How to find quantity of Tube Settler Media in MBBR based STP
Tube settler media is an essential part of a Moving Bed Biofilm Reactor (MBBR) based Sewage Treatment Plant (STP). It increases the surface area available for the growth of microorganisms and aids in the settling of sewage's solids. It is typically made from PVC or PP material and is available in different sizes and shapes.
We will go over how to figure out how much tube settler media is needed for an MBBR-based STP below.
How to find quantity of Tube Settler Media?
The tube settler media comes in a variety of sizes and forms and is commonly constructed of PVC or PP material. The hexagonal shape, which offers the largest surface area for the establishment of biofilm, is the most frequently employed shape.
Some variablesaffect how much tube settler medium is needed are:
· Design flow rate
· Surface loading rate
· Settling velocity
· Number of settling tanks
For a Moving Bed Biofilm Reactor based Sewage Treatment Plant, the amount of tube settler medium needed can be calculated using the method below:
Q = (A × H × V × S × F)/1000
Where,
Q = Quantity of Tube settler media required in m3
A = Surface area of the settling tank in m2
H = Height of the settling tank in m
V = Design flow rate of the STP in m3/day
S = Surface loading rate in m3/m2/day
F = Factor of Safety (mostly taken as 1.2)
Let us try to understand each of these parameters
How to calculate Surface Area of the Settling Tank?
The area accessible for the tube settler media to settle is the surface area of the settling tank. It can be calculated by dividing the design flow rate (V) with the hydraulic loading rate (HLR).
HLR is the rate at which wastewater or sewage is applied to the settling tank and is calculated by dividing the total volume of the settling tank by the design flow rate.
Surface area of settling tank (A) = V/HLR
Calculation for Height of the Settling Tank
The height of the settling tank is influenced by the sewage's solids' settling velocity. The Stokes Law can be used to determine the settling velocity, which is the rate at which solids in sewage settle out.
Stokes Law states that the settling velocity of particles is directly proportional to the particle diameter and the difference between the density of the particle and the density of the fluid.
Settling velocity (Vs) = (2/9) × (ρp-ρf) × g × (dp)2 / η
Where,
ρp = Density of the particle
ρf = Density of the fluid
g = Acceleration due to gravity (9.81 m/s2)
dp = Particle diameter
η = Viscosity of the fluid
The settling velocity needs to be such that the particles reach the settling tank's bottom in the specified amount of time. The typical settling period is between two and four hours. As a result, the height of the settling tank can be easily calculated using the settling velocity and the settling time.
Height of settling tank (H) = Vs × T
Where,
Vs = Settling Velocity
T = Settling time
Surface Loading Rate
The surface loading rate is the rate at which sewage is applied to the tube settler media. It is calculated by dividing the design flow rate with surface area of the settling tank.
Surface loading rate (S) = V/A
Factor of Safety
The factor of safety is the safety margin added to the calculated quantity of tube settler media to account for any uncertainties which may rise in the design. It is usually taken as 1.2.
Conclusion
In conclusion, tube settler media is an essential component of an MBBR STP plant and their proper quantity is a must for effective treatment.
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