea
(or lake
or river) as would discharging the same amount of the clean water from your
home
CA 02538635 2006-03-02
6
faucet. The system of the present invention is also capable of automatically
shutting
down the disinfection system if a critical component fails, or when the
nitrate or
phosphate reducing media has been consumed, therefore preventing the
accidental
overboard discharge of untreated sewage into the waters surrounding the
vessel.
In one preferred embodiment of the system of the present invention, which can
be used in vessels with single or multiple toilet facilities, the system
comprises the
following major components: (a) an electrically operated toilet, (b) an
automatic
dispenser of denitrifying and liquefying media, (c) a conventional sewage
holding tank
such as the one normally installed in most medium and large size boats, (d) a
"fuil°
level sensor deployed inside said holing tank, (e) an "empty" level sensor
deployed
inside said holding tank, (f) a microwave resonant cavity containing a series
of
undulating tubes forming a radiation loop through which the sewage flows
during the
disinfection cycle, (g) a microwave generator utilized to radiate microwave
energy into
the resonant cavity, (h) a macerator pump utilized to fragment human waste
solids
into much smaller pieces and for pumping raw sewage into a radiation loop, (i)
a first
vented loop plumbed between the outlet of the holding tank and the inlet of a
radiation
loop which is utilized for preventing cross contamination between the infected
sewage
in the holding tank and the disinfected sewage in the radiation loop even as
the boat
rolls in a seaway, (j) a first flow sensor to detect a faulty macerator pump,
(k) a
radiation sensor which is utilized to detect a malfunctioning microwave
generator, (I) a
self priming effluent discharge pump utilized for overboard discharge of the
disinfected sewage, (m) a second flow sensor to detect a faulty effluent
discharge
pump, and (n) an electrical controller and display panel utilized to control
activation of
the different parts of the system, to alert the user and automatically shut
down the
marine sewage treatment system when a particular treatment media has run out
or
when a critical component fails to operate properly therefore preventing
accidental
overboard discharge of contaminated sewage.
It is one objective of the system of the present invention to provide a marine
sewage treatment system capable of producing a treated effluent having zero
(0) fecal
Coliform, zero total Coliform, and zero E. Coli or Enterococcus.
CA 02538635 2006-03-02
7
It is another objective of the system of the present invention to provide a
marine sewage treatment system capable of automatic unattended operation and
without periodic mechanical maintenance or cleaning.
It is a further objective of the system of the present invention to provide a
total
sewage treatment system that not only thoroughly disinfects the sewage, but
that also
reduces other harmful pollutants, such as nitrates, nitrites and phosphates to
levels
signficantly below the EPA standards for drinking water.
It is an additional objective of the system of the present invention to
provide a
marine sewage treatment system capable of producing a thoroughly disinfected
effluent with a BOD5 significantly below the EPA standards for modem large
scale
municipal sewage treatment plants.
It is another objective of the system of the present invention to provide a
marine sewage treatment system incorporating a self diagnostic automatic shut
down
system to prevent accidental overboard discharge of contaminated sewage.
It is a final objective of the system of the present invention to provide a
marine
sewage treatment system capable of producing a treated effluent containing
less than
500 parts per 100 milliliters of Total Suspended Solids (a 50 % reduction
relative to
the best MSD in the market).
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 is a graphic representation of a sewage disinfection system intended
for
use in vessels having one or more toilet facilities.
FIG. 2 is a block diagram of the controNer utilized to (1) manage the
activation
of the different components of the sewage disinfection system shown in FIG. 1,
and
(2) detect and display any detrimental faults and automaticaNy revert the
system to
"holding tank onlyn operation (no overboard discharge) in order to prevent
accidental
overboard discharge of contaminated sewage.
FIG. 3 is a perspective view of an undulating radiation loop used in the
system
illustrated in FIG. I
CA 02538635 2006-03-02
8
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT
Referring now to FIG. 1, the sewage treatment system or process of the
present invention comprises four sequential cycles: The 1 st cycle comprises
the steps
of dispensing a controlled amount of denitrifying and liquefying bacteria
culture into a
holding tank containing the wastewater to be treated and allowing a dwell time
of at
least one day before initiating cycles 2, 3 and 4. The 2nd cycle comprises the
steps
of macerating and filling a radiation pipe loop with wastewater. The 3rd cycle
comprises the step of disinfecting the wastewater with microwave radiation.
The 4th
cycle comprises the steps of reducing the phosphate level of the disinfected
wastewater and discharging overboard the treated effluent.
Referring to FIG. 1, a first stage of the sewage treatment system of the
present
invention comprises an electric toilet 72, a dispenser 81 for dispensing
denitrifying
and liquefying media into the toilet flush water and a holding tank 10 into
which the
effluent from various toilets is discharged through sanitation hoses 12 and
13. The
denitrifying media is a specialized blend of heterotrophic bacterial culture
which
substantially converts harmful nitrates and nitrites found in human waste into
harmless nitrogen gas and also liquefies the solids and digests the toilet
paper.
The 1gt treatment cycle (the denitrifying and liquefying cycle) is initiated
by
depressing the "flush° push button 103 which momentarily turns on the
toilet's motor
to draw flush water into the toilet and also triggers "dispenser'" 81 to
dispense a
controlled amount of heterotrophic bacteria into the flush water being mixed
with
human waste and deposit the resulting wastewater into the holding tank for a
typical
dwell time of several days. As an example, let's assume that the holding tank
has a
capacity of only 40 gallons and let's assume that each flush produces a mix of
water
and waste equivalent to about 0.5 gallons. Let's also assume that the boat
crew
comprises four persons, each person flushing the toilet about three times per
day.
The math tells us that the holding tank wilt be near a full condition in about
6 days (0.5
gallons X 3 flushes X 4 persons = 6 gallons of sewage per day, and a 40 gallon
tank
divided 6 gallons per day = 6.67 days). This will be more than enough time for
the
heterotrophic bacteria to substantially denitrify, digest the toilet paper and
liquefy the
solids.
CA 02538635 2006-03-02
9
Next the "Full" level sensor 15 initiates the 2"d treatment cycle (the
macerating
and filling cycle) by signaling controller 18 (via a cable 71 ) that holding
tank 10 is near
a full condition. This causes controller 18 to tum on a green "sewage
treatment" light
22 and activate a macerator pump 24 (via a line 26) for a predetermined
duration,
e.g., 10 seconds to 2 minutes, thus injecting a predetermined batch of
contaminated
sewage into a microwave radiation loop 30 which is made from radiation
transparent
material, such as CPVC, high density polyethylene, polypropylene or silicon
rubber.
Next, the controller 18 stops the macerator pump 24 and the subsequent
pressure drop causes vented loop 86 to allow air to enter hoses 32 and 41,
therefore
any contaminated sewage remaining in sanitation hose 32 will fall by gravity
back into
holding tank 10 for further denitrifying and liquefying, thus ensuring a
physical air
space separation between the contaminated sewage at holding tank 10 and the
sewage just injected into the radiation loop 30 which is to be disinfected in
the next
cycle.
Next the 3~d treatment cycle (the disinfection cycle) is initiated by
controller 18
activating a microwave generator 34. for a predetermined duration, e.g., 3 to
8
minutes, preferably 5 minutes, in order to disinfect the sewage contained
within
radiation loop 30. The micro-wave generator is operated to produce microwave
radiation with a frequency between I and 5 GHt. Next the 4~' treatment cycle
(the
phosphate reduction and overboard discharge cycle) is initiated by the
controller 18
turning on an effluent pump 36 for a predetermined duration to evacuate the
disinfected sewage within radiation loop 30 and discharge it overboard via
hoses 41
and 42, seacock 44 and throughhull 45. During this overboard discharge process
the
hot disinfected sewage is forced through phosphate filter 93 which i5 filled
with iron
powder to substantially reduce the phosphate level of the effluent before
overboard
discharge.
Controller 18 will continue to repeat the sequential sewage treatment cycles
2,
3 and 4 many times until the "empty level sensor 14 is activated indicating
that all of
the sewage in holding tank 10 has been fully treated and discharged overboard.
Effluent pump 36 is a self priming, bellows type pump capable of pumping dry
the entire disinfected sewage out of the radiation loop 30. A conventional 12
VDC
CA 02538635 2006-03-02
battery 50 powers the sewage disinfection system of FIG. I via input lines 54
and 55,
a fuse 56 and a ground connection 58. The controller 18 powers the microwave
generator via a line 60. The controller 18 powers the effluent pump 36 via a
line 62.
The controller 18 monitors the output of a flow sensor 64 via line 66. A
throughhull 67
provides outside venting for vented loop 43 to prevent foul odors from
reaching the
interior of the vessel's cabin and also to prevent siphoning of seawater into
the
radiation loop and holding tank.
The entire sewage treatment system is contained within the vessel's hull 68
and deck 70. Sea water for flushing is pumped in by toilet 72 into ~s bowl via
a
throughhull 74, seacock 75 and a hose 76. This flushing sea water is mixed
with the
human waste and the denitrifying media and discharged into the holding tank 10
via
sanitation hose 12 and holding tank inlet 78. The sanitation hose 13 brings
additional
human waste and denitrifying media from other toilets within the vessel. A
sanitation
hose 80 connects an outlet 82 of holding tank 10 to an inlet 84 of macerator
pump 24.
A sanitation hose 32 connects an outlet 31 of macerator pump 24 to an inlet of
vented
loop 86. A sanitation hose 33 connects an outlet of vented loop 86 to an inlet
of
radiation loop 30. A sanitation hose 92 connects an outlet of the radiation
loop 30 to
an inlet of phosphate filter 93. A sanitation hose 95 connects an outlet of
phosphate
filter 93 to an inlet of effluent pump 36. A sanitation hose 40 connects an
outlet of
effluent pump 36 to an inlet of vented loop 43. A sanitation hose 42 connects
an
outlet of vented loop 43 to an inlet of seacoclc 44 and throughhull 45.
A flow sensor 94 is utilized to detect any malfunction of the macerator pump
24. A line 90 signals the controller 18 of a low flow condition which causes
the
controller 18 to tum on a red light 96 to alert the user of the need to repair
or replace
the macerator pump 24.
A radiation sensor 98 is utilized to monitor the microwave field strength
during
the disinfection cycle in order to detect any fault in the operation of the
microwave
generator 34. If the field strength doesn't rise above a predetermined value,
a line
100 signals the controller 18 of this abnormal condition, causing the
controller 18 to
tum on a "disinfeetion faultp light 102 to alert the user of a faulty
microwave generator
34. In this case the sewage treatment system shown in FIG. 1 will be shut down
and
CA 02538635 2006-03-02
11
revert to "holding tank only" operation to prevent overboard discharge of
contaminated
sewage. In such a situation, the holding tank 10 must be pumped out via a
sanitation
hose 104 through a deck plate 106. After the microwave generator 34 is
repaired,
pushing a reset button 105 will restore normal operation of the system.
The flow sensor 64 is utilized to detect a faulty effluent pump 36 by
detecting
an inadequate flow. In this case the controller 18 wiN (a) alert the user of a
faulty
effluent pump 36 by turning on a "pump-out fault red light 107, and (b) shut
down the
sewage treatment system until the effluent pump 36 is repaired or replaced.
During
this shut down state, the holding tank 10 must be pumped out via the
sanitation hose
104 through the deck plate 106. After the waste pump 36 is repaired or
replaced,
pushing the reset button 105 restores normal operation of the sewage
disinfecting
system shown in FIG. 1.
Referring now to FIG. 2, flushing of the toilet is initiated by pressing the
"flush°
push button 103 which triggers a toilet timer 108 (via fine 101 ), turns on a
toilet pump
65 (via line 69) for a predetermined duration and triggers a media dispenser
81 to
inject a controlled amount of denitrifying/liquefying bacterial culture into
the flush
water. This denitrifyinglliquefiying media is a specialized blend of
heterotrophic
bacterial culture which substantially converts harmful nitrates and nitrites
found in
human waste into harmless nitrogen gas and also liquefies the solids and
digests the
toilet paper. Each time the flush push button 103 is pressed additional
denitrifyinglliquefying media is injected into the flush water and is
deposited into a
holding tank 10, thus ensuring that enough heterotrophic bacteria is always
present
inside holding tank 10. Typically the bacteria will be in contact with the raw
sewage
for several days (actual time depends on the capacity of holding tank 10),
resulting in
substantial denitrifying, decomposition of solids and digestion of the toilet
paper.
Referring again to FIG. 2, a sewage treatment cycle is initiated upon
controller
18 receiving a signal via line 16 from the "full" level sensor 15 indicating
that the raw
sewage at holding tank 10 is nearing a "fulln level. This triggers a macerator
timer 108
in the controller 18 to run (via line 26) the macerator pump 24 for a
predetermined
duration. Upon completion of the maceratinglpump cycle, line 26 will turn off
the
macerator pump 24 and then trigger a radiation timer 110 in controller 18 to
activate
CA 02538635 2006-03-02
12
(via tine 60) the microwave generator 34 for a predetermined duration. Then,
upon
completion of the radiation cycle, line 60 will trigger an effluent pump timer
111 in the
controller 18 to activate the effluent pump 36 (via line 62) for a
predetermined
duration. Note that the waste pump 36 is a self priming bellows type pump
which can
run dry without damage. Momentary reset switch 105 is used to get the
treatment
system out of the shut-down mode after a fault has been detected and servicing
has
been completed.
The conventional 12 VDC battery 50 is used to power the sewage disinfection
system of FIG. 1. The conventional fuse 56 is used to protect the electronics
within
the sewage treatment system shown in FIG. I and the ship's electrical system.
A fault detection block 112 receives fault signals from flow sensors 94 and 64
and radiation sensor 98 and toms on the respective red lights 96, 102 and/or
107 to
alert the user of specific faulty condition(s).
Referring to FIG. 3, a perspective view of the °radiation loop" 30 of
tubing or
pipe 30 is shown. This 4radiation loop" 30 is made from radiation absorbing
pipe
material as to allow the radiation to penetrate the sewage within, and has an
internal
diameter not exceeding the effective penetration of microwaves into the sewage
(about 2 inches). CPVC and silicone tubing work very well, although high
density
polyethylene and polypropylene tubing also can be used. The internal diameter
of the
pipe or tubing 30 is between I and 3 inches and, preferably, approximately 2
inches.
The wall thickness of the tubing is between 0.03 inch and 0.25 inch, depending
on the
tubing material selected. Infected sewage enters through inlet 115, flows
though loop
30 and the disinfected sewage exits through an outlet 126. The "radiation
loop" 30 is
formed so that it travels up-and-down and back-and-forth to cover as much of
the
interior volume within °n~sonant cavity" 28 as possible. The undulating
or twisting
pattern effectively results in an extremely long radiation pipe, permitting
each batch of
infected sewage to receive the same average dose of microwave radiation to be
applied evenly as the sewage moves between spots of higher and lower field
strengths within the "resonant cavity" 28. Tests conducted by independent
testing
laboratories have shown that 100% bacterial inactivation is obtained with
microwave
treatment of raw sewage and with the sewage reaching a maximum temperature of
CA 02538635 2006-03-02
13
only 60° C. It is to be noted that prior art electrical and microwave
sewage heaters
and incinerators heat the sewage to over 100°C in order to obtain 100%
bacterial
inactivation.
From the foregoing description, it will be apparent that the marine sewage
treatment system and method of the present invention have a number of
advantages
some of which have been described above and others of which are adherent in
the
invention.
For example:
Microwave energy is used to totally disinfect human fecal and urine waste
without the waste having to reach the so called bacterial inactivation
temperature of
100°C. Empirical tests have obtained 100°!° bacterial
inactivation with the waste only
reaching 60° C while prior art devices using electric heaters and
incinerators heat the
waste to temperatures much higher than 100°C.
Microwave energy is used as a disinfecting medium in order to design a
completely unattended sewage disinfection apparatus. All prior art systems
require
user intervention to perform either periodic mechanical maintenance to
cieanlreplace
ultraviolet bulbs or to clean/replace electrolyzing electrodes or to
periodically toad
chlorine tablets or formaldehyde.
A loop of radiation absorbing tubing is used inside a microwave resonant
cavity
where the waste to be disinfected within the tubing having a diameter not
exceeding
the effective penetration of microwaves into water in the tubing. This concept
produces a surprisingly improved absorption rate of microwaves by the waste,
resulting in a much shorter disinfection cycle.
The purpose of forming the tubing for the radiation loop 30 is so that the
waste
travels up-and-down and back-and-forth to cover as much of the interior volume
of the
resonant cavity 28 as possible. This concept results in an extremely long
radiation
tubing or pipe, permitting each batch of waste to receive an equally average
dose of
radiation as the waste moves between spots of higher and lower radiation field
strengths levels within the resonant cavity.
The purpose of an air space between the infected raw sewage in the holding
tank 10 and the disinfected waste in the radiation loop 30 is to inhibit cross
CA 02538635 2006-03-02
14
contamination. This concept ensures that the waste being disinfected will not
be
contaminated with the raw waste in the holding tank. Note that the hose 32 and
vented loop 86 are located much above the top surface of the holding tank 10,
therefore preventing movement of the vessel from spilling raw waste into the
inlet of
radiation loop 30 and contaminating the waste being disinfected within the
radiation
loop 30.
The use of a "full" level sensor 15 to trigger a series of disinfection and
phosphate reducing cycles to treat the entire contents of a "fullp holding
tank, instead
of the disinfecting each toilet flush immediately and independently as the in
prior art,
allows the denitrifyinglliquefying media dispensed into the holding tank with
each
flush, to be in contact with the raw sewage for several days before the
disinfection
and pump-out cycle begins. This long contact time between the media and the
sewage results in substantial reduction of nitrates and a thorough breakdown
of solids
and toilet paper.
The disinfection of wastewater in small batches having a volume smaller than
the total volume of the radiation loop 30, allows each batch to receive
multiple
radiation doses as it moves through the radiation loop 30, thereby ensuring
100°!°
bacterial and viral inactivation of the waste exiting the radiation loop 30.
The stepped or indexed pushing along of hot waste water through the
phosphate filter results in relatively long dwell time with the iron power
media, thereby
improving the level of phosphate reduction.
The use of appropriate sensors to detect critical component failures, allows
to
diagnose and identify the faulty component to the user and to shut down the
sewage
treatment in order to prevent accidental overboard discharge of infected
sewage.
Also it will be understood that modifications can be made to the marine toilet
method, system and apparatus of the present invention without departing from
the
teachings of the invention.
Accordingly, the scope of the invention is only to be limited as necessitated
by
the accompanying claims.
