Purifying Polluted Water: Is It Possible?

Water is essential for human life, but it is also something we often take for granted. Water pollution is a serious and growing problem, with natural causes such as volcanic eruptions and human-made causes such as industrial waste contributing to the contamination of water sources. Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water, and there are several methods that can be used to achieve this. Boiling water is a simple and cheap method of water purification that is effective at killing micro-organisms, but it does not remove heavy metals or dissolved solids. Other methods of water purification include distillation, chlorination, reverse osmosis, and ultraviolet light treatment. Each method has its own advantages and disadvantages, and often a combination of methods is required to achieve potable water.

Boiling water

Water boils at 212°F (100°C), whereas most microorganisms cannot survive in water above 160°F (71°C) for more than 30 minutes. Boiling water kills harmful bacteria, viruses, and other organisms through denaturation, rendering them unable to reproduce. The high temperature and time spent boiling are critical to effectively killing the organisms in the water.

The boiling process involves bringing water to a rolling boil for at least one minute, with an additional minute or two for added security. At elevations above 5,000 or 6,500 feet, it is recommended to boil the water for three minutes.

While boiling water is an excellent temporary solution, it has some limitations. Boiling does not eliminate biological contaminants, pharmaceuticals, or chemicals like lead, fluoride, and arsenic. In fact, boiling may increase the concentration of certain contaminants, such as lead, making the water more dangerous to consume.

Additionally, boiling water is not a comprehensive purification method as it does not remove all types of contaminants. For example, it is ineffective against "forever chemicals" (PFAS), nitrate from fertilizers, disinfection byproducts, and minerals that contribute to water hardness.

In summary, boiling water can be a useful short-term solution for purifying water, especially in outdoor or emergency situations. However, for long-term use, it is recommended to employ a filtering system or other purification methods to ensure the complete removal of all contaminants.

Distillation

The boiling process kills biological contaminants and separates the water from most dissolved materials and contaminants. The water is placed in a container and heated to a temperature above 212°F (100°C), causing the water to evaporate, leaving behind most contaminants. As the steam rises, it cools and condenses into small droplets of water, which are then collected.

• Bacteria and viruses
• Heavy metals such as lead, arsenic, mercury, and copper
• Soluble minerals such as calcium, magnesium, and phosphorus
• Chemicals like chlorine
• Protozoa, such as Giardia

While distillation is a simple and affordable method of water purification, it does have some disadvantages. It is an energy-intensive process and can be time-consuming. Additionally, distillation removes natural minerals and electrolytes, such as calcium and magnesium, which are important for human health.

Distilled water is commonly used in laboratories and medical facilities due to its purity, and it is also suitable for drinking, especially for those with weakened immune systems. However, it is recommended to consume other types of water as well, as distilled water does not contain the electrolytes and minerals needed by the body.

Chlorination

There are different methods of chlorination in water treatment:

• Plain chlorination: This method is used when the water source is clear and requires no additional treatment for sediment or particulate removal.
• Pre-chlorination: Chlorine is introduced to untreated raw water to enhance coagulation and eliminate taste, odour, and colour issues.
• Post-chlorination: Chlorine is added to treated water after all other treatment stages to provide a final dose that maintains a residual disinfectant in the water during distribution.
• Double or multiple chlorinations: This approach combines pre-chlorination and post-chlorination to address both initial contamination and residual disinfection, effectively treating heavily polluted water sources.
• Breakpoint chlorination: This technique helps determine the optimal amount of chlorine required to achieve the desired level of residual chlorine, ensuring effective disinfection without excessive chlorine use.
• Super chlorination: Chlorine is deliberately added beyond the breakpoint stage, often in response to waterborne disease outbreaks. However, excess chlorine must be removed before supplying the treated water to consumers.

While chlorination has revolutionized water safety and reliability, it has limitations. It may cause allergic reactions in some individuals and is corrosive to certain materials and equipment. Additionally, it has limited effectiveness against some parasites and viruses, such as protozoan cysts, which are resistant to chlorine.

Filtration

The traditional method of filtration is cost-effective but does not deliver completely pure and potable drinking water. An example of a traditional method is the use of a screen with tiny holes to filter out protozoa and some bacteria. However, viruses are too small to be captured by this method.

Modern methods of filtration, such as Reverse Osmosis (RO), Ultraviolet (UV), and Ultrafiltration (UF) purification technologies, are more effective at removing impurities such as chemicals, dissolved solids, and microorganisms. RO, for instance, uses a membrane with fine pores to trap germs and dissolved chemicals, allowing only purified water to pass through. UV filtration, on the other hand, exposes water to ultraviolet light, deactivating microorganisms. UF uses a membrane similar to RO but with larger pores, effectively removing physical impurities, including pathogenic organisms and turbidity.

Reverse osmosis

The reverse osmosis process typically involves four stages of filtration: a sediment filter, pre-carbon block, reverse osmosis membrane, and post-carbon filter. The sediment filter removes the largest particles, like dirt, sand, and rust, to prevent clogging of the subsequent filters. The pre-carbon filter uses activated carbon to prevent anything larger than a speck of flour from passing through, as well as attracting and bonding with positively charged ions to prevent chemical compounds like chlorine and chloramines from passing through to the third filter. The reverse osmosis membrane then removes molecules heavier than water, such as sodium, high levels of lead, dissolved minerals, and fluoride. Finally, the post-carbon filter polishes the water, ensuring it is safe and suitable for its intended use.

Frequently asked questions