Which one of these sequences correctly sum-marises the order in which different processes are carried out at a water purification plant?

Options

A. Sedimentation `to` filtration `to` coagulation `to` chlorination
B. Sedimentation `to` coagulation `to` filtration `to` chlorination
C. Chlorination `to` coagulation `to` sedimentation `to` filtration
D. Sedimentation `to` chlorination `to` coagulation `to` filtration

Explanation

To determine the correct sequence of processes carried out at a water purification plant, we can break down the steps involved in the purification of water. Here’s the step-by-step solution:

### Step 1: Understand the Initial Process
The first step in water purification is **screening**, where large debris and impurities are physically removed from the wastewater.

**Hint:** Think about what happens first when you want to clean something; you often remove the big stuff first.

### Step 2: Sedimentation
After screening, the next step is **sedimentation**. In this process, the wastewater is allowed to sit in a tank so that heavier particles, such as sand and silt, can settle at the bottom. This leaves clearer water on top.

**Hint:** Consider how sediment settles in a jar of water if left undisturbed.

### Step 3: Coagulation
Following sedimentation, the water undergoes **coagulation**. In this step, chemicals called coagulants (like alum) are added to the water. These chemicals help to bind smaller particles together, forming larger clumps that can be more easily removed.

**Hint:** Think of how mixing flour and water can create dough; the particles stick together.

### Step 4: Filtration
Once coagulation has occurred, the water is then subjected to **filtration**. This process involves passing the water through filters that remove remaining impurities, including larger particles and some dissolved substances.

**Hint:** Imagine using a coffee filter to separate coffee grounds from liquid.

### Step 5: Chlorination
The final step in the purification process is **chlorination**. Here, chlorine is added to the water to kill any remaining microbes and pathogens, ensuring that the water is safe for consumption.

**Hint:** Think about how chlorine is used in swimming pools to keep the water clean and safe.

### Conclusion: Correct Sequence
Putting all these steps together, the correct order of processes at a water purification plant is:
1. Sedimentation
2. Coagulation
3. Filtration
4. Chlorination

Thus, the correct answer is **B**: Sedimentation, Coagulation, Filtration, and Chlorination.

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