Water Purification Methods

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Water purification methods are used to meet water quality standards for individual households and whole cities. Purification methods include boiling water, distillation, disinfection, and filtration, however, less common ways to purify water like solar purification and adding iodine are also sometimes used. 

Water purification involves removing unwanted chemicals, contaminants, suspended solids, and gasses from the water to make it suitable for human use. 

Most drinking water is disinfected and purified to make it safe for human consumption, but water purification methods are also used for a variety of other applications, such as in industrial and pharmaceutical settings. 

Why Is Water Purification Important?

Water purification is important to reduce and remove the number of suspended particles, parasites, algae, viruses, bacteria, and fungi that may harbor inside the water. 

In drinking water, water quality must follow governmental or international standards. For example, according to the EPA (American Environmental Protection Agency), drinking water must have a pH between 6.5 and 8.5. (To measure the pH of your household water, Atlas Scientific has you covered, with our wide range of pH probes and sensors.)

The World Health Organization (WHO) reported that in 2019, billions of people around the world lack access to improved drinking water, and therefore, annual cases of diarrheal diseases due to poor access to water, sanitation, and hygiene contribute to 1.8 million deaths every year.

Deaths from waterborne diseases can easily be preventable using simple techniques to purify water and store it in safe containers.

How To Test Water Quality?

Testing the quality of water is extremely important, particularly when water is going to be used for human consumption. 

To determine water quality, the following variables are measured:

By testing water quality, we can understand the condition of the water and if it needs any treatment before use. This is why water is often purified. 

What Methods Are Used To Purify Water?

Methods to determine water purification are required, as visual inspections alone cannot determine if the water meets the water quality standards. 

When we talk about water purification methods, it is important to understand the difference between a water filter and a water purifier. 

A water filter removes sediment and harmful chemicals and toxins from water. Water filters are also used to make the water look, smell, and taste better.

A water purifier is similar to a water filter, as it also removes impurities, however, they also remove 90-95% of biological contaminants and minerals from the water. The three main water purification methods are reverse osmosis (RO), deionization (using UV), and distillation.

Boiling Water

Boiling water is the safest and cheapest way to purify water; boiling water makes it microbiologically safe and you can easily do it in your home. By increasing the temperature of the water, bacteria, viruses, and some impurities can be removed, as most organisms cannot survive in water above 212 °F. 

However, dead microorganisms and many impurities can still settle at the bottom of the water, therefore boiling will not remove all impurities that thrive in water. To remove all impurities, the water must be strained through a microporous sieve. 

After boiling water, it should be covered and left to cool down before drinking it.

If you can’t boil water, you should use one or more methods to purify water to make it safe to drink. 

Filtration

Filtration is one of the most cost-effective, and commonly used methods to purify water. Filtration is also considered the best at producing healthier purified water, as it doesn’t deplete all the minerals in the water. It uses chemical and physical processes to remove compounds to make water safe for human consumption. Filtrating water is also simple and fast at removing both large and small dangerous compounds that may aggregate inside water, known for causing waterborne diseases. 

Electric reverse osmosis (RO) purifiers that contain UV (ultraviolet) and UF (ultra-filtration) filters are the most trusted method used in houses today. However, there are many other ways you can filtrate water, which we will cover below.

Rapid Sand Filters

Rapid sand filters are the most common type of filter to purify water. Water passes through the sand, which usually has a layer of activated carbon (or anthracite coal) directly above the sand. The carbon filters out organic compounds and improves the taste and odor of the water. Rapid sand filters without additional carbon filters are ineffective against taste and odor. 

Sand filters can filter out any suspended solids larger than the pore sizes between the sand, can easily be cleaned (via a back-flush system), and reused. The constant backwashing can, however, throw off the chemical balance of the water, therefore extra treatments may be required which is an added cost to the purification treatment. 

Rapid sand filters are commonly used in developing countries to treat large amounts of drinking water in a large area.

Slow Sand Filters

When land and space are an issue, a slow sand filter can be used to purify drinking water. The difference between a slow and rapid sand filter is not the filtration speed, but the treatment process. Slow sand filtration systems rely on biological processes rather than physical filtration like rapid sand filters. 

Water flows very slowly through the sand filter, using graded layers, with the finest at the top. The grains of sand are sharp, so they can easily catch dirt, debris, and waste materials as they pass through the layers.

Slow sand filters cannot be backwashed, but they must still be maintained by scraping the top layer of sand from the filter. This prevents any obstructions from biological growth. They are relatively cheap to build, but they require a skilled worker to operate them. 

Bank Filtration

Bank filtration is a simple and cost-effective natural treatment to filter water. Operating well systems are dug in sandy sediments near water bodies, where water can be naturally filtered through the soil/sediment and easily extracted. While bank filtration is not always clean enough for drinking water, water collected from the natural sediments in river banks is much better than directly collecting water from rivers. 

However, bank filtration is sometimes still used as the first stage of contaminant filtration, but usually, other methods such as oxidation and adsorption will need to be used after to purify it to drinking water standards.

Membrane Filtration

Membrane filters are widely used to purify drinking water and sewage by preventing the formation and spread of bacteria and viruses. The filters can also remove suspended solids and sediments, and are commonly used in wastewater applications, as they can operate under pressure or vacuum.

Unfortunately, no filtration method can remove dissolved properties such as phosphates, nitrates, ions, and heavy metals, therefore other purification methods must be used such as distillation or disinfection. 

Distillation

Distillation is a water purification process that utilizes heat, collecting the condensed water in the form of vapor. This process ensures that the water is free from contaminants, heavy metals, and disease-causing properties naturally found in water. However, distillation is not as effective as filtration as it is a very time-consuming process, it requires a heat source, it is expensive, and it eliminates beneficial minerals in the water. 

During the distillation process, the water is heated until it reaches boiling point and left until it vaporizes. The vaporized water is then collected into a condenser to cool. As it cools, the vapor is converted into liquid water, safe for drinking. 

This method is best for small amounts of water, therefore, other purification methods are used for commercial and industrial water purification systems. 

Disinfection

Disinfection both filters harmful microorganisms and utilizes disinfectants to purify water. Water is disinfected to kill any pathogens (viruses and bacteria) as it passes through filters. The filters do this by dosing the water with a disinfectant such as chlorine. 

When a disinfectant is added to the water, it is held in a storage unit such as a tank or clear well to allow the disinfection process to be completed.

Chlorine Disinfection

Chlorination is an older, yet effective technique to purify water, often used in emergencies when other methods are not readily available. A mild bleach, containing ~5% of chlorine, is added to oxidize and kill microorganisms in the water. 

Chlorine tablets or liquid can easily be added to water to make it drinkable, but the tablets must be added to heated water to allow them to dissolve. 

It is important to also note that people suffering from thyroid problems must talk to a doctor before dosing chlorine in water, as chlorine is related to low thyroid issues. 

Chlorine Dioxide Disinfection

Chlorine dioxide is sometimes used, as it is much faster at disinfecting the water than chlorine. Chlorine dioxide purifies water via oxidation. Bacteria are removed when chlorine dioxide penetrates the cell wall, but viruses are a little more complicated to eliminate. To eliminate viruses, chlorine dioxide must react with peptone, preventing protein formation in viruses.

Chlorine dioxide is a small, volatile, and strong molecule that can be found in aqueous solutions to avoid gas handling. As chlorine dioxide contains a lot of chlorite, it is now rarely used because of regulations in the US. 

Chloramine Disinfection

Purifying water with chloramine is becoming more common because it has a lower redox potential compared to chlorine. However, chloramine is not as strong as chlorine, and water that is disinfected with chloramines can experience nitrification. Nitrification can occur in the water because chloramines contain ammonia (and chlorine).

Ozone Disinfection

Ozone is an unstable molecule that happily gives away an oxygen molecule. As dissolved oxygen is toxic to most waterborne organisms, ozone is used to disinfect water in Europe, Canada, and the US to remove pathogens. The use of ozone is often preferred over chlorine as it doesn’t change the taste and odor of drinking water.

However, ozone disinfection is very energy-intensive and is very reactive and corrosive. When working with ozone, the off-gasses must be destroyed to protect workers from exposure.

Ultraviolet (UV) Disinfection

In low turbid water, UV disinfection is very effective at purifying water because it is powerful at inactivating bacteria and viruses. However, as turbidity increases in the water, the effectiveness of using UV disinfection methods is reduced because of the number of suspended solids. 

To measure turbidity levels in samples, a turbidity sensor is used. 

Another issue with UV radiation is that it removes all residual disinfectants in the water, therefore, you will often have to add residual disinfectants such as chloramines to the water after the disinfection process. 

This method is used daily in developing countries to disinfect drinking water.

Other Ways You Can Purify Water

As many people do not have access to the above methods or stronger methods are required, there are also some less common ways to purify water that are worth mentioning. These include solar purification and adding iodine to water. 

Solar Purification & UV Radiation

Solar purification can be used as an alternative to UV filtration/disinfection methods. This involves treating the contaminated water with UV radiation from the sun. 

A container or bottle is filled with the water, shaken to excite the oxygen molecules, and left horizontally in the sun. This simple process effectively kills any bacteria and viruses that may be present in the water, making it safe for drinking. 

When the water is exposed to UV light/radiation, the microorganisms cannot breed further, however, if an RO filter is not used any impurities or heavy metals cannot be removed.

Adding Iodine

Iodine tablets or liquids can easily be added to water to kill bacteria and viruses. This purification method is very powerful, however, it adds an undesirable taste to the water, and in high concentrations, iodine can be fatal to humans. 

Adding iodine to purify water should only be used if no other methods of purification are available. 

Summing Up

It is significant to purify water to remove contaminants and improve the taste, odor, and appearance of drinking water. Water can be purified using simple methods such as boiling water, but other methods such as filtration, distillation, and disinfection are also widely used. 

If you have any questions regarding water quality and water purification methods, or you want to know more about the water quality testing kits we have to offer, please do not hesitate to contact our world-class team at Atlas Scientific

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