What is tube settling tank? Design, Calculation in STP Plant
Tube settler tanks are commonly used in MBBR (Moving Bed Biofilm Reactor) based Sewage Treatment Plants (STPs) to improve the settling of suspended solids and biomass. The tube settler tank is a type of clarifier that uses closely spaced vertical tubes to enhance the settling process.
The capacity of the tube settler tank is an important parameter in designing an MBBR based sewage treatment plant.
Below, we will discuss how to calculate the tube settler tank capacity in MBBR based sewage treatment plants and the retention time required for efficient treatment.
How to calculate tube settler tank capacity?
Calculating Tube Settler Tank Capacity:
The tube settler tank capacity can be calculated based on the design flow rate of the sewage treatment plant and the settling velocity of the suspended solids. The settling velocity is the rate at which the suspended solids in the sewage settle in the tube settler tank.
The formula for calculating the tube settler tank capacity is as follows:
Tank Capacity (m3) = Design Flow(m3/day) x Retention Time(Days) x (Settling Velocity(m/day) / Surface Loading Rate(m/day))
In this formula:
1. Design flow is the volume of sewage that the treatment plant is designed to treat per day.
2. Retention time is the time for which the sewage is held in the tube settler tank for settling.
3. Settling velocity is the rate at which the suspended solids settle in the tube settler tank.
4. Surface loading rate is the area of the tank surface available for settling per unit volume of sewage.
What is the retention time of tube settler and how do you calculate it?
Retention Time for Efficient Treatment:
The retention time in the tube settler tank is an important parameter for efficient treatment. It determines the time for which the sewage is held in the tank for settling. A longer retention time allows for better settling of the suspended solids and biomass, resulting in a higher quality effluent. However, a longer retention time also means a larger tank size, which may not be feasible in all cases.
The retention time required for efficient treatment depends on the settling characteristics of the suspended solids and biomass in the sewage. In general, a retention time of 2-3 hours is sufficient for most sewage treatment plants. However, for sewage with high concentrations of suspended solids or biomass, a longer retention time may be required.
The retention time can be calculated using the formula:
Retention Time (hours) = Tank Volume (m3) / Design Flow (m3/hour)
An Example for finding capacity:
Let's consider an example to understand finding tube settler tank capacity calculation better.
Suppose we have an MBBR based sewage treatment plant with a design flow rate of 1000 m3/day. We want to design a tube settler tank that can achieve a settling velocity of 30 m/day and a retention time of 2 hours. The surface loading rate of the tank is 6 m/day.
We can calculate the tank capacity using the formula as follows:
Retention Time = 2 hours = 2/24 days = 0.083 days
Tank Capacity (m3) = 1000 x 0.083 x (30/6) = 415 m3
Therefore, the tube settler tank capacity required for this MBBR based sewage treatment plant is 415 m3.
Conclusion:
In conclusion, the tube settler tank capacity is an important parameter in designing an MBBR based sewage treatment plant. The capacity can be calculated based on the design flow rate, settling velocity, and surface loading rate of the tank. The retention time in the tank is also an important parameter for efficient treatment.
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