Question

Describe the function of (a) aeration and (b) addition of aluminum or iron sulfate in the purification of drinking water.

Short answer

Aeration increases oxygen and removes gases, while aluminum or iron sulfate aids in coagulation and removal of particulates.

Step-by-step solution

Understanding Aeration

Aeration is the process of exposing water to air by forcing air through the water or by trickling it over the surface. The main function of aeration in the purification of drinking water is to increase the oxygen content of the water. This helps to remove dissolved gases such as carbon dioxide, hydrogen sulfide, or volatile organic compounds. It also aids in the oxidation of dissolved metals like iron and manganese, which can then be more easily filtered out.

Role of Aluminum or Iron Sulfate

The addition of aluminum or iron sulfate in the purification process is used for coagulation and flocculation. These chemicals help to gather tiny particles, minerals, and organic material into larger clusters, known as flocs, which can be easily filtered out of the water. The process essentially helps clear the water of suspended solids, reducing turbidity and allowing for clearer, cleaner drinking water.

Key concepts

Aeration

Aeration is a fundamental step in the water purification process. It involves the process of exposing water to air, which can be achieved by forcing air through the water or by letting water trickle over the surface. This exposure to air serves a crucial purpose: it increases the oxygen content of the water. With more oxygen, harmful dissolved gases such as carbon dioxide and hydrogen sulfide can be effectively removed.

Additionally, aeration aids in the oxidation of dissolved metals. Metals like iron and manganese, when oxidized, convert into forms that are more easily filtered out of the water. This process not only improves water quality but also enhances its taste and smell, making it more suitable for drinking. Aeration is indeed an essential starting point in ensuring that water is being properly treated before further processes.

Coagulation

Coagulation is a critical step in drinking water treatment that works by neutralizing the charges on particles suspended in water. These particles can include colloidal substances and organic materials that contribute to water turbidity. By adding coagulants such as aluminum or iron sulfate, we enable the aggregation of these particles.

Coagulants work by binding to the particles, neutralizing their charges, and bringing them together into larger, heavier clusters known as "flocs." This process is essential for managing very fine particles that would otherwise be difficult to remove by simply filtering. The clearer the water is, the better it reflects contamination control, which is crucial for safe drinking water.

Flocculation

Once coagulation takes its effect, flocculation comes into play as the following step. This process involves the gentle and continuous mixing of water to encourage the formed flocs to grow in size. The gentle stirring allows these flocs to bump into each other, combining into larger, more stable aggregates.

The interaction during flocculation encourages enhanced particle collision, which leads to even further growth of the flocs. Larger flocs are much easier to remove via sedimentation or filtration methods. By effectively removing these impurities, flocculation ensures that the final water has reduced turbidity and is clearer, improving the overall safety and quality of drinking water.

Drinking Water Treatment

The treatment process of drinking water involves multiple integrated steps, each playing a vital role in ensuring that the water is safe for human consumption. This multi-step procedure includes physical, chemical, and biological processes designed to remove contaminants, both visible and invisible, from the water.

The major steps usually include:

• Aeration: Oxygenates and removes gases
• Coagulation: Neutralizes particles for easier filtration
• Flocculation: Forms larger flocs for efficient removal
• Filtration: Physically removes particulates
• Disinfection: Destroys harmful microorganisms

Together, these processes ensure that drinking water meets safety standards to protect public health. With each step thoroughly designed and executed, treated water is free from harmful impurities, thereby maintaining its clarity, quality, and safety, essential for all who consume it.