Airlift pump apparatus and method

An airlift pump apparatus and method is based on the practice of injecting air intermittently into a vertical riser tube at a location above a bottom open end of the riser tube which is submerged in the liquid to be pumped. The intermittently injected air is used to create intermittent airlifts within the tube and cause aerated liquid to be discharged intermittently from an output port of the tube.

FIELD OF THE INVENTION 
The invention generally relates to an airlift pumping apparatus and method 
for general application and is described in reference to an airlift 
pumping apparatus and method used for both pumping and aerating household 
wastewater discharged from a septic tank to a drainage field. 
BACKGROUND OF THE INVENTION 
A typical airlift pump, illustrated in FIG. 1, consists of an open ended 
vertical riser tube, partially submerged in a liquid and near the bottom 
of which compressed air or another gas is injected. Once the air or other 
gas is injected into the liquid, the average density of the air-liquid 
mixture in the riser tube becomes less than the density of the surrounding 
liquid. The resulting buoyant force causes a pumping action in the riser 
tube and the air-liquid mixture is discharged at the top of the riser 
tube. 
Airlift pumps are widely applied for the purpose of pumping liquids. For 
example, an airlift pump is described in the article entitled "Airlift 
Pump Cleans Around Subsea Wellhead", Oil and Gas Journal, Volume 90, Aug. 
3, 1992, pages 62-64. A lift pump operation is also explained in reference 
to FIGS. 45 and 46 in Encyclopedia Of Fluid Mechanics, Volume 2, Dynamics 
of Single Fluid Flows and Mixing, Nicholas P. Cheremisinoff, Editor. 
In the article entitled "Simulation Of Airlift Pumps For Deep Water Wells", 
The Canadian Journal Of Chemical Engineering, Volume 74, August, 1996, 
pages 448-456, mention is made that airlift pumps offer simplicity of 
construction and lack of moving mechanical parts as their main advantages. 
This article also illustrates both external airline and internal airlift 
pump systems. In another article entitled "Explore The Potential Of 
Airlift Pumps And Multiphase", Chemical Engineering Progress, August 1993, 
pages 51-56, a discussion is given of the effect of liquid density on the 
operation of an airlift pump. A discussion of how the ratio of the length 
of submerged riser tube to the total riser tube length affects the airlift 
pump performance is found in the article entitled "Visual Study Of An 
Airlift Pump Operating At Low Submergence Ratios", The Canadian Journal Of 
Chemical Engineering, Volume 73, October, 1995. In a wastewater system 
marketed as the Nibbler, Jr..TM. by Northwest Cascade-Stuth of 16207 
Meridian, Puyallup, Wash. 98373, an airlift system is used to lift 
wastewater. 
In the particular context of treatment of wastewater, it is recognized by 
the present invention that the typical airlift pump tends to aerate the 
liquid being pumped and that aeration of the wastewater could become an 
advantage when the wastewater is liquid being pumped from a septic tank to 
a drain field having a clay-like character which makes liquid that is not 
aerated difficult to absorb. Also recognized by the invention is the 
potential advantage of pumping wastewater to a drain field intermittently 
rather than constantly so as to permit the drain field to absorb 
intermittently and the drain field pipes to be flushed intermittently. 
In the typical application of an airlift pump, the inflow to the tank, 
vessel or other body holding the liquid to be pumped and in which the 
riser tube is submerged, the air flow rate and the depth of submergence of 
the riser tube are all relatively constant and the airlift pump outflow is 
continous. So far as is known, an airlift pump has never been constructed 
such that without requiring moving parts or controls, it can be made to 
pump intermittently. While the conventional airlift pump construction and 
operation is well understood, what has not been recognized is that by 
making a significant modification of the conventional airlift pump 
construction as provided by the present invention, the airlift pump can be 
made to operate intermittently. It has been shown that the airlift pump of 
the present invention, under selected conditions, is significantly more 
efficient than traditional airlift pumps, providing for increased output 
flow rate. 
The airlift pump of the present invention may be particularly suited for 
many applications, including subsea wellheads, water wells, and like 
applications. The particular application described in detail herein is for 
pumping and aerating household wastewater in septic tank systems, it being 
understood that the airlift pump so described is equally applicable to 
many different applications. 
With the foregoing in mind, the object of the present invention becomes 
that of providing an improved airlift pump apparatus and method for 
general application. 
A further object of the present invention is to provide an airlift pump 
apparatus that operates using reduced air supply power. 
Another object of the present invention is to provide an airlift pump 
apparatus and method, wherein the discharged liquid is caused to be 
emitted in intermittent powerful bursts. 
Yet another object of the present invention is to provide an airlift pump 
apparatus and method, wherein the rate of liquid output is increased 
compared to the rate of liquid output of a typical airlift pump. 
Yet another object of the present invention is to provide an airlift pump 
apparatus and method that is suited to the needs of pumping wastewater 
from septic tanks to drain fields, wherein the liquid is pumped 
intermittently, but substantially evenly over the course of a day during 
which liquid input to the septic tank may vary substantially and is also 
pumped in a manner which causes the discharge water directed to the drain 
field to be highly and intermittently aerated and therefore more suitable 
for absorption by clay and other soils of like character. 
Other objects will become apparent as the description proceeds. 
SUMMARY OF THE INVENTION 
An improved airlift pump apparatus and method of general application is 
illustrated, by way of example, as being applied to pumping wastewater 
(fluid) from a septic tank (reservoir of fluid) to a drain field (outlet 
end). The airlift pump apparatus of the invention as illustrated by way of 
example incorporates an inverted cylindrical chamber having a closed upper 
end, an open bottom end continuous within the fluid held with the septic 
tank, and a source of air connected to the closed upper end. This chamber 
effectively serves as an air tank and within the chamber there is mounted 
a vertical pipe of substantially less diameter than that of the chamber 
and having an open upper end located at an internal elevation within the 
chamber which is higher than the elevation of the open bottom end of the 
chamber. The vertical pipe connects through a horizontal run of pipe to a 
riser tube into which air accumulated in the air tank formed by the 
chamber is intermittently discharged whenever the water level in the air 
tank is forced down to the level of the horizontal run of pipe connecting 
the referred to vertical pipe and riser tube. 
In operation, air accumulates in the air tank and forces liquid down within 
the air tank until it reaches the level of the horizontal run of pipe 
connecting the vertical pipe and riser tube at which stage a mixture of 
liquid and air is discharged as a powerful burst of aerated liquid from an 
upper output port of the riser tube. When applied to a septic tank system, 
the aerated water is typically directed to a drain-field associated with 
the septic tank. The system of the invention automatically recycles after 
each burst of aerated liquid.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
In the typical airlift pump apparatus 18 as illustrated in FIG. 1, air is 
supplied from a compressed air source 20 connected to input end 22 of an 
air supply line 24 and whose output end 26 is connected through a port 30 
to the lower end of a riser tube 32 with port 30 being submerged below 
liquid level LL to a depth S in the liquid L being pumped. The lower 
intake port 57 of riser tube 32 is maintained at a distance D above the 
bottom wall 33 of vessel V. The air flowing through the liquid L in the 
portion of the riser tube above the port 30 creates an air-liquid mix ALM 
which is less dense than the liquid L and thus tends to rise and is 
discharged through output port 36. Liquid L is transferred from liquid 
supply 31 to illustrative vessel V holding the liquid L. The flow of air 
through air supply line 24 and port 30 remains constant, and thus, using a 
typical airlift pump apparatus, the air-liquid mix ALM lifted by the head 
distance H and discharged through output port 36 is continuous, provided 
liquid level LL does not fall below port 30. 
By contrast, the apparatus and method of the invention recognizes that for 
many applications including the application related to pumping wastewater 
from a septic tank to a drain field, advantages accrue when the airlift 
pump is made to operate intermittently. Furthermore, most all applications 
can benefit from the increased rate of liquid output from the airlift pump 
of the present invention. An increased rate of liquid output as provided 
by the present invention means that the power needed to pump a specified 
volume of air into the airlift pump of the invention for a specified 
liquid output is lower (when compared to a typical airlift pump), thereby 
lowering the size and cost of air pumps, which would be especially 
important in the context of massive airlift pumping applications, such as 
removal of liquid from the ocean floor or from deep wells. The manner in 
which this is accomplished is next described in reference to FIGS. 2-9, 
showing by way of example, the airlift pump of the present invention 
applied to a septic tank system. 
In the description to follow, the vessel V of FIG. 1 may for reference be 
thought of as one portion of a septic tank and the liquid supply 31 as a 
supply of wastewater liquid L contained in another portion of the same 
septic tank. It will nevertheless be apparent that liquid supply 31 could 
be any suitable liquid supply such as a river or precipitation, and vessel 
V could be any reservoir for holding liquid, including a natural body of 
water such as a lake or ocean. Liquid supply 31 and vessel V could also 
constitute together a single source of liquid. 
Making reference initially to FIGS. 2-3, there is shown somewhat 
schematically in FIG. 2 a first embodiment and in FIG. 3 a second 
embodiment of a modified airlift pump apparatus according to the invention 
and characterized by exhibiting an intermittent operation. The liquid L 
and air-liquid mix ALM seen in FIG. 1 are not shown in FIGS. 2 and 3 for 
simplification. Referring further to FIG. 2, there is shown a modified 
airlift pump system 40 in which air is supplied from an air source 42 
connected to input port 44 of an air supply line 46 and whose output port 
48 is connected to the upper closed end 50 of what is referred to as an 
air tank 52. Air tank 52 has an upper closed end 50 and is illustrated as 
being of cylindrical construction with a bottom open end 54 continuous 
with liquid L. 
Continuing in reference to FIG. 2, a cylindrical riser tube 56 is formed 
with a connected elbow 58 having an upper vertical intake end 60 with an 
intake port 62 and a lower horizontal discharge end 64 with a discharge 
port 66 connected to a lower intermittent portion of riser tube 56 the 
upper portion of which extends through a suitable relatively tight opening 
68 in the upper closed end 50 of air tank 52. The airlift assembly 
comprising air tank 52 and riser tube 56 mounts in a suitable septic tank 
or other vessel VV connected to a liquid supply 43 and containing the 
wastewater liquid L to be pumped through intake port 53 of riser tube 56 
in the manner described below for discharge through output port 70. 
Distances H, S and D in FIG. 2 represent distances of similar notation as 
seen in FIG. 1. 
In a second embodiment illustrated in FIG. 3, the airlift pump apparatus 
40' utilizes many of the same components as previously referred to and are 
identified in FIG. 3 by the same numerals and letter notation as used in 
FIG. 2. As will be readily seen by a comparison of FIG. 2 with that of 
FIG. 3, it will be seen that the riser tube 56 is mounted externally of 
air tank 52 and has the lower horizontal discharge end 64 of elbow 58 
mounted through a relatively tight side wall opening 74 in air tank 52. 
The invention apparatus lends itself to being formed in many different ways 
and sizes with each such form being capable of the intermittent operation 
described below. Simply by way of illustration, the air tank 52 in one 
example was formed of plastic tubing of approximately 4 inches internal 
diameter. In the same example, riser tube 56 and elbow 58 were formed of 
plastic tube of approximately 1-inch internal diameter. The relative 
height of the air tank 52 and length of riser tube 56 were generally as 
indicated in FIGS. 2 and 3. 
With the above background in mind, the explanation next proceeds to FIGS. 
4-8 and a description of the manner of operation in which the FIG. 3 
second embodiment is used by way of reference. In this explanation, liquid 
L is assumed to be wastewater being pumped from a septic tank assumed to 
be vessel VV, to a drain field, not shown. At the beginning of a cycle of 
operation, FIG. 4 illustrates the airlift pump system 40' of FIG. 3 with 
the air tank 52, riser tube 56 including its elbow 58 with upper vertical 
end 60 and lower horizontal discharge end 64 all filled with the liquid L 
and with little or no air present in air tank 52. 
In FIG. 5, there is shown the effect of admitting and storing air in air 
tank 52 and forcing the liquid L through air tank 52 to move to a level 
L-1. At this level L-1 stage, the airlift pump of the invention is not 
discharging liquid through output port 70 In a more advanced stage 
depicted in FIG. 6, the air emitted into air tank 52 has caused the liquid 
L within air tank 52 to reach a lower level L-2 at which the air in air 
tank 52 is shown just prior to being released through the discharge end 64 
of elbow 58. Again, at this level L-2 stage, the airlift pump of the 
invention is not discharging liquid through output port 70. 
In the next stage shown in FIG. 7, the stored pressurized air from air tank 
52 is assumed to have been released into airlift riser tube 56 along with 
such liquid as was stored in discharge end 64 of elbow 58 so as to form 
the air-liquid mix ALM which because of its reduced density, is indicated 
in FIG. 7 as rising and liquid drawn through intake port 53 is indicated 
being pumped through output port 70 for discharge to a drain field or 
other location (not shown). The amount of air-liquid mix ALM contained in 
each intermittent discharge burst of the present invention is 
significantly larger and more powerful than the air-liquid mix ALM output 
of a typical airlift apparatus. It has been shown that the large and 
powerful intermittent air-liquid mix ALM output burst of the present 
invention tends to dislodge the bioorganisms from the inside surface of 
the riser tube 56 and its output port 70 as well from the inside surface 
of any pipe, drain field tile or the like connected directly to the output 
port 70, thereby preventing clogging of the septic tank system in these 
areas. FIG. 7 also illustrates the liquid L refilling the air tank 52 and 
in FIG. 8, the end of the airlift is illustrated preparatory to the 
beginning of a new cycle. 
The source of air 42 is assumed to continuously feed air through air supply 
line 46. Air source 42 can be a compressed air source, a fan-type air 
source, or any other air source known in the art. It is also assumed that 
the liquid L is fed from the appropriate liquid supply 43 to the septic 
tank or vessel VV intermittently as is common with both household and 
commercial septic tank systems, and with other liquid collection and 
transfer systems. As best illustrated in FIG. 9 based on use of the 
invention apparatus in a typical household septic tank system, the overall 
result from using the improved airlift system of the invention is that 
even though in the example being used for illustration, the inflow to the 
septic tank or vessel VV varies as indicated by representative curve 80, 
the discharge from the vessel VV by reason of being intermittent tends to 
be more regular as indicated by representative curve 81. In other words, 
the airlift of the present invention prevents the septic tank system from 
tending toward a 1:1 ratio of liquid input to output as shown by FIG. 9. 
Thus, the invention apparatus and method causes the input wastewater to 
reside in vessel VV for some amount of time prior to being discharged 
through port 70. This residence time of the wastewater in vessel VV of the 
present invention thus allows for more thorough digestion and treatment of 
the wastewater while within the septic tank prior to going into the drain 
field. Further, as indicated by curve 81 in FIG. 9, there is achieved a 
substantially equal output flow over time. 
Variations in the head distance H, submerged distance S and intake distance 
D have all been found to affect the manner in which the invention system 
operates. However, so long as the operating conditions are such as to make 
the supply of liquid L available to intermittently fill and replenish air 
tank 52, the numerous advantages of the invention are obtained in that the 
liquid is pumped intermittently, is aerated and caused to enter the drain 
field intermittently and thereby enhance the absorption of the liquid by 
the soil. 
It has also been found that with the intermittent mode of operation, less 
energy is required to operate an airlift system made according to the 
invention as compared to an airlift system constructed according to the 
prior art such as shown in FIG. 1, when both the prior art system and the 
invention system such as shown in FIG. 3 are assumed to have the same 
pressurized air source, the same 1-inch size riser tube and the same 
dimensions H, S and D. The following table illustrates that the airlift 
pump of the present invention, whose air tank was formed of 4-inch pipe, 
had a rate of output which was greater than the typical airlift pump 
operating under the same conditions. 
__________________________________________________________________________ 
Table Comparing Prior Art And Invention Airlift Pumps 
Ss H Flow 
Air Flow 
W Wa Efficiency 
[mm] [mm] 
Ss/(Ss + H) 
[1/min] 
[1/min] 
[W/min] 
[W/min] 
W/Wa 
__________________________________________________________________________ 
Invention 
254 
616 
29.2% 0.00 
7.84 
0.000 
0.332 
0.0% 
Air-Lift 
305 
565 
35.1% 0.17 
7.36 
0.015 
0.373 
4.1% 
Pump 356 
514 
40.9% 0.85 
6.89 
0.072 
0.407 
17.6% 
406 
464 
46.7% 2.58 
6.63 
0.196 
0.445 
44.0% 
457 
413 
52.5% 3.39 
6.37 
0.229 
0.481 
47.6% 
508 
362 
58.4% 3.93 
6.11 
0.233 
0.512 
45.5% 
559 
311 
54.3% 4.67 
5.86 
0.237 
0.538 
44.1% 
610 
260 
70.1% 5.36 
5.60 
0.228 
0.560 
40.7% 
Typical 
457 
413 
52.6% 0.00 
6.37 
0.000 
0.481 
0.0% 
Airlift 
508 
362 
58.4% 0.37 
6.11 
0.022 
0.512 
4.3% 
Pump 559 
311 
64.2% 2.14 
5.86 
0.109 
0.538 
20.3% 
610 
260 
70.1% 2.90 
5.61 
0.124 
0.560 
22.1% 
__________________________________________________________________________ 
Ss: Submerged distance [mm 
H: Head distance [mm 
Ss/(Ss + H): Submergence Ratio 
Flow: Rate of water discharge [1/min 
Air Flow: Air supplied to the pump at the submergence [1/min 
W: Work done by lifting water per unit time [W/min] in watts 
Wa: Work done per unit time by the air in expanding isothermally [W/min] 
in watts 
W/Wa: Efficiency of the pump 
The table shows in one example that when Ss=610, H=260, and airflow 
approximately 5.60 liters/minute, the airlift pump of the invention has a 
liquid flow rate of 5.36 liters/minute and an efficiency of 40.7%. The 
submerged distance Ss in the table is equivalent to the distance 
represented by the letter S of FIGS. 1-8. In significant contrast, under 
the same same conditions, the comparable prior art airlift pump has a 
liquid flow rate of 2.90 liters/minute and an efficiency of 22.1%. As 
stated above, an increased rate of air-liquid mix ALM output as provided 
by the present invention means that the power needed to pump a specified 
volume of air into the airlift pump of the invention for a specified 
liquid output is lower. Thus, when using the airlift pump of the present 
invention for massive airlift pumping applications, such as removal of 
liquid from the ocean floor or from deep wells, the size and cost of the 
pressurized air source needed for massive airlift pumping applications is 
significantly reduced. The increase in pumping efficiency of the present 
invention also has a significant impact on smaller pumping applications as 
well, such as in the above described septic tank wastewater system. 
In summary, it will be seen that the airlift pumping apparatus and method 
of the invention provides a unique and advantageous intermittent operation 
which leads to improvement in pumping efficiency, to improved aeration of 
the liquid being pumped, to a more equal and uniform outflow in those 
systems in which the inflow fluctuates, and to a reduction in bioorganism 
growth particularly when applied to septic tank systems. 
While the invention has thus been described with specific embodiments 
thereof, it will be appreciated that numerous variations, modifications, 
and embodiments are to be regarded as being within the spirit and scope of 
the invention.