Water Purification System

Water purification is the elimination of all contaminants which are both organic and inorganic in nature. We have summed up all the purifications systems onto this page to provide users with options when they want to install one. Different locations have different geographical conditions which affects the quality of water available.

Starting with the classification of water. Depending on the type of source, water can be classified into:

Groundwater
Surface water

From these sources to our drinking glass, water travels a long distance. Water during its course picks up a lot of impurities. These impurities if left untreated could become a source of a lot of diseases.

Impurities based on their composition can be classified as:

Physical - suspended particulate matter, sand, dirt
Chemicals - arsenic, lead, chromium

Biological - algae, bacteria, fungi

Conventional water treatment methods such as Boiling, Sedimentation and Decantation is insufficient to effectively treat them all. Hence we apply different treatment measures to impurities based on their composition in order to eliminate their effects. 

Around a couple of centuries back surface water was as pure as ground water. But with rapid industrialization and urbanization even ground water has become unfit for raw consumption.

Thankfully with time we have experienced great advancement in science and technology. Government control has been helpful in ensuring optimum level of water quality.

But there is always a margin of error and that could cost us dearly if we aren't careful and aware! Below are defined different measures of water treatment.

Sedimentation is perhaps the oldest method known to humans for separating physical contaminants from water.

The impure water is allowed to remain stationary for quite some time. This results into heavy physical particles, under the force of gravity to settle down at the bottom of the container known as 'sludge'. This is Sedimentation.
Water is then poured out of the container without disturbing the sludge. This process is known as Decantation.

There are certain disadvantages associated with Sedimentation and Decantation as we know.

Coagulation on the other hand takes physical water treatment to another level.

It makes use of inorganic coagulants such as aluminium sulfate (or alum) or salts like Iron(III) chloride.
These coagulants neutralizes the free ions in water.
The Iron from the salt Iron(III) chloride interacts and form Hydroxides in water which then precipitates.
This precipitate easily settles at the bottom of the container.
The precipitate is in form of flakes or floc which is removed. This process is known as Flocculation.

Boiling of water is perhaps one of the oldest methods of water purification. As we know water boils at about 100 °C or 212°F at sea level. Heating at such high temperature sterile the water off pathogens like bacteria, virus, etc.

Distillation is composed of two basic processes:

Heating the impure water solution at its boiling point (100°C or 212°F at sea level).
Cooling the evaporated water molecules to condense them into liquid state
Water distiller boils water into vapor and condenses it back into liquid form in a separate container. The condensed purified water is distilled water and the entire process is known as distillation.

It makes use of a physical filter that could accurately let water pass while preventing the impurities to do so. Chemicals or microscopic biological components can also be added to increase the effectiveness of the filter.

The working is simple.

The impure water solution is made to pass through a filter.
The water escapes the fine filter (mostly 0.2 microns in size) but impurities are caught behind.
Thus separating the water from impurities.
The fluids which is able to cross through it is called the filtrate.
Water through filtration is good for human consumption. It ensures safety while maintaining other aesthetic quality of water such as taste and odor.

Filters can remove most of the chemicals and physical impurities. But biological impurities are still a threat. Use of Activated Carbon can solve that problem.

Depending on the type of impurity, the stage of purification and the type of filter is determined.

Screening is first step of water purification. This is a very essential component of the entire filtration process. It separates big, sizable impurities such as boulder, gravel, metals, etc from water. This is important for these impurities could not only damage the equipment and filter membranes but also clog the supply pipeline. The screening process is of two types:

Screening for big coarse particles
Screening for small fine particles
Besides, it also comprise of Trash Plate where big size debris are collected after being separated. This prevents any damage to the filter equipments.

Water is used for many purpose at our homes. Filtering the water at the very source of release i.e. the tap or faucet is a good idea. Many a times we need clean water to wash fruits and vegetables. Why clean water only for drinking.

Make sure to buy the best faucet water purifier for your home.

Based on the size of the impurities to filter, the membrane filter could be classified into four types.

The pore size of the Micro membrane is approximately 0.01 to 10 micron.

Removes Impurities at Macro molecular level.

The pore size of the Ultra membrane is approximately 0.05 to 0.001 micron.

Removes impurities at molecular level. Eg. Bacteria, etc.

The pore size of the Nano membrane is approximately 0.02 to 0.002 micron.

Removes Impurities like ions.E.g. Calcium Ions.

The key advantage of the Nanofiltration membrane over RO and UF membranes is that at the same operating pressure

It provides much higher flux compared to RO and
Exhibits much better salt rejection compared to UF

The pore size of the RO membrane is approximately 0.005 to 0.0001 micron.

Uses a semi-permeable membrane. Removes almost all kinds of impurities of varying size. One of the most popular and recommended household water purification product.

(Due to its popularity it is covered in detail in the section Advance Water Purification Systems)

Chemicals are deployed in this category of water purification systems to treat its impurities.

Chlorine is one of the most popular and powerful water purification agent. It can kill and inhibit the growth of pathogens, parasites, and other disease-causing microbes in water. Cost-effectiveness and easy availability makes it a popular water purification agent.

The most common form of chlorine use is in its compound form of chloramine and chlorine dioxide. Chlorine being a strong oxidant rapidly kills many harmful microorganisms as in bacteria and viruses.

Note: But since chlorine is a toxic gas, it should be used with utmost care. To avoid using chlorine directly, liquid bleach or Sodium hypochlorite (NaOCl) should be used. It releases chlorine when it comes in contact with water. It could typically have 4%-6% chlorine concentration.

Chloramines are formed when chlorine and ammonia come in contact and react with each other. Chloramines are generally preferred over any other forms of chlorine for it produces less amount of by-products.

Though chloramine is not as strong an oxidant as free chlorine but it generates a longer-lasting residual than free chlorine.

To prepare Chloramine : Chlorine +Water + Ammonia

Chlorine maybe one of the powerful disinfectants for purification. But Chlorine is also a threat to human life if consumed with water. It may lead to fatal diseases such as cardiovascular diseases and lung malfunctioning among others. Post disinfection chlorine level should be checked and regulated.

Hydrogen peroxide (H2O2) is a chemical compound formed when water reacts with hydrogen. Works as a mild disinfectant for eliminating the impurities in water. Since it is mild in nature hence it takes more time to work than chlorine.

Fluoride is known for its ability to neutralize bacteria responsible for dental plaque. Hence it is sometimes added to water to prevent tooth decay. It is also known as an anti caries agent.

Fluoride works well for humans but only in minimal quantity in water. Excessive levels of natural fluoride in the source water can be toxic to health. It could cause staining of teeth. The fluoride level should be strictly regulated.

Iodine is more popularly known as a powerful disinfectant. A tincture of iodine could help disinfect wounds and sanitize water for drinking. Insufficient Iodine intake could lead to 'Goitre' or enlargement of thyroid gland.

Iodine is so powerful a chemical that it kills bacteria and viruses at the cellular level. Hence it can be very harmful to humans if taken in high doses. Should generally be avoided as a disinfectant if other defined sources are available.

Ozone is a gas consisting of 3 molecules of oxygen. It is mostly used to remove organic and microbial contamination in water.

(Since it is a very popular technology, it is covered in detail under the section Advanced water purification systems.)

Ultraviolet (UV) radiation is another very powerful disinfectant.

(Since it is a very popular technology, it is covered in detail under the section Advanced water purification systems.)

It is a form of carbon which is processed to have millions of small, low volume micro pores. This increases its surface area for adsorption. Adsorption is the adhesion of atoms or ions of a gas/liquid/solid to a given surface. The aim of the activated carbon also called activated charcoal is to increase this adsorption. Adsorption is more of a surface phenomenon.

It is used because of its ability to trap impurities in its pores. Due to this property it may clear water of certain minerals thus affecting its taste and odor. It is very handy when it comes to removing excessive chlorine in water. It can also successfully capture certain microorganisms and pesticides.

It is however non effective when it comes to trap big sizable impurities or heavy metals. Hence a screening element is used before activated carbon filter. The Carbon Adsorption is dependent on:

Type of Carbon it is made from
Amount of Activated Carbon used in the filter
Design of the filter
Size of the impurity - Big sizable impurities remain unaffected by the filter
Type of Impurity - Doesn't work with heavy metals

Insitu is an advanced water treatment method. Water is treated at its very source (soil or groundwater) instead of treating at the destination of the water supply. It is more of an environmental remediation technique to limit the concentrations of targeted contaminants up to certain acceptable levels.

This is accomplished by injecting strong chemical oxidizers directly into the contaminated medium (soil or groundwater). The oxidation process eliminates the environmental threat.

In this process, organic waste is decomposed by microorganisms such as bacteria and protozoa. The end result of this decomposition is biogas. This biogas contains a high concentration of methane and carbon dioxide. It can be used a flammable material.

It is mostly used to treat the sludge. Due to its way of decomposition it is an energy efficient process.

Anaerobic Decomposition is slower process than aerobic decomposition. Decomposition may take 3-6 months to complete. This is called anaerobic because the bacterial decomposition occurs in lack of oxygen. The anaerobic bacteria converts organic waste into biogas. This biogas is an inflammable gas for its high concentration of methane.

The natural occurring bacteria in Granular Activated Carbon (GAC) is mostly responsible for water treatment.
It can treat a significant amount of Dissolved Organic Carbon.
The biological oxidation in GAC can also remove inorganic compounds such as Ammonia.
This is important as ammonia reacts with chlorine to slow down the disinfection process.

Bioremediation is the use of beneficial microorganisms such as bacteria to eliminate harmful pathogens in water. It is obtained through creating favorable conditions so that our beneficial bacteria population could thrive. Bio-remediation is helpful in treating impurities in water such as :

Alkanes
Perchlorates
Metals
Challenges faced while implementing bio-remediation:

Difficulty in controlling the rate of Microbial activity

Ozone has a very low boiling and freezing point. It has:

Boiling Point : -112 °C

Freezing Point : -192.2 °C at 1 atm

As we know ozone is a gas consisting of 3 molecules of oxygen. Ozone is formed by passing oxygen through a chamber containing ultraviolet (UV) light or through extremely high voltage. Oxygen in its divalent molecular (O2) form is its most stable form. Ozone which is trivalent, is a highly unstable molecule. It is ready to give up its oxygen atom to gain stability. This property makes it a very powerful oxidizing agent. The oxidizing nature of ozone is toxic to most pathogens.

Harmful protozoa forms a protective shield called cysts. This cysts protects not only the protozoa but also other pathogens like bacteria. Ozone disinfection is very effective against this cysts unlike other disinfecting agents. It also works well against almost all other pathogens like fungi, virus.

It is a mostly considered safe and is widely used in Europe and in a few states of United States and Canada.

Reverse osmosis makes use of a Semi-Permeable membrane. Semi-permeable membrane allows selective passage of materials through it. It distinguishes between components at the molecular level. This in essence can differentiate molecular water from pathogens, physical impurities such as debris, salts or inorganic compounds and effectively separates them.

Principal of working:

External mechanical pressure is applied onto the impure water solution in an enclosed container.
Due to this pressure, the ions and compounds are forced to move through the semi-permeable membrane.
The semi-permeable membrane being selective in nature allows only the fine molecules of water to pass.
Since the molecular size of the impurities are large enough, they are left behind.
Pure water is collected and is ready for human consumption.
One important thing to note is that the solvent and impurities eg. dissolved pesticides that are small enough (mostly monovalent) can pass through the membrane. Higher the charge, greater is the rejection by the membrane.In spite of this fact, the success rate of purification for reverse osmosis is around 95%-99%.

The pore structure of this semi-permeable membrane is better than Ultra Filtration membrane.

Reverse osmosis is highly effective in removing impurities such as total dissolved solids (TDS), turbidity, lead and other toxic heavy metals.

References

WHO

USGS

Wikipedia