CA1040759A - Methods and apparatus for treating wastewater - Google Patents

Abstract

ABSTRACT

Apparatus for oxygenating a body of wastewater includes a chamber into which an oxygenating gas is introduced to form a gas space. A weir and a baffle are provided in the chamber to define a gravitational fall zone while a pump is provided for introducing wastewater into the chamber and for subjecting such wastewater to a gravitational fall over the weir and through the gas space to render the wastewater turbulent in the fall zone and thereby oxygenating such wastewater. A nozzle is also provided at the chamber outlet such that oxygenated wastewater is discharged into a body of wastewater under treatment.

Description

~040759 ., .
BACKGROUND
This invention rela~es generally to water treatment technology and more specifically to methods and apparatus for dissolving oxygen in wastewater such as water received for purification in municipal sewage plants and the like.
The conventional activated sludge process for the treatment of wastewater involves the biological degradation of organic materials contained therein. This requires the , maintenance of aerobic conditions, normally achieved by relying on open aeration to dissolve oxygen from ambient air into i~ .
; wastewater. While such processes have been used successfully ,3j for many years there are definite limits on the speed and efficiency of such processes. For example both the rate at which oxygen can be dissolved in the water and the maximum oxygen ~, concentration that can be achieved are clearly limited. As a result the ever expanding needs for more and better wastewater treatment to protect the eoology in our expanding society can be met, using existing ,.. ~ -1-' ' '' ~ . , 1040~59 processes, only by a proliferation of plants for such processes at great capital expense and with the utilization of vast quanti-ties of power in their operation.
The present invention is directed to methods and apparatus for more ~uickly and efficiently dissolving oxygen in wastewater to accelerate the biodegradation of organic material.
This, in turn, increases the through-put of any given treatment fa~ility and reduces the unit cost of wastewater treatment.
Cost reduction can be effected even though oxygen or oxygen enriched air (which costs money)is utilized in place of air (which is "free"). However, to keep the treatment cost to a minimum, the oxygen must be used efficiently, i.e., a high per-centage of the oxygen suppl~ed must be dissolved in and retained by the wastewater.

OBJECTS
It is an ob~ect of the present invention to provide improved methods and apparatus for the dissolution of oxygen in wastewater.
Another ob~ect Or the present invention is to provide methods and apparatus for the dissolution of oxygen in waste-water at a faster rate than heretofore.
; Another ob~ect Or the present invention is to provide methods and apparatus for the dissolution of oxygen in wastewater with a minimum consumption of power.
Another ob~ect of the present inventlon is to provide ; methods and apparatus that will enable hlgher concentrations of di~solved oxygen than heretofore Another ob~ect of the invention is to provide a self-contained unit or module that can be used directly in or ad~a-cent an existing tank or pond to dissolve oxygen in all Or the water in the said tank or pond without requiring sign1ficant .
, structural modifications, such as covers or the like, to the tank or pond.
It is a further object of the present invention to provide methods and apparatus for dissolving oxygen in waste-water wherein an efficient utilization of supplied oxygen is enabled.
Yet another ob~ect of the present invention is to provide methods and apparatus correctly stirring wastewater in a treatment tank at sufficient velocities to prevent settling of suspended solids.
SUMNARY
In accordance with one aspect, the present invention ~- relates to apparatus for oxygenating a body of wastewater containing organic solids compri~ing a generally enclosed oxygenating chamber emplaceable in said body of wastewater: means for pumping wastewater under treatment into said chamber; means ] for $ntroducing an oxygenating gas into said chamber to form a gas space therein containing said oxygenating gas; means for rendering gaid pumped wastewater turbulent by sub~ecting said pumped wastewater to a gravitational fall over a weir through said oxygenating gas and into a gravitational fall zone substantially defined by said weir with the resu~lting llquid-gas turbulence in said fall zone being effective to oxygenate said turbulent wastewater and entrain undissolved oxygenating gas therein; liquid accumulation means for receiving oxygenated wastewater from said fall zone and for dissipating said turbulence to enable disentrainment and recovery within said chamber of said undissolved entrained oxygenating gas; and nozzle means for discharglng ~aid oxygenated wastewater from said liquid accumulation means into said body of wastewater at a velocity such that said body of wastewater is sufficiently stirrea to maintain sald organic solids suspended therein.

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'~ In accordance with another aspect, the invention relates to a met~od of dissolving oxygen ~n a body of water having a dissolved oxygen demand which comprises: ta) withdrawing water from said body and pumping it through a treatment chamber;
(b) introducing an oxygenating gas into said treatment chamber at a superatmospheric pressure to-form a body of gas therein;
(c) creating a turbulent condition in said pumped water by subjecting said pumped water to a~gravitational fall over a weir into a gravitational fall zone w',ithin said chamber and in direct contact with said body of-oxygenating gas whereby oxygen is dissolved and undissolved oxygenating gas is entrained in said turbulent water; (d) passing said turbulent water to a quiescent zone within said chamber ~o' dissipate said turbulence-'' and cause disentrainment and re,covery'within said chamber of undissolved oxygenating gas; and (ej discharging said water ~-containing dissolved oxygen from said qùiescent zone of said chamber through a nozzle into s~d body of w~ter-at a sufficient velocity to stlr said body and sub-tantially uniformly'~,, - distribute the discharged water th~oughout the body of water from which it was withdrawn. '' :-, It was known prior to 'the pFesent invention to ,, ~ . . s .. . . . ..
accelerate the activated sludge wastewateF treatment process by substituting an oxygen enri~hed atmosphere for ambient air as - . .... - . . . . " , .. . .
the medium for sustain,ing aerobic condi'tions in an aeration , basin. Such a process is~d,escribed in the article ~AeratiOn With A High-Oxygen Atmosph e In A.S. Proce~s~, by ~arold E.
Babbitt, and was published in Wastes Engineering, May l9S2,-pp. 258-259. The Babbit article de~cribes a process for oxygen~ting w~stewater wherein a gas-tight cover i8 provided across the top of an aeration tank with an oxygen-enriched r~

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atmosphere being maintained in the head space between the surface of the wastewater and the tank cover. A feed gas comprised of 95% oxygen is introduced into the aeration tank by means of a submerged aerating device and the aeration gas collected in the head space is recirculated through a compressor to the aerating device. Although the aforedescribed process has resulted in relatively high levels of dissolved oxygen within acceptable time periods, the accumulation of large amounts of an oxygen enriched aeration gas in the head space of the aeration tank represents a serious safety hazard.

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More recently, similar waæte treatment processes utilizing oxygen enriched atmospheres ln the head space of a covered aeration tank and mechanical agitators for dynamically mixing oxygen and wastewater have been devised in an effort to more efficiently utilize the oxygen. For example, systems simi-lar to the apparatus and methods described in the Babbitt arti-cle are also described in five U. S. Patents numbered 3,547,811 through 3,547,815. Again, systems illustrated in the foregoing references require the maintenance of an oxygen enriched atmo-sphere in a large head space of covered tanks and, therefore,provide an abundant supply of combustion supporting material.
Furthermore, by employing mechanical agitators in the form of shaft-driven impellers, surface aerators and the like, the possi-~ bility of inadvertently producing a spark which could trigger a ; fire or explosion in such an oxygen enriched atmosphere is sub-stantially increased.
In addition to preventing a possible safety hazard the foregoing attempts to upgrade the activated sludge process in an existing facility reguired substantial structural modifi-cation of such a facility with attendant down time and capitalexpense.
In U. S. Patent No. 3,503,593, the use of surface aerators in a submerged chamber for dissolving a gas such as air in a liquid is described. An air space is formed in the chamber by introduction of air under pressure. Although such a device avoids the foregoing safety hazards associated with utilization of surface aerators in an oxygen enriched atmosphere, a rela-tively high expenditure of mechanical power is required to dis-solve oxygen in the introduced air into a liquid such as waste-water. Other apparatus for dissolving a gas in a liquid by pro-longing gas bubble-liquid contact time are described in U. S.
Patent Nos. 3,476,366 and 3,643,403. This technique relies upon .

the introduction of gas bubbles into a downward-flowlng llquid in a submerged funnel. Upwardly acting buoyant forces and down-wardly acting drag forces tend to increase the contact time between gas bubbles and the liquid. Such techniques, however, generally fall to adequately mix the liquid discharged from such a ~unnel with a surrounding larger body of the llquid as is re-quired in an activated sludge process. Furthermore, such dis-solution processes place heavy reliance on mere gas-liquld con-tact to e~fect a mass transfer which transfer does not necessar-ily occur in an efficient manner in practical applicat~onæ.

-~ BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more clearly understood by reference to the followlng detailed description of an exemplary embodiment thereof in con~unction with the following drawings ln which:
Fig. 1 is a sectional elevational view of an exem-plary oxygenating apparatus;
Fig. 2 is a side sectional view Or the exemplary oxy-genating apparatus illustrated in Fig. 1.
Fig. 3 i8 a plan view of the exemplary oxygenatingapparatus illustrated ln Pig. 1, Fig. 4 is an elevational sectlonal view of a further exemplary embodiment of an oxygenating apparatus in accordance with the present invention;
Fig. 5 is a sectional view of an exemplary embodi-ment of an outlet nozzle;
Fig. 6 is a graphical representation of oxygen con-8umption with respect to the superficial flow velocity of waste-water in an oxygenating apparatus according to the present in-vention;
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l04n7ss Fig. 7 is a sectional elevational view of yet another exemplary embodiment of oxygenating apparatus in accordance with the present invention;
Flg. 8 is a profile of dissolved oxygen levels in wastewater treated with oxygenating apparatus in accordance with the present invention; and Fig. 9 is a velocity profile of wastewater in a treat-ment tank during operation of the oxggenating apparatus ln accordance with the present invention.
DESCRIPTION OF PREFERRED EMBOM MENTS
Referring now to the drawing, and in particular to Fig. 1, illustrated therein i8 an exemplary embodiment of an apparatus for oxygenating wastewater which may be utilized in an activated sludge waste treatment process. In this process, untreated wa~tewater is commonly admitted to a primary settling basln wherein readily settlable solids are permitted to settle and are collected on the bottom of such a basin. Wa9tewater i8 then pas~ed to a treatment tank along with activated sludge and an oxygen supplied ln a feed gas is dissolved therein At thi~
stage of the process, the combined wastewater and activated sludge is many times referred to as a "mixed liquor" although for purposes of convenience, the term wastewater will be used as a full equlvalent. After retaining wastewater for a sufficient tlme to permit reduction in the biological oxygen demand of the wastewater to a desired level, the wastewater i8 pa~sed to a clarifier wherein purified effluent is decanted and activated sludge is settled out. In order to maintain a sufficient level of microbial activity, a predetermined portion of the collected sludge is returned to the treatment tank.
The oxygenating apparatus 10 is comprised of a pair of substantially identical generally enclosed chambers 11 and 11' which are emplaced in a body of wastewater 12. A tank 13, :;
~ 7 1~)4~J759 which may comprise a conventional open, secondary treatment tank for receiving wastewater to be oxygenated, i8 provided to confine wastewater 12 therein.
Chamber 11 is posltioned within tank 13 and by way of suitable bracket members i8 mounted on ad~ustable legs 14. The upper extremities of chamber 11 extend above the surface of wastewater 12 although chamber 11 may be totally æubmerged in a particular tank. The bottom of chamber 11 is sufficiently spaced from the bottom of tank 13 to permit predetermined flows of oxy-genated wastewater to be established in tank 13. Oxygenating apparatus 10 is provided with an inlet 15 in the form of a con-ventional pipe which is positioned below the surface of waste-water 12 and between chambers 11 and 11'. A pump 17 which may comprise a conventional axial flow impeller pump is disposed within inlet 15 and is mounted for rotation on a shaft in known manner. An electrical motor 16 mounted above wastewater 12 is dri~ingly coupled through the shaft to pump 17. In this manner a flow of wastewater 12 is forced through plenum 18 into cham-....
bers 11 and 11'. Plenum 18 may take the form o~ a bilateral fluid flow divider whlch is provlded wlth bracket members 19 forrlgldly connectlng the lower portlons of chambers 11 and 11'.
Addltlonally, the upper portlons of chambers 11 and 11' may be afflxed to one another by suitable bracket members 22 Altern-ately, chambers 11 and 11' may be posltioned externally of tank 13 and adapted to receive wastewater from and dlscharge oxygen-ated wastewater into tank 13.
Chamber 11, which ls generally enclosed, is comprised o~ lnlet 20, static mixing zone 24, liquld and gaæ accumulation spaces 25 and 26, respectively, and an outlet 31. Inlet 20 of chamber 11 is a substantially vertical channel defined by an external vertical wall of chamber 11 and partition 21. A verti-cal baffle 23 is suitably mounted in chamber 11 spaced away from lV4~759 and parallel to a portion of partition 21 The top of baffle 23 is spaced away from the ceiling of chamber ll and the lower extremity of baffle 23 is spaced away from a substantially horizontal portion of baffle 27 extending from partition 21.
Accordingly, partition 21 and baffle 23 are effective to define a static mixing zone 24 as will be described in greater detail hereafter, A gas accumulation space 26 is formed in the upper reaches of chamber ll by the introduction therein of an oxygen containing feed gas under an appropriate pressure The extent of gas accumulation space 26 and, therefore, the depth of liquid in space 2~, is determined by the pressure of the gas fed through inlet 29 to the upper reaches of chamber ll. It will be appre-ciated that the gas present in space 26 during operation of ap-paratus lO is comprised of the feed gas, oxygen disentrained ~rom wastewater in liquid accumulation ~pace 25 and other gases stripped from the wastewater Accordingly, the gas within gas space 26 i8 hereafter referred to as the "oxygenating gaæ"
Communication between gas accumulation space 26 and the static mixing zone 24 is provided through passage 28 which passage is defined by the top of chamber ll and the uppermost extremity of baffle 23. The feed gas introduced into the upper reaches of chamber ll i8 preferably comprised Or an oxygen enriched gas con- -taining at least 40% oxygen A vent, or outlet, 30 is provided to permit the removal of spent or waste gases such as nitrogen which is strlpped from wastewater during the oxygenation thereof . and is collected in gas accumulation space 26. Preferably, vent ;~ 30 ls located away from gas accumulation space 26 in order to : prevent any foam, which may develop therein in the course of oxy-genating wastewater, from entering the vent llne.
~; A discharge outlet for oxygenated wastewater is pro-vided ln the lower reaches of cha~bers ll and ll'. The _9_ - - ~

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lV4()759 particular configuration of such an outlet will be determined by the particular flow pattern to be maintained in wastewater 12 to maintain activated solids (suspended solids) in suspension and to mix oxygenated wastewater with wastewater 12. As requir-ed flow patterns of wastewater 12 are additionally affected by the particular geometry of tank 13, it will be appreciated that either flap 31 or nozzle 33 (Fig. 2), or a combination of both, may be utilized to produce such flow patterns. An ad~ustable flap 31 which is hinged about, and pre~erably extends across, the bottom of chamber 11 is provided. A similar flap is provided in like manner with chamber 11' A control rod 32 is suitably connected at the lower extremity thereof to flap 31 and extends upwardly through and is sealed to the top of chamber 11. Exter-nally effected ad~ustments of the opening of flap 31, and hence, the velocity of oxygenated wastewater discharged from chamber 11, are achleved by manually raising or lowering control rod 32.
A nozzle 33 and a mechanical control arrangement therefor are provided with chamber 11 and for purposes of clarity, thls structure is illustrated in Fig. 2. The nozzle 33, which may generally comprise a spout is configured to extend over a substantially shorter portion of the bottom of chamber 11 than does flap 31. Accordingly, the oxygenated wastewater discharged from chamber 11 through nozzle 33 will exhibit a greater velocity and smaller cross-section area than the oxygenated wastewater discharged through flap 31. As will be described in greater de-tail hereafter, the directionality and opening of nozzle 33 may be controlled to establish predetermined flow patterns in waste-water 12.
Referring now to Fig. 2, an exemplary mechanical ar-rangement for enabling externally effected adjustments to be made to flap 31 and nozzle 33 is illustrated. It is realized that although the foregoing mechanical arrangement is depicted ,.

lV4~759 in conjunction with chamber 11, a substantially identical ar-rangement (not shown) is provided to control a similar flap and nozzle outlet configuration of chamber 11'.
The control arrangement for nozzle 33 is specifically adapted to facilitate nozzle opening and direction control by an operator from a point external to chamber 11 above wastewater 12.
Although a detailed description of nozzle 33 iæ set forth here-after in conneetion with the nozzle illustrated in Fig. 5, other suitable nozzle conflgurations may be utilized. The control ar-rangement for nozzle 33 comprises a torque tube 34 having a handle 36 affixed thereto and a control rod 35. The directional-ity of nozzle 33 is controlled by rotating handle 36 and conse-quently torque tube 34 ln a horizontal plane while the opening of nozzle 33 is controlled by merely raising and lowering rod 35 which in turn closes and opens a discharge spout of nozzle 33 as will be aescribed in greater detail hereafter.
A pressure relief device is provided as a precaution-ary measure in chamber 11 and is comprises of a tubular cup 37 and conduit 39 having an outlet at the upper end thereof. Tubular cup 37 and conduit 39 are disposed about torque tube 34 at a pre-determined level in llquid accumulation space 25 and form a liq-uid seal which under normal conditions inhibits the escape of any gas from the outlet of con~uit 39. However, in the event that the pressure of an oxygenating gas supplied to the upper reacheæ
of chamber 11 is sufficient to depress the level of water in liq-uid accumulation space 25 below the lower extremity of conduit 39, the aforedescribed water seal is broken thereby venting such gas and imposing an upper limit to the pressure of a supplied oxygen-~' ating gas by venting such gas to the atmosphere. In addition, the water seal acts as a bubble baffle to prevent bubble~ of oxy-genating gas from escaping upwardly through tube 39.

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1~40~S9 A plan view of chambers 11 and 11' i8 shown in Fig. 3.
In addition, the flow of wastewater 12, particularly at the sur-face thereof, is schematically lllustrated by arrows. It will be realized that as motor 16 drives pump 17 (Fig. 1) wastewater 12 is sub~ected to a suction force and is drawn into the space between chambers 11 and 11' prior to the actual pumping of waste-water into such chambers as previously mentioned.
Prior to descr~bing the operation of the oxygenating apparatus 10, illustrated in Fig. 1, it is important that sever-al requlsites of wastewater treatment to be satisfied by such an apparatus are clearly understood and appreciated. A first re-quirement for effective operation is to maximize the amount of oxygen dissolved in wastewater in relation to the energy requir- -ed to effect such diæsolution. A second requirement ls to dis-solve in wastewater as much of the supplied oxygen as possible and accordingly, to vent a minimum amount of oxygen from the apparatus. Thus, the greater the percent of oxygen consumption by an oxygenating apparatus, the more efficient i8 such an appa-ratus in terms of oxygen utilization and hence, in terms of the cost of oxygen supplled thereto. A third requirement is particu-larly important with respect to the oxygenating apparatus utiliz-ed in connection with activated æludge waste treatment processes wherein in order to permit the consumption of organic waste material by bacterial action, the bacterial sludge must be main-ta~ned in suspension in the wastewater. Accordingly, the waste-water in an aeration tank must be stirred effectively notwith-standing the fact that such stirring has previously resulted in increased "mlxing" energy consumed in terms of the amount of oxy-gen dissolved in the wastewater. In the course of describing the operation of oxygenating apparatus 10 hereafter, the ability of the present invention to satisfy the foregoing requirements will become readily apparent.

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104(~7S9 The operation of the oxygenating apparatus as illus-trated in Fig. 1 is as follows. Wastewater 12 in tank 13 is introduced into an inlet conduit 15 and is pumped by way of pump 17 into plenum 18. Hydraulic kinetic energy is thus im-parted to wastewater 12 which is div~ded into two approximately equal flow streams in plenum 18 and i8 then pumped under pres-sure upwardly through inlet channel 20 of chamber 11 and flows over the top edge of partition 21. It i8 noted that by virtue of forclng a flow of wastewater upwardly through inlet channel 20, a water seal ls malntalned between a gas accumulatlon space ; ln 26 ln chamber 11 and hydraullc pump 17.
Simultaneous wlth the introduction of wastewater 12 into chamber 11, an oxygen-containlng feed gas is introduced under pressure through inlet 29 into the upper reaches of cham-ber 11 thereby depressing the level of wastewater within liquid accumulation ~pace 25 to a point corresponding to the magnitude of the pressure of the oxygenating gas.
As previou~ly mentioned, static mixlng zone 24 ls de-fined by partition 21 and baffles 23 and 27 with the partlcular type of statlc mixlng zone lllustrated hereln belng of the gravl-tational fall type. It is realized that other forms of static mixing devices, such as an eductor may be utllized ~n li~u of a gravitational fall zone. Wastewater is caused to flow over the top of baffle 21 and then falls under the lnfluence of gravlty lnto zone 24 to lmpinge upon wastewater therein. This impinge-ment results in a state of high wastewater-gas turbulence and the production of a froth column within mixlng zone 24. As a consequence of providing a hlgh degree of liquld turbulence, bubbles of oxygenating gas, having relatively large surface areas are thoroughly dispersed in the liquid. In addition, the high .
; liquid phase turbulence is effective to promote a greater rate of mass transfer across the interfacial area created by the bubbles formed in zone 24.

1t)4~759 Although the lmportance Or creatlng a turbulent condi-tion will be understood from the foregoing discussion, a further parameter, namely the "superficial" flow velocity of water through zone 24 is also an important factor in obtaining a maxi-mum utilization of the oxygenating gas supplled to zone 24. The superficial flow velocity of wastewater may readily be calculated by dividing the flow rate by the cross-sectlon area between parti-tion 21 and baffle 23. It has been round that for a particular fall height which ls defined, ror example, by the distance be-tween the top of a partition or weir and the depressed level of such water as tap water in a liquid accumulation space, the amount of oxygen disæolved in tap water will vary as a function of the superficial rlow velocity of water through a static mixing zone.
Thus, for a particular fall zone, the "deficit reduction ration of oxygen may be plotted against different superficial flow velo-clties of water. Sucha graphical representation is depicted in Fig. 6, wherein the deficit reductlon ratlo, whlch may be defined by the expresslon C Ci is plotted ~long the ordlnate. The terms C0ut and Cin represent the concentratlons of oxygen dis-solved ln tap water after and before, respectively, the water has undergone a gravitational fall in a static mixing zone. The term C8 represents the saturated concentration Or dissolved oxygen in water under experimental conditions. Thus, the roregoing ex-pression, or the deflcit reductlon ratio, represents a measure Or the efflciency of the gravitational fall zone ln utilizing sup-plied oxygen. Accordingly, this ratio reflects the amount of oxygen actually dissolved in water in the fall zone against the experimental maxlmum amount which could be so dissolved m e superricial flow velocity Or water is plotted on the abcissa and this velocity may be easily varied by controlling - the speed of operation of hydraulic pump 17 ln a conventional manner.

lV4(~759 Referring again to Flg. 6, it is noted that for a particular fall height a maximum deficit reduction ratio occurs at approximately the same æuperficial flow velocity of water therethrough. That is, a maximum deficit reduction ratio occurs at a superficial flow velocity of approximately 1.0 ft.~sec.
regardlesæ of the fall height of a gravitational fall zone One possible explanation of the occurrence of an opti-mum superficial flow velocity and the relationships between superficial flow velocitieæ and deficit reduction ratios illu-strated in Fig. 6 is as follows. As the superficial flow velo-clty of water increases, additional turbulence in the fall zone can be expected to occur which promotes greater oxygenation, i e greater dissolution of oxygen in water as previously men-tioned. However, as the superficial flow velocity increases the period of time during which oxygenation may take place in the fall zone is reduced and accordingly, the actual degree of oxy-genation in the fall zone is correspondingly diminished It has been found that ~uperficial flow velocities in the range of 0.33 ft./sec to 3.0 ft./sec. will result in maximum deficit reduc-tion ratios for a particular fall height.
From the foregoing, it will be appreciated that by maintaining a highly turbulent condition of wastewater in a con-. .
fined static mixlng zone 24, and by providing an optimum super-ficial flow velocity of wastewater therethrough, a high concen-tration of dissolved oxygen in wastewater is achieved.
m e flow of wastewater exiting from static mixing zone 24 carries therewith entrained bubbles of the oxygenating eas Thus, as wastewater flows beneath the lowermost extremity of baffle 23 and upwardly toward the depressed wastewater level in liquid accumulation space 25, a circulating pattern of wastewater with gas bubbles entrained therein, is established generally in accordance with the arrows depicted in Fig 1. In the course of .~

lV41n7S9 such a ~low, the turbulence is dissipated in the relatively quiescent liquid accumulation zone 25 which permits the disen-trainment of gas bubbles. Larger gas bubbles are disentrained into gas accumulation space 26 relatively rapidly a~ the velocity o~ the flow from mixlng zone 24 dlminishes in liquid accumulation æpace 25. Smaller gas bubbles will also be disentrained ~rom the wastewater although a greater tendency to drag such smaller bubbles downwardly within li~uid accumulation space 25 exi~ts, A further opportunity for dissolution of the oxygenating gas into the llquid in liquid accumulation space 25 is thus provided and although some very small gas bubbles are emitted from this space through flap 31 or nozzle 33 or both, such amounts are emltted near the bottom of tank 13 and are stlll available for dissolu-; tion in wastewater 12, AdditlOnally, the amounts of oxygenatlnggas which may escape to the surface of wastewater 12 are well within both economical and safety limits even during the treat-ment of wastewater exhibiting high detergent concentrations.
It has been found in practice that most of the entrain-ed oxygenating gas in wastewater exiting from static mixing zone 24 is disentrained into gas accumulation space 26. The disen-tralned oxygenating gas is thus returned or recycled to the static mixing zone 24 via passage 28.
The dissolution of oxygen in wastewater causes certain other gases such as nitrogen to be stripped from the wastewater and relea~ed into gas accumulation space 26. In order to prevent the excessive buildup of impurities such as nitrogen which would ; reduce the oxygen content of the oxygenating gas below accept-able levels, a venting conduit 30 is provided. The venting o~
the oxygenating gas containing such impurities may be either intermittent or continuous and may be controlled by suitable valve devices (not shown) in a conventional manner. It has been found that the amount of oxygen vented along with the waste gases is well within economical limits.

lV40759 It will be understood that efficient dissolution o~
oxygen is facilitated by recycling the oxygenating not initlal-ly dissolved in zone 24. The flow of wastewater through the mixing zone is effective to sweep gas downwardly through zone 24 into liquid accumulation space 25. However, the normal buoy-ant forces acting on bubbles of the entrained oxygenating gas ~ causes a disentrainment of the gas into gas accumulation space -~ 26 and thereby forces the oxygenating gas upwardly toward pas-sage 28. In this manner, the oxygenating gas i8 recycled to mixing zone 24 and is again available for dissolution in the incoming wastewater The oxygenated wastewater contained within liquid ac-cumulation space 25, which will have a relatively high oxygen concentration, such as for example, 15 mg./l., is emitted from chamber 1~ at an increased velocity through flap 31 or nozzle 33 or both into the main body of wastewater 12. The oxygenated wastewater in liquid accumulation space 25 is maintained under a pressure head such that oxygenated wastewater may be emitted from chamber 11 at an increased velocity sufficient to cause an adequate stirring of wastewater 12 in tank 13 and thereby main-tain activated æludge particles in suspension. Furthermore, by ad~usting the opening of flap 31 and/or ~he directionality and opening of nozzle 33, a predetermined flow pattern of highly oxygenated wastewater may be e~tablished in tank 13. Production of such a flow pattern will permit a relatively constant dilu-tion of the highly oxygenated wastewater emitted from liquid accumulation space 25 thereby assuring that wastewater in sub-stantially all parts of tank 13 will be oxygenated to a level, such as 0.5 p.p.m., which level is sufficient to sustain aerobic ~ 30 conditions therein. Furthermore, by ad~usting the opening and ; directionality of each of nozzles 33 in chambers 11 and 11', the effluent from such nozzles may be arranged to cooperate in lQ~V759 establishing a predetermined flow pattern of highly oxygenated wastewater within tank 13.
It iæ realized that the foregoing tank stirring opera-tions may be effected by utilization of oxygenatian apparatus 10 without the additional requirement of mechanical agitating de-vices. A1SO~ in accordance with the present invention, the en-riched oxygen atmosphere maintained within oxygenating apparatus 10 does not extend across the surface of wastewater 12 and as no moving parts are utilized within gas accumulation space 26, the possibility of a spark being produced therein is highly unlikely Moreover, as the oxygenating apparatus 10 according to the pres-ent invention is at least partially submerged in wastewater 12 and contains only relatively small amounts of oxygenating gas, the possibility of fire damage is still further minimized. At certain portions and particularly lower depths in tank 13, rela-tively high dissolved oxygen levels are exhib~ted. This effect occur~ prlmarily due to the discharge of highly oxygenated waste-water from the bottom of apparatus 10 which achieves a "bottom scouring" of tank 13 as will be described in greater detail here-after. However, notwithstanding such high dissolved oxygen levels below the surface at wastewater 12, surface oxygen concen-trations are clearly within prescribed safety limits.
The oxygenating apparatus 10 illustrated in Figs.1-3 has been experimentally tested. The wastewater to be treated experimentally comprised the lndustrial waste of a meat proces-sing plant fed to a treatment tank 13 from a stirred retention basin. The particular treatment tank 13 utilized in the acti-vated sludge waste treatment process is 25 feet square and 10 feet deep. Each of chambers 11 and 11' of apparatus 10 are ; 3 approximately 4 feet square and exhibit a height of approximate-ly 10 feet. Both flaps 31 and nozzles 33 were ad~usted to estab-lish predetermined flow patterns of oxygenated wastewater within the treatment tank.

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1~;J4(;~759 The biological oxygen demand (BOD) of the industrial wastewater to be treated typically ranged from 800 to 2500 mg/l which demands are considerably greater than the average BOD of sewage to be treated in municipal facilities. Although the sub-~ect treatment tank was orlginally designed to process 40,000 gallons of 400 p.p.m. BOD wastewater per day using a conventional sur~ace aerator, treatment rates of up to 100,000 g.p.d. of approximately 1100 p.p.m. BOD have been obtained utilizing only oxygenating apparatus 10 in ~uch a treatment tank.
Referring now to Fig. 8, there is illustrated a profile of the levels o~ oxygen dissolved in the wastewater taken at twelve points throughout the treatment tank. In addition, at each such measurement point, DO levels were read at several test depths of 9.5, 7.0, 4.6 and 1.0 feet below the wastewater surface.
A standard membrane dissolved oxygen probe was utilized to meaæure such concentrations which are depicted in Fig. 8 in units o~
milligrams per liter. In the tests conducted, each of flaps 31 and 31' were ad~usted to a 2 inch opening whlle nozzles 33 and ; 33' were closed. Untreated wastewater was admitted to the treat-ment tank at a corner remote from apparatus 10 with the treated effluent being removed from a point on the side of the tank oppo-site to the wastewater inlet. A sludge return line was arranged to discharge sludge into the treatment tank at a point ad~acent to the wastewater inlet.
From the DO level measurements obtained a generally even distribution of such levels throughout the treatment tank is observed. m us, at each of points 1-12 and at various depths at ~ each point, dissolved oxygen levels between 4.5 and 7.0 mg/l have `` been observed. Furthermore, such dissolved oxygen levels are more than adequate for maintaining aerobic conditions in the in-dustrial wastewater to be treated. Certain higher DO levels have ~- been measured during the operation of oxygenating apparatus 10.

- ~V40759 For example, at point 3, depth D, a D0 level of 11.0 mg/l has been measured. As this measurement is taken in close proximity to flap 31 (which as aforesaid is provided at the bottom of chamber 11) a relatively high DO level is to be expected as the highly oxygenated wastewater from chamber ll has not been thor-oughly diluted in the wastewater within the treatment tank. In addition, it is noted that relatively high D0 levels have been obtained at depth D for points 4 and 5 which points are a~igned with flap 31 and are at approximately the same depth within the treatment tank. Similarly, relatively high DO levels are obtain-ed at depth D for points 6, 7 and 8 which points are aligned wlth flap 31' of chamber ll'. Satisfactory DO levels have also been measured at points l and 9 which points are not dlrectly exposed to the dlscharged oxygenated wastewater from apparatus 10. Accordingly, the measured D0 levels at points l and 9 lndi-cate that an adequate dilutlon and mixing of wastewater ln the treatment tank has been effected and that su~ficient oxygen i8 dls~olved to maintain aerobic conditlons ln substantially all ; portlons of the treatment tank.
Measurements of flow velocitles at several polnt~ in the treatment tank have been made and a profile of such veloci-ties ls deplcted in Fig. 9. At each of polnts 1-7, ~low veloci-tles were measured at several test depths although the accuracy of such measurements 18 not consldered to be totally reliable be-cause of the partlcular instrumentation utilized. Measurements of flow velocities at a depth of 8.5 feet below the wastewater surface at points 2-5 ranged from 0.67 to 0.95 ft./sec The hlgher flow velocities at this depth are not unexpected as such readings were taken at points and at a depth aligned with the dis-charge of flaps 31 and 31' prior to substantial dilution of the hlghly oxygenated wastewater. However, lower readings of flow velocities at other depths and at other points within the treatment lv4a7ss tank appear to result ~rom the general mixing and dilution of the highly oxygenated wastewater within the treatment tank.
Furthermore, the rate at which wastewater waæ admitted to the treatment tank waæ æubject to fluctuations which were reflected ln uneven flow velocities at various measurement points.
Several flow velocities measured at various depths at points 1-7, are near the lower end of the range of flow veloci-tieæ generally considered as acceptable for adequate mixing of the suspended solids in the secondary stage of an activated sludge process. However, for the velocity profile ~llustrated in Fig. 9, nozzles 33 and 33' were cloæed. Thus, further ad~uæt-ment of flapæ 31 and 31' and the opening of nozzles 33 and 33' may be effected to obtain other flow patterns and velocitieæ
within the treatment tank. Although flow velocities in certain portions of tank 13 are less than the velocitie~ traditionally considered necessary ~or maintaining ~olids in suspension (e.g.
0.5-1.0 ft./sec. at the wastewater surface), apparatus 10 is particularly efrective to generate satisfactory flow velocities at lower depths in tank 13. The importance of this effect re-sides in the fact that most solids tend to accumulate toward the bottom of tank 13 and as lower portions of the tank are sub~ect-ed to the greatest flow velocities, activated sludge particles are consistently stirredGand thereby malntained in suspension.
Thus, the foregoing "bottom scouring~ of tank 13 effectively provides the requisite stirring of wastewater 12 without reliance upon mechanical devices. Accordingly, the greatest flow veloci-ties of oxygenated wastewater di~charged from apparatus 10 are provided at depths at which stirring is most important Preliminary measurements of mixed liquor suspended solids have indicated uniform concentrations of approximately 3200 mg/l. with volatile solids comprising 75-80% of the total ~(~4(i759 suspended solids, The foregoing suspended solids concentra-tions have been recorded at depths of 1,5, 5,0 and 8,o feet below the wastewater surface in tank 13, Accordingly, the stir-ring of wastewater 12 by apparatus 10 i8 ~ufficient to maintain suspended solids concentrations necessary for continuance of the activated sludge proceæs, In addition to measuring dissolved oxygen levels and flow velocities at various points within treatment tank 13, several operating parameters of oxygenating apparatus 10 have been recorded. As indicated in Table I, the rates at which oxygen is supplied to and vented from apparatuæ 10 have been measured for varying fall heights, Particular fall heights were measured by means of a calibrated differential pressure gauge and oxygen ~low rates were measured by conventional flow meters, The dissolved oxygen levels of wastewater at the inlet and outlet of oxygenating apparatus 10 were measured by a standard membrane dissolved oxygen probe with the change in DO
levels indicated below, TABLE _ Fall Change in Oxygen Oxygen Percent Height Diæsolved Supply Vent 2 in (in,) 2 Level (lb/hr,) (lb/hr.) Gas Space (p,p,m,) 21 9.0 15.9 2,1 63 37 12,0 15.9 2,0 67 42 14,0 22,8 6,o 71 52 15.5 23,2 7.4 69 63 16,5 24,8 9,2 72 Pump 17 was operated to supply wastewater to plenum ~` 18 at a flow rate which was measured by a weir measurement technique at approximately 2,000 g,p,m, '" ' . :. ", ' . ' :, '' .

104~7S9 Samples of wastewater 12 taken during testing of oxygenating apparatus 10 indicated an average wastewater temper-ature of 29C. The input wastewater contalned an average BOD
of lloomg/l with 99% BOD removal measurements being consistent-ly obtained.
As the data set forth above have been observed during the experimental testing of oxygenating apparatus 10, it will be understood that such data are merely exemplary of this oper-ation. Accordingly, operating conditions have not been opti-mized although it is clearly desirable to increase the ratio of dissolved oxygen per horsepower hour and to reduce the percent-age Or oxygen vented from apparatus 10 as far as possible. For example, in order to preclude the possibility of a 'short circulting' of the feed gas supplied through inlet 29 to vent 30, it may be deslrable to rearrange the location of the feed and vent conduits. Furthermore, although a commercially pure oxygen supply has been utilized in the course of testing appar-atus 10, less than commercially pure oxygen may be utilized Preferably, the oxygen supply will exhlbit an oxygen concentra-tion of at least 40~
Referring now to Fig. 4 of the drawing, illustrated therein i8 a further exemplary embodiment of oxygenating appara-tus 40 suitable for emplacement within a bOdy of wastewater 12.
Oxygenating apparatus 40 is comprised of a generally enclosed submerged chamber 43 having an inlet 45 in the form of a suitable pipe or conduit sealed to the top of chamber 43 by suitable seal-ing means 44. A hydraulic pump 46 which may comprise a rotatable impeller pump mounted for rotation on shaft 47 is disposed with-in inlet conduit 45. The outlet of condult 45 communicates with a liquid space defined by a portion of the exterior 43, a portion 1~4t;~759 of baffle 50 and a portion of a substantia lly vertically dis-posed partitlon 49 which, at the lower extremity thereof, i8 rigidly affixed to baffle 50. A static mixing zone 51 is defined within chamber 43 by a further portion of baffle 50 and a baffle 52, which is spaced away from and oriented substantially paral-lel with baffle 49. The lower portion of static mixing zone 51 communicates with liquid accumulation space 53 with the remain-ing portion of chamber 43 being substantially compri~ed of gas accumulation space 54 formed in the upper reaches thereof. An lnlet 56 iB provided to permit the introduction of a feed gQS
under pressure into the upper reaches of chamber 43 and a pas-sage 55 is defined by the upper extremity of baffle 52 and the top wall of chamber 43 thereby providing communication between gas accumulation space 54 and the upper reaches of the static : mixing zone 51. A suitable venting means, schematically illus-trated as conduit 57, i8 provided to permit the venting of waste `
gases from gas accumulation space 54.
An outlet from chamber 43 i8 provlded in a lower por-tion thereof and may take the form of a nozzle 58, the opening and directionality of which may be controlled by an operator located exterior to apparatus 40 and above wastewater 12. An exemplary control arrangement for nozzle 58 may comprise a torque tube 59 extending from an accessible point above wastewater 12 through the top wall of chamber 43 to nozzle 58. A control rod 60 is loo~ely fitted within torque tube 59 and, by raising the lo~ering control rod 60, the extent of opening of nozzle 58 may be controlled. Similarly, rotation of torque tube 59 which is nested within conduit 61 is effective to control the direction-ality of flow through nozzle 58. Conduit 61 is utilized to form a pressure relief and bubble baffle in a manner similar to like structure illustrated in Fig. 2. A detailed description of a nozzle suitable for use with oxygenating apparatus 40 will be , . .
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lV4~759 described hereafter in connection with Fig. 5 Oxygenating apparatus 40 i8 similar to apparatus 10 in that both are designed for ready insertion into a wastewater tr~atment tank 13. However, it is realized that upon insertion of apparatus 40 (which preferably represents one half of a twin unit) in such a tank, buoyant forces acting on chamber 43 will tend to prevent the proper orientation of the apparatus in tank 13. Unbalanced buoyant forces act on chamber 43 as a result of ga~ accumulation in space 54 not being symmetrically formed there-ln. Accordingly, oxygenating apparatus 40 iæ especially suited to treatment tank 13 wherein chamber 43 may be rigidly affixed to elther a side wall or mounted on legs (not shown) and affixed to a bottom wall of such a treatment tank. In Fig. 4, bracket means 62 are illustrated as ~uitable connecting elements for affixing chamber 43 to a side wall of treatment tank 13. However, it will be understood that other means for retaining chamber 43 in order to provide a proper orientation thereof may be utilized. In ad-dltlon, supportlng legs (not shown) may be utillzed to maintaln chamber 43, spaced away from the bottom of treatment tank 13.
The operation of oxygenating apparatu6 40 is substanti-; ally ldentlcal to the operation of apparatus 10 illustrated in Fig. 1. In oxygenating apparatus 40, wastewater iæ pumped under pressure by pump 43 through conduit 45. Wastewater exiting from conduit 45 is then caused to flow upwardly through channel 48 formed between conduit 45 and baffle 49, as well as through chan-nel 48' which is defined by a side wall of chamber 43 and conduit 45. It will be understood that a water seal i8 provided between gas accumulation space 54 and pump 46 in a manner similar to the water seal provided in the oxygenating apparatus 10 illustrated in Fig. 1. Wastewater is then sub~ected to a gravitational fall upon passing over the uppermost edge of baffle 49.

:104~)759 An oxygen-containing feed gas is lntroduced through conduit 56 into the upper reaches of chamber 43 under a pressure which is effective to depress the level of water therein to a predetermined level. A gas accumulatlon space 54 is thereby formed in chamber 43 with the extent of this spa¢e being deter-mined by the pressure of the supplied feed gas.
The wAstewater undergoing a gravitational fall within the upper reaches of static mixing zone 51 impinges upon the wastewater therein which results in a highly turbulent condi-tion and promotes an effective dissolution of oxygen supplied to zone 51 in the turbulent wastewater in a manner substantially identical to the oxygenation of wastewater in static mixing zone 24 of the apparatus illustrated in Fig. 1, It wlll be appreciated that the flow rate of wastewater into static mixing zone 51 is ad~usted to an optimum superficial velocity, which for example may be approximately 1 ft.~sec.
Oxygenated wastewater is emitted from static mixing zone 53 into a liquid accumulation space 53 through an opening provided between the lowermost edge of baffle 52 and baffle 50.
The general flow pattern of wastewater within space 53 is a circulating one wherein wastewater initially flows upwardly to-ward gas accumulation space 54 and æubsequently rlows downward-ly toward the lower reaches of chamber 43. As the oxygenated wastewater rlows toward gas accumulation space 54, large en-trained bubbles of theoxygenating gas are rapidly disentrained into gas accumulation space 54 and may be recycled through pas-sage 55 to static mlxing zone 51. Upon entering the liquid accumulation space 53, the velocity of oxygenated wastewater decreases to a relatively low value which in turn promotes the disentrainment f eas bubbles therefrom. In add1tion, a further dissolution of the oxygenating gas into the wastewater in liquid accumulation space 53 i8 also effected. Although some smaller - ~ ., .

gas bubble~ are not disentrained from the oxygenated wastewater and are dragged downwardly toward the lower reaches of chamber 43, it has been found that only a small fraction of oxygenating gas is emitted through nozzle 58 into wastewater 12.
Durine the process of oxygenating wastewater in static mixing zone 51, certain impurities in the wastewater such as for example nitrogen gases are stripped therefrom and are diæentrain-ed into gas accumulation space 54. A venting conduit 57 is pro-vided in communication with gas space 54 and through either a continuous or intermittent venting operation by conventional valving means (not shown), such impurities are removed from cham-ber 43. Although such venting also entails removal of oxygen, it has been found that only a minor portion of such gas is vented.
Oxygenated wastewater contained in liquid accumulation space 53 is discharged from chamber 43 through nozzle 58 in a manner substantlally identical to the discharge of oxygenated wastewater from chamber 11 as previously described in connection with the apparatus illustrated in Fig. 1 Thus, torque tube 59 and control rod 60 are operated to control the directionality and opening of nozzle 58, respectively, to thereby establish a ; predetermined flow Or oxygenated wastewater within the main body of wastewater 12 In this manner, wastewater 12 is stirred and the dissolved oxygen content thereof i8 increased such that in an activated sludge process, sludge will be maintained in suspen-sion in wastewater 12 and aerobic conditions will be sustained as well.
Referring now to Fig. 5, there is illustrated an exem-. ,.
plary embodiment of a discharge nozzle suitable for use in con-nection with oxygenating apparatus illustrated in Fies. 2 and 4.
Nozzle 33 is comprised of a plate 100, a spout 102 and control means in the form of torque tube 34 and control rod 35 for con-trolling the opening and directionality of spout 102. Plate 100 extends across a substantially circular aperture in the bottom :
:

wall of chamber 11 (Fig. 1) and, if desired, may be rotatably sealed thereto by means of a suitable circumferential seal means 101. Spout 102 i8 cQmprised of an upper inclined portion 103 which is rigidly affixed to torque tube 34 with the lower end of portion 103 being flrmly attached to plate 100 at point 109.
The upper end of portion 103 is rigidly affixed to bracing rods 105 and 106 which in turn are likewise affixed at the lower ends thereof to plate 100. An aperture is defined in plate 100, which aperture is preferably rectangular. A lower portion 104 of spout 102 is pivotable along a line extending through point 107. A substantially vertical rear wall 110 of spout 102 is . formed between portions 103 and 104 Control rod 35 is loo~ely po~itioned within torque tube 34 and extends downwardly through lower portion 104 of spout 102. Rod 35 is operatively connected to portion 104 by way of a protrusion or a clevis nut formed at the lower extremity of rod 35.
The operation of nozzle 33 will now be described As prevlously mentloned, torque tube 34 and control rod 35 extend upwardly from chamber 11 above wastewater 12, preferably to a polnt at whlch external operation of such members may be effected.
The extent of the opening of nozzle 102 ig controlled by the raislng or lowering of rod 35 which in turn is effective to pivot the lower portion 104 of spout 103 about a line through point 107. Thus, upon raising control rod 35, portion 104 of spout 102 18 translated to a position indicated by the dashed line illustrated in Fig. 5. During this operation, however, upper portion 103 of spout 102 rem~ins substantially stationary Accordingly, in the foregoing manner, the extent of the opening of nozzle 33 may be simply controlled. In order to control the directionality of the flow of wastewater emitted through nozzle 33, torque tube 34 is rotated in a substantially horizontal plane As upper portion 103 of the spout is rigidly affixed to plate 100 and to torque tube 34 plate 100 is rotated about its axis with the extent of such rotation being determinative of the azimuthal direction of wastewater diæcharged through nozzle 33.
It will be appreciated that as plate lOo is seated on a shoulder formed in the bottom wall of chamber 11, the pressure of waste-water thereabove is effective to assist in sealing plate 100 to . such a bottom wall, yet nonetheless permit rotation of plate 100 in response to a simllar rotation Or torque tube 34. In the . ~oregoing manner, therefore, a relatively simple directionality control of nozzle 33 is effected.
In accordance with another exemplary embodiment of an apparatus for oxygenating wastewater, there is illustrated in Fig. 7 an apparatuæ 70 generally suitable for emplacement within a waste treatment tank containing a body of wastewater 12. A
generally enclosed chamber 71 having an open bottom i8 provided with an inlet.72 for admitting wastewater into the upper reaches thereof. A hydraullc pump 73, which may comprise a con~entional axial ilow impeller pump mounted for rotation on a shaft 74. An electrical motor (not shown) is positioned at a suitable loca-tion above wastewater 12 for rotating shaft 74 thereby driving pump 73 and forcing wastewater into chamber 71. A partition 76 1~ dlsposed interiorally of chamber 71 and preferably comprises a substantially horizontal portion 77 extending from one slde-wall of chamber 71 and a substantially vertical portion 78 de-pending from the opposite end of horizontal portion 77. A small passage 87 i9 defined in the horizontal portion 77 preferably at a point remote from inlet 72; or such a passage may be formed in vertical portion 78 of partition 76 immediately below horizon-tal portion 77. A substantially horizontal channel 75 is thus formed and extends from inlet 72 across the upper reacheæ of chamber 7$ to a point approximately above the upper portions of partition 78. The latter partition and a sidewall of chamber 71 , ' 1~)4(~759 are so disposed 80 as to form a static mixing zone 88 of the gravitational fall type within chamber 71. A baffle 79 is pro-vided at the lower portion of static mixing zone 78 and is spaced away from the lower extremity of partition 78 to permit llquid flow from static mixing zone 88 into a liquid accumula-tion space 8~. A conduit 80 is provided to communicate between chamber 71 and through valve 82 to a source of feed gas. As will be described herea~ter, a gas accumulation space 84 i8 formed immediately beneath horizontal portion 77 of partition 76 and the oxygenating gas within space 84 i8 permitted to communi-cate ~ith the upper reaches of the static mixing device and channel 75 through passage 87 in portion 77 A conduit 85 is also provided to communicate with the upper reaches of the static mixing zone 88 ~or the purpose of venting gas therefrom through a suitable valve means 86 In addition, a pressure regulating device 81 may be used in connection with valve 82 in order to maintaln the oxygenating gas under a predetermined pressure and hence maintain the liquid level wlthin llquld accumulatlon space 83 at a substantially constant height.
The operation of the wastewater oxygenating apparatus 70 lllustrated in Fig. 7 will now be described. Prior to oper-ation of apparatus 70, chamber 71 is substantially filled with wastewater. Pump 73 is energized and thereby forces wastewater into channel 75 under pressure. Upon the subsequent introduc-tion of a feed gas under pressure through conduit 80 into cham-ber 71, the level of wastewater within chamber 71 is depressed to an extent corresponding to the magnitude o~ the pressure of the supplied feed gas. Accordingly, a gas accumulation space 84 is formed within chamber 71. The wastewater admitted into chan-nel 75 then undergoes a gravitational fall at the upper portion of static mixing zone 88. However, as the oxygenating gas is maintained in communication with channel 75 through an aperture -3o-- ,.

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1~407S9 87 formed in portion 77 of partitlon 76, a further gas space is maintained in the upper reaches of the static mixing zone 88.
As the wastewater undergoes the aforementioned gravitational fall, a highly turbulent condition is caused in the static mix-ing zone 88 which in turn results in a high level of oxygen dis-solution in the wastewater in a manner substantially identical to that as previously de~cribed in connection with oxygenating apparatus 10 illustrated in Fig. 1 The oxygenated wastewater 18 subsequently emitted from static mlxing zone 88 and enters the liquid accumulation space 83 while entrained bubbles of the oxygenating gas are disentrained from the wastewater in space 83 and returned to gas accumulatlon ~pace 84. The oxygenating gas so returned to space 84 is thus available for recycling and is subsequently returned to the static mixing zone 88 through aperture 87 as previously described m e oxygenated wastewater introduced into liquid accumulatlon space 83 i8 permitted to flow irom the lower reaches of chamber 71 lnto the main body of wastewater 12 ~or admixture therein. In the foregoing manner, the highly oxygenated wastewater emitted from liquid accumulation space 83 of the chamber 81 is diluted in the body of wastewater 12. Accordingly, the dissolved oxygen level of wastewater 12 is increased to a level such as 0.5 p.p.m. which is suitable for sustaining aerobic conditlons wlthln wastewater 12.
The methods and apparatus according to the present in-vention have been described herelnbefore in connection wlth the oxygenation of wastewater and particularly in an activated sludge waste treatment process. It will be appreciated by tho~e skilled ln the art that the present invention is not limited to the dis-solution of oxygen in wastewater but may be utilized generally to dissolve a gas in a liquid such as, for example, ozone in water, or to dissolve carbon dioxide in an aqueous solution to ad~ust the pH level thereof. Alternatively, the present invention may be utilized to oxygenate industrial waste materials such as "black liquor" in paper production proce~ses.
It will also be understood that the apparatus embody-ing the present invention i8 hlghly modular in and readily in-sertable in a body of wastewater to be oxygenated. Thus, a plurality of oxygenating apparatus such as apparatus 10 or 40 CoRld be poeitioned in such wastewater with the discharge of each apparatus cooperating to provide a predetermined flow pat-tern in, for example, a treatment tank.
While the foregoing oxygenating apparatus has been described as positioned within a treatment tank, it will be real-ized that this apparatus may be arranged to float in or be posi-tioned ad~acent to a treatment tank. In the latter inætance, suit~ble piping and conduits may be provided to introduce un-treated wastewater into the oxygenating apparatus and to return oxygenated wastewater to the treatment tank. Addit~onally, it will be real~zed that the present oxygenatlng apQaratus may be formed in geometries other than rectangular.
While the present invention has been particularly described in terms of specific embodiments thereof, it will be understood that numerous variations upon the invention are now enabled to those skilled in the art, which variationæ are yet within the scope Or the instant teaching. Accordingly, the present invention is to be broadly construed and limited only by the scope and the splrit of the claims now appended hereto.

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Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for oxygenating a body of wastewater containing organic solids comprising a generally enclosed oxy-genating chamber emplaceable in said body of wastewater; means for pumping wastewater under treatment into said chamber; means for introducing an oxygenating gas into said chamber to form a gas space therein containing said oxygenating gas; means for rendering said pumped wastewater turbulent by subjecting said pumped wastewater to a gravitational fall over a weir through said oxygenating gas and into a gravitational fall zone substantially defined by said weir with the resulting liquid-gas turbulence in said fall zone being effective to oxygenate said turbulent wastewater and entrain undissolved oxygenating gas therein; liquid accumulation means for receiving oxygenated wastewater from said fall zone and for dissipating said turbulence to enable disentrainment and recovery within said chamber of said undissolved entrained oxygenating gas; and nozzle means for discharging said oxygenated wastewater from said liquid accumulation means into said body of wastewater at a velocity such that said body of wastewater is sufficiently stirred to maintain said organic solids suspended therein.

2. Apparatus as defined in Claim 1 including baffle means spaced from said weir to define said gravitational fall zone and extending below the surface of oxygenated waste-water in said liquid accumulation means such that said oxygenated wastewater and said undissolved entrained oxygenating gas flow from said gravitational fall zone under said baffle means into said liquid accumulation means.

3. Apparatus in accordance with Claim 2 wherein said baffle means comprise a baffle disposed generally vertically;

a portion of said weir extending therefrom to define the bottom of said fall zone with the bottom of said baffle being spaced from said portion to permit wastewater dropping through said fall zone and entraining said oxygenating gas therein, to pass under said baffle into said liquid accumulation means.

4. Apparatus as defined in Claim 2 wherein said chamber includes means for returning at least a portion of said disentrained oxygenating gas to said gravitational fall zone.

5. Apparatus as defined in Claim 1 wherein said chamber is emplaced in said body of wastewater under treatment.

6. Apparatus as defined in Claim l additionally comprising a re-entrant well disposed between said pumping means and said means for rendering said pumped wastewater turbulent whereby an escape of said introduced oxygenating gas through said pumping means is substantially inhibited.

7. A method of dissolving oxygen in a body of water having a dissolved oxygen demand which comprises:

(a) withdrawing water from said body and pumping it through a treatment chamber;

(b) introducing an oxygenating gas into said treat-ment chamber at a superatmospheric pressure to form a body of gas therein;

(c) creating a turbulent condition in said pumped water by subjecting said pumped water to a gravitational fall over a weir into a gravitational fall zone within said chamber and in direct contact with said body of oxygenating gas whereby oxygen is dissolved and undissolved oxygenating gas is entrained in said turbulent water;

(d) passing said turbulent water to a quiescent zone within said chamber to dissipate said turbulence and cause disentrainment and recovery within said chamber of undissolved oxygenating gas; and (e) discharging said water containing dissolved oxygen from said quiescent zone of said chamber through a nozzle into said body of water at a sufficient velocity to stir said body and substantially uniformly distribute the discharged water throughout the body of water from which it was withdrawn.