Question

A fluoride tracer study is being conducted at a \(15.5\) MGD capacity water treatment plant. The contact time through the coagulation and flocculation process is \(2.45\) hours. If the sedimentation basin has a capacity of 500,000 gallons, what is the total detention time through the 3 processes?

Short answer

3.22 hours

Step-by-step solution

Understand the Problem

The task is to find the total detention time for a water treatment plant with a given capacity and a known contact time through coagulation and flocculation processes, as well as the capacity of the sedimentation basin.

Identify Given Values

The water treatment plant capacity is 15.5 MGD (Million Gallons per Day). The contact time through coagulation and flocculation is 2.45 hours. The sedimentation basin capacity is 500,000 gallons.

Calculate Sedimentation Basin Detention Time

To find the detention time for the sedimentation basin, use the formula: \[ \text{Detention Time (hours)} = \frac{\text{Sedimentation Basin Capacity (gallons)}}{\text{Plant Capacity (MGD)} \times 1,000,000} \times 24 \text{ hours/day} \] Substitute the given values: \[ \text{Detention Time} = \frac{500,000 \text{ gallons}}{15.5 \text{ MGD} \times 1,000,000} \times 24 \text{ hours/day} \] \[ \text{Detention Time} = \frac{500,000}{15,500,000} \times 24 = 0.03226 \times 24 = 0.77424 \text{ hours} \]

Calculate Total Detention Time

Add the contact time through coagulation and flocculation with the sedimentation basin detention time: \[ \text{Total Detention Time} = 2.45 \text{ hours} + 0.77424 \text{ hours} = 3.22424 \text{ hours} \]

Key concepts

Fluoride Tracer Study

A fluoride tracer study is a method used to analyze the efficiency and performance of a water treatment plant. It involves adding a known amount of fluoride, which acts as a tracer, into the water stream. The movement of this tracer through the plant helps in determining the contact time and flow patterns. This information is crucial for optimizing treatment processes and ensuring regulatory compliance. The study can reveal dead zones, short-circuiting, or areas where the flow might affect the overall treatment quality. In our problem, the fluoride tracer study helps calculate the detention time through various stages of the treatment process.

Coagulation and Flocculation Process

The coagulation and flocculation process is vital in water treatment for removing suspended solids and contaminants. During coagulation, chemicals (coagulants) are added to the water, which destabilizes the particles. These particles then clump together to form larger particles called flocs.

Once coagulation occurs, flocculation follows. This step involves gentle mixing to encourage the formation of larger, settleable flocs without breaking them apart. The larger flocs are easier to remove in subsequent treatment steps, such as sedimentation and filtration.

In our exercise, the contact time for this process is given as 2.45 hours. This time ensures that the flocculation results in adequately-sized particles for the sedimentation basin.

Sedimentation Basin

The sedimentation basin is a critical component in the water treatment process. Its primary function is to allow flocculated particles to settle by gravity. As water flows through the basin at a slow rate, the heavy particles settle at the bottom, forming a sludge layer, which is then removed.

The detention time in the sedimentation basin depends on its capacity and the flow rate of the water treatment plant. In our problem, the basin has a capacity of 500,000 gallons. Using the plant's flow rate of 15.5 MGD, we calculated a detention time of approximately 0.77424 hours.

Combined with the coagulation and flocculation contact time, the total detention time through the three processes is 3.22424 hours, ensuring adequate treatment before the water moves to the next stage.