Lesson 1:

Introduction to Water Treatment

 

Types of Water Contaminants

Adequate supplies of water are necessary for agriculture, human consumption, industry and recreation. With the advancement of technology and industrial growth, fresh water resources all over the world are threatened. One-sixth of the world population suffers from unavailable freshwater. It is seen that developed countries suffer most from chemical discharge problems to health and leads to waterborne diseases which can be prevented by taking measures even at the household level. Providing safe water for all is a challenging task. Basically the types of water contaminants are four types associated with water pollution, including inorganic, organic, biological and radiological.

The types and concentrations of natural contaminants depend on the nature of the geological materials through which the groundwater flows and quality of the recharge water. Groundwater moving through sedimentary rocks and soils may pick up a wide range of compounds, such as magnesium, calcium, and chloride, arsenate, fluoride, nitrate and iron; thus, the effect of these natural contaminants depends on their types and concentrations. Other contaminants are man-made by-products of industry and agriculture, including heavy metals like mercury, copper, chromium, lead and hazardous chemicals, dyes and compounds like insecticides and fertilizers. Improper storing or disposing of household chemicals such as paints, synthetic detergents, solvents, oils, medicines, disinfectants, pool chemicals, pesticides, batteries, gasoline and diesel fuel can lead to groundwater contamination. The microbial contaminants include pathogens like bacteria, viruses, and parasites such as microscopic protozoa and worms. These living organisms can be spread by human and animal wastes knowing or unknowingly.

Some contaminants can be easily identified by assessing color, odor, turbidity and the taste of the water. However, most cannot be easily detected and require testing to reveal whether water is contaminated or not. Thus, the contaminants may result in unappealing taste or odor and staining as well as health effects. The presence of clays, silts or sand, or organic, algae, and leaf particles results in turbidity. The turbidity may shield bacteria, preventing disinfection chemicals from attacking and destroying the cells. The presence of organic materials in conjunction with chlorine can form trihalomethanes and other potentially harmful chemicals. Generally, surface water sources have higher turbidity compared to groundwater sources.

 

 

Organic Contaminants

Organic contaminants are composed of two basic elements: carbon and hydrogen. They are often responsible for taste, odor, and color problems in groundwaters. They can occur naturally from things like decaying vegetation, or they can be man-made. These decay compounds are called lignins or tannins. Pollution of organic chemicals in water sources occur from natural products of aquatic microorganisms and artificial contaminants from industrial chemicals or human wastes. The effects of organic pollutants on water sources differ for each contaminant. Only a few of the thousands of toxic organic chemicals that occur in drinking water are regulated by drinking water standards. You can view a list of organic pollutants that are regulated at https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations#Organic. The upper acceptable concentration of regulated contaminants in drinking water is called the Maximum Contaminant Level (MCL).

Estimated organic contaminants are as follows:

 

These manmade organic contaminants can be grouped into subcategories that are often more recognized than the more formal chemical name. These subcategories include:

Disinfection by-products like trihalomethanes (THMs) and haloacetic acids (HAAs), which are formed when chlorine in treated drinking water combines with naturally occurring organic matter is one form of organic contaminant. These are known to be potent carcinogens, but the EPA didn't mandate limits until 2004. These naturally occurring carbon compounds are not hazardous by themselves, but when combined with chlorine, produce byproduct reactants that have a health concern.

Pesticides, herbicides, insecticides, and fungicides are man-made chemicals that get into the water supply from run-off, sewers, and landfills. Many are extremely dangerous. The numbers of these things are proliferating rapidly and the amounts that are showing up in water supplies is increasing as well. Volatile organic compounds (VOCs), are man-made chemicals which include solvents, degreasers, adhesives, gasoline additives, and fuels additives. Possible chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects. All of these contaminant subcategories, with the exception of trihalomethanes, are manmade and the result of land use or other human activity such as agriculture, manufacturing or improper waste disposal.

Sources of organic compounds (VOCs, taste and odor compounds, disinfection byproducts, and free chlorine) found in groundwaters may include:

 

There are three treatment methods that have been shown to be effective in removing organics from drinking water. These include aeration, adsorption using activated carbon, and oxidation. If the concentration of the contaminant is high, two treatment units (using different methods) are typically installed. The first unit is used to remove the "heavy" contaminant load, while the second provides a "polishing step" to assure full removal of the contaminant(s) and to address "breakthrough". This sequential treatment configuration is called a series configuration. If appropriate for your contaminant, aeration is often the first method used, while activated carbon is often used as the polishing step.

 

 

Inorganic Contaminants

Inorganic contaminants include the entire spectrum of non-carbon based elements and chemicals. The presence of contaminants can also be measured by its chemical parameters. Hardness of the drinking water is a naturally occurring contaminant, which basically depends on the geographical status. It is caused by significant amounts of calcium or magnesium components; the hardness is classified into carbonate or non-carbonate hardness depending on what molecules are combined with calcium or magnesium. Apart from carbonate/noncarbonate hardness, there are several inorganic substances, such as fluoride, arsenic, lead, copper, chromium, mercury, antimony, and cyanide, that contaminate water resources. They can get into drinking water from natural sources, industrial processes, as well as from plumbing systems. Inorganic chemicals are metals, salts, and other compounds that typically do not contain carbon. Inorganic chemicals occur naturally and can also come from human activities. Lead and copper are inorganic compounds that are different because they are rarely found in the sources of our drinking water. Usually these contaminants enter the water as it passes through pipes and plumbing systems. You can view a list of regulated inorganic contaminants at https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations#Inorganic.

As a rule inorganic contaminants don't contain carbon and commonly occur in nature. Contaminants like arsenic, chromium, iron and manganese are widely present on the earth's surface and naturally end up in our water. Not all inorganic contaminants occur naturally, some are the result of pollution. Some are a consequence of the interplay of pollution and natural processes. For instance, nitrate is naturally formed by the oxidation of ammonia in fertilizer or leaks from septic systems.

Some inorganics are harmful to human health. Nitrate and lead present many problems for drinking water utilities. Both are harmful to vulnerable populations such as infants and children and are hard to manage. We can effectively remove nitrate from water, but the disposal of the treated waste stream is challenging and expensive. Lead doesn't present a treatment issue since most water sources contain trivial amounts of lead. Instead it is mainly tied to existing distribution system infrastructures. Exposure to lead, released from lead pipes and lead-containing fixtures used in the 20th century is a serious health risk. These pipes and fixtures, sometimes installed 50 to 100 years ago, may leach lead into water at the customer's tap.

In several cases, small amounts of some inorganics are beneficial to human health; while a large amount of the same inorganic is harmful. It is a delicate balancing act. For instance, within a narrow range, fluoride promotes dental health. On the other hand, exposure to too much fluoride can discolor teeth and weaken bones.

 

 

Part 3: Water Quality Characteristics