Drinking water treatment

Introduction to water

Water, odorless, tasteless, transparent liquid that is colorless in small amounts but exhibits a bluish tinge in large quantities. It is the most familiar and abundant liquid on earth Water covers 71% of the Earth’s surface. It is vital for all known forms of life. On Earth, 96.5% of the planet’s water is found in seas and oceans, 1.7% in groundwater, 1.7% in glaciers and the ice caps of Antarctica and Greenland, a small fraction in other large water bodies, and 0.001% in the air as vapor, clouds (formed of solid and liquid water particles suspended in air), and precipitation. Only 2.5% of the Earth’s water is freshwater, and 98.8% of that water is in ice and groundwater. Less than 0.3% of all freshwater is in rivers, lakes, and the atmosphere, and an even smaller amount of the Earth’s freshwater (0.003%) is contained within biological bodies and manufactured products.

Getting enough water every day is important for your health. Healthy people meet their fluid needs by drinking when thirsty and drinking with meals. Most of your fluid needs are met through the water and beverages you drink. However, you can get some fluids through the foods that you eat. For example, broth soups and foods with high water content such as celery, tomatoes, or melons can contribute to fluid intake.

Water helps your body:

Helps Maintain the Balance of Body Fluids.Your body is composed of about 60% water. The functions of these bodily fluids include digestion, absorption, circulation, creation of saliva, transportation of nutrients, and maintenance of body temperature.

Water Can Help Control Calories. For years, dieters have been drinking lots of water as a weight loss While water doesn’t have any magical effect on weight loss, substituting it for higher calorie beverages can certainly help. Drinking it helps you think, focus and concentrate better and be more alert. As an added bonus, your energy levels are also boosted

Flushes Out Toxins – Gets rid of waste through sweat and urination which reduces the risk of kidney stones and UTI’s (urinary tract infections).

Improves Skin Complexion – Moisturizes your skin, keeps it fresh, soft, glowing and smooth. Gets rid of wrinkles. It’s the best anti-aging treatment around!

Maintains Regularity– Aids in digestion as water is essential to digest your food and prevents constipation.

Boosts Immune System– A water guzzler is less likely to get sick. And who wouldn’t rather feel healthy the majority of the time? Drinking plenty of water helps fight against flu, cancer and other ailments like heart attacks.

Prevents Cramps & Sprains- Proper hydration helps keep joints lubricated and muscles more elastic so joint pain is less likely.

Regulation:

All public water systems in the U.S. are required to follow the standards and regulations set by the U.S. Environmental Protection Agency (EPA).

EPA regulations that protect public water systems do not apply to privately owned wells or other individual water systems. Owners of private wells are responsible forensuring that their well water is safe from contaminants.

Prevention:

The impact of clean water technologies on public health in the U.S is estimated to have had a rate of return of 23 to 1 for investments in water filtration and chlorination during the first half of the 20th century.

Community water fluoridation prevents tooth decay safely and effectively. Water fluoridation has been named one of 10 great public health achievements of the 20th century.

Drinking water treatment

Different companies using the same technique with different equipment

Process diagram for a conventional water treatment plant. The combination of the first 3 steps primarily removes colloids (including some microorganisms) and natural organic matter (NOM). Step 4 (rapid sand filtration) is a polishing step that removes much of the   colloidal material remaining after step 3 (sedimentation)

Stages of water treatment:

Preliminary Treatment

Preliminary treatment or pretreatment is any physical, chemical or mechanical process used on water before it undergoes the main treatment process. During preliminary treatment:

Screens ( Membranes) may be used to remove rocks, sticks, leaves and other debris

Chemicals may be added to control the growth of algae; and

Presedimentation stage can settle out sand, grit and gravel from raw water.

Coagulation

After preliminary treatment, the next step is coagulation.   Coagulation removes small particles that are made up of microbes, silt and other suspended material in the water.  Treatment chemicals such as alum are added to the water and mixed rapidly in a large basin. The chemicals cause small particles to clump together (coagulate). Gentle mixing brings smaller clumps of particles together to form larger groups called “floc”. Some of the floc begins to settle during this stage

Flocculation

During the flocculation stage, the heavy, dense floc settles to the bottom of the water in large tanks. As you can imagine, this can be a slow process! Once the floc settles, the water is ready for the next stage of treatment.

Clarification

Clarification occurs in a large basin where water is again allowed to flow very slowly. Sludge, a residue of solids and water, accumulates at the basin’s bottom and is pumped or scraped out for eventual disposal. Clarification is also sometimes called sedimentation.

Softeningand Stabilization

When water is too “hard” (i.e. contains too much calcium, magnesium or other minerals), it forms scale and causes a variety of problems in pipes. Hard water can also result in laundering and washing problems, because it reduces the effectiveness of soaps and detergents. Conversely, when too many of these minerals are removed, water can become too “soft”.  Soft water can cause corrosion in pipes. Drinking water plants attempt to maintain a desirable balance between hardness and softness. This is accomplished by adding minerals to soft water and removing them from hard water. (Measure hardness as CaCO3 with a Hatch titration procedure based on the USEPA-approved method.)

Filtration

Turbidity is a physical characteristic that makes water appear cloudy when suspended matter is present. The filtration process removes suspended matter, which can consist of floc, microorganisms (including protozoan cysts such as Giardia and Cryptosporidium), algae, silt, iron, and manganese precipitates from ground-water sources, as well as precipitants which remain after the softening process. These suspended materials are filtered out when water passes through beds of granular material, usually composed of layers of sand, gravel, coal, garnet, or related substances. (Measure turbidity with a Hatch turbid meter.)

Fluoridation & Disinfection

Fluoride (F-) is added to water to reduce tooth decay. Fluoridation is an effective, economical process endorsed by many public health groups worldwide. Fluoride is fed into the water system as either a dry powder or in solution. (A Hatch fluoride test detects fluoride levels in the water.)During disinfection, disease-causing organisms are destroyed or disabled. Chlorine (Cl2) is the most common disinfectant used in the United States because it is practical, effective and economical. Because chlorine dissipates rapidly, it is important to add the right amount of chlorine at the water treatment plant to make sure disinfection continues while the water is flowing through the distribution system. (Use a USEPA-approved Hatch method to measure chlorine in water.)

Holding Tanks

Finished water (the term water treatment professional use) is stored in holding tanks.  The tanks provide a water reserve to meet the changing water demands of the communities they serve.

ABMA and ASME Standards

The American Boiler Manufacturers’ Association (ABMA) and the American Society of Mechanical Engineers (ASME) have developed suggested limits for boiler water composition which depend upon the type of boiler and the boiler operating pressure. These control limits for boiler water solids are based upon one or more of the following factors:

Sludge and Total Suspended Solids — these result from the precipitation in the boiler of feed water hardness constituents due to heat and to interaction of treatment chemicals, and from corrosion products in the feed They can contribute to boiler tube deposits and enhance foaming characteristics, leading to increased carryover.

Total Dissolved Solids — these consist of all salts naturally present in the feed water, of soluble silica, and of any chemical treatment added. Dissolved solids do not normally contribute to scale formation but excessively high concentrations can cause foaming and carryover or can enhance “under deposit” boiler tube corrosion.

Silica — this may be the blow down controlling factor in softened waters containing high silica. High boiler water silica content can result in silica vaporization with the steam, and under certain circumstances, siliceous scale. This is illustrated by Silica content of the boiler water is not as critical for steam systems without steam turbines.

Iron — occasionally in high pressure boilers where the iron content is high in relation to total solids, blow down may be based upon controlling iron concentrations. High concentrations of suspended iron in boiler water can produce serious boiler deposit problems and are often indications of potentially serious corrosion in the steam/steam condensate systems.

Conclusion

In the developing world today, poor access to safe water and adequate sanitation continues to be a threat to human health. In 2003, 1.6 million deaths were estimated to be attributable to unsafe water and sanitation, including lack of hygiene; 90% of this burden is concentrated on children under five, mostly in developing countries. In spite of the considerable investment in the provision of water supply and sanitation in the 1980s and 1990s, in 2000 a significant proportion of the world’s population remained without access: an estimated 1.1 billion people were without access to improved water sources and 2.4 billion people lacked access to improved sanitation. Expanding this access is essential to reduce the burden of water-related diseases and to improve the well-being of a large part of the world’s population. It is also a vital input into economic development and poverty alleviation. Evaluating the health and the socio-economic benefits of safe water and adequate sanitation results in a compelling argument in support of further resource allocations to improving access. Therefore, assessing the costs, the health benefits and the additional benefits of improving access to safe water supply and sanitation helps to support rational and informed decision-making, for resource allocation. Among the many possible and valid criteria, the ratio of economic costs and benefits of different intervention options is critically important. Based on the present analysis, achieving the water and sanitation MDG target would definitely bring economic benefits, ranging from US$3 to US$34 per US$ invested, depending on the region. Additional improvement of drinking-water quality, such as point-of-use disinfection, in addition to access to improved water and sanitation would lead to a benefit ranging from US$5 to US$60 per US$ invested. From a health point of view, achieving the water and sanitation MDG target, by using simple technologies, would lead to a global average reduction of 10% of episodes of diarrhea. Choosing more advanced types of technologies such as provision of regulated in-house piped water would lead to massive overall health gains, but it is also the most expensive intervention. The burden of disease associated with lack of access to safe water supply, adequate sanitation and lack of hygiene is concentrated on children under five in developing countries. Accordingly, emphasis should be placed on interventions likely to yield an accelerated, affordable and sustainable health gain amongst this group. The present analysis points to household water treatment and safe storage as one option of particular potential. This intervention results in high health improvements while incremental costs remain low compared to other types of interventions.