aeration units

PAKISTAN COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH LABORATORIES COMPLEX, KARACHI

OFF: UNIVERSITY ROAD, KARACHI-75280.

AERATION UNITS...



Unit process in which air and water are brought into intimate contact.

The contact time and ratio of air to water must be sufficient for exchange sufficient oxygen.

Advantages Providing O2 for purification and improving

overall quality. CO2 reduction-reduces the corrosion. Raising the pH. VOC removal Effective method for bacterial control



Methods of aeration

Diffused aeration

Spray aeration

Turbine aeration

Surface aeration



Diffused aeration Providing maximum water surface per unit

volume of air. Air bubbles brought with water in a mixing

or contact chamber. A common way to aerate water is via

diffused air. Air is pumped through some sort of diffuser

to generate small bubbles.



Usually gas is injected into the bottom of the aeration tank and is allowed to rise to the surface in an open tank.

The rising bubbles transfer oxygen to the water, as well as transport bottom water to the surface.

The bubbles raising through water create turbulence.

Untreated water is allowed to enter the tank from top and exit from bottom.



Efficiency of diffused aeration can be improved:

Fine bubbles (0.2 cm dia) as compared to coarse bubble (2.5 cm dia)

By increasing water depth (9-15 ft) By improving the basin geometry (width to

depth ratio not exceed 2) By increasing the retention time (10-30 min)



Typical diffused aeration system looks like:



There are a large variety of diffuser types. For example ceramic plates



These plates are arranged on manifolds at the bottom of aeration tanks as shown here.



Other types of diffusers include coarse aerators



To determine the oxygen transfer rate in these diffused aeration systems, first define the pressure difference from top to bottom of the tank. At the surface:

14.7(1 0.032 AlPsurfac t)e

Alt = altitude in thousands feet above sea level Psurface has units of psi



H = depth of tank (depth of discharge point) in feet.

62.4 HP P (psi)bottom surface 144



Mechanical Aeration

Basically there are two types of mechanical aeration.

Turbine Aeration:

In this system coarse bubbles are injected into

the bottom of the tank and then a turbine

shears the bubbles for better oxygen transfer.

Efficiency of turbine aerators is generally higher

than diffused aeration.



Surface Aeration:

In this case a mixing device is used to agitate the surface so that there is increased interfacial area between liquid and air.

There are many different proprietary types of surface aerators .



Common surface aerators



Design consideration for mechanical

aerators is usually based on

Eckenfelder and Ford equation. T 20C Cw lN N (1.02)0 9.17

Notice that there is no depth consideration for mechanical aeration.



Where as: N = actual transfer rate (lb-O2/hr)

N0 = manufacturer specified transfer rate ( lb/hr) for clean water, 20oC, zero DO.

Cw = saturation value for oxygen for wastewater under operating conditions.

9.17 = saturation DO for clean water, 20oC.

Cl = the design oxygen concentration in the aeration basin.

T = Temp. α = oxygen transfer correction factor for

waste water



NIAZ AHMEDSOCES

PCSIR LAB COMPLEXCELL NO.

03333259613

THANK YOU!!!

aeration units

Documents

university road

aeration units

aeration tanks

diffused aeration systems

water depth

diffused air

untreated water

air bubbles