||Welcome to Ask Tom!, a monthly column by our resident water treatment guru, Tom Keenan of
National Environmental Services Agency (NESA). Tom addresses the issues that bug you the most. And Tom knows!! With 35 years experience in providing environmental support services to public and private sector clients on a wide range of environmental issues. Tom has also co-authored and presented training courses on wastewater treatment systems.
articles visit the Ask Tom!
New Aeration Technology Improves
Guest article by Mike Meyer, Mazzei Injector Company, LLC
Printer friendly PDF
Activated Sludge Process has been employed for human waste treatment
for over one hundred years. Many variations of the process have been
employed to optimize it for the specific applications. Regardless of
the specific configuration of the process, the Activated Sludge
Process employs microorganisms to assimilate and digest organic
carbon compounds in the influent wastewater stream. The
microorganisms can range from simple single cell bacteria to more
complex life forms such as protozoa.
The role of aeration in the activated
sludge process is to provide oxygen to the microorganisms as they
assimilate the organic carbon compounds and digest a portion of them
to carbon dioxide and water, Sulfate and Nitrate compounds. The
remaining waste solids are changed to a form that can be settled and
removed as sludge by sedimentation.
Regardless of the configuration of
the Activated Sludge Process, Biological Treatment and Secondary
Clarification (for MLVSS concentration) and sludge wasting must be
included. In addition, WWTP’s may employ the follows processes:
- Influent Gross Solids Removal -
- Solids Grinding - Commutators
- Flow Equalization - Equalization
- Grit Removal - Grit Ditch Primary
- Clarification - Primary
- Sludge Digestion - Anaerobic or
- Disinfection - Chlorination, UV,
Following is a generalized flow
diagram for a conventional Activated Sludge WWTP:
There are many processes used for
aeration in the activated sludge process. The more commonly employed
are coarse of fine bubble diffusion, surface aerators, brush
aerators, jet aeration and venturi aeration systems. Bubble
diffusion processes can be highly efficient but limited water depths
of less than 20 feet, and noisy blowers/compressors are required.
Surface aerators and brush aerators can also be highly efficient but
do not mix deep tanks or basins effectively. Jet aeration is
energy-efficient and mixes well, however blowers or compressors are
The Mazzei AirJection aeration
process utilizes special venturi injectors in conjunction with
nozzles, for aeration of wastewater. The AirJection Process is
composed of three basic units:
The process has been thoroughly
tested, with both clean water & process (dirty) water following
standards and guideline established by the American Society of Civil
Engineers (ASCE). The results of this testing have been certified by
a licensed professional engineer. The data resulting from this
testing have been incorporated into design spreadsheets which
facilitate accurate & quick system design.
The Airjection process is unique in
that the energy efficiency (Standard Aerator Efficiency, SAE)
increases with increasing water depth as demonstrated in the
A critical aspect of activated sludge
process design is estimation of the process (dirty water) oxygen
transfer from clean water test results. Under estimation of the
process water transfer will result in inadequate aeration, while
over estimation will result in unnecessary (and costly) energy
expenditure. The ratio of dirty water transfer to clean water
transfer is known as the Alpha factor.
An Alpha of 0.5 would mean that the
dirty water transfer under a given set of operating condition would
be 50% of the transfer in clean water. Alpha factors from as low as
0.3 for fine bubble diffusion, to as high as 0.85 for low speed
surface aerators have been reported. Extensive Dirty water transfer
testing has shown the Alpha Factor for the Airjection Process to be
equal to or greater than ≥0.90 in nearly all cases.
The oxygen transfer capability of the
AirJection aeration process has been thoroughly tested in both clean
and process water. The results of this testing have been compiled
into design spreadsheets which facilitate fast and accurate system
design. The versatile nature of the process affords ease of
installation for a wide array of aeration tank/pond configurations.
The lack of blowers or compressors affords installation in
environments where noise is an issue.
About Our Author
Mr. Mike Meyer
Mazzei Injector Company, LLC
500 Rooster Drive Bakersfield
Web site: http://www.mazzei.net/
Help others by posting
your comments, suggestions and experiences with water or
wastewater treatment or any other concerns you may have on
our On-Line Help Forum. For
past Ask Tom! Articles, visit the Ask Tom!
Guest articles for the
Ask Tom! Column are always welcome, for more information please
contact Tom Keenan directly at his email address: firstname.lastname@example.org