WELL-WATER (TANK) AERATION

By Patrick Udeh, Ph.D.

1.0. Definition of Aeration: Aeration may be defined as the process by
which a gaseous phase, such as air and water are brought in contact with
each other for the purpose of transferring volatile substances to or from
the water. These volatile substances may include, but not limited to oxygen,
carbon dioxide, hydrogen sulfide, nitrogen, methane, Trihalomethane
compounds such as chloroform, dibromochloromethane, bromodichloromethane,
bromoform and other VOCs, as well as various unidentified organic compounds
responsible for taste and odor.

2.0. Uses of Aeration: Aeration may be used in water treatment for the
following reasons:
ß Use for a air stripping of odor causing compounds (taste and odor) such as
H2S, NH3, and CO2
ß Used for air stripping of volatile organic compounds (VOCs) such as
Trihalomethanes (THMs) from water
ß Used to precipitation of inorganic contaminants such as iron and
manganese (oxidation of Fe and Mn to form insoluble oxidize that
precipitates)
ß Used to removed radon and silver.
ß Used for water stabilization and disinfection

3.0. Types of Aerator: There are several types of aerator, namely:
1. Waterfall aerators, which may be spray nozzles, cascades, or multiple
trays
2. Diffusion or bubble aerators, which bubble compressed air through the
water, and
3. Mechanical aerators, which employ motor driven impellers or combination
air-injection devices.

4.0. Limitations of Aeration: The greatest application of aeration is
absorption and release of gas such as O2,CO2, and H2S. This may render some
water to become corrosive.

5.0. Recommended Aerator for well water: Diffused or bubble aeration is
recommended for well (tank) water. The process consists of contacting gas
bubbles with water for the purpose transferring gas to the water or removing
VOCs from the water by stripping. The process can be carried out in a tank
or clear-well. In bubble aeration, it is assumed that 1) the liquid phase is
completely mixed 2) the gas phase is plug flow 3) the process is at stead
state, and 4) the inlet VOC gas concentration is zero. The existing air is
in equilibrium with the bulk liquid, which is for the minimum air-to-water
ratio for bubble aeration. The minimum air-to-water ratio represents the
smallest air-to-water ratio that can be applied to a bubble aeration tank to
meet the treatment objective.

6.0. Do we need aeration in our systems? And if so, why is it required?:
Yes, aeration is required in our systems for the following reasons:

ß We have high THM levels in some of our systems
ß By 2006, each monitoring system will have to meet the prescribed 80 ppm
MCL, rather than averaging all systems in order to meet the required 80 ppm
MCL and
ß We have taste and odor problem in some of our systems, evidence from water
quality customer complaints.

7.0. Are we sure for certain, that the problem with the THMs and taste and
odor could be resolved by the use of aeration? Yes, based on previous works,
past and present literatures, aeration can be used to remove THM compounds
such as chloroform, dibromochloromethane, bromodichloromethane, bromoform,
and other VOCs. Nevertheless, the distributor, Malibu Water Resource, has
volunteer to provide us with their "Koender Electric Aerator System" for
trial, which means we could use this system for pilot scale studies.

8.0. What is Koender Electric Aerator System? This is a bubble aerator,
specifically made for well waters, which is stored in tanks or clear-wells
or reservoirs. The system consists of inlet and outlet zones, and air
compressor, which are used to bubble compressed air into water. This aerator
is powered by a _ horse power (110 AC) energy efficient electric motor.
The system is designed to produce 1.5ft3 of air per minute at 5 psi pressure
with a maximum 35 psi.

9.0. How much does Koender Electric Aerator System cost?

Koender Electric Aerator Package(1.5 CFM) = $ 500.00 plus Shipping
Electric operating costs
o _ horse power energy efficient motor
o maximum 2.5 amp/operates at 1.75 amps x 110 volts
o Less than 0.40¢ per day i.e. 365 days x 0.40¢ = $146.00 per year