The U.S. Navy is investing in a combination of new and old-age
technologies to make ships compliant with international treaties
that ban waste dumping at sea.
The agency in charge of fielding and testing these technologies
is the Pollution Prevention and Material Safety Branch at the Carderock
Division Naval Surface Warfare Center, located in Bethesda, Md.
“[We do] research and development for pollution-control technology
that will enable ships and submarines to operate in the 21st century
and be environmentally sound. We provide them with the technologies
and procedures to comply with current legislation,” said Gary
Alexander, technical area manager for the solid waste program.
There are three main areas of research: solid waste, liquid waste
and hazardous materials.
Currently, there are four pieces of equipment in use aboard ships
that were developed by the solid waste program at Carderock, explained
Alexander. To dispose of paper, food and cardboard, they have large
and small pulpers. In the pulpers, the waste is chopped up and mixed
with water to form a slurry that is then dumped into the wake of
the ship, as long as it is three nautical miles from any shoreline.
It is biodegradable and “basically fish food,” said
Alexander. The large pulper can handle 1,000 pounds of waste an
hour and the small one, 200 pounds.
Plastic waste is shredded and fed into a processor which melts
and compresses it into hard, solid “pizzas” that are
approximately 20 inches in diameter and one to two inches thick.
The discs can then be stored aboard for later transfer to a landfill.
The processor has led to a 30-to-1 reduction in onboard waste volume.
It presently is aboard 200 ships. Alexander stated that research
has been done into recycling the plastic for use as core material
in pier pilings, but thus far that has not proved cost efficient.
The fourth piece of equipment is a shredder for metal and glass.
Once broken down, the metal and glass will sink instead of bobbing
on the surface when discarded.
Solid waste disposal on submarines is a bit different, explained
Tim Bond, one of the developers for submarine plastic waste management.
Currently, crews use hydraulic compactors to get rid of solid waste.
Pre-made cans are assembled, the waste is compacted into them, they
are weighted to sink and then discharged through a hull-penetration
valve.
However, amendments to the Act to Prevent Pollution from Ships
forbid the discharge of plastic waste after 2008. As a result, changes
will be needed to allow onboard storage of waste. “We use
the same cans that are used for normal trash compaction, but we
line it with the odor-barrier bags. We compact the plastic into
the odor-barrier bags, then put it in a second bag, and heat seal
it. Then, [it is stored] in a locker onboard” for later disposal,
said Bond.
Food waste is ground, placed in plastic mesh “wet bags,”
weighted for negative buoyancy and discharged with the cans. Bond
stated that they are replacing the plastic mesh bags with cloth
ones to comply with the no-plastic discharge policy. These changes
have led to a 20-to-1 reduction in waste volume.
The technology emphasized in solid-waste disposal is the plasma
arc waste-destruction system. Plasma is created when an electric
arc is formed in a gas. This technology is more than 100 years old.
The systems are large, use heavy refractories and require a skilled
workforce. But the system developed by the Navy has done away with
that.
John Cofold, a plasma arc expert at Carderock, explained, “One
of the reasons plasma arc turned out to be one of best ways to go
is it will allow an intimate mixing between the waste and the fuel.
Doing so means [that] you can get combustion to take place very
quickly in a small space.” Waste is either pulped or shredded
by the conventional machines onboard. Then, a hopper delivers it
to a hammer mill that reduces the size of the particles for high-temperature
thermal destruction.
The particles are blown into the eductor, which causes it to react
very rapidly with the plasma plume, turning the particles of waste
into syngas, which is made up of carbon monoxide and hydrogen. The
gases then are burned in the secondary combustion chamber. “The
beauty of this system is that it is a cold-wall system. There are
no refractories, unlike a tradition incinerator. Because there are
no refractories and you have this intimidate mixing between the
plasma plume and the fuel, there is only a small amount of material
in there at any one time, about 35 grams a second,” he said.
“What this means is that it is a true on/off system. In traditional
incineration, there is a warm-up time and a cool-down time, and
when you put the waste in, it actually smolders first before igniting.
In this system by the time it is completely through the eductor,
it is gasified. Because it is gas, it doesn’t require much
space to burn, and so the system can be made small.”
Another benefit, cited by Cofold, is the fact that the system is
modular, making it possible to reconfigure it based on shipboard
needs.
The research program ends this fiscal year. It will be followed
up with land-based, engineering-design models, a ship model and
then it will be demonstrated and evaluated in time to be aboard
the Navy’s new aircraft carrier, the CVN-77.
Pyrogenesis Inc., a Canadian company based in Montreal, has a cooperative
research and development agreement with the government and is attempting
to put plasma arc waste disposal systems aboard cruise ships. Officials
believe this system will have appeal, because the current systems
are the size of two decks, explained Cofold. The commercial industry
has to comply with the Marine Pollution treaty before the military
does. Plus, said Cofold, “They are very eager to get this
into the cruise line industry, because that would be very beneficial
to us. It would shorten the amount of time and study you would need
to put it aboard a carrier.”
Liquid waste also is a problem aboard Navy vessels. There are two
kinds of liquid waste, non-oily or gray water and oily or black
water. Gray water comes from showers, sinks, the galley and laundry
facilities. Black water is sewage and bilge water. Currently, the
ships have collection and holding tanks (CHTs), and they either
discharge the waste three nautical miles out to sea with a salt
water flush or they pay to have it off-loaded when they are in port,
explained Tina Lerke, a member of the gray-water research group.
She added that some vessels now have a vacuum CHT that uses low
levels of fresh water for the flush. However, she said, “Because
you can only hold so much waste in a tank, it is becoming a problem
onboard.”
One of the current projects is called the developmental gray water
treatment unit. It is run in the liquid waste lab at Carderock and
also on the USS Bonhomme Richard, an amphibious assault vessel,
for a 15-month evaluation. The unit is a membrane bioreactor. A
membrane—made up of hollow fibers that look like spaghetti—is
immersed in the bioreactor. “A vacuum is pulled from the interior
of the membranes, providing the driving force for the liquid to
flow through the membrane and into the center of the hollow tube
leaving the solids behind in the bioreactor,” explained Lerke.
In the bioreactor, organisms that are naturally present are aerated
and allowed to grow, and they dispose of the solid waste left behind.
Everything also is treated with ultraviolet light.
The unit is made-up of three tanks, Lerke said. The first is the
equalization tank. “It equalizes the volume so that you always
have a certain volume in here to run the reactors. There’s
not going to be a high point and a low point ... for different loadings
of wastes and for temperature. We also start to aerate it here.
We give it oxygen to get the bacteria growing, to keep it moving,
to keep it mixed.”
The second tank is the bioreactor, and the third tank is to contain
the overflow of foam that is created by the bioreactor. Lerke said,
“Foam is a common problem in different kinds of bioreactors.
It is especially tricky here, because you can’t use chemicals
to treat [the water] onboard for safety and logistical reasons.”
The unit in the lab currently is running with a 40-to-1 volume reduction.
Mike Kelly, part of the oily water team, has been working on a
new system for the filtration of bilge water. According to Kelly,
the primary system now onboard ships is 20-year-old technology.
It basically consists of a box that contains parallel plates. As
the bilge water flows into the box the parallel plates make everything
slow down, so the oil has time to rise to the top. It is then separated
and placed in a holding tank. The “clean” water is discharged
overboard only if it shows an oil content of less than 15 parts-per-million.
If it is too high, it is fed back through the process until it
meets the requirement. A problem arises when detergent used to clean
the bilge ends up in the mix. “You get a really stable emulsion
in there, and when you fire it into the box, it goes right on through.
So the end result is a higher oil concentration in the discharge,”
explained Kelly.
The new system also uses membranes. The bilge water is run through
cartridges containing ceramic ultrafiltration membranes that are
made up of tiny holes in a grid formation. The oil molecules are
too big to permeate the wall of the membrane, but the water molecules
pass through and empty into a trough outside the casing. Then it
is discharged overboard, and the oil is stored for later disposal.
There is a large system that has 12 cartridges and can run 50 gallons
of water a minute running in the lab. Results have been very good,
Kelly said. Smaller systems that run 10 gallons a minute and have
three cartridges have been tested onboard two ships, one for about
two years. According to Kelly, now researchers are looking for an
amphibious vessel to begin an extended evaluation of the larger
system in September.
To reduce the amount of hazardous waste material off-loaded from
ships, the engineers at Carderock turned to commercial-off-the-shelf
technology, according to Drew Jackson, an environmental engineer.
“We are looking at the shipboard problems and what we can
do with this hazardous material. We look at what they use, where
they use it, what ideas they had, what might facilitate and possible
substitutions of equipment or material or a process, in order to
reduce the amount of hazardous material they deal with.”
One of the premises of the program, he said, was to ensure that
investments offered a payback within approximately three years.
Once a solution was found, they worked with the vendors to make
modifications in the land-based units to facilitate use aboard ships.
One example is a top-loading parts washer. Various models were
tested aboard a destroyer. New features were added based on suggestions
from the sailors. For instance, the access panel was moved to the
front to make maintenance easier.
One of the biggest problems cited was the state of most ships’
paint lockers. Paint dispensers were developed to cut back on the
mess. “The 25-gallon tank holds paint, using a pneumatic pump
to re-circulate it, keep it mixed, then, like a soda fountain, the
sailor can dispense it in just the amount he/she needs. Frequently
what we found was paint was being returned in excess quantities
than what the job required,” said Jackson.
Other equipment that has been developed are paint gun cleaners,
a system that makes cleaning up paint chips easier, an explosion
vacuum for fuel spills, maintenance free batteries and a medical
waste processor. “Basically, [everything is] low tech and
low cost, but the pay off is really high,” said Mary Jo Bieberich,
another member of the hazardous waste team.