Small wastewater plants and lagoon systems needing to meet tougher effluent-quality standards may find themselves in need of additional aeration that their existing facilities are poorly-equipped to supply. A technological solution that takes up almost no space, requires little to no earth work, and can be easily operated and maintained is available.

1. Aeration from Afar
Brian Gongol, M.Ed.
DJ Gongol & Associates, Inc.
IAMU Water and Wastewater Operators’ Training Workshop
Altoona, Iowa | November 29, 2023

2. Aeration and you
Nebraska wastewater facilities:
• 3 | RBCs
• 9 | trickling filters
• 23 | SBRs
• 26 | oxidation ditches
• 64 | activated sludge

3. Aeration and you
Nebraska wastewater facilities:
• 3 | RBCs
• 9 | trickling filters
• 23 | SBRs
• 26 | oxidation ditches
• 64 | activated sludge
10 | aerated lagoons
319 | non-aerated lagoons

4. Aeration and you
Iowa wastewater facilities:
• 10 | RBCs
• 17 | oxidation ditches
• 41 | SBRs
• 50 | trickling filters
• 182 | activated sludge

5. Aeration and you
Iowa wastewater facilities:
• 10 | RBCs
• 17 | oxidation ditches
• 41 | SBRs
• 50 | trickling filters
• 182 | activated sludge
• 206 | aerated lagoons
• 432 | non-aerated lagoons

6. Nothing is certain about the future

7. Except maybe more stringent standards
• No backsliding
• No degradation
• No fewer problems than we had yesterday

8. Except maybe more stringent standards
• No backsliding
• No degradation
• No fewer problems than we had yesterday

9. Hot
off
the
press

10. Almost anything you do is going to
require more or better air

11. How do you get more air?
Option #1: Push it in
Mechanically displace the
water with air, using paddles,
propellers, brushes, or turbines

12. How do you get more air?
Option #2: Diffuse it in
Compress air to high pressure
and introduce it at a low spot
inside a volume of water

13. How do you get more air?
Option #3: Induce it in
Use Bernoulli’s
Principle to create a
low-pressure zone in a
moving flow of water,
and allow atmospheric
pressure to supply a gas
(air) to fill the void

14. How do you get better air?
• Option #1: Higher O2 concentrations
• Atmospheric oxygen is about 21%
• If you diffuse pure oxygen into the
water, you’d theoretically need about
1/5th as much gas volume to get the
same transfer

15. How do you get better air?
• Option #2: More contact surface area
• The interior of a bubble doesn’t
transfer oxygen to the water
• Only the surface area really counts
• For the same volume of gas, the
smaller the bubbles, the greater the
surface area
• Plus: Smaller bubbles take longer to
rise, giving them more contact time

16. Why we need air
to rehabilitate our water

17. BOD removal
• 1.5 lbs. of oxygen to remove
1 lb. of biochemical oxygen demand (BOD)

18. BOD removal
• 1.5 lbs. of oxygen to remove
1 lb. of biochemical oxygen demand (BOD)

19. Setting the nitrogen free
• Raw wastewater enters the plant containing organic nitrogen and
ammonia (NH3) and ammonium (NH4
+)
• First (mathematically), we satisfy demand related to BOD
• Then, we convert the organic nitrogen and ammonia nitrogen
using oxygen
• Aerobic bacteria consume dissolved oxygen to break ammonium
into nitrate nitrogen
• 4.6 lbs. of oxygen per pound of ammonium converted to nitrate
• When free oxygen is depleted in the aerobic stage, anaerobic
bugs convert the nitrate (NO3
-) into nitrite (NO2
-), then nitrous
oxide (N2O), then to nitrogen gas (N2)

20. Setting nitrogen free takes a lot more
oxygen than removing BOD
• 1.5 lbs. of oxygen to remove
1 lb. of biological oxygen
demand (BOD)
• 4.6 lbs. of oxygen to convert
1 lb. of ammonium to nitrate

21. In simple terms, you need two zones or
two phases
• Aerated zone (or phase) to
remove BOD and break the
ammonia and ammonium
into nitrate nitrogen
• Anaerobic zone (or phase) to
convert the nitrate down to
nitrogen gas

22. Retrofitting:
The name of the game

23. Most communities have some
treatment
• We’re rarely looking at a blank slate
• If there’s a system in place, better to upgrade than to replace
• Upgrades run up against inconvenient limitations

24. Who faces inconvenient limitations?
• Hint:
It’s probably you

25. Constrained sites
• Not a lot of available
room to put new
facilities or equipment
• “Landlocked” conditions
• Resistance from nearby
landowners

26. Capacity limitations
• Need to conserve volume inside
existing tanks to maximize room
available for incoming flows
• Existing buildings or concrete
prevent new additions

27. Workforce limitations
• Hard to find skilled workers
• Service calls can be expensive and backlogged
• Increasingly specialized equipment is hard to maintain
• Lone operators
• We’re all getting older every day

28. Resource limitations
• Wastewater treatment isn’t
any community’s top priority
for spending
• Spending is usually driven by
regulatory requirements
• Most utilities are not spilling
over with excess cash

29. Big mechanical plants are hard to build,
fund, operate, and maintain

30. What you need is air

31. Let’s talk Venturi aeration

32. Static device added
after the pump
discharge

33. Pump discharge pressure induces
ambient air

34. High velocity through the nozzle
creates the pressure drop

35. It’s the same principle that
allows airplanes to fly

36. Air mixes with
the pumped
liquid almost
instantly

37. Size ranges
• 2” pipe | 50-150 gpm | 82 lb/day oxygen
• 3” pipe | 180-350 gpm | 253 lb/day oxygen
• 4” pipe | 400-650 gpm | 359 lb/day oxygen
• 6” pipe | 800-1300 gpm | 857 lb/day oxygen
(maximum amount of transferred useable oxygen, not the
actual amount of oxygen produced by the Venturi)

38. Easy to install and monitor

39. No moving parts

40. No moving parts

41. Pumps sized to fit

42. Generally
fits within
a 6’ x 6’
footprint

43. Inlet and outlet
locations piped as
needed

44. Easy to isolate
for maintenance

45. Reasons for hesitation about
other options

46. Mechanical pushing
Don’t put power cords in the
water unless you’ve
exhausted your other options

47. Mechanical pushing
High ratio of energy use
to move the water itself

48. Mechanical pushing
Don’t send equipment “out to sea”, making it hard to recover

49. Diffusion
Submerged diffusers are hard to retrieve

50. Diffusion
Diffusers are very
good at promoting
sedimentation
(which you don’t
want)

51. Diffusion
Sooner or later, you’ll have to clean them

52. Aerating from shore

53. Gives equipment
climate control
• Heating
• Ventilation
• Cooling

54. Aerating from
shore favors
oiling and
greasing

55. Permits monitoring for signs of trouble
Everyone keeps better track of
what’s at-grade and accessible
than what’s below ground, down a
hole, or out of reach

56. If you need a boat to get there,
how often are you really going to check it?

57. Permits ease of access

58. Show of hands
How many of you work solo
either some or all of the time?

59. Allows lone-operator O&M

60. Permits fine-tuning of performance
• DO monitoring
• A simple control loop
• A VFD or a timing circuit

61. Decreases volume required in existing
tanks and spaces
• Here you see two units
operating on the berm
between two lagoons
• Not one extra square
inch required
• No heavy dirt work,
either!

62. How does this look
in practice?

63. Lagoon retrofitting

64. Lagoon retrofitting
• Discharge above the waterline for
increased aeration (via cascading)

65. Lagoon retrofitting
• Discharge above the waterline for
increased aeration (via cascading)
• Discharge below the waterline for
increased mixing

66. Lagoon retrofitting
• Discharge above the waterline for
increased aeration (via cascading)
• Discharge below the waterline for
increased mixing
• Simple intake design using
perforated suction piping

67. Tank retrofitting

68. Tank retrofitting

69. Tank
retrofitting
• Compact footprint
• Thermal mixing
• Destratification
• Can configure with
multiple selectable
discharge points

70. Tank retrofitting
• Operators and
equipment can
remain above the
water line
• Variable-drive
control can dose
air as needed

71. Oxidation
ditch
retrofitting

72. A matter of operations

73. The mechanics of the problem
• Whether you push (via mechanical aeration), diffuse in the
basin, or induce from on shore, it’s hard to gain a big
advantage in the actual oxygen transfer without going to a
significant change in technology (like a membrane-aerated
biofilm reactor [MABR])
• But shoreside aeration stands out for its operational features

74. Can be portable/engine-driven for
seasonal applications

75. Don’t sleep on what portability means
It means that neighboring
towns can share the
equipment and split the cost

76. Process simplification
• If there’s one thing you know how
to operate, it’s a pump
• That’s the only moving, energized,
or mechanical component

77. Easy scalability
Run more units in
parallel without
crowding the basin

78. And don’t overlook the advantages of a
compact footprint, either
• Farm fence to the west
• Farm fence to the south
• Creek and wetlands to the north and east
• It still fits

79. Lots of detention time? Perfect!
• Treat it like a barbecue:
Aerate low and slow
• Unlike other
technologies, shoreside
aeration can turn the
basin into a loop
• With enough detention
time, you can perform
multiple passes through
the process

80. A little planning, piping, and baffling
BAD: Snakes in your plant
GOOD: Serpentine flow paths

81. Example 1
• Center inlet
• Corner outlet

82. Example 1
• Two baffles
• Create a long path
from inlet to
outlet

83. Example 1
• Aeration on shore
• Suction near
the lagoon outlet
• Discharge near
the lagoon inlet

84. Example 1
• Even a simple
duplex baffle
system creates
a longer flow path
• Aerobic phase
around the inlet
• Anaerobic phase
around the outlet
• Cycle as needed

85. Example 1
• Treat the lagoons
separately or
treat them as stages
• Mirror the baffles
and piping
• Duplicate the
aeration system or
alternate which
cell you aerate

86. Example 2
• Center inlet
• Corner outlet

87. Example 2
• Add lots of baffles (6 shown here)
• Create a very long serpentine path
• Seek a high rate of mixing and
aeration in cell 1

88. Example 2
• Install two (or more) aeration
systems
• Maximize the aerobic activity in
one cell
• Treat the second cell as anaerobic

89. Example 2
• The baffles don’t do the mixing
• But they do create a “racetrack”
• The same volume of water has to
move much faster if the path is
longer
• More motion means more
uniformity

90. Example 2
• Say the lagoon volume is 400,000
cf, or about 3 million gallons
• If two stations each run at 500
gpm, that’s 1,000 gpm
• Theoretically, that’s 3,000 minutes
for complete turnover of the
lagoon, or a little more than two
days
• Add or upsize pumps to go faster

91. Example 3

92. Example 3

93. These are only theoretical examples!
• Hire an engineer to crunch real numbers for you
• Every system has its own characteristics (and its own permit)

94. What are the advantages?

95. ① Modularity with
scalability
• Pipe one unit to serve
two different lagoons
or basins
• Install multiple
discharge points to
isolate zones or
increase circulation
• Install multiple units
side-by-side without
interference

96. ② A tiny footprint Even with an all-
weather enclosure,
still smaller than
the bed of an F-250

97. ③ No moving parts in the water
You can save the boat for fishing

98. ④ No electricity in the water
Safety first: You know the two shouldn’t mix!

99. ⑤ No new equipment types to learn
You already know how to operate a pump.
Why make things harder?

100. ⑥ Little or no earth work required
• The pump unit only
needs a flat pad
• Depending on cold-
weather operation
needs, you could...
• Bury the pipes
• Insulate and heat-tape
the pipes
• Drain them for winter

101. But what if we don’t have
power nearby?

102. Power doesn’t have to be a limiting factor

103. Power doesn’t have to be a limiting factor
 Want the pump right next to the lagoon or tank?
✓ Sure!
 Want to discharge a few hundred feet away?
✓ OK!
 Want to put the pump near the power drop at the road?
✓ You can do that: Just bury some collection pipe.
 Want to aerate at the main lift station before the plant?
✓ If your force main has a smooth uphill profile, go for it.
✓ If it’s hilly, upsize your pumps and put the aerator at the outlet
 Want to use a portable, engine-driven unit?
✓ If it makes you happy, let’s do it!
 Want to run your system off LP or natural gas?
✓ We already have a system to do that.

104. If at first you don’t succeed…
• It’s basically impossible to
move a fixed diffuser grid
• It’s hard to move a floating
aerator on a frozen lagoon
• A blower sized for hot
summer air may be
oversized for cold, dense
winter air

105. If at first you don’t succeed…
• It’s basically impossible to
move a fixed diffuser grid
• It’s hard to move a floating
aerator on a frozen lagoon
• A blower sized for hot
summer air may be
oversized for cold, dense
winter air
• Shore-based aeration opens
up possibilities and creates
workable alternatives
• Use piping and valves to
make changes based on
seasons, influent loadings, or
other changing needs

106. But what about the costs?

107. Comparable horsepower-to-oxygen for
floating mechanical aerators
• Shoreside aeration is easier
to access
• Baffle curtains and floating
aerators have to be kept
apart
• Machinery in mid-lagoon
can be a challenge to reach

108. Comparable horsepower-to-oxygen for
blowers
• Blowers have to
overcome backpressure
from the water column
• Venturi aeration moves
the water efficiently,
which you need to do
anyway for good mixing

109. Comparable horsepower-to-oxygen for
blowers
• Blowers typically have
high-speed rotation,
which contributes to
wear
• A Venturi aerator has no
moving parts of its own,
and the pump runs at
slower speeds than
most blowers

110. Comparable horsepower-to-oxygen for
blowers
• Blowers can be sensitive
to inlet air quality
• A Venturi aerator
introduces the air after
any moving parts, so air
quality, humidity, and
cleanliness really don’t
matter

111. A filter vacuum gauge on a blower
The red means “Danger”

112. The pump doesn’t
care about the air

113. Diffusers can move more oxygen, but…

114. Cleaning is a pain

115. Breaks and tears are hard to detect and
repair when fully submerged

116. Who wants the
thankless task of
fixing this leak?

117. Diffusers only mix
vertically unless aided
by horizontal mixers

118. Thrust from mixers can be
hazardous to diffusers

119. Designed well, a Venturi & pump system
delivers both oxygen transfer and mixing

120. Don’t under-estimate the importance
of mixing: Water motion matters!
Who wants to play “Hide and Seek the Submerged Diffusers”?

121. Both horizontal and vertical mixing
Distance between inlet and
outlet (plus baffles)
Elevation difference between
inlet and outlet

122. Vertical mixing ① Inhibits freezing in winter

123. Vertical mixing
② Counteracts stratification
(which disrupts O2 transfer)

124. Vertical mixing
③ Discourages odor-
causing seasonal inversions

125. A 3-for-1 deal
• Aeration
• Mixing
• Pumping

126. To recap
• Tighter nutrient standards
ordinarily call for much more
oxygen
• Treatment effectiveness is
often defeated by short-
circuiting, especially in lagoons
• Mixing and baffling help to
overcome short-circuiting
• Combining mixing and
aeration can reduce
equipment costs
• Mixing that is both horizontal
and vertical helps a lot,
especially in our climate
• Taking electricity, moving
parts, and equipment needing
maintenance out of the water
saves trouble

127. Questions?
• Thank you for your time
and attention!
• These slides can be found at
gongol.net/presentations
• Brian Gongol
DJ Gongol & Associates
• 515-223-4144
• brian@gongol.net
• @djgongol
on social networks

128. Credits
• Aerial photos obtained from public-domain sources
• Paddle aerator photo obtained from the public domain:
Ben May Charitable Trust Collection of Mississippi Photographs in the Carol M.
Highsmith Archive, Library of Congress, Prints and Photographs Division
https://www.loc.gov/item/2017879339/
• Portrait of Bernoulli obtained from the public domain:
https://archive.org/details/EST87_RES_P26
• Atmospheric oxygen concentration:
https://climate.nasa.gov/news/2491/10-interesting-things-about-air/
• F-250 dimensions:
https://www.ford.com/trucks/super-duty/models/f250-xlt/
• EPA compliance advisory for small lagoons:
https://www.epa.gov/system/files/documents/2022-03/lagoon-
complianceadvisory.pdf
• All other photographs supplied either by the author or by the Gorman-Rupp Co.