Chlorination, ozone, ultraviolet light, and chloramines are primary methods for disinfection. However, potassium permanganate, photocatalytic disinfection, nanofiltration, and chlorine dioxide can also be used. Organic material is naturally present in water.
When bacteria are eliminated, the cell wall is penetrated by chlorine dioxide. Viruses are eliminated in a different way; chlorine dioxide reacts with peptone, a water-soluble substance that originates from hydrolisis of proteins to amino acids. Chlorine dioxide kills viruses by prevention of protein formation.
There are three levels of disinfection: high, intermediate, and low.
Chlorine and ozone are two chemicals used to purify water.
The 5 major unit processes include chemical coagulation, flocculation, sedimentation, filtration, and disinfection (described below). There are chemicals added to the water as it enters the various treatment processes.
Chlorine kills pathogens such as bacteria and viruses by breaking the chemical bonds in their molecules. Disinfectants that are used for this purpose consist of chlorine compounds which can exchange atoms with other compounds, such as enzymes in bacteria and other cells. This results in disinfection.
Disinfection and sterilization are both decontamination processes. While disinfection is the process of eliminating or reducing harmful microorganisms from inanimate objects and surfaces, sterilization is the process of killing all microorganisms.
Community Water Treatment
- Coagulation and Flocculation. Coagulation and flocculation are often the first steps in water treatment.
- Sedimentation. During sedimentation, floc settles to the bottom of the water supply, due to its weight.
- Filtration.
- Disinfection.
Water chlorination is the process of adding chlorine or chlorine compounds such as sodium hypochlorite to water. This method is used to kill bacteria, viruses and other microbes in water.
Chlorine and chlorine-based compounds are the only disinfectants that can efficiently kill microorganisms during water treatment, and maintain the quality of the water as it flows from the treatment plant to the consumer's tap.
Top 7 Methods of Water Treatment
- Coagulation / Flocculation. Coagulation is adding liquid aluminum sulfate or alum and/or polymer to raw or untreated water.
- Sedimentation. When water and flocs undergo the treatment process, they go into sedimentation basins.
- Filtration.
- Disinfection.
- Sludge Drying.
- Fluoridation.
- pH Correction.
Chlorine dioxide (ClO2) is a chemical compound consisting of one chlorine atom and two oxygen atoms. It is a reddish to yellowish-green gas at room temperature that dissolves in water.
Distilled Water Removes Minerals and ContaminantsDistillation will not remove all the chemicals but removes soluble minerals (i.e., calcium, magnesium, and phosphorous) and dangerous heavy metals like lead, arsenic, and mercury. Some of the chemicals of concern produce hazardous compounds during the heating process.
Sedimentation is a physical water treatment process using gravity to remove suspended solids from water. Solid particles entrained by the turbulence of moving water may be removed naturally by sedimentation in the still water of lakes and oceans.
Chemical Coagulants Used In Water Treatment
- Aluminum Sulfate (Alum) – One of the most commonly used water treatment chemicals in the world.
- Aluminum Chloride – A second choice to Alum as it is more expensive, hazardous and corrosive.
- Polyaluminum Chloride (PAC) & Aluminum Chlorohydrate (ACH)
Disinfection
- Chemical Disinfectants. Alcohol. Chlorine and chlorine compounds. Formaldehyde. Glutaraldehyde. Hydrogen peroxide. Iodophors.
- Miscellaneous Inactivating Agents. Other germicides. Metals as microbicides. Ultraviolet radiation. Pasteurization. Flushing- and washer-disinfectors.
- Regulatory Framework for Disinfectants and Sterilants.
Ozone (O3) is an unstable gas comprising three atoms of oxygen. The free oxygen atoms or radicals are highly reactive and they will oxidize almost anything (including viruses, bacteria, organic and inorganic compounds) in contacts, making ozone an enormously powerful disinfectant and oxidizer.
Stringent disinfection reduces the risk of healthcare-associated infections (HAIs). Currently, there are five main EPA-registered chemicals that hospitals use for disinfectants: Quaternary Ammonium, Hypochlorite, Accelerated Hydrogen Peroxide, Phenolics, and Peracetic Acid.
Chloramine levels up to 4 milligrams per liter (mg/L) or 4 parts per million (ppm) are considered safe in drinking water. At these levels, no harmful health effects are likely to occur 5.
They often contribute to poor indoor air quality and may contain chemicals that cause cancer, reproductive disorders, respiratory ailments (including occupational asthma), eye and skin irritation, central nervous system impairment, and other human health effects.
Disinfection by-products (DBPs) result from chemical reactions between organic and inorganic matter in water with chemical treatment agents during the water disinfection process.
Chlorine can react with organic materials in water to form disinfection byproducts (DBPs). Surface water sources are more likely to contain the organic materials that combine with chlorine to form DBPs. Scientists have identified hundreds of DBPs.
Trihalomethanes (THMs) are chemical compounds in which three of the four hydrogen atoms of methane (CH4) are replaced by halogen atoms. THMs are also environmental pollutants, and many are considered carcinogenic. Trihalomethanes with all the same halogen atoms are called haloforms.
Chloramines (also known as secondary disinfection) are disinfectants used to treat drinking water and they: Are most commonly formed when ammonia is added to chlorine to treat drinking water. Provide longer-lasting disinfection as the water moves through pipes to consumers.
The level of chlorine in tap water is very low in England and Wales which contrasts very favourably with practices in other countries where much higher levels are common. Typically water companies keep the level of residual disinfectant in the form of free or combined chlorine to 0.5 mg/l or less.
Safe drinking waterCurrent studies indicate that using or drinking water with small amounts of chlorine does not cause harmful health effects and provides protection against waterborne disease outbreaks 2.
Is chlorinated water safe to drink? Yes. The U.S. Environmental Protection Agency (EPA) limits the amount of chlorine in drinking water to levels that are safe for human consumption. The levels of chlorine used for drinking water disinfection are unlikely to cause long-term health effects.
Boil water, if you do not have bottled water. Boiling is sufficient to kill pathogenic bacteria, viruses and protozoa (WHO, 2015). If water is cloudy, let it settle and filter it through a clean cloth, paperboiling water towel, or coffee filter. Bring water to a rolling boil for at least one minute.
Breathing high levels of chlorine causes fluid build-up in the lungs, a condition known as pulmonary edema. The development of pulmonary edema may be delayed for several hours after exposure to chlorine. Contact with compressed liquid chlorine may cause frostbite of the skin and eyes.
The Dangers of Chlorine in Your Drinking WaterStomachaches, vomiting, and diarrhea can all be effects of ingesting chlorine, and it can also cause dry, itchy skin. Severe chlorine poisoning can be far worse – a significant dose of liquid chlorine can be extremely toxic and even fatal to humans.
Filtration - The clear water on top passes through filters composed of sand, gravel and charcoal to remove dissolved particles such as dust, parasites, bacteria, viruses and chemicals. Disinfection - Chlorine or chloramine is added to kill parasites, bacteria, viruses and germs.
A number of commercially available alternative processes, such as membrane processes, are able to remove bacteria, viruses and protozoa as well as a range of chemical contaminants. Alternatives to chemical disinfection, such as UV irradiation, are also being used for disinfection of drinking water.
