Question

The phosphates present in sewage water which cause eutrophication can be removed by adding: (a) Alum (b) Chlorine (c) Lime (d) Permanganate

Short answer

The phosphates can be removed by adding Lime (option c).

Step-by-step solution

Understanding the Problem

The objective is to determine which chemical compound can remove phosphates from sewage water. Phosphates cause eutrophication, which is the excessive growth of algae in water bodies.

Exploring Options for Phosphate Removal

Consider the options presented: Alum (aluminum sulfate), Chlorine, Lime, and Permanganate. We must identify which one binds or reacts with phosphates.

Option Analysis: Alum

Alum can react with phosphates to form insoluble aluminum phosphate, which can then be removed through filtration or sedimentation.

Option Analysis: Chlorine

Chlorine is primarily used for disinfecting water and does not react with phosphates to remove them.

Option Analysis: Lime

Lime, or calcium oxide, can react with phosphates to form calcium phosphate, which precipitates and can be filtered out.

Option Analysis: Permanganate

Permanganate is also used for disinfection and oxidation processes and does not specifically target phosphate removal.

Choosing the Correct Option

Both Alum and Lime can effectively remove phosphates by forming insoluble compounds. However, considering common practices, Lime is more frequently used for phosphate precipitation in water treatment.

Key concepts

Phosphate Removal

Phosphate removal is an essential process in water treatment, especially for managing wastewater. Phosphates are minerals that can make their way into water bodies primarily through agricultural runoff and sewage discharge. If not properly managed, they facilitate algal blooms, leading to water quality problems.

There are various chemical methods for phosphate removal, of which two common techniques involve using Alum (aluminum sulfate) and Lime (calcium oxide):

• Alum: Alum interacts with phosphates to form aluminum phosphate, which is insoluble. This compound can then be removed through sedimentation or filtration.
• Lime: This compound reacts with phosphates to produce calcium phosphate, which also precipitates out of the water and can be filtered away.

Both methods are effective, but Lime is often preferred in water treatment facilities due to its cost-effectiveness and ease of use.

Eutrophication

Eutrophication is a process where water bodies become overly enriched with nutrients, such as phosphates and nitrates. This overabundance often leads to excessive algae growth. This phenomenon can have several negative impacts on aquatic ecosystems.

Key aspects of eutrophication's effects include:

• Algal Blooms: The rapid growth of algae on the surface of water bodies blocks sunlight, affecting aquatic plants beneath.
• Oxygen Depletion: As algae die and decompose, the decomposition process consumes a significant amount of oxygen, leading to hypoxic (low oxygen) conditions detrimental to aquatic life.
• Water Quality Deterioration: Algal blooms can produce toxins harmful to both aquatic species and humans. These toxins may affect drinking water supplies and recreational activities.

To combat eutrophication, reducing nutrient loads from agricultural sources and improving sewage treatment processes are crucial.

Sewage Treatment

Sewage treatment is a critical process for managing wastewater from homes, industries, and stormwater. The goal is to remove contaminants before the water is released back into the environment or reused.

The treatment process typically involves several stages:

• Primary Treatment: This initial step removes large solids through sedimentation. Materials that settle are then separated.
• Secondary Treatment: Microorganisms are introduced to break down organic matter. This biological process reduces the nutrient content, lowering the risk of eutrophication.
• Tertiary Treatment: This stage aims to further polish the water. It might include phosphate removal methods like adding Lime or Alum to target excess nutrients.

These steps ensure that the water treated has minimal environmental impact and is safe for release. Continuous improvements in sewage treatment, like effective phosphate removal, play a vital role in protecting water bodies from pollution and eutrophication.