Water Treatment

Pure water (H20) is colorless, tasteless, and odorless. It is composed of hydrogen and oxygen. Because water becomes contaminated by the substances with which it comes into contact, it is not available for use in its pure state. To some degree, water can dissolve every naturally occurring substance on the earth. Because of this property, water has been termed a “universal solvent.” Although beneficial to mankind, the solvency power of water can pose a major threat to industrial equipment. Corrosion reactions cause the slow dissolution of metals by water. Deposition reactions, which produce scale on heat transfer surfaces, represent a change in the solvency power of water as its temperature is varied. The control of corrosion and scale is a major focus of water treatment technology.

Waste Water Treatment

Water treatment is an important industry requirement and comes under 4 main branches which include boiler water treatment, cooling water treatment, water purification and the treatment of wastewater effluent. It is considered that these cover the majority of Water treatment processes across the globe. water treatment can be hugely beneficial to your business not least because it can save you tens of thousands of Rupees per year in operating costs but because of reduced maintenance it can also increase efficiency and output. It is an industry which can quickly pay for itself and give back in spades. In addition to the financial benefits it is also important to remember operating efficiently and safely of your employees is too, efficiency and safety come hand in hand.

Type of Impurities in Water

3.1  Physical impurities:

(i)Colour: Yellowish thing indicates the presence of chromium and appreciable amount of organic matter. Yellowish red colour indicates the presence of iron, while red brown colour indicates the presence of peaty matter.

(ii) Turbidity: It is due to the colloidal ,extermely fine suspension such as clay, slit,finely divided matters(organic and inorganic) micro organisms like plankton etc.

(iii)Taste: It is due to the prsence of dissloved mineral in water produces taste, but not odour.

Bitter taste can be due to the prsence of iron, alumminium, maganese, sulphate or excess of lime.Soapy taste can be due to the presence of large amount of sodium bi carbonate.Brackish taste is due to the presence of unusual amount of salts.Polatable Taste is due to the presence of dissolved gases and minerals like nitrates in water.

(iv) Odour: It is in water due to undesirable for domestic as well as industrial purposes.

3.2 Chemical impurities in water:

(i) Acidity: It is not any specific pollutant and it simply determines the power to neutralise hydroxyl ions and is, usually expressed in terms of ppm( or mg/L) of calcium carbonate equivalent.Surface waters and ground waters attain acidity from industrial wastes like acid, mine, drainage, pickling liquors etc.

(ii) Gases: All natural waters contain dissolved atmosphere Co2. Its solubility depends upon temperature, pressure and dissolved mineral content of water.

On the other hand dissolved oxygen in water is essential to the life of aquatic organisms such as fishes. Polluted waters and sewages contains nitrogen in the form of nitrogenous organic compounds and urea, which are partially converted in to NH3.

3.3 biological Impurities

Bacteria, fungi and algae are found in most surface waters. Bacteria are measured by culturing a sample and counting the colony forming units per milliliter (CFU/ml). City water treatment facilities commonly add chlorine to kill microorganisms. This chlorine is removed in the first step of most water purification systems which allows bacteria to multiply in the system. Distillation effectively kills microorganisms, reverse osmosis removes them and UV light can control their growth. All ultrapure water systems must have a 0.2 micron or smaller absolute filter on the outlet to prevent bacteria from contaminating the ultrapure product water. In addition, all water pathways in the system should be regularly sanitized.

Gaseous Impurities

CO2 dissolves in water to form weakly acidic carbonic acid (H2CO3). This gas can be measured with a conductivity/resistivity meter. CO2 is only removed by strong base anion exchange resins. Oxygen is the most common non-ionized gas and is monitored with oxygen sensing electrodes. Oxygen may cause corrosion of metal surfaces and is removed by anion exchange resins in the sulfide form.

Treated Water uses & application

4.1 Boiler Water Treatment

Boiler water treatment is a popular treatment process in industrial plants because of the problem caused by scale formation and corrosion within the system which comes with stream. This at best can cause increased energy costs and a much decreased level of efficiency and a shorter plant life. At worst this can lead to a catastrophic failure with the damage of machinery and more seriously injury and loss of life. Boilers have to work with incredible pressures as water heated in to steam expands in volume over 1000 times and has to travel down narrow steam pipes at over 100 kilometres an hour. Water treatment is an important aspect in making sure this process is kept safe and efficient.

4.1..1 Low pressure Boiler Water Treatment

Lower pressure Boiler & its Use

In a low-pressure boiler the pressure does not exceed 15 psi, and hot water heating boilers are not designed to exceed over 260 psig. The temperature in a low-pressure boiler will not rise above 250 degrees F. Because these types of boilers operate at lower pressures, they don’t need to be monitored regularly and only have to be checked when the appliance begins to break down.

Low-pressure boilers are often used in buildings and designed to heat rooms through radiators. Types of buildings may include restaurants, hospitals, office buildings and schools. The boilers are able to heat the water used in bathrooms and use steam to heat the different rooms throughout the building, allowing them to become warm.

4.1.2 High pressure Boiler Water Treatment

High-Pressure Boiler Definition

High-pressure boilers will heat steam above 15 psi and water at pressures that exceed 160 psig. Temperatures in high-pressure boilers will exceed 250 degrees F. Because of the elevated pressure at which these boilers operate, they need to be monitored to ensure safety at all times. High-pressure boiler operators must inspect switches, valves, safety devices and leaks on a regular basis. Any malfunctions need to be fixed immediately to prevent further damage from occurring.

High-Pressure Boiler Uses

High-pressure boilers are used in industries and designed to generate the steam found in power plants, dry cleaners and laundromats. These boilers were also used in locomotive steam engines to give them the necessary power to run. Individuals who maintain these boilers need to follow certain precautions to avoid burns, shocks and other hazardous conditions.

Boiler Water Treatment

The treatment and conditioning of boiler feed water must satisfy three main objectives:

  • Continuous heat exchange
  • Corrosion protection
  • Production of high quality steam

The primary function of a boiler water treatment program is to keep heat transfer surfaces (stream generating and associated tubes) free from scale and deposition. The second requirement is corrosion inhibition. Boiler deposits are problematical, as they typically contain undesirable levels of metal oxides, mineral scale, sludge, or various combinations.

The components of boiler tube deposits and the mechanisms by which they form are varied and can be complex. Corrosion generally occurs because of excessive levels of dissolved oxygen but can also develop under tube deposits. Deposits and corrosion can lead to boiler tube failures that result in costly repairs and downtime. Boiler systems require effective chemical treatment, accurate monitoring and control

External treatment is the reduction or removal of impurities from water outside the boiler. In general, external treatment is used when the amount of one or more of the feed water impurities is too high to be tolerated by the boiler system in question. There are many types of external treatment (softening, evaporation, deaeration, membrane contractors etc.) which can be used to tailor make feed-water for a particular system. Internal treatment is the conditioning of impurities within the boiler system. The reactions occur either in the feed lines or in the boiler proper. Internal treatment may be used alone or in conjunction with external treatment. Its purpose is to properly react with feed water hardness, condition sludge, scavenge oxygen and prevent boiler water foaming.

The water treatment facilities purify and deaerate make-up water or feed water. Water is sometimes pretreated by evaporation to produce relatively pure vapor, which is then condensed and used for boiler feed purposes. Evaporators are of several different types, the simplest being a tank of water through which steam coils are passed to heat the water to the boiling point. Sometimes to increase the efficiency the vapor from the first tank is passed through coils in a second tank of water to produce additional heating and evaporation. Evaporators are suitable where steam as a source of heat is readily available. They have particular advantages over demineralization, for example, when the dissolved solids in the raw water are very high.

4.2 Cooing Tower Water Treatment

Cooling water systems are an integral part of process operations in many industries. For continuous plant productivity, these systems require proper chemical treatment and preventive maintenance.

Most industrial production processes need cooling water for efficient, proper operation. Refineries, steel mills, petrochemical plants, manufacturing facilities, food plants, large buildings, chemical processing plants, and electric utilities all rely on the cooling water system to do its job. Cooling water systems control temperatures and pressures by transferring heat from hot process fluids into the cooling water, which carries the heat away. As this happens, the cooling water heats up and must be either cooled before it can be used again or replaced with fresh makeup water. The total value of the production process will be sustained only if the cooling system can maintain the proper process temperature and pressure. The cooling system design, effectiveness and efficiency depends on the type of process being cooled, the characteristics of the water and environmental considerations.

4.3 Pharmaceutical Water Treatment (High Purity)

                        4.3.1    Water For Injection (EFI)

                        4.3.2    Water For other process.

Pharmaceutical water treatment requires removing contaminents from municipal drinking water to meet USP standards. There are two basic types of pharmaceutical water; water for topical use or cleaning (sterle purified water, or PW), or water for injection(WFI) which includes sterile water for irrigation and most sterile water for inhalation.

For PW, USP guidelines require a conductivity limit of 0.6–4.7 µS/cm, a total organic carbon or total oxidizable carbon (TOC) limit of 500 ppb (µg/L), and a bacteria-count limit of 100 cfu/mL.

For WFI, the USP guidelines require a conductivity limit of 0.6–4.7 µS/cm, a TOC limit of 500 ppb (µg/L), an endotoxin limit of 0.25 end toxin units/mL and a bacteria-count limit of 10 cfu/100 mL.

The main difference between PW and WFI is the amount of bacterial contamination allowed, measured by colony count and by endotoxin level.

Every water treatment plant is unique, but may include a combination of these methods:

  • Multimedia filtration: Multimedia filters are designed to remove the bulk of suspended contaminants whose size exceeds 10–30 µm.
  • Activated carbon (AC): AC beds, also known as activated carbon filters, most commonly are used to remove chlorine and chloramine compounds from feed water. This filtration process protects downstream equipment such as RO membranes and IX resin beads from the damaging oxidizing action of chlorine and chloramine compounds.
  • Ion Exchange (IX) units: IX technology exchanges undesirable feed water cations and anions with desirable cations and anions. Cations are positively charged atoms and molecules. Anions are negatively charged atoms and molecules. Cation IX units exchange undesirable feed water cations such as calcium, magnesium, lead, and copper with desirable hydrogen ions. Anion IX units exchange undesirable feed water anions such as chloride, sulfate, phosphate, and nitrate with desirable hydroxide ions. The resulting hydrogen and hydroxide ions then combine to form water.
  • Distillation: Distillation units heat the feed water to its boiling point. Most dissolved and suspended contaminants remain in the water phase. The steam that is produced is condensed and typically meets WFI and PW standards.
  • Reverse Osmosis (RO) water treatment: RO water treatment has become the standard at many pharmaceutical water treatment plants. RO technology can be a costeffective replacement for dual cation and anion IX units. RO systems reduce the need to use costly chemicals, especially those that are caustic, and they curtail the ever-increasing cost of regeneration waste disposal. The payback that results from using an RO system can be achieved in less than two years in some situations. An RO membrane system can remove as much as 98–99% or more of all dissolved contaminants and can remove essentially all suspended (particulate) contaminants. However, RO units require pretreatment to prevent scaling, fouling with living and nonliving particulate materials, and chemical attack, commonly by oxidizing agents.
  • Softening: A softener is a type of IX technology that controls scaling in downstream equipment. A softener controls scaling by removing hard scale–forming cations such as calcium and magnesium and exchanging (i.e., replacing) these ions for nonscale- forming sodium ions. An older term, sodium zeolite softening, frequently is used to describe water softening.
  • Cartridge filtration: Cartridge filtration or other prefiltration technology is used ahead of RO units to protect against fouling from suspended particles in the feed water. RO membrane systems may become fouled if sufficient suspended solids (particulate) removal is not accomplished. Typically, 1–5-µm nominally rated filter cartridges are used.
  • Mixed-bed IX units usually are positioned after an RO subsystem. The effluent from a mixed-bed IX unit meets USP conductivity limits for PW and WFI.
  • UV irradiation may be used for bacterial control.
  • Electrodeionization (EDI): EDI units in many cases can cost-effectively replace mixed-bed IX units. The resin beads in EDI units do not require chemical regeneration by acid and caustic. EDI units are continuously regenerated electrically.

Technologies and treatment

5.1 Membranes & separation

5.1.1 Reverse Osmosis Plant

5.1.2 Ultra Filtration Plant

5.1.3 Nano Filtration Plant

5.1.4 Micro Filtration Plant

Reverse osmosis (RO) is a water purification technology that uses a semipermeable membrane. This membrane-technology is not properly a filtration method. In RO, an applied pressure is used to overcome osmotic pressure, a colligative property, that is driven by chemical potential, a thermodynamic parameter. RO can remove many types of molecules and ions from solutions and is used in both industrial processes and in producing potable water. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be “selective,” this membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (such as the solvent) to pass freely.

In the normal osmosis process, the solvent naturally moves from an area of low solute concentration (High Water Potential), through a membrane, to an area of high solute concentration (Low Water Potential). The movement of a pure solvent is driven to reduce the free energy of the system by equalizing solute concentrations on each side of a membrane, generating osmotic pressure. Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications. However, there are key differences between reverse osmosis and filtration. The predominant removal mechanism in membrane filtration is straining, or size exclusion, so the process can theoretically achieve perfect exclusion of particles regardless of operational parameters such as influent pressure and concentration. Moreover, reverse osmosis involves a diffusive mechanism so that separation efficiency is dependent on solute concentration, pressure, and water flux rate.[1] Reverse osmosis is most commonly known for its use in drinking water purification from seawater, removing the salt and othereffluent materials from the water molecules.

Ultrafiltration (UF)

Ultrafiltration (UF) is a variety of membrane filtration in which forces like pressure or concentration gradients leads to a separation through a semipermeable membrane. Suspended solids andsolutes of high molecular weight are retained in the so-called retentate, while water and low molecular weight solutes pass through the membrane in the permeate. This separation process is used in industry and research for purifying and concentrating macromolecular (103 – 106 Da) solutions, especially protein solutions. Ultrafiltration is not fundamentally different from microfiltration,nanofiltration or membrane gas separation, except in terms of the size of the molecules it retains – it is defined by the Molecular Weight Cut Off (MWCO) of the membrane used. Ultrafiltration is applied in cross-flow or dead-end mode.

Industries such as chemical and pharmaceutical manufacturing, food and beverage processing, and waste water treatment, employ ultrafiltration in order to recycle flow or add value to later products. But also blood dialysis belongs to ultrafiltration.


Nanofiltration is a relatively recent membrane filtration process used most often with low total dissolved solids water such as surface water and fresh groundwater, with the purpose of softening (polyvalent cation removal) and removal of disinfection by-product precursors such as natural organic matter and synthetic organic matter. [1] [2]

Nanofiltration is also becoming more widely used in food processing applications such as dairy, for simultaneous concentration and partial (monovalent ion) demineralisatio

Nanofiltration is a membrane filtration based method that uses nanometer sized cylindrical through-pores that pass through the membrane at a 90°. Nanofiltration membranes have pore sizes from 1-10 Angstrom, smaller than that used in microfiltration and ultrafiltration, but just larger than that in reverse osmosis. Membranes used are predominantly created from polymer thin films. Materials that are commonly used include polyethylene terephthalate or metals such as aluminum.[3] Pore dimensions are controlled by pH, temperature and time during development with pore densities ranging from 1 to 106 pores per cm2. Membranes made from polyethylene terephthalate and other similar materials, are referred to as “track-etch” membranes, named after the way the pores on the membranes are made.[4] “Tracking” involves bombarding the polymer thin film with high energy particles. This results in making tracks that are chemically developed into the membrane, or “etched” into the membrane, which are the pores. Membranes created from metal such as alumina membranes, are made by electrochemically growing a thin layer of aluminum oxide from aluminum metal in an acidic medium.

Range of applications

Sr NoIndustryUses
1Fine chemistry and PharmaceuticalsNon-thermal solvent recovery and management
Room temperature solvent exchange
2Oil and Petroleum chemistryRemoval of tar components in feed
Purification of gas condensates
3Bulk ChemistryProduct Polishing
Continuous recovery of homogeneous catalysts
4Natural Essential Oils and similar productsFractionation of crude extracts
Enrichment of natural compounds Gentle Separations
5MedicineAble to extract amino acids and lipids from blood and other cell culture


Microfiltration (commonly abbreviated to MF) is a type of physical filtration process where a contaminated fluid is passed through a special pore-sized membrane to separate microorganismsand suspended particles from process liquid. It is commonly used in conjunction with various other separation processes such as ultrafiltration and reverse osmosis to provide a product stream which is free of undesired contaminants.

Microfiltration usually serves as a pre-treatment for other separation processes such as ultrafiltration, and a post-treatment for granular media filtration. The typical particle size used for microfiltration ranges from about 0.1 to 10 µm.[1] In terms of approximate molecular weight these membranes can separate macromolecules generally less than 100,000 g/mol.[2] The filters used in the microfiltration process are specially designed to prevent particles such as, sediment, algae, protozoa or large bacteria from passing through a specially designed filter. More microscopic, atomic or ionic materials such as water (H2O), monovalent species such as Sodium (Na+) or Chloride (Cl-) ions, dissolved or natural organic matter, and small colloids and viruses will still be able to pass through the filter.[3]

The suspended liquid is passed though at a relatively high velocity of around 1–3 m/s and at low to moderate pressures (around 100-400 kPa) parallel or tangential to the semi-permeable membrane in a sheet or tubular form.[4] A pump is commonly fitted onto the processing equipment to allow the liquid to pass through the membrane filter. There are also two pump configurations, either pressure driven or vacuum. A differential or regular pressure gauge is commonly attached to measure the pressure drop between the outlet and inlet streams. See Figure 1 for a general setup.

Figure 1: Overall setup for the Microfiltration system

The most abundant use of microfiltration membranes are in the water, beverage and bio-processing industries (see below). The exit process stream after treatment using a micro-filter has a recovery rate which generally ranges to about 90-98 %.[6]

Membrane filtration processes can be distinguished by three major characteristics; Driving force, retentate stream and permeate streams. The microfiltration process is pressure driven with suspended particles and water as retentate and dissolved solutes plus water as permeate. The use of hydraulic pressure accelerates the separation process by increasing the flow rate (flux) of the liquid stream but does not affect the chemical composition of the species in the retentate and product streams.[14]

A major characteristic that limits the performance of microfiltration or any membrane technology is a process known as fouling. Fouling describes the deposition and accumulation of feed components such as suspended particles, impermeable dissolved solutes or even permeable solutes, on the membrane surface and or within the pores of the membrane. Fouling of the membrane during the filtration processes decreases the flux and thus overall efficiency of the operation. This is indicated when the pressure drop increases to a certain point. It occurs even when operating parameters are constant (pressure, flow rate, temperature and concentration) Fouling is mostly irreversible although a portion of the fouling layer can be reversed by cleaning for short periods of time.

Microfiltration membranes can generally operate in one of two configurations.

Cross-flow filtration: where the fluid is passed through tangentially with respect to the membrane.[16] Part of the feed stream containing the treated liquid is collected below the filter while parts of the water are passed through the membrane untreated. Cross flow filtration is understood to be a unit operation rather than a process. Refer to Figure 2 for a general schematic for the process.

Dead-end filtration; all of the process fluid flows and all particles larger than the pore sizes of the membrane are stopped at its surface. All of the feed water is treated at once subject to cake formation.[17] This process is mostly used for batch or semicontinuous filtration of low concentrated solutions,

Power plant

A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to the different fossil fuelresources generally used to heat the water. Some prefer to use the term energy center because such facilities convert forms of heat energy into electrical energy.[1] Certain thermal power plants also are designed to produce heat energy for industrial purposes of district heating, ordesalination of water, in addition to generating electrical power. Globally, fossil fueled thermal power plants produce a large part of man-made CO2emissions to the atmosphere, and efforts to reduce these are varied and widespread

Textile industry and water treatment

The textile industry is very water intensive. Water is used for cleaning the raw material and for many flushing steps during the whole production. Produced waste water has to be cleaned from, fat, oil, color and other chemicals, which are used during the several production steps. The cleaning process is depending on the kind of waste water (not every plant use the same way of production) and also on the amount of used water. Also not all plants uses the same chemicals, especially companies with a special standard (environmental) try to keep water cleaned in all steps of production. So the concepts, to treat the water can differ from each other.

Water treatment with different kind of pollutants, is large-scale, because of many cleaning and removing steps involved.


The diagram above shows a general overview over the several steps in water treatment in the textile industry.

Screening, straining

This first step of treatment is to remove small particles from the process water. In this way the water will cleaned from fibres, fluff and cotton flock. Fore these filter steps drum- and bag filters are used.

Oil removal (if required)

If during the step of wool treatment, solvents like white spirit or others are used they have to be removed from the waste water. Membranes or oil removers are useful. Because of oil or other organic solvents in the water, microorganisms can be killed.


This step is useful to mix the water. With this step, the pollution is better distributed. That makes it more easy for microorganisms to treat the water. Result is a more effective biological cleaning step.


After homogenization, the solution has a pH of around 9 to 10. Neutralization of the water can be done by acid or air flow injector depending on the pH value.

Physical- chemical- treatment

If the concentration of dissolved solids is very high (sulfides, chromates, etc.) and/ or color is also in the water, the kind of treatment is various.

Possible are the following procedures:

  • catalyzed oxidation of sulfides
  • flocculation
  • decoloring with flotation

Biological purification

The type of biological treatment depends on the concentration and kind of pollutant. Two biological steps are used:

trickling filter

The construction is a great reservoir, which is filled with plastic “pieces”, crushed siliceous rocks or other materials which have a very large surface. The large surface gives microorganisms an easy chance to grow. The trickling apparatus sprinkles the waste water over the loaded material. Air is blowing into the pool from top or from below to give the aerobe bacteria the right living conditions. With the growing of the bacteria the biologic dismantlement particles in the waste water will be treated.

This easiest step of biological treatment is reducing the BOD5 between 50 and 70%. A disadvantage is a very good filtrated water without particles which could clog the spray nozzles. Depending on this fact a flocculation process before trickling is necessary.

activated sludge

With this kind of procedure the waste water does not have to be flocculated because the bacteria live in the sludge. The principle is easy, waste water is filled into a pool where the bacteria are living. By a fan air is blowing into the water to give the aerobe bacteria the right growing conditions. The sludge, together with the bacteria are the activated sludge. BOD5removal rates reach 90 to 95%.

To dump the sludge, it has to be thicken. This can be done by different procedures, depending on the amounted sludge, which have to be dumped.


If it is necessary this last step of treatment will remove the color by oxidation, adsorption or other procedures.

  • Demineralization Plant:

Demineralization or Deionisation is the process of removing mineral salts from water by using the ion exchange process. Impurities that remains dissolved in water dissociate to form positive and negative charged particles known as ions. An ion-exchange vessel holds ion-exchange resin of the required type through which water is allowed to pass. The selective ions in the water are exchanged with ions or radicals loosely held by the resin. In this way, the water is passed through several vessels or a mixed bed vessel so that both positive and negative ions are removed and water is dematerialized.

  • Water Softening :

ion-exchange resins are used to replace the magnesium and calcium ions found in hard water with sodium ions. When the resin is fresh, it contains sodium ions at its active sites. When in contact with a solution containing magnesium and calcium ions (but a low concentration of sodium ions), the magnesium and calcium ions preferentially migrate out of solution to the active sites on the resin, being replaced in solution by sodium ions. This process reaches equilibrium with a much lower concentration of magnesium and calcium ions in solution than was started with.

The resin can be recharged by washing it with a solution containing a high concentration of sodium ions (e.g. it has large amounts of common salt (NaCl) dissolved in it). The calcium and magnesium ions migrate off the resin, being replaced by sodium ions from the solution until a new equilibrium is reached. The salt is used to recharge an ion-exchange resin which itself is used to soften the water.

Filtration :

  • Slow sand filters :

Slow sand filters :are used in water purification for treating raw water to produce a potable product. They are typically 1 to 2 metres deep, can be rectangular or cylindrical in cross section and are used primarily to treat surface water. The length and breadth of the tanks are determined by the flow rate desired by the filters, which typically have a loading rate of 0.1 to 0.2 metres per hour (or cubic metres per square metre per hour). Slow sand filters differ from all other filters used to treat drinking water in that they work by using a complex biological film that grows naturally on the surface of the sand. The sand itself does not perform any filtration function but simply acts as a substrate.

  • Rapid sand filter

The rapid sand filter or rapid gravity filter is a type of filter used in water purification and is commonly used in municipal drinking water facilities as part of a multiple-stage treatment system.[1]Rapid sand filters use relatively coarse sand and other granular media to remove particles and impurities that have been trapped in a floc through the use of flocculation chemicals—typically salts of aluminium or iron. Water and flocs flows through the filter medium under gravity or under pumped pressure and the flocculated material is trapped in the sand matrix.

Mixing, flocculation and sedimentation processes are typical treatment stages that precede filtration. Chemical additives, such as coagulants, are often used in conjunction with the filtration system.

  • Screen Filter

A screen filter is a type of filter using a rigid or flexible screen to separate sand and other fine particles out of water for irrigation or industrial applications. These are generally not recommended for filtering out organic matter such as algae, since these types of contaminants can be extruded into spaghetti-like strings through the filter if enough pressure drop occurs across the filter surface. Typical screen materials include stainless steel (mesh), polypropylene, nylon and polyester.

  • Coagulation

Coagulation (thrombogenesis) is the process by which blood forms clots. It is an important part of hemostasis, the cessation of blood loss from a damaged vessel, wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel. Disorders of coagulation can lead to an increased risk of bleeding (hemorrhage) or obstructive clotting (thrombosis).[1]

Coagulation is highly conserved throughout biology; in all mammals, coagulation involves both a cellular (platelet) and a protein (coagulation factor) component.[2] The system in humans has been the most extensively researched and is the best understood.[citation needed]

Coagulation begins almost instantly after an injury to the blood vessel has damaged the endothelium lining the vessel. Exposure of the blood to proteins such as tissue factor initiates changes to blood platelets and the plasma protein fibrinogen, a clotting factor. Platelets immediately form a plug at the site of injury; this is called primary hemostasisSecondary hemostasis occurs simultaneously: Proteins in the blood plasma, called coagulation factors or clotting factors, respond in a complex cascade to form fibrin strands, which strengthen the platelet plug.[

  • Flocculation

Flocculation, in the field of chemistry, is a process wherein colloids come out of suspension in the form of floc or flake; either spontaneously or due to the addition of a clarifying agent. The action differs from precipitation in that, prior to flocculation, colloids are merely suspended in a liquid and not actually dissolved in a solution. In the flocculated system, there is no formation of a cake, since all the flocs are in the suspension.

  • Neutralization 

In chemistry, neutralization (or neutralisation, see spelling differences) is a chemical reaction in which an acid and a base react to form a salt.Water is frequently, but not necessarily, produced as well. Neutralizations with Arrhenius acids and bases always produce water where acid–alkali reactions produce water and a metal salt.

Often, neutralization reactions are exothermic (the enthalpy of neutralization). For example, the reaction of sodium hydroxide and hydrochloric acid. However, forms of endothermic neutralization do exist, such as the reaction between sodium bicarbonate (baking soda) and acetic acid (vinegar).

Neutralization reactions do not necessarily imply a resultant pH of 7. The resultant pH will vary based on the respective strengths of the acid and base reactants.

  • Sedimentation

Sedimentation is a physical water treatment process using gravity to remove suspended solids from water.Solid particles entrained by the turbulence of moving water may be removed naturally by sedimentation in the still water of lakes and oceans. Settling basins are ponds constructed for the purpose of removing entrained solids by sedimentation. Clarifiers are tanks built with mechanical means for continuous removal of solids being deposited by sedimentation.