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Welcome to Ask Tom!, a monthly column by our resident water treatment guru, Tom Keenan of
National Environmental Services Agency (NESA). Tom addresses the issues that bug you the most. And Tom knows!! With 35 years experience in providing environmental support services to public and private sector clients on a wide range of environmental issues. Tom has also co-authored and presented training courses on wastewater treatment systems.
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A Case for Thermal Oxidization
of Wastewater
Guest article by Ronald G. Fink, Andrew C. Hyatt and Michael L.
Chaudron
"Imagine yourself
completely separating the water from the plant waste stream
and then paying only for the disposal of the dry contaminants..."
Introduction
 Thermal
Oxidization, a technology used for many years to control plant air
emissions, now economically eliminates wastewater. With the
standards for wastewater discharge into municipal sewers tightening,
sewer costs skyrocketing, and wastewater hauling charges ranging
from $0.25 to $2.50 per gallon, onsite treatment often makes sense.
The hauling of wastewater also puts your company at risk for clean
up costs if you wastewater is not disposed of correctly or
accidentally discharged.
Wastewater treatment systems are
plentiful, using roughly 25 basic water technologies in various
combinations including; absorption, nanofiltration, aeration,
oxidization, bag/screen clarifier, air stripping, centrifugal
separation, dissolved air floatation, precipitators, ion exchange,
ozone, membranes floccing/clay systems, reverse osmosis, oil
water separators, distillation and ultra filtration to name but a
few.
Facing a barrage of conflicting
demands and options, a plant manager usually ends up hiring an
engineering firm to make the right choice for the plant. In recent
years, wastewater recycling has become a politically correct
buzzword. And rightly so.
Two Reasons to Recycle Water
The first is economic. Sewer costs
are calculated on the basis of your water meter readings. Every
gallon you recycle also saves the sewer discharge cost.
The second is moral. With the world
population doubling every 30 years, water becomes an increasingly
valuable resource. This is especially true when you consider there
is not one more drop of water today than there was a million years
ago.
The likelihood of science developing
a synthetic substitute is highly improbable. Whenever possible, we
must recycle and conserve our water. At the present rate of water
pollution and consumption, we are rapidly running out of our most
precious natural resource.
How Thermal Oxidization Works
 Most
packaged water treatment systems have one thing in common:
separation. The system must separate the effluent water from the
contaminates to meet its goal. This usually generates two water
streams- one of cleaned water, the other containing concentrated
contaminants. There are problems associated with the concentrated
waste stream. In addition, plants are often plagued with highly
contaminated water that defies any practical water treatment
technology.
For these cases, thermal oxidization
may be the answer. Thermal Oxidization is the complete breakdown of
the wastewater to hydrogen, oxygen, and the contaminates using
extreme heat. Thermal Oxidization could also be referred to liquid
incineration. Unlike most separation technologies, thermal
oxidization leaves nothing to dispose of but a dry ash. Thousands of
gallons of water can be reduced to a few ounces of dry power.
Comparing With Evaporation
Thermal Oxidization is often compared
to evaporation, and it can effectively replace or augment
evaporation in many cases. Evaporation technology has been around
for 100 years and has always had the following inherent four (4)
problems:
- Fuel Cost: Traditional
evaporators maintain a wastewater reservoir of 100 or more
gallons. This reservoir must be heated, brought to temperature,
and maintained at 212 degrees Fahrenheit. This involves a lot of
wasted energy. Continual “shrinks” (evaporating and refilling
while in automatic operation) concentrates solid content, which
absorbs heat and reduces efficiency. The first shrink will be the
most efficient.
- Corrosion: Traditional
evaporators usually rely on a heat source (flame) to heat steel to
boil the wastewater. Flame impingement causes corrosion problems
In addition, the combination of water, chlorides, sodium, and heat
create the most corrosive atmosphere known to man. Even stainless
steel develops stress corrosion cracking, inter-granular corrosion
and carbide precipitation – all of which result in premature metal
failure. No matter what type of steel is used, the continuous
cycles of heating and cooling coupled with the very corrosive
elements will lead to early metal failure.
- Residual Slurry: Traditional
evaporators present a handling and disposal problem because they
require the periodic removal of the concentrated slurry that can
consist of highly concentrated wastes. In order to facilitate ease
in removal, the concentrated slurry must consist of 60% water.
Even then solids will remain that will need to be washed with
fresh water, adding to amount to be hauled. Another solid present
is the free oil content in the system that floats on the surface.
This material will coat level sensing devices causing malfunctions
and also contributes to emissions concerns.
- Air Emissions: Traditional
evaporators simply heat water to boiling, which evaporates the
wastewater. This drives off volatile organic compounds with the
steam, producing potential air pollution problems. As the
evaporator concentrates the waste, the emissions increase.
Thermal oxidization alleviates the
four long-standing evaporator problems. Spraying an atomized flow of
wastewater directly into the combustion chamber eliminates the need
to maintain a hot reservoir of water at the boiling point, thereby
reducing fuel consumption.
The Thermo Oxidizer meets the strict
NFPA 86 gas train regulations while utilizing the latest in control
functions, including programmable logic controllers that receive
information from various monitoring sources to control temperature,
air flow, and fuel flow to provide extremely efficient operations.
So efficient, that the system will oscillate 50 degrees +/- the
desired temperature. The waste streams solids content dictates the
amount of heat required to evaporate it. The Thermo Oxidizer can be
programmed to operate at the optimum temperature for the waste
stream. The Thermo Oxidizer also captures and utilizes convected
heat to further increase efficiency.
 Costs
as low as $0.06 per gallon of oxidized wastewater has been achieved
by using natural gas fuel. By using a waste oil burner, operating
costs can be even lower. If you are presently paying to have waste
oil removed, using a waste oil fired burner could actually save
money and resources. The PLC and burner controller detect the
presence of additional heat from the waste oil source and
automatically reduce main fuel consumption. A dual-pour high
temperature cast ceramic liner eliminates the corrosion problem by
eliminating any water to steel contact.
It is relatively easy to treat
wastewater with very small levels of insoluble suspended
contaminates. The oxidization process using atomizers is very
effective on waste streams pretreated to remove suspended solids
larger than 200 microns. The atomization nozzles are automatically
cleaned during its operating cycle, ensuring a consistent process
flow.
Dissolved Solids
Dissolved solids, on the other hand,
are very difficult to remove. These are soluble contaminates that
dissolve in water much like salt in seawater, which can be crystal
clear yet contain 35,000 ppm of salt. Thermal Oxidization is a
viable technology for highly concentrated waste streams with high
levels of dissolved solids. Thermal Oxidization literally
incinerates the wastewater, leaving the dissolved and suspended
solids as a dry ash. Tests on water with dissolved solids as high as
65,000 ppm has been successful.
Thermal Oxidization, at temperatures
between 300 and 1400 F completely oxidize most waste streams leaving
only a dry ash. It is no longer necessary to deal with the
concentrated slurry associated with traditional evaporators. Thermal
Oxidization also eliminates air emission problems. The atomized
wastewater is sprayed directly into the combustion chamber, then
burning any volatile material in a 300 to 400 F secondary chamber.
Subjecting difficult waste streams to temperatures of 1400 to 1600F
totally oxidizes contaminates and eliminates any air emission
problems. When dealing with combustion, safety is always a major
concern.
Waste Haulage
Another major issue is hauling waste.
The “cradle to grave” issue, until recently, has been lessened to
the point that generators have become complacent to the fact that
you own the waste. Many companies that haul wastewater can provide a
certificate of indemnity to cover any spills or mismanagement while
disposing. More companies do not and that would mean that if they
spill or mismanage your waste, you, the generator, are responsible
for cleanup costs. Forever.
Imagine the company that offers their
certificate of indemnity goes out of business or bankrupt. If it is
found that they engaged in practices that lead to mismanagement of
your wastewater, you will be responsible for clean up. Remember the
paper you signed when they carted off your wastewater? From a risk
management standpoint it would stand to reason that if you are going
to be held responsible, why not do the job yourself on site and
avoid the transportation issue.
Thermal Oxidization is a viable
option to consider for eliminating difficult or highly concentrated
wastewater streams.
About our authors
For more information and to contact
our authors:
Mr. Ronald G. Fink, President
Mr. Andrew C. Hyatt, Vice President
RGF Environmental Group, Inc.
3875 Fiscal Court
West Palm Beach, Florida 33404
Telephone: 561-848-1826
Email: rgf@rgf.com
Web site: http://www.rgf.com/
Mr. Michael L. Chaudron
Director of Environmental Systems
MSE Environmental and Safety, Inc.
P.O. Box 5667
Johnson City, Tennessee 37602
Telephone: 423-791-4662
Email:
mchaudron@msees.com
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Guest articles for the
Ask Tom! Column are always welcome, for more information please
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