There is a requirement for some type of raw water treatment system to ensure an efficient process as well as a quality product, for any industrial company that uses a raw water source for its facility. The most effective raw water treatment system will help the facility to avoid the following:
1.avoid costly plant downtime,
2.avoid expensive maintenance fees, and
3.not being able to sell its products in the market
What is a raw water treatment system?
How does the raw water treatment system function?
The answer to this query primarily depends on the quality of the raw water source in relation to the quality of water needed for the factory.
What is a raw water treatment system?
A raw water treatment system consists of multiple individual technologies which address the facility’s particular raw water treatment needs.
Treating raw water is mostly not a static process. A raw water treatment system that is designed, engineered and built to accommodate fluctuations in treatment needs will facilitate in avoiding costly replacements or upgrades in the future.
An efficient cum well-designed raw water treatment system must have the ability to handle the following:
- seasonal variations in turbidity as well as flow
2.·variations in water chemistry needs as well as requisite chemical volumes adjustments
- changes in water quality requirements (the quality of feed water needed for a fresh new boiler)
What are the elements of a basic raw water treatment system?
The list of components of a raw water treatment system will depend on the quality of water being drawn from the source in relation to the quality of water required.
Generally, a basic raw water treatment system shall include the following:
- chemical feed to trigger the flocculation/coagulation of any suspended solid matter
- clarifier to settle out the bigger solid matter
- filtration to remove the tiny particles
- control panel (based on the level of automated operation required)
Based on the requirements of the plant as well as process, these standard components are normally sufficient. If the plant requires a customized or sophisticated system, then one needs to add on some features/technologies.
What does a raw water treatment system facilitate to remove?
A raw water treatment system consists of the technologies necessary to remove the following:
- Suspended/colloidal solids: These cause
- Unpleasant odors in food/beverage product
- Foul process equipment
- Energy losses for the plant
- Silica/colloidal silica: These cause
- Foul/scale boiler equipment
- Reduce the efficiency of plant equipment
- Product contamination
Iron: These cause
- coats fixtures,
- fouls industrial processes,
- foul tastes/odors in products.
- Bacteria: These cause
1.sickness and severe digestive issues/health problems
2.coating in cooling tower components.
- Hardness: These cause
1.Coating in equipment fixtures
2.Plugs in pipes
3.Scales in equipment
4.Buildup of sludge
How does a raw water treatment system function?
A raw water treatment facility process shall consist of the following steps:
Raw water intake
Raw water is defined as the untreated water found naturally in the surrounding environment. This water can come from several sources, including groundwater, rivers, oceans or lakes, An industrial plant takes in the water from the surface water source.
During this process water is pulled in through pipes or by gravitational force through a mesh-screen/grate. This mesh-screen/gate help to eliminate the larger objects, such as leaves, twigs and fish. The water is thereafter pumped into the main facility where treatment starts.
Coagulation
Subsequent to removal of all the large objects from the raw water source, different chemicals are added to a reaction tank to remove the bulk suspended solids as well as other various contaminants.
This process begins with an assortment of mixing reactors either one or two reactors. These reactors add particular chemicals to remove all the finer particles in the water. This happens as a result of the combination of these particles into heavier particles that settle out.
The aluminum-based coagulates such as alum and polyaluminum chloride are the most widely and commonly used coagulates. Coagulation of the particles can also be done by a slight pH adjustment also.
Flocculation
After the completion of coagulation, the water moves into a flocculation chamber. In this chamber, the coagulated particles are slowly stirred along with long-chain polymers. These long-chain polymers are charged molecules that grab all the colloidal as well as coagulated particles and pull these together. This creates visible particles that settle down and look like snowflakes.
Sedimentation
The gravity settler forms the sedimentation part of the raw water treatment process. This is normally a large circular device where flocculated material as well as water flow into the chamber and circulate from the center out. In a very slow settling process, the water rises to the top and overflows at the perimeter of the clarifier.
This allows the solids to settle down to the bottom of the clarifier forming a sludge blanket.
The solids are then brought to the center of the clarifier into a cylindrical tube. In this process, a slow mixing takes place, resulting in the sludge to be pumped out of the bottom into a sludge-handling/ dewatering operation. The dewatering process removes all the water out of the sludge with filter/belt presses, resulting in a solid cake.
The sludge water is put onto the press where the water runs between two belts that squeeze the water out. Subsequently, the sludge is put into a big hopper that goes to either a landfill or to a sludge reuse facility. The water from this process is normally reused as well as added to the front end of the clarifier.
Filtration
This step involves the running of the water overflow into gravity sand filters. These filters are big areas where they put 2-4 feet of sand, which is a finely crushed silica sand with jagged edges. The sand is normally installed in the filter at a depth of 2-4 feet, where it packs tightly. The feed water is then passed through the sand that helps in trapping the particles.
For smaller industrial systems, a packed-bed pressure multimedia filter can be used instead of gravity sand filtration. In some cases, based on the water source and the quantum of iron, one can also use a green sand filter in place of the sand filter. Mostly, the polishing step for conventional raw water treatment is sand filtration.
Ultrafiltration (UF) can also be used after the clarifiers in place of the gravity sand filter in some cases. UF can replace the entire clarification process in total. Membranes have become the newest technology for treatment.
In this technology, water is pumped directly from the raw water source through the UF after the chlorination process. This eliminates the need for the entire clarifier, filtration train.
Disinfection
The next step after the water flows through the gravity sand filter, is disinfection/chlorination to eliminate the bacteria in the water. In some cases, this particular step is performed upstream prior to filtration which will keep the filters disinfected and clean.
In such a case where this step is prior to filtration, larger quantities of disinfectant will be required. In this manner, the filters are disinfected as well as kept free from bacteria as well as the filtered water.
If chlorine is added upfront, then bacteria gets killed and will result in less fouling. If there is bacteria in the bed, one need to grow slime and also need to backwash the filters very often. Hence it depends upon how the system operates, whether the system is set up to chlorinate upstream before filtration or to chlorinate downstream subsequent to filtration.
Distribution
In the case of the raw water treatment being used in an industrial process, the raw water is normally pumped into a holding tank. The water can then be used based on the demands of the facility. For municipal use, the treated water is normally pumped into a distribution system of water towers. Water is also pumped into different collections as well as distribution devices in a loop throughout the city.
Other steps for the raw water treatment process
In some cases, depending upon the plant’s process and quality requirements, some raw water treatment systems might include:
Lime softening
In case of high hardness or sulfates, or other constituents in the water, one need to precipitate or take out, a lime/lime soda process must be used. This increases the pH, resulting in hardness in the water to precipitate out. Cold, hot or warm lime processes will yield a different efficiency in each case. Normally, hotter water eliminates more hardness.
Ion exchange softening
In some industrial as well as municipal applications, if there’s high hardness, there can be post treatment required for the elimination of the hardness. A softening resin can be used instead of using lime. This is a strong acidification exchange process. In this process, resin is charged with a sodium ion.
As the hardness comes through, the resin has a higher affinity for calcium, magnesium, and iron. Hence, the resin will grab that molecule and release the sodium molecule into the water.