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News
CROWN
Solutions, Inc. Technical Resource
Biodetergents for Cooling Water
By Dave Christophersen, CWT
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Before
applying a coat of paint to a car, the surface
should be clean to allow the paint to spread evenly
and adhere properly. In a cooling system, for
corrosion inhibitors to react properly with the
metal and form a corrosion barrier, the surface
needs to be clean and free of biofilm, suspended
solids, or scale.
Biodetergents
(Also called Biodispersants or Biopenetrants
or Organic Dispersants)
Chemicals
that can penetrate and loosen the complex matrix
of biofilms allow biocides to reach the organisms
for more effective kill and control.
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Figure
1:
Dirt and biofilm on a cooling tower distribution
deck is shown sloughing off after an application
of a biodetergent.
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These
chemicals are typically shot fed at dosages that break
down polysaccharides, emulsify oils, release minerals
and foulants, or disperse the biopolymers. Sometimes
they are fed continuously.
The
biofilms are often the glue that allows suspended solids
found in recirculating water to be bound to the surface
of the cooling system components including heat exchangers,
piping, and the cooling tower structure. Mineral deposits
are also commonly found within this matrix. Calcium
and magnesium offer bridging mechanisms to strengthen
the polysaccharide polymer chains. Corrosion occurs
underneath the biofilms, releasing corrosion byproducts
that become part of the matrix also.
Because
accumulations of dirt and the formation of biofilms
can lead to corrosion and scaling, their prevention
through the use of filtration, biocides, and biodetergents
can be extremely important for a successful water management
program.
Biodetergents
help keep cooling systems clean or help clean up fouled
systems by dispersing the extracellular material created
by bacteria, algae, and fungus. They help biocides to
penetrate and kill the biological growth. By keeping
the surfaces clean, they allow scale and corrosion inhibitors
to perform better.
Some
biodetergents can create foaming conditions especially
at high dosages, so care must be taken in product selection
and applying the product. Also, the compatibility with
other treatment chemistry, especially oxidizing biocides,
should be considered.
Some
biodetergents include:
- DTEA
II (2-Decylthio ethanamine)
- DMAD
(Fatty acid amide)
- Dodecylamine
acetate
- Polyquaternary
amines
- DOSS
(Dioctylsulfosuccinate)
- Polyoxyalkylenes
- Enzymes
Applications
A.
Routine Treatment: Apply biodetergents regularly
as a part of any cooling water treatment chemistry to
enhance the other chemicals and minimize scale, corrosion,
fouling, and biofouling.
B.
Cleanup After Contamination: Some cooling systems
may experience unusual process contamination, loss of
control, temporary poor quality makeup water, or other
short-term contamination where the application of a
biodetergent can help with recovery and cleanup.
C.
Wastewater Recycle: Where treated wastewater is
used as a cooling makeup source that provides consistent
stress on the system or contaminants such as fats, oil,
or greases, or other organics, incorporating a biodetergent
as part of the ongoing treatment strategy may be advisable.
D.
Cooling Efficiency Optimization: Where the load
on heat exchangers or cooling towers are at their peak,
the use of biodetergents can aid in achieving the maximum
available cooling.
E.
Biocide Sensitive Discharges: It is often necessary
or desirable to limit as much as possible the application
of oxidizing and non-oxidizing biocides because of their
toxicities. In these cases, biodetergents can be a great
aid in allowing minimal biocide dosages while still
maintaining effective control of bacteria, fungus, and
algae.
Case
Studies
A.
An aluminum die cast plant needed to recycle treated
wastewater for use as cooling tower makeup because they
were quantitatively limited by the city regulator on
the amount of discharge water from their plant. Although
the wastewater was treated onsite for oil and metal
removals, the treated wastewater still contained residual
amounts of oils and a relatively high BOD. Efforts to
recycle in the past prior to their discharge flow limitations
had created severe fouling in their cooling towers consisting
of microbiological slime, oils, and suspended solids.
This
time around a biodetergent product containing DOSS and
DMAD were applied and fed continuously to emulsify oils
and to penetrate biomasses. The improved results were
obvious as the systems remained cleaned and corrosion
rates were held very low.
B.
An oilseed plant experienced a persistent leak of vegetable
oil into the cooling system through a plate and frame
heat exchanger and production demands did not allow
down time to repair the leak. The cooling tower wood
splash fill became loaded with biological slime and
even with the addition of high residuals of bromine
and chlorine, some of the fill eventually collapsed.
Shot
feeding of DTEA II biocide was initiated and after several
weeks the fouling on the fill was mostly eliminated.
C.
An air separation plant using clarified river water
as cooling tower makeup was experiencing high approach
temperatures on some of their heat exchangers due to
river mud making it past their clarifier, and because
of algal and fungal mats. After one high dosage application
of DTEA II, the approach temperature on one critical
heat exchanger dropped by 10 °F.
D.
An ethanol plant experienced an ethanol leak into the
cooling tower, which created a rich food supply for
biological growth. Applications of chlorine and non-oxidizing
biocides did not allow the removal of biofilm persistently
hanging from the cooling tower fill. Application of
biodetergent shot fed 2 – 3 days per week allowed the
system to recover.
E.
A greenfield ammonia plant treatment strategy was designed
to provide optimal water system conditions, so as part
of the program a biodetergent was included. The treatment
included continuous chlorination, periodic non-oxidizing
biocide addition, and a phosphate/zinc/phosphonate/polymer/azole
program. Mild steel corrosion rates of <1 mpy and copper
rates of <0.1 mpy have consistently been obtained along
with clean heat exchanger and cooling tower surfaces.
More
Reading on Water
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