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Problems with Raw Water Treatment
Five
Common Problems with Raw Water Treatment and How to Avoid Them
SAMCO
For industrial
companies treating a raw water source for its processes, there are several
issues that can surface during treatment that we see on a regular basis.
We’ve broken out
the five most common problems with raw water treatment and how to avoid
them below.
Whether you’re
designing a new plant or updating existing equipment, avoiding these five
common raw water treatment problems might help you operate your process more
efficiently down the line, so they’re important to keep in mind and plan for
ahead of time, if possible:
1. Variation in turbidity
When plants begin
to experience a variation in turbidity — the cloudiness of water due to the
presence of a large number of particles — it can have negative effects on the
quality of the process and effluent from the plant.
It’s helpful to
have a consistent year’s worth of data to evaluate the turbidity levels coming
into the plant from season to season prior to designing the system.
When the plant is
designed around the seasonal turbidity flow without taking into consideration
any of the changes it might see — if the turbidity increases without the plant
being ready for this change — there are several problems that might occur.
When the turbidity
is too high for the plant to remove it efficiently, it often carries over to
production and can be present in your discharge, contaminating your
process and causing fines when local discharge regulations are not met.
Another issue we
see when turbidity levels vary, is the amount of sludge that’s generated from
treating the turbidity.
Oftentimes
secondary sludge systems can’t handle the load, and therefore the sludge
backs up in the clarifier and shuts down the pretreatment system.
The best way to
combat this problem is to design a slightly oversized treatment system for
turbidity, anticipating that variations will occur.
It’s also
beneficial to design a recycle system so if the water doesn’t
meet the quality requirements as it moves through the process, it can be
recycled through and retreated more thoroughly.
Another way to prepare
for varying turbidity is to include variable controls on your chemical
feed systems so you can adjust chemical feed rates.
You can also oversize
the sludge handling system so when you pump out the sludge in the
clarifiers filters, you have a sludge handling system that, if the turbidity
does fluctuate, has the ability to manage it.
2. Variation in flow
Many times,
industrial companies make educated guesses as to what they think their flow
rates are going to be.
If an industrial
facility is not equipped to handle these variations, they’ll likely
experience upsets to the system that will carry turbidity over
and plug any downstream filters.
Understanding what
peak demand is and using holding tanks to try to buffer out the peak demands is one way to
prepare for flow variations.
Typically, you want
to design the system with an excess flow buffering/holding capacity so you can
run your plant as consistently as possible and then use the holding tanks
downstream to handle surges in production needs.
Another thing you
can do is put variable controls on your chemical feed systems, so
as your flow changes, your chemical feeders can ramp up and ramp down to handle
it.
With a combination
of variable flows on feed treatment equipment and storage on peak demands, you
can get your system to balance out more easily and increase functionality.
If you don’t have
the ability to automate chemicals, you will need to test more often. You can
try to run your plant at a consistent flow rate to avoid these upsets and
turbidity issues.
Raw water treatment
plants do not handle variations in flow well, so it’s helpful to design the
system with this in mind from the start.
3. Changing feed chemistry
Many surface
and well waters have seasonal variations in water chemistry.
Industrial plants
need to be very careful in the design of any raw water treatment systems to be
large enough to handle these changes.
Let’s say, for
example, you have a problem with raw water iron or silica and it changes
seasonally.
If you haven’t
designed your clarifiers large enough to get the proper retention times and you
haven’t designed your feed systems large enough to handle the increased load,
you’ll get carryover with either silica and/or iron into the
downstream equipment where they cause all sorts of problems such as
scaling and fouling.
Secondarily, if you
don’t anticipate the higher seasonal loads of iron and silica and try to
precipitate it out, you may then have particulate carryover to your sludge
handling systems, causing them to fail.
All in all, it’s
very important to understand the variations of the contaminants feed water
chemistry and design a system accordingly.
Physical chemical
processes to remove the iron and silica is typically an oxidation chemical
(such as oxygen) and an aluminum-based coagulant such as alum that will
precipitate out the iron and silica and allow them to settle so they can be
removed in a clarification filtration system.
If you don’t have a
chemical feeder size large enough, you may get carryover of iron and silica.
Or if you’re able
to precipitate higher, unanticipated volumes of iron and silica, your underflow
handling systems such as your sludge thickening and filter pressing operations
may not be able to handle the increased amount of sludge.
4. Being unaware of updates/changes to quality requirements
When you design a
plant for a certain process and to make sure you meet stringent requirements,
sometimes you might find out later you need to adapt your equipment to
account for recent changes in regulations.
This is a common
occurrence that sometimes happens after plants have been installed for years.
The plant may be
running well and designed to deliver a certain kind of effluent quality, and
then one day the standards of the quality requirements become more stringent
and the plant no longer meets the requirements at the facility.
As an example,
let’s say you are feeding water to a low-pressure boiler and you put in a
bigger boiler that runs at a higher pressure.
Depending on the
requirements of the new boiler, the quality of the feed water to the boiler might
no longer be adequate.
You might need to
ensure the feed water is a better quality and add ancillary equipment to the
system.
For this
reason, plants should be designed with some forward thinking in
mind of what might be anticipated.
It is also helpful
to plant for expansion and quality improvement and allow space in the plant for
adding additional equipment to handle changes in quality requirements.
5. Secondary waste
One of the biggest
mistakes made in designing raw water treatment plants is not looking
carefully at the secondary waste generated by the process.
Contaminants from
the feed water impact the volume and processing requirements in secondary
waste.
Also, sometimes
these secondary wastes need to be treated and discharged, yet many times they
are discharged to a publicly owned treatment works or wastewater facility and
they must meet the requirements of that facility.
It’s best to get
a copy of the permit requirements, carefully analyze them, and design your
wastewater secondary treatment processes and sludge handling to meet the
effluent discharge of the plant water to the municipality.
Sometimes this
includes releasing to the environment under a SPEDES permit. These permissions
need to be negotiated in advance to be sure that the plant will achieve the
effluent goals or discharge.
How SAMCO can help with your raw water treatment needs
SAMCO has over
40 years of experience helping our customers evaluate their potential
raw water treatment issues, so if you have any questions, be sure to visit our
website for more information about raw water treatment here.
We also have an
article you might be interested in about how much a raw water treatment system might cost you and
who we recommend as qualified raw water treatment companies for
you to consider as you search for all the options available for your plant.
ABOUT
SAMCO
Established
in Western New York in the 1950s as a soft water provider. Current owner
purchased the industrial portion of that company in 1987 to form CS Kimeric. In
1998, after identifying the need for an integrated solutions partner – a
company who could offer everything from concept to design fabrication – SAMCO
was born.
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