Water Treatment and Purification

Water treatment and purification reduces the concentration of suspended solid particles and micro-organisms; a range of dissolved inorganic and organic materials; and chemical pollutants. There are many techniques for removing these contaminants.

These include filtration, sedimentation, distillation and membrane processing. Some of these processes are based on physical phenomena such as osmosis, whereas others like chlorine, irradiation and ion exchange rely on chemicals.

Pretreatment

The pretreatment of water is a series of processes used to remove detrimental substances from the water. This can include dissolved minerals, organic pollutants, pharmaceuticals, chemicals, and toxins. These are then used to treat water that can be used for drinking, sanitary, industrial, or other purposes.

Pretreatment can be accomplished by physical methods, such as separation (settling, thermal distillation, filtration and membrane separation) or chemical processes (disinfection and coagulation). It can also involve a combination of these techniques.

Boiling water is the most common and simplest method of pretreatment. This method makes the water microbiologically safe by killing bacteria and other organisms. It is effective even at high water treatment and purification altitudes where the boiling point of water is lower. However, boiling does not remove all impurities from the water, and is best used when other treatment methods are not available.

In many cases, groundwater that is extracted from aquifers may require pretreatment before it can be considered potable. This includes reduction of the iron or manganese content and primary disinfection. The pretreatment of surface waters can be more complicated, as these waters can contain a variety of contaminants and ions from the geology of the area where they originate. For this reason, it is important to understand the water history of a particular water source before using it for human consumption.

Filtration

Water filters are used to remove bacteria and other harmful substances from your home water supply. There are many different types of water treatment systems available. Some are installed at the point of entry to your home’s plumbing system (known as a whole-house filter), while others are installed at the point where the water enters your house or office (an in-home filter). All types of water treatment systems should be tested regularly by a state certified laboratory to ensure they are working properly.

During the filtration process, the water is gently mixed to create larger, heavier particles (known as flocs). Additional chemicals may be added during this stage to help the flocs form easily. The flocs are allowed to settle to the bottom of the water because they are heavier than the surrounding water. This step is called sedimentation. The clear water on top then goes to filtration.

The filtered water now passes through filters that have different pore sizes and are made of materials such as sand, gravel, activated carbon and other minerals. These filters help remove dissolved particles and germs such as dust, chemicals, parasites and bacteria, as well as bad odors. Chemical disinfectants may also be added during this time to kill any remaining organisms that might be present in the water. Once the filtered water is free of unwanted contaminants, it can be stored in tanks or distributed to homes and businesses.

Disinfection

The final step in water treatment is disinfection, which kills or inactivates harmful microorganisms such as bacteria, viruses and parasites. This process may use chemical agents such as chloride and its derivatives or heat, radiation, ultraviolet (UV) light and ozone. The goal is to remove or inactivate pathogenic organisms to ensure that the finished water is safe for human consumption.

Before the disinfection stage, presedimentation to remove fine solids and coagulation with alum reduce organic material in the water that can contaminate pumps. Organic scavenging resins are also used to remove organic compounds that require oxidizing disinfectants such as chlorine. Removal of ferrous iron, nitrites and hydrogen sulfide reduces the demand for these chemicals as well.

Chlorine is the most widely-used oxidizing disinfectant and has been in continuous use for more than 60 years as the primary disinfectant at water treatment plants. However, other disinfectants such as chlorine dioxide, bromine and iodine are also widely employed.

Disinfection is usually performed in the filtration plant to ensure that the disinfectant is present at the point of final water delivery. The amount of time the water is exposed to UV light directly impacts the disinfection effectiveness, and flow patterns and UV lamp fluences steel water purifier are chosen based on the inactivation characteristics of pathogenic organisms such as Giardia cysts and Cryptosporidium spores. The effectiveness of various disinfection methods and their propensity to produce unwanted by-products are carefully compared and weighed against the cost and safety of delivering safe drinking water.

Storage

Often water will be stored in large cement underground tanks called clear wells until it is needed. This storage system needs to be resistant to weather and temperature variations, handle snow and rain, minimize the formation of algae and reduce chlorine treatment costs, and provide an aesthetically-pleasing architectural appearance that reflects community values and contributes to a positive environmental impact.

Filtration is used to reduce turbidity by passing the water through filter media such as sand, gravel, charcoal or granules. This process can also remove pathogens such as worms and bacteria through straining or adsorption.

Chemical treatments can also be used to remove dissolved and suspended contaminants. Coagulants such as aluminum sulfate (alum), ferric sulfate and sodium aluminate have a positive charge that binds negative ions together and causes them to clump into larger, thicker clusters of particles called flocs. Organic polymers are also used as coagulants and flocculants because of their high molecular weights that help them clump more quickly.

Another common way to purify water is by distillation, which involves heating the water until it boils and then collecting the pure water vapor in a separate container. This process is capable of removing bacteria and other disease-causing materials, since they have lower boiling points than the water. Distillation does not, however, remove soluble minerals or prevent the growth of microorganisms such as cryptosporidia and Giardia cysts in stored water.