Cascade Aerators are commonly used in water and wastewater treatment. These introduce air into a flowing stream of water to oxidize iron, and reduce dissolved gases. It aids in the removal of dissolved gas, iron, and manganese from groundwater, particularly when the metal concentrations are high.
Let us understand the designing of cascade aerators in WWTPs.
What are Cascade Aerators?
A cascade aerator (the most common and oldest type of aerator) is composed of a series of steps, through which water flows similar to a flowing stream. Aeration occurs in all cascade aerators' splash zones.
Splash zones are created by placing blocks on the slope. These can be used to oxidize iron and, to some extent, reduce dissolved gases.
What happens in Cascade aerators?
Aeration is accomplished with cascade aerators through natural draft units, which mix cascading water with air that is naturally inducted into the water flow. Cascade water is pumped to the aerator's top and cascades down a series of trays. To achieve iron oxidation and some reduction in dissolved gasses, air is naturally introduced into the water flow.
How are cascade aerators designed in WWTP?
Design criteria for cascade aerators:
Area required for Aerator Design = 0.015 - 0.045 m2 /m3 /hr
Cascade number = 3 to 9.
Aerator height = 1 to 3m.
Each step has a rise of 20 to 50 cm.
Inlet pipe velocity = 0.3 to 0.9 m/s
Let us illustrate this with an example that will provide you with a clear design procedure.
If you want to create a cascade aerator with a 12 MLD inflow assume appropriate data.
A. Inlet pipe design
Flow = Q = 12 MLD = (12x106x10-3)/(24x60x60) = 0.138 m3 /s
Assuming a velocity of 0.6 m/s through the pipe
Inlet pipe area = (Q/v) = 0.138 / 0.6 = 0.23 = (π/4)dp2,
wheredp = Diameter of Inlet Pipe =0.6m
B. Aerator Design
Assume that th?e area required for Aerator Design is 0.030 m2 /m3/hr.
Q = 12 MLD = 500 m3 per hour
Bottom Cascade Aerator Area = 0.03 x 500 = 15 m2.
Total bottom cascade aerator area = area of bottom aerator plus area of inlet pipe
= 15 + {(π/4)0.62} = 15.28 m2.
The total area of the bottom cascade aerator is 15.28 m2.
Assuming a total of 5 steps
Bottom diameter = (π/4)dx52 = 15.28 m2x d5 = 4.5 m Cascade
Now, suppose Aerator height = 2m
Each step has a rise of 2/5 = 0.4m.
4th Cascade Aerator Diameter: - (4.5 / 2) = d4 / (2 - 0.4) d4 = 3.6 m
3rd Cascade Aerator Diameter: - (4.5 / 2) = d3 / (2 - 0.8) d3 = 2.7 m
2nd Cascade Aerator Diameter: - (4.5 / 2) = d4 / (2 – 1.2) d2 = 1.8 m
1st Cascade Aerator Diameter: - (4.5 / 2) = d3 / (2 – 1.6) d1 = 0.9 m
C. Design of Collecting Channel
Diameter of Collecting Channel = 4.5 + 1 + 1 =6.5m
Also, q = Q / 2
=1.375 (b x h) (3/2)
Where, q = discharge through channel in m3/s
b = width of channel in m
h = height of channel
Thus, q= 0.138 / 2 = 1.375 x 1 x h (3/2) h = 0.14 m
How can we assist?
Netsol Water customizes wastewater treatment systems to the needs of its clients, with each unit developed and constructed as per order.
Still not sure if cascade aeration is the best solution for your wastewater treatment plant?
The first step is to determine the quality of wastewater you have and the water you require. To assist you with this procedure, we provide a free water analysis test. Please contact us as soon as possible to make arrangements for you, so that we can assist you with design of WWTPs, its installation and services as well.
Netsol Water is Greater Noida-based leading water & wastewater treatment plant manufacturer. We are industry's most demanding company based on client review and work quality. We are known as best commercial RO plant manufacturers, industrial RO plant manufacturer, sewage treatment plant manufacturer, Water Softener Plant Manufacturers and effluent treatment plant manufacturers. Apart from this 24x7 customer support is our USP. Call on +91-9650608473, or write us at enquiry@netsolwater.com for any support, inquiry or product-purchase related query.
