Contaminants transportation & Water Quality (CVE 814) Module 4-6.pptx

Lecture slide

1. CVE 814

2. Contaminants in the Water There are a variety of substances that can negatively affect water quality. They are generally grouped by their characteristics: Microorganisms, inorganic and organic chemicals and radiological compounds.

3. Microorganisms Microorganisms are a group of living organisms that include protozoa, bacteria and viruses. They can live in water, soil and in the atmosphere and are found in surface water bodies, water wells, under the earths crust and even on rocks. While there are many microorganisms that are not harmful to humans others can make humans sick or even cause death. The identification of the type and number of microorganisms in water should be done by an accredited laboratory

4. Inorganic chemicals Inorganic chemicals are generally naturally occurring. Chemicals in this category are the result of non-living natural processes. Most of the earth is considered to be inorganic. Inorganic compounds are created by the elements that are found on the earth. Some of these compounds are toxic to human health while others may be considered a nuisance. Examples of inorganic chemicals (elements) found in water are arsenic, calcium, iron and sulphate. Even though most inorganic compounds occur naturally, some can be man-made. For example, nitrate occurs in both organic and inorganic forms. Two common inorganic forms, potassium nitrate and ammonium nitrate, are commonly used as fertilizers.

5. O rganic compounds/chemicals The definition of an organic compound is not exact, but generally refers to compounds which contain carbon as part of their structure. Organic chemicals can occur naturally in the environment from certain plants and sugars, but many occur as a result of man made production processes, such as petroleum products, agricultural pesticides, plastics and rubber manufacturing. A general rule of thumb is that organic chemicals are usually produced by man-made processes. Some examples of organic chemicals are atrazine (a herbicide), benzene (a solvent derived from crude oil) and polyvinyl chloride (PVC – a plastic).

6. Radionuclides Radionuclides are found in the environment (including water) as naturally occurring elements, and also are produced as by-products of nuclear technologies. The most common naturally occurring radiological compounds include radium, radon and uranium, but many more exist. Radionuclides commonly found in water include those associated with radium and lead.

7. Multi-Barrier Approach Without constant monitoring and testing of water quality, it is difficult to ensure that water is consistently safe and potable. A system that includes more than one barrier to contaminants will have a higher factor of safety than a system with a single barrier. For example, a system with a filter and a disinfection process would have two barriers to most microbiological contaminants, whereas a system with a filter alone would only have one barrier.

8. Barriers for contaminants Barriers include not only physical devices or processes , but also actions to indirectly or directly affect or monitor the contaminants in water, such as taking actions to protect the water source, or a regular program of water quality sampling, testing, evaluation and reporting .

9. Fig. The Multi-barrier Approach

10. Multi-Barrier Approach Cont . Full knowledge of the water supply system, from the source to the tap, is a key component of a multi-barrier approach. This knowledge is gained through a variety of tools as outlined in the Guidance document. A “vulnerabilities assessment” considers the water source, identifies any potential hazards from the environment and what effect those hazards will have on the water. Another tool is a “sanitary survey”, which is a comprehensive survey of the water supply system and the procedures use to operate and monitor the system. This survey identifies potential problems in the physical components of the water supply system and the operation, maintenance and monitoring activities. A third tool is a full analysis of the raw source water, called a “baseline analysis”. This analysis provides an understanding of the contaminants in the water and the treatment required, as well as information for monitoring requirements.

11. Multi-Barrier Approach Cont . Other barriers include source protection (both surface and groundwater sources, including well development and decommissioning), treatment devices and processes, sampling and monitoring, regular operation and maintenance procedures, consistent reporting and ongoing training.

12. Treatment Processes There are many conventional and innovative water treatment processes. Some examples of water treatment processes include: Coagulation , a process where an added chemical attracts floating suspended particles to form larger and denser clumps of suspended material that will be heavy enough to settle to the bottom faster than the individual smaller particles would have. Flocculation , a slow mixing process where a coagulant is added to water and mixed to bind the particles into a flocculent (the “floc”) so it increases in weight and settles by gravity to the bottom of the flocculation tank. Filtration , a process which removes suspended particles by passing water through various types of filter media including sand, gravel, granular carbon, and a variety of cloth, fibre and ceramic filters. Most filters function by a physical sieving process, but some also rely on chemical mechanisms. For example, granular activated carbon filters trap dissolved organic matter in the carbon filter media by a process called adsorption , but only until the media reaches its adsorption capacity. Some filters also rely on biological processes (e.g. slow sand filtration and biological activated carbon filters). Nanofiltration and reverse osmosis filtration are membrane filter processes which are capable of removing very small particles including minerals that are dissolved in the water.

13. Treatment Processes Cont. Ion exchange systems remove specific chemical constituents from water using a resin media specifically designed to exchange one chemical compound for a different one. One of the most common ion exchange processes is a water softener, which exchanges sodium ions on the resin for calcium and magnesium ions. This ion exchange reduces water hardness but at the same time increases the sodium content in the treated water. Disinfection processes rely on either destroying disease-causing microbiological contaminants at the cellular level (usually by oxidation using compounds such as chlorine, ozone and in some cases like emergency situations, iodine), or disrupting or damaging the cells genetic ability to reproduce (via radiation from an ultraviolet light). Chlorination is the most common form of disinfection. In order to ensure that treated water remains safe throughout distribution pipes, it is important that a small amount of residual chlorine is present after the disinfection process.

14. Targets for Safe Drinking Water It is important to know the levels of contaminants in source water in order to know how the water must be treated to remove the contaminants and make it potable. It is also important to know the Maximum Acceptable Concentrations (MACs) for these contaminants so that their reduced levels can be verified in the treated water. Both surface and groundwater can contain some or all of the groups of contaminants. Groundwater from wells deeper than 30 m will likely not contain organic or bacteriological contaminants; however, a baseline chemical analysis should be carried out to verify that they are not present.

15. Distribution Systems Once water is treated it is delivered to the point of use by a distribution system. The distribution system often includes some type of water storage reservoir such as a pressure tank or a cistern. There may also be a pump to maintain distribution system pressure and there will be piping and valves. Depending on the system design, there may be devices incorporated to release air when necessary or other devices to prevent backflow and siphoning in the system. In order to ensure that water remains potable in the distribution system it should have enough chlorine residual everywhere in the pipeline system to prevent the re-growth of microbiological contaminants.

16. What’s In the Water Water that occurs naturally in the environment contains much more than just water. In addition to the hydrogen and oxygen that combine to form water molecules (H2 O), there are also many contaminants. Some of these contaminants are visible, and can make the water cloudy or murky. These contaminants are not dissolved into the water, but rather, they are suspended. But even if water looks perfectly clear it can contain a variety of contaminants that are either microscopic in size or are dissolved in the water. Contaminants in water are generally grouped by their characteristics: microorganisms, organic and inorganic chemicals and radiological compounds . Water is generally described by its various chemical , biological , physical and radiological characteristics. It is unusual to find several sources of water that are exactly the same; all water supplies have different characteristics.

17. What’s In the Water Cont. Microorganisms occur in water in three main groups: bacteria, viruses and protozoa . They may be in the water from natural sources or as a result of human or animal activities. While some of these microorganisms are harmless, others are capable of causing serious illness in humans.

18. Microbiological Contamination The most significant health risk from drinking water is microorganisms. Of course this opens the door for many questions: What are microorganisms? Are there different types of microorganisms? Are all microorganisms harmful? The word microorganism is a very general term that is used to describe a multitude of different, tiny living organisms. When it comes to drinking water, the 3 main groups of microorganisms of concern are: bacteria, protozoa, and viruses .

19. Microbiological Contamination Cont. It would be extremely difficult and time-consuming to individually test for all of the known harmful microorganisms, so drinking water experts use an indicator approach to make the process a bit easier. Microbiologists (scientists who study bacteria and other microorganisms) have found that microorganisms found in water are often linked to faecal contamination. Coliforms are a group of bacteria that are naturally found on plants and in soils, water, and in the intestines of humans and warm-blooded animals. If a test is positive for E. coli, that water sample has certainly come into contact with animal faeces and is therefore unsafe to drink.

20. Microbiological Contamination Cont. Total Coliform test by itself can show that a sample might be harmful, an E. coli test can confirm that a sample definitely IS harmful.