133 Myths in Diffuser Design

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by:

Technical Bullet

Environmental Dynam

Published: February 8,

Myths in Diffuse

n 133

ics International

2012

Design



1

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particular bulletin or your specInternational by calling +1.573.

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Technical Bulletin 133

Copyright © Environmental Dynamics International

ed as a service by Environmental Dynamics

souri USA. For additional more information r

ific aeration application contact Environment74.9456, toll free at +1.877.EDI.AIR8 (877.3

water.com.

Myths in Diffuser Design

2012 – All Rights Reserved

International

garding this

l Dynamics4-2478), or



2

TECHNICAL BULLETIN 133

Myth Number 1 - Tube Diffusers

Properly designed tube diffuser sy

requires low flux rates of air per squ

engineered membrane openings.

by vertical liquid pumping from the

Myth Number 2 -Tubes Use Only

Properly engineered tubes use th

distribution features such as the f

produce proper utilization of the Einlet designs may not utilize the enti

Myth Number 3 - Tube Diffusers

The EDI diffuser assembly is an

available. EDI assemblies that uti

mounting system of tubes or disc u

Myth Number 4 - Disc Diffusers a

Performance of any membrane s

Actual performance of any geom

engineered and properly applied o

efficiency of the system. Geomet

oxygen transfer efficiency desired

SOTE.

Myth Number 5 - Brand "X" Can

Actual air handling capacity of all mAir flux rate (cfm of air per sq. ft.

efficiency and will absolutely contr

high f lux rates through their mem

efficiency and increase stress i.e.,

air flux rates for similar long term p



– MYTHS IN DIFFUSER DESIGN

reate Coalescing

stems at proper airflows do not coalesce. Maxim

are foot of active membrane surface area and prop

Properly designed systems produce discreet bubbl

iffuser units.

the Top 1/2 of the Surface

e entire surface of the membrane. Engineered

ll support frame with bottom outlets in the EDI di

TIRE surface. Note: Systems with 1/2 support frre surface so equipment design is important.

re Structurally Weak

engineered system and is the STRONGEST dif

lize the Spectrum™ Saddle Mount are stronger th

its.

re More Efficient than Tubes

stem depends on proper engineering of the sp

try diffuser (tube, disc, or panel) is the SAME

r installed. Diffuser geometry is not a controlling

ry of the diffuser is NOT a performance criterion.

and confirm with a test, why argue about "best"

andle Much More Air Flow Per Unit than Any Ot

embrane diffusers is the same to produce SIMILARr NM3/M2 of active surface area) will absolutely c

l membrane life. Systems which propose high ai

rane systems with high cfm per square foot (N

educe the life of the unit. All membrane diffusers r

rformance.



um efficiency

r numbers of

es separated

slits and air

ffuser design

ames or poor

fuser system

an any other

cific system.

hen properly

factor in the

Specify the

; just specify

her Diffuser

performance.ntrol diffuser

rflow rates or3 /m

2) reduce

equire similar



3Technical Bulletin 133 – Myths in Diffuser Design

Copyright © Environmental Dynamics International 2012 – All Rights Reserved

Myth Number 6 - Ceramic Diffusers are More Efficient Than Membranes

Ceramic diffusers and membrane diffusers can offer identical oxygen transfer efficiencies in clean

water. In field performance, membrane diffusers can offer as much as 50% greater efficiency than

ceramic diffusers because membranes can operate at less airflow per square foot. Ceramic

diffusers will clog when operated below the critical airflow for flushing (cleaning velocity) and utilizing

the entire diffuser surface. Membranes can run at very low air flux rates in dirty water and improveoxygen transfer efficiency versus ceramic.

Myth Number 7 - Membranes Require Substantial Maintenance and Must Be Replaced Every

Three Years

Actual performance of EDI advanced technology EPDM or urethane membranes has been excellent

in the field. Properly engineered membrane systems should not require significant maintenance.

Membranes properly designed at reasonable air flux rates typically provide five to ten years of

membrane life.

Myth Number 8 - Piping Systems Should Use 2% TIO2 FOR UV Protection

Standard plastic pipe institute specifications for all PVC piping require use of TIO2 for aesthetic

appearances. Some manufacturers have specified special percentage of TIO2 as part of their

standard equipment spec. This is to obscure the fact they are using extremely thin wall PVC pipe

that is vulnerable to mechanical damage, vulnerable to UV degradation and/or heat. Addition of

proper amounts of TIO2 could be helpful for UV protection but pipe manufacturers recommend that

at least 7-10% TIO2 if any significant UV protection is to be achieved. Unfortunately the addition of

7-10% TIO2 creates substantial negative characteristics in piping systems, i.e., brittle. Based on

pipe manufacturer recommendations, EDI recommends standard heavy wall PVC pipe in place of

special concentrations of TIO2 and thin wall pipe. NOTE: EDI can furnish 2% TIO2 on its heavy wall

pipe for extra protection.

Myth Number 9 - Coarse Bubble Diffusers are Better Mixers

Mixing is a term that must be defined. If mixing is described as blending, coarse bubble diffusers are

more efficient because they create a mass liquids or solids displacement at the diffuser assembly

itself. If mixing is defined as liquid pumping and circulation, fine bubble diffusers are superior

mixers. Fine bubble diffusers will mix biological systems at airflows substantially below the airflow

rate required for coarse bubble diffusers. Coarse bubble diffusers demonstrate substantial

turbulence; fine bubble diffusers demonstrate superior liquid flow or pumpage. See Technical

Bulletins: Number 103 - Coarse Bubble Diffusers; Number 104 – Fine Bubble Aeration; and,

Number 105 - Converting Coarse Bubble Aeration to Fine Bubble Aeration.



4

Myth Number 10 - Coarse Bubble

History would suggest that coar

application of rigid media fine pore

diffusers generally require less mai

are present as they exclude solids

do not have to be as concerned asystem. EDI is successfully repla

maintenance and clogging from rag

while delivering 40%-50% energy s

Myth Number 11 - Surface Aerato

High efficiency EDI FlexAir™ mem

lowest Total Ownership Cost aer

platforms offered by EDI and the a

engineering needs of each projectentire project life. Not only is the

approximately 1/2 the energy cost.

life of the project will always result i

101 - Proper Design Consideration

Myth Number 12 – All Fine Bubbl

This is a myth presented for diffu

systems of similar type and qualit

bubble size and wastewater char

bubble as it is a different type of diff

to 3.0 mm Ø bubble have very simil

Myth Number 13 – Stainless Stee

Clearly stainless steel pipe can be

option. However, properly enginee

advantages over their stainless st

corrosive even in hi chloride or TD

Plastic piping systems properly sel

aeration systems with submerged p



Diffusers Require Less Maintenance

e bubble diffusers may require less maintena

diffusers in the past. Advanced technology flexib

tenance than coarse bubble diffusers when heavy

nd liquids from the system. If you exclude solids a

out being able to blow those solids and liquids bing coarse bubble diffusers with membrane diffus

s, etc… Membrane diffusers generally require less

vings.

rs are the Lowest Cost Aeration Systems

brane diffusers and efficiently designed blower syst

tion systems currently available. The high effici

bility to use floating laterals or fixed header system

allow the system to deliver lowest total ownershipDI system economical on a capital cost basis but

Present worth cost or evaluated cost of the aeratio

in selection of diffused aeration systems! See Tec

.

e Systems have a Different Alpha

er systems that have limited long term experienc

y have exactly the same alpha that is controlled

cteristics. Note: Alpha for coarse bubble is differ

user. Disc and tubes of typical design air flow rates

ar alpha when properly applied.

l Pipe is a Premium Pipe System

a premium pipe system and it is often the most ex

red plastic piping systems can offer superior perf

el counter-part such as: light weight and easy to

S; easy to fabricate, install, and repair; and a lowe

ected and engineered also offer advantages & ben

iping.



ce than the

le membrane

solids or rags

d liquids you

ck out of theers to reduce

maintenance

ems offer the

ency diffuser

s to meet the

osts over theit operates at

system over

nical Bulletin

. All diffuser

by the same

ent than fine

delivering 1.0

ensive piping

ormance and

handle; non-

r capital cost.

efits on most

Documents

133 Myths in Diffuser Design