Purifying Polluted Water: Methods And Techniques For Clean H2o

Water is essential for all life on Earth, and it is used for almost all household purposes such as drinking, cooking, and cleaning. However, water pollution has become a serious problem and is increasing at an alarming rate. There are many sources of water pollution, including domestic wastewater, industrial waste, agricultural effluents, and natural causes such as volcanic eruptions and earthquakes. These sources can contaminate water with a range of pollutants, including particulates, bacteria, minerals, chemicals, and pharmaceuticals.

Water purification is the process of removing these undesirable contaminants from water to make it fit for specific purposes, most commonly human consumption. There are several methods to purify water, including boiling, distillation, filtration, chlorination, and reverse osmosis. Each method has its advantages and disadvantages, and often multiple technologies must be combined to achieve potable water.

Boiling water

The boiling process involves heating water to 100°C, causing physical changes to occur. Bubbles form at the bottom of the container, gradually rising to the surface before the water transitions into steam and vapour. This process removes some chemicals, such as chlorine, and significantly reduces heavy metals like lead. However, boiling water does not remove all contaminants. It is ineffective against biological contaminants, pharmaceuticals, and other chemicals like fluoride, arsenic, and pesticides. Boiling may even increase the concentration of certain contaminants.

To ensure safe drinking water, it is recommended to combine boiling with other purification methods, such as filtration. Water filters can remove larger particles, sediments, and some bacteria, but they are ineffective against viruses. Reverse osmosis is a type of filtration that can effectively remove contaminants like lead, fluoride, and nitrates, but it is a costly method that produces wastewater. Distillation is another purification method that involves boiling water, collecting the condensed steam, and leaving impurities behind. While distillation is highly effective in removing bacteria, viruses, heavy metals, and minerals, it is a slow process that requires a lot of energy, making it impractical for everyday use. It also removes beneficial minerals from the water.

To purify water by boiling, follow these steps:

• If the water appears cloudy, filter it through a clean cloth, paper towel, or coffee filter.
• Bring the water to a rolling boil. At altitudes below 6,500 feet (or 1,000 to 5,000 feet meters), boil for at least one minute. At higher altitudes, boil for three minutes.
• Allow the water to cool naturally.
• Store the cooled, boiled water in clean, sanitized containers with tight-fitting covers.

While boiling water is an effective short-term solution, it is recommended to use a comprehensive water treatment system or a filtering system for long-term protection and to ensure the complete removal of all contaminants.

Distillation

The process involves subjecting water to a heat source until it reaches its boiling point. It is then left to vaporise. This vapour is then directed into a condenser, where it cools and turns back into liquid water. This water is now clean and safe for drinking. Other substances with a higher boiling point are left behind as sediments in the container.

Chlorination

Chlorine inactivates microorganisms by damaging their cell membranes and disrupting cell respiration and DNA activity. It is effective against most bacteria and viruses but cannot inactivate all microbes, as some protozoan cysts are resistant to chlorine.

Chlorine also has other benefits besides disinfection. It can be used to remove iron, manganese, taste and odour compounds, and colour from the water. It also aids in the sedimentation and filtration processes.

While chlorination is a popular and cost-effective method of water purification, there are some concerns about the health effects of chlorinated water. Chlorinated water has been linked to an increased risk of bladder, colon, and rectal cancer due to the formation of trihalomethanes and other disinfection by-products. However, studies have shown that the benefits of chlorinated water in controlling infectious diseases outweigh the potential risks associated with chlorination.

Filtration

There are several types of filters that can be used to purify water:

• Slow Sand Filters — Water flows very slowly through these filters, relying on biological treatment processes for their action rather than physical filtration. They are carefully constructed using graded layers of sand, with the coarsest sand and some gravel at the bottom and the finest sand at the top. An effective slow sand filter may remain in service for many weeks or even months if the pretreatment is well designed, and it produces water with a very low available nutrient level which physical methods of treatment rarely achieve.
• Rapid Sand Filters — Water moves vertically downward through sand, which often has a layer of activated carbon or anthracite coal above it. The top layer removes organic compounds that contribute to taste and odour. The space between sand particles is larger than the smallest suspended particles, so simple filtration is not enough. Most particles pass through surface layers but are trapped in pore spaces or adhere to sand particles.
• Pressure Filters — These work on the same principle as rapid gravity filters, but the filter medium is enclosed in a steel vessel and the water is forced through it under pressure.
• Membrane Filters — These can remove virtually all particles larger than 0.2 μm, including Giardia and Cryptosporidium. They are widely used for filtering both drinking water and sewage.
• Charcoal Filters — There are three types of charcoal filters: compressed charcoal/carbon block, granular charcoal, and powdered charcoal. The first type is the best as it can remove chemicals and lead, but it is easily clogged, so it should be used with a sediment prefilter. Granular charcoal is cheaper, but water can flow around the granules without being treated. Powdered charcoal is a very fine dust useful for spot-cleaning larger bodies of water, but it is messy and can pass through some filters and be consumed.

In summary, filtration is an effective method for purifying water, especially when combined with other technologies. It is important to use the right type of filter and to maintain them properly to ensure their effectiveness.

Reverse osmosis

The process typically involves several stages of filtration:

• Pre-treatment stage: Sediment filters remove larger particles such as sediment, chlorine, and organic matter that could damage or clog the RO membrane.
• Reverse osmosis filtration: High pressure is applied to push water through the semi-permeable membrane, which has tiny pores (about 0.0001 microns) that block impurities.
• Wastewater disposal: The concentrated contaminants that do not pass through the membrane are expelled as wastewater or "brine".
• Storage and delivery: The purified water is stored in a tank until needed and then delivered through a dedicated faucet.
• Post-treatment stage: On demand, water passes through a post-filter, often a carbon filter, to remove any residual taste before consumption.

One disadvantage of reverse osmosis systems is that they can waste water, with most systems wasting about four gallons of water for every gallon produced. However, this wastewater is not exactly wasted, as it serves the purpose of cleaning the water.

Overall, reverse osmosis is a proven and effective technology for reducing water contaminants, offering clean and safe drinking water.

Frequently asked questions