Question

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Q. 2. Explain the four stages of water treatment. How is it possible for waterborne pathogens such as Cryptosporidium to contaminate water that has been treated in modern treatment plants? (3 to 5 sentences )

Q. 3. What are some examples of toxic chemicals that may enter the public water supply? Describe some of the health effects that are attributed to toxic chemicals present in drinking water. (3 to 5 sentences )

Answer 1

1.Coagulation and Flocculation

In this (coagulation) positively charged chemicals such as aluminum sulphate, polyaluminum chloride or ferric sulphate are introduced to the water to neutralize the negative charges held by solids, including dirt, clay, and dissolved organic particles. After neutralizing the charge, slightly larger particles called microflocs are formed from the binding of smaller particles with the added chemicals.

After completion of coagulation, a gentle mixing known as flocculation occurs, causing microflocs to collide with each other and bond together to form visible suspended particles. These particles, called flocs, continue to increase in size with additional mixing and reach an optimum size and strength, preparing them for the next stage in the process.

2. Sedimentation

The second stage takes place when the suspended matter and pathogens settle at the bottom of a container. The longer the water sits undisturbed, the more solids will succumb to gravity and fall to the container floor. Coagulation makes the sedimentation process more effective because it makes the particles larger and heavier, causing them to sink more quickly. For a community water supply, the sedimentation process must happen continuously and in large sedimentation basins. This simple, low-cost application is a necessary pre-treatment step before the filtration and disinfection stages.

3. Filtration

In this stage, the floc particles have settled to the bottom of the water supply and the clear water is ready for further treatment. Filtration is necessary due to the small, dissolved particles that are still present in clear water, which include dust, parasites, chemicals, viruses, and bacteria.

In filtration, water passes through physical particles that vary in size and composition. Commonly used materials include sand, gravel, and charcoal. Slow sand filtration has been used for more than 150 years, with a successful record for removing bacteria that causes gastrointestinal disorders. Slow sand filtration combines biological, physical, and chemical processes in a single step. On the other hand, rapid sand filtration is a purely physical purification step. Sophisticated and complex, it is used in developed countries that have sufficient resources for treating large quantities of water. Rapid sand filtration is a cost-intensive method compared to other options, requiring power-operated pumps, regular cleaning, flow control, skilled labor, and continuous energy.

4. Disinfection

The final stage in the community water treatment process involves adding a disinfectant such as chlorine or chloramine to the water supply. Chlorine has been used since the late 1800s. The type of chlorine used in water treatment is monochloramine. This is different than the type that can harm the indoor air quality around swimming pools. The main effect of the disinfection process is to oxidize and eliminate organic matter, which prevents the spread of parasites, viruses, and bacteria that may remain in the drinking water. Disinfecting also serves to protect the water from germs it may be exposed to during distribution as it is piped to homes, schools, businesses, and other destinations.

Ans:2

Toxic chemicals that may enter in water are inorganic chemicals (e.g., lead, arsenic, nitrates, and nitrites), organic chemicals (e.g., atrazine, glyphosate, trichloroethylene, and tetrachloroethylene), and disinfection byproducts (e.g., chloroform