From the lake to the tap, drinking water undergoes a long process of treatment that is essential to our health. This article discusses some of the key aspects of drinking water treatment.
In addition to pathogens, a variety of inorganic and organic
contaminants may interfere with the disinfection process or pose a risk to the
finished product. These contaminants include pharmaceuticals, hormones,
detergents, plasticizers, fire retardants, and pesticides.
Coagulation and Flocculation
Coagulation and flocculation are two key processes in
drinking water treatment. They help remove the turbidity that is commonly found
in raw water.
Coagulation is a process of adding chemicals that cause
particles to clump together and form 'flocs'. These clumps then sink to the
bottom of the treatment chamber where they can be removed later on.
The most common coagulants used in drinking water and
wastewater treatment are alum, aluminum chloride and polyaluminum chloride
(PAC). Alum is the most widely used coagulant due to its low cost, safety and
corrosion resistance.
In contrast, aluminum chloride and PAC are more expensive and
hazardous. They're also more corrosive and can be toxic to human health.
A water-soluble polymer, called a flocculant, helps bring the
coagulated clumps together to form larger, heavier chains. The flocculant can
be natural or synthetic.
Sedimentation
Sedimentation is the process of particles settling to the
bottom of a body of water. This process occurs naturally in lakes and oceans,
but it is also used in drinking water treatment to remove suspended solids from
water that is high in turbidity.
The size and shape of a particle are also important factors
in sedimentation. Smoother particles settle out quicker and easier than jagged
ones, which can be difficult to deal with.
In drinking water treatment, sedimentation is often performed
using large chambers or basins that allow the particles to settle out in a
controlled manner. The design of these chambers and basins depends on the
turbidity level that needs to be removed.
Smaller sedimentation chambers are made of concrete
rectangular tanks with horizontal flow through them, while larger sedimentation
basins have round shapes. They typically have an inlet at one end that feeds in
a hopper that flows out of the other end of the tank. The inlet and outlet of
these tanks are often shaped to facilitate the settling of particles and reduce
hydraulic short-circuiting.
Filtration
Water is filtered to remove any contaminants that may have
settled on the surface of the water. This includes dissolved minerals and
chemicals, parasites, bacteria, viruses, and toxic substances like herbicides
and pesticides.
Several different chemical processes are used throughout the
treatment process. These include disinfectants, corrosion inhibitors, pH
balancers, and other chemicals that help keep the water safe.
All chemicals that come in contact with the water must be
certified to NSF/ANSI Standard 60 or 61, which ensures they are safe for use.
If you are looking for a specific chemical, it is best to review the product
label or do some research online to find out if it is certified.
Disinfection
Disinfection is the process of using chemicals to kill germs
(microorganisms) on surfaces or objects. This is a very important step in
drinking water treatment, as germs can spread diseases to people.
A disinfectant is a chemical that can kill certain bacteria,
fungi, and viruses. Read the label of the product you choose to disinfect, to
find out what kinds of bacteria it is designed to kill.
Apply the disinfectant to the item or area specified on the
label. Usually, the application method is listed, along with the contact time
and safety measures.
Use a disinfectant that is registered by the EPA, and follow
all instructions on the label for safe handling. This includes wearing gloves
and eye protection, and making sure the surface is completely dry before wiping
or washing away the disinfectant.