Water Treatment: Keeping it Pure

Resources in Technology

Water Treatment: Keeping it Pure

By Petros J. Katsioloudis

A simple activity that can be conducted with students is the filtration of water with the use of a homemade filter.

The availability of water has dictated the location and survival of civilizations through the ages. Nearly 1.1 billion people around the world lack access to potable drinking water sources, and 2.2 million die from basic hygiene-related disease, an issue that can easily be justified as the most important environmental problem of all (World Health Organization, 2007). The majority of these deaths are wholly preventable through effective improvements in water, sanitation, and hygiene. The United States remains strongly committed to providing safe drinking water for all of its citizens (Environmental Protection Agency (EPA, 2005)).

The national goal for sanitary drinking water has been to provide water that meets all health-based standards to 95% of the population served by public drinking water supplies by 2005 (EPA, 1999). In 2002, the level of compliance with these health-based issues was 94% (EPA, 2003). However, conventional piped water systems using effective treatment to deliver safe water to households may be decades

away in much of the developing world. This leaves the majority of the poorest people in the world with the task

Photo 1. Wastewater Treatment

As agriculture and industry use more and more water to meet crop and manufacturing needs, there is a growing need to process and clean wastewater for recycling and consumer use. Agricultural runoff may include nutrients and other chemi-cals that can have negative impacts on public health and the ­environment. Efforts are being made to control runoff and remove contaminants from such water.

of collecting water outside the home, then treating and storing it themselves (Sobsey, 2002). Even though water is essential for human life and its quantity and quality are equally imperative, natural waters are in most cases not

Credit: Department of Primary Industries

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aesthetically or hygienically appropriate to be consumed, thus calling for some means of treatment. Appearance, taste, and odor are useful indicators for the quality of drinking water, but the critical suitability factor in terms of public health is determined by microbiological, physical, chemical, and radiological characteristics. As far as is known, the

first instance of filtration as a means of water treatment dates from 1804, when John Gibb designed and built an experimental slow -sand filter for his bleachery in Paisley, Scotland, and sold the surplus treated water to the public at a halfpenny per gallon (Baker, 1949). In 1855 the first mechanical filters were installed in the U.S. (Baker, 1949). Since then a number of modifications and improvements have been introduced and have attained varying degrees of

popularity. Table 1 describes a number of the most common water-treatment methods. A variety of technologies for water treatment exist; some are based on historical water-

treatment techniques. However, there is new research that has found effective reduction of waterborne pathogens using innovative technologies (Lantagne, 2007).

Historical Background

According to the Public Health Service (PHS), (2005) the federal regulation of drinking water quality began in 1914, when standards were set for the bacteriological quality

of drinking water (PHS, 2005). The standards, however, applied only to water systems that provided drinking water to interstate carriers such as ships and trains, and only applied to contaminants capable of causing contagious disease. Upon revision in 1925, 1946, and 1962, PHS revised the standards to regulate 28 substances, establishing the most comprehensive federal drinking water standards

in existence before the Safe Drinking Water Act of 1974.

Table 1. Most Common Water-Treatment Methods

Boiling Blends

1.  Simple method for the inactivation of viral, parasitic, 1.  Sachet: a packet containing powdered ferrous sulfate (a

and bacterial pathogens. flocculant) and calcium hypochlorite (a disinfectant).

2.  Often economically and environmentally Very effective even with turbid water.

unsustainable.

3.  Provides no residual protection. (Mintz et al., 2001)

Solar Disinfection Filtration

1.  Uses the synergy of solar UV and heat. 1.  Many types available for water treatment

2.  Simple, inexpensive, does not affect taste.   •  Granular media: Bio-sand, slow sand

3.  Ineffective with turbid water.   •  Vegetable- and animal-derived depth filters

4.  Not good for large volumes. (Mintz et al., 2001)   •  Membrane filters: paper, cloth, plastic

  •  Porous cast filters: ceramic pots

  •  Septum and body-feed filters

2.  Filtration alone, at a household level, has not proved

effective for viruses and acceptable reductions of

bacteria. (Sobsey, 2002)

Chlorination Ultraviolet

1.  Sodium hypochlorite has proven the safest, most 1.  Works very well on all waterborne pathogens in

effective, and least expensive chemical disinfectant for combination in parallel with a turbidity reducing

point-of-use treatment. treatment such as coagulation/flocculation or

2.  It can be produced on-site or created on-site through filtration.

electrolysis. 2.  No odor or taste problems.

3.  Relatively ineffective against parasites and viruses. 3.  Requires significant energy input: batteries or

4.  The taste and odor of chlorinated water can reduce electricity. (Sobsey, 2002)

use. (Mintz et al., 2001)

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With minor modifications, all 50 U.S states adopted the Public Health Service standards either as regulations or as guidelines for all of the public water systems in their jurisdictions. However, the aesthetic problems, pathogens, and chemicals identified by the Public Health Service in the late 1960s were not the only drinking water quality concerns, since industrial and agricultural advances and

the creation of new man-made chemicals also had negative impacts on the environment and public health.

The main sources of drinking water are often polluted by industrial and municipal chemicals (Gevod et al., 2003). While filtration was a fairly effective treatment method for reducing turbidity, disinfectants such as chlorine played the largest role in reducing the number of waterborne disease outbreaks in the early 1900s. In 1908, chlorine was used for the first time as a primary disinfectant of drinking water in Jersey City, New Jersey. Even though water treatment plants reduce the concentrations of harmful chemicals in waters to a safe level, the use of chlorine results in the formation of disinfectant by-products, which have been proved to be strongly carcinogenic (Gevod et al., 2003). The use of other disinfectants such as ozone also began in Europe around this time, but was not employed in the U.S. until several decades later.

Even though the new chemicals were effective for water treatment, many others were finding their way into water supplies through factory discharges, street and farm-field runoff, and leaking underground storage and disposal tanks. Although treatment techniques such as aeration, flocculation, and granular-activated carbon adsorption existed at the time, they were either underutilized by water systems or ineffective at removing some new contaminants.

Several studies conducted by the Public Health Service in 1969, and later in 1972, showed that only 60% of the systems surveyed delivered water that met all the Public Health Service standards, and 36 chemicals were found in treated water taken from treatment plants. Over half of the treatment facilities surveyed had major deficiencies involving disinfection.

The combination of health issues and increased awareness eventually led to the passage of several federal environmental and health laws, one of which was the Safe Drinking Water Act of 1974. This law, with significant

amendments in 1986 and 1996, is administered today by the U.S. Environmental Protection Agency’s Office of Ground Water and Drinking Water (EPA) and its local partners (EPA, 1996). According to several EPA surveys, from 1976 to

1995 the percentage of small and medium community water systems (systems serving people year-round) that treat their water has steadily increased (EPA, 1995).

Recently, the Centers for Disease Control and Prevention and the National Academy of Engineering named water treatment as one of the most significant public health advancements of the twentieth century (NAE, 2007). Today, filtration and chlorination remain effective treatment techniques for protecting U.S. water supplies from harmful microbes,

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