Question

The water supply for a midwestern city contains the following impurities: coarse sand, finely divided particulates, nitrate ion, trihalomethanes, dissolved phosphorus in the form of phosphates, potentially harmful bacterial strains, dissolved organic substances. Which of the following processes or agents, if any, is effective in removing each of these impurities: coarse sand filtration, activated carbon filtration, acration, ozonization, precipitation with aluminum hydroxide?

Short answer

The effective processes or agents for removing each impurity in the midwestern city's water supply are: 1. Coarse sand: Coarse sand filtration. 2. Finely divided particulates: Precipitation with aluminum hydroxide. 3. Nitrate ion: Ozonization. 4. Trihalomethanes: Activated carbon filtration. 5. Dissolved phosphorus (phosphates): Precipitation with aluminum hydroxide. 6. Potentially harmful bacterial strains: Ozonization. 7. Dissolved organic substances: Activated carbon filtration and ozonization. A combination of these methods is needed for effective water treatment and impurity removal.

Step-by-step solution

1. Coarse sand

Coarse sand filtration is effective in removing large particles like coarse sand from water.

2. Finely divided particulates

Coarse sand filtration can help remove some finely divided particulates, but for a more effective removal, we can use precipitation with aluminum hydroxide, which can cause particulates to clump together and settle at the bottom of the water, making it easier to remove them.

3. Nitrate ion

Nitrate ions can be removed effectively through the process of ozonization, which breaks down many chemical impurities, including nitrate ions.

4. Trihalomethanes

Activated carbon filtration is an effective way to remove trihalomethanes as it can adsorb a wide range of organic contaminants.

5. Dissolved phosphorus (phosphates)

Dissolved phosphorus in the form of phosphates can be removed effectively by precipitation with aluminum hydroxide, which forms an insoluble compound with phosphates that can be easily removed via sedimentation and filtration.

6. Potentially harmful bacterial strains

Ozonization is a powerful disinfection process that can effectively eliminate harmful bacteria, viruses, and other microorganisms in water.

7. Dissolved organic substances

Dissolved organic substances can be removed by a combination of treatments. Activated carbon filtration is particularly effective in removing dissolved organics due to its large surface area and affinity for organic compounds. Ozonization also aids in breaking down dissolved organic matter. In summary, to effectively treat the water supply for the midwestern city and remove the listed impurities, a combination of coarse sand filtration, activated carbon filtration, ozonization, and precipitation with aluminum hydroxide is needed.

Key concepts

Coarse Sand Filtration

Coarse sand filtration is one of the most straightforward methods used in water purification. It functions by allowing water to pass through layers of coarse sand that trap larger particles and debris. When dirty water flows through the sand, the large particles, like sand and gravel found in natural water sources, are physically trapped.
This makes coarse sand filtration especially effective in filtering out sizeable impurities.
Although coarse sand filtration helps in eliminating large debris, it isn't sufficient for smaller, finely divided particulates or soluble impurities. For this reason, it's usually part of a multi-step water purification process.

Activated Carbon Filtration

Activated carbon filtration is highly effective for removing a variety of organic chemicals, odors, and chlorine from water. This method uses activated carbon made from materials like coal or bamboo, which is processed to have numerous tiny, absorbent pores.
These pores provide a large surface area that helps trap organic substances and chemicals as the water passes through. Do you wonder how this works? It's due to adsorption, a process where charged particles in the water adhere to the surface of the carbon filter.

• This makes it perfect for removing compounds like trihalomethanes, which might form during water disinfection.
• It's also effective for most dissolved organic substances, giving water a cleaner taste and odor.

Though incredibly useful, activated carbon filtration must often be combined with other methods to ensure full purification.

Ozonization

Ozonization is a water treatment process that injects ozone, a powerful oxidizing agent, into water. Once introduced, ozone reacts with various contaminants, breaking them down into less harmful substances.
This method is particularly effective in oxidizing and thus removing impurities like nitrate ions, which can be harmful to human health. Ozonization is also remarkable for its efficiency in killing microorganisms, ensuring that bacteria and viruses are radically reduced.
Unlike many other purification processes, ozonization does not add any toxins or residues to the water, making it a clean option. It pairs well with other purification methods to offer comprehensive treatment, particularly when biological contamination is a concern.

Precipitation with Aluminum Hydroxide

Precipitation with aluminum hydroxide is a chemical method used in water treatment especially to remove certain inorganic impurities. When aluminum sulfate is added to water, it reacts to form aluminum hydroxide, a gelatinous substance.

• This compound can capture finely divided particulates like silt, clay, and some dissolved phosphates.
• The aluminum hydroxide forms a precipitate that settles at the bottom, carrying with it the impurities.

This allows for the easier removal of these impurities through sedimentation and filtration, enhancing the clarity and quality of the water.
While precipitation with aluminum hydroxide is very effective, it is usually not used alone but combined with other purification steps to ensure that the water is free of all undesired components.