Abstract:
An apparatus ( 100 ) and process ( 400 ) for the treatment of wastewater and biological nutrient removal in activated sludge systems. The process uses substantially vertically downwardly presented inlet jets for delivering the incoming wastewater and recycled activated sludge into the body of liquid in a reactor, in a vertically downward direction and at a location just below the surface of the body of liquid. An effective circulating flow pattern of liquid is thereby established, along with optional concomitant entraining, dispersion or dissolving a fluid throughout the volume of the liquid body, facilitating a universal apparatus for mixing of anaerobic, anoxic, aerobic and oxic reactors or accommodating alternating said process conditions in one reactor. When an oxygen containing gas is entrained for aerobic fermentation, optimum gas bubble size is generated for efficient reaction with the digestion bacteria throughout the volume of the liquid body. Efficient mixing and maximum utilization of the bacteria suspended in the body of liquid is thereby approached, whether the digestion is conducted aerobically, anaerobically or anoxically.

Description:
BACKGROUND 
     1. Field of the Invention 
     This invention pertains generally to an apparatus and process for the treatment of wastewater and biological nutrient removal in activated sludge systems. The apparatus facilitates universal equipment providing substantially steady agitation while accommodating alternating process conditions (such as anaerobic, anoxic, aerobic, and oxic conditions) in a reactor. 
     2. Prior-Art 
     Municipal and industrial wastewaters contain significant quantities of phosphorus and nitrogen, and the removal of these nutrients has become an important facet of wastewater treatment. In a wastewater treatment plant, phosphorus and nitrogen can be removed by both biological and physical chemical means. Biological means of nutrient removal are generally preferred, as they result in lower waste sludge production, produce a sludge that is more amenable to land application, and have the public perception that biological processes are more “environmentally friendly” than chemical processes. Processes using biological mechanisms for phosphorus and nitrogen removal are generally referred to as biological nutrient removal, or BNR, processes. 
     Biological nitrogen removal in the activated sludge process takes place in two sequential reactions—nitrification and denitrification. Nitrification is the biological oxidation of ammonia to nitrate and nitrite by two specialized groups of autotrophic bacteria that takes place under aerobic conditions. Denitrification is the biological reduction of nitrate and nitrite to nitrogen gas that takes place under anoxic conditions. During the 1960s, North American research focused on the development of two- and three-stage processes for nitrogen removal, with separate stages for carbon removal, nitrification, and denitrification. Each stage had the prerequisite conditions required to sustain its biological reaction followed by a set of clarifiers. Researchers in Europe, meanwhile, developed single sludge systems in which all of these reactions take place simultaneously in a single process in which the sludge is sequentially subjected to anoxic and aerobic conditions. Recent examples of single sludge applications are SHARON (Single reactor system for High activity Ammonium Removal Over Nitrite) and ANAMMOX (ANoxic AMMonium OXidation). 
     Some of the technologies focused on satisfying high oxygen requirement per unit volume and therefore targeted to hold more biological activated sludge in activated sludge reactors. For example, UNOX system developed in the 1960s used high purity oxygen (HPO) as an alternative to air provided by surface aerators and upgraded existing aerobic reactors by simply altering the same infrastructure and covering aeration tanks. In the 1970s, open-tank HPO systems were developed such as the BOC VITOX system by British Oxygen Company, eliminated the confined space limitations and exhaust-gas troubles of the UNOX system and also made possible to have deeper aeration tanks in resulting footprint reduction and capital cost savings. 
     In the late 1980s, by incorporating an engineered plastic media to activated sludge system Moving Bed Bio-Reactor (MBBR) systems were developed and combined suspended-growth and attached-growth advantages into one system. By adding a recycle activated sludge line to the MBBR system, integration of suspended-growth and attached-growth was further enhanced and was referred to as Integrated Fixed-film Activated Sludge (IFAS). In the 1990s, the Membrane Bioreactor (MBR) was developed as a robust solid-separation mechanism, and integrated into activated sludge systems to meet more stringent suspended solids and phosphorus effluent targets. 
     MBR, MBBR, and IFAS systems are often called hybrid systems. Most of the hybrid systems&#39; performances rely on aeration method they use. In most existing aeration devices, rate of hydraulic-mixing and degree of aeration are simultaneously dependent on each other as, for example, in surface aerators and air-blowing diffused aeration systems (such as those disclosed in U.S. Pat. No. 6,372,140). When more air is required, more mixing is inadvertently and unnecessarily provided. 
     Excessive mixing energy and agitation in activated sludge system can cause adverse effects on system performance, such as a pin-floc problem in suspended-growth systems or excessive bio-film sloughing-off in attached-growth systems, which in turn can lead to sedimentation and solids separation problems. 
     MBR, MBBR and IFAS systems are examples of wastewater treatment systems that are the most vulnerable to the problem of excessive agitation. All of those systems often use diffused aeration and therefore their efficiency relies on that particular aeration method&#39;s pros and cons. For example, MBR systems rely on micro-filtration taking place in an activated sludge reactor with high level of suspended solids, and therefore usually require a high degree of agitation in the aeration reactor to keep the membranes&#39; surfaces clean and reduce their reject time. However, excessive agitation has adverse effects on the treatment performance mentioned above. Some of the MBBR and IFAS systems rely on the development of bio-film on small, lightweight, rigid plastic floatable carrier elements that fill the aeration basin and are kept agitated by means of diffused aeration. Homogeneous mixing of MBBR and IFAS plastic floating media has been a challenging issue since the mixing of floating media by means of diffused aeration is more challenging then mixing of settling solids. (Conventional activated sludge systems do not contain artificially added floating media and therefore are relatively less vulnerable to this problem.) Excessive agitation is definitely a serious problem and limiting the theoretically expected actual performance of MBR, MBBR and IFAS systems. 
     There are commercially available aeration systems that provide an independent aeration-rate with respect to the hydraulic-mixing-rate, such as BOC VITOX, MTSJETS and another system disclosed in patent WO/2001/002308. However, due to their potential high energy requirements (for air blowers or oxygen-generators in addition to liquid recirculation pumps), as well as their complexity in installation, operation, and maintenance, they may not be the best solutions for every single scenario. Most of those systems using jet ejectors suffer from a number of disadvantages, for example:
         (a) they are usually horizontally submersed into the liquid adjacent to the bottom of a typically 4 to 6 meters deep reactor. They use high-velocity coherent jets which are adapted to overcome water pressure at the bottom of the reactor, consequently providing high liquid flux and relatively much more energy to entrain desired quantities of atmospheric air. Thus, they are often adapted to feed forced air provided by air blowers which also require additional energy. Despite the optimization efforts the energy utilization per unit volume is still considered high   (b) none of them can control entraining gas flow at single nozzle level, the control mechanisms are usually outside and centralized to provide uniform air flowrate to every nozzle. This arrangement is potentially a disadvantage for adjusting aeration levels in a plug-flow reactor.   (c) having submersed jet mixing apparatus approximately 5 meters under water makes the system vulnerable for any operation and maintenance concern such as potential nozzle clogging. In that case, the reactor is required to be emptied or alternatively a professional wastewater diver must be hired for the underwater repair work. There are some retrievable apparatuses also available, but retrieving a 5-meter-wide and 5-meter-tall nozzle manifold is not a simple maintenance job.       

     The prior art comprises submersed liquid jet ejectors horizontal or with an approximate 45° trajectory angle (to horizontal XY-plane) and vertically plunging jet ejectors over and above the liquid surface. The following are examples of technical articles from plunging liquid jet literature and related prior arts or patents.
     H. Chanson, R. Manasseh (2003) “Air entrainment processes in a circular plunging jet: Void Fraction and Acoustic Measurements”, Journal of Fluids Engineering, ASME, September 2003 Vol. 125 pg 910.   T. Bagatur and N. Sekerdag (2003) “Air-entraintment characteristics in a plunging water jet system using rectangular nozzles with rounded ends” ISSN 0378-4738, Water SA Vol. 29 No. 1 Jan. 2003.   Ito, K. Yamagiwa et al (2000) “Maximum Penetration depth of Air bubbles entrained by vertical liquid jet”, Journal of Chemical Engineering of Japan Vol 33 pg. 898   Liu, G., Evans, G. M., (1998). “Gas entrainment and gas holdup in a confined plunging liquid jet reactor”, Proceedings of the 26 th  Australian Chemical Eng. Conference, (Chemeca 98), Port Douglas, Australia.   

     The above technical articles focus on a plunging liquid jet over and outside the liquid body where the liquid jet is in contact with the gas above the liquid surface in a reactor so that it will usually entrain ambient gas by the impingement at the liquid surface (such as disclosed in PCT patent applications, WO/2005/108549 and WO/1992/03218). 
     Based on literature and model study results for the present invention, a jet ejector can generate a ratio of entrained air to motion water 2 to 4 air per water (volume/volume) as also disclosed in U.S. Pat. No. 4,690,764. However, dispersing and effectively dissolving of the entrained gas in an energy-efficient means still remains as a challenge for the prior art and this was mentioned above. 
     The plunging jet mix prior art suffer from a number of disadvantages:
         (a) all of the above plunging jet aerators claim and rely on a jet ejector located over and outside of the liquid to be aerated, therefore air (gas) entraining is dependent on a high-speed coherent jet impingement on a liquid surface which can generate a high ratio of entrained air per liquid flux; however, the more the gas entraining, the less dissolution efficiency. Therefore, those prior art items often utilize relatively excessive hydraulic energy deliberately to shear gas bubbles into very small size to increase bubble penetration depth (energy efficiency suffers).   (b) despite being not very energy efficient, those prior art items have another potential problem: coalescence of small bubbles into larger bubbles due to high concentration of small bubbles and in turn causing dissolution efficiency and unwanted foaming problems.   (c) even though some of those prior art items disclose a controllable gas entraining mechanism, most of them are strictly designed for maximizing gas entrapping by coherent liquid jet impingement and therefore they are not capable of turning the gas completely off and accommodating anaerobic mixing conditions   (d) none of those prior art items disclose entraining of any other fluid other than an oxygen-containing gas or air, therefore they are not designed to entering any other fluid to accommodate alternating process conditions such as anaerobic, anoxic, aerobic, and oxic conditions in a liquid reactor   (e) none of those prior art items disclose any particular floatable matter de-stratification mechanism in addition to keeping settleable matter in suspension. Most of them do not define specific mixing patterns for energy-efficiency; their focus is strictly on entraining oxygen-containing gas or air since concomitantly provided mixing is usually chaotic and very high in both degree and energy utilization       

     It is an object of the present invention to provide a liquid treatment process and apparatus which reduces at least one of the aforementioned disadvantages. 
     SUMMARY 
     In accordance with one aspect of the present invention, efficient mixing and circulation of inputted wastewater into a body of liquid, for micro-organism reaction and digestion throughout the body of liquid, is achieved by delivering the input wastewater or activated sludge in a substantially vertically downward direction in the body of liquid, through a constricted delivery opening (jet) disposed a short distance below the surface of the body of liquid. By suitable, routine adjustment of the input flow rate, the input liquid can be made to travel downwardly to the bottom of the body of liquid initially, and then to move outwardly and upwardly in a circulating manner, throughout a substantial portion of the volume of body of liquid, preferably throughout substantially the entire volume thereof. Efficient mixing and maximum utilization of the bacteria suspended in the body of liquid is thereby approached, whether the digestion is conducted aerobically, anaerobically or anoxically. Treated water can be led off from a location near the surface of the body of liquid, but displaced a significant distance from the input location, to keep the volume of the body of liquid constant. 
     The disposition of the inlet jet for the wastewater just below the surface of the body of liquid, and delivery in a downward direction, has a number of other advantages, besides the establishment of desirable flow circulation patterns, as described. When, as is commonly but not invariably the case, it is desired to supply oxygen-containing fluid such as air to create aerobic fermentation, the gas can be supplied along with the input wastewater for dissolution or entrainment therein, without the use of pumps, compressors, blowers or the like which would need to be used if the input wastewater were to be delivered at a deep location within the body of water. This represents a significant energy saving, and a significant reduction in noise associated with operating such equipment (e.g. blower). The outlet jets are located at a position where they are readily accessible for cleaning and maintenance purposes, as opposed to deeply within a large tank of wastewater into which personnel and equipment needs to be submerged for such purposes. Moreover, the surface splashing of a delivery system located above the surface of the body of liquid, with its accompanying noise, mess and lack of control of air entrapment is avoided. Further, the energy involved in delivering the wastewater to such a location is minimal, requiring little more than gravity feed, as opposed to the heavy duty pumping required for delivery to a significant depth in a body of liquid. 
     In a preferred embodiment, baffle plates are provided around the delivery jet and at a level shortly below its opening, further to control the flow of liquid and any suspended solids within the body of liquid. These baffle plates are suitably inclined at an acute angle directed downwardly towards the input location. This assists in a movement of solids and liquids from the surface of the body of liquid near the input location, in a downward direction along with the liquid input. The circulating motion of the body of liquid and solids therein is thereby assisted, and accumulation of floatable solids at the surface is reduced. Similarly, the circulation developed in the body of liquid, involving travel of input liquid to the bottom, reduces or prevents settling of solids at the bottom of the body of liquid. 
     An important feature underlying the successful operation of further preferred embodiments of the present invention is entrained gas bubble size control. When a gas such as air is being supplied in order to conduct aerobic fermentation in the body of liquid, the gas is best provided along with the input liquid, and in the form of gas bubbles of a size such that they will circulate throughout substantially the whole volume of the body of liquid. In this way, oxygen is available at all locations in the body of liquid where the fermentable material encounters the bacteria, to lead to the most efficient fermentation. If the gas bubbles are too large, they will float to the surface too quickly, and will not circulate throughout the body of liquid. Supplying large quantities of air often generates larger air bubbles which will not have enough penetration depth into the body of liquid, and will not distribute properly. Minute gas bubbles, but large enough to be visible, which will circulate throughout the body of liquid, are most efficient. The present invention, in a preferred embodiment, provides for this, along with a simple means for controlling bubble size and for controlling the amount of gas, e.g. air, which is delivered in bubbles of optimum size, from zero supply for anaerobic fermentation, up through the whole useful range for anoxic and aerobic fermentation. 
     For this purpose, the wastewater jet input nozzle described above, for disposition a short distance below the surface, is associated with a fluid inlet means provided in close proximity so that gas such as air from the fluid inlet means becomes entrained, entrapped or dissolved in the wastewater flowing from the inlet nozzle. The fluid outlet means may be provided alongside the wastewater input jet, but preferably surrounds it. The adjustment of the size of the gap between the fluid outlet means and the wastewater input jet allows for adjustment of the gas bubble size. The gas bubbles may be further reduced in size by the shearing action of their impingement on the edge surfaces of the jets 
     Preferably, the fluid outlet jet and the wastewater inlet jet are disposed one within the other, e.g. concentrically, and both terminate in downwardly extending frusto-conical outlets. Then adjustment of the gap size between them, for bubble size control, can readily be done by moving one telescopically relative to the other. 
     The present invention aims to provide optimum gas entrainment (not maximum) so as to achieve, in an energy efficient manner, optimum bubble size and gas transfer rates. Since the fluid entraining mechanism is controllable and can be isolated from ambient air, it allows oxygen containing fluid addition when the optimum air entrainment is exceeded. The present invention allows entraining not only oxygen containing fluids but other fluids that are suitable for the treatment of wastewater. Examples of such fluids comprise the following: activated sludge, raw wastewater, biosolids supernatant liquid, high purity oxygen gas, ozone gas, hydroxyl-radicals, hydrogen-peroxide, sodium-hypochlorite, chlorine gas, methanol, aluminum-sulfate, sodium-bisulfate and etc. 
     Embodiments of the present invention provide apparatus for the treatment of wastewater and biological nutrient removal in activated sludge systems to provide steady and adequate but not excessive mixing in a liquid reactor and effectively de-stratify one or both of solid and fluid layers that may also be contained in the liquid body, while independently alternating the entraining, dispersing and dissolving a fluid at atmospheric or higher pressure. 
     The present invention also provides, in preferred embodiments, a single apparatus and method to provide steady mixing in a liquid reactor regardless of the rate of fluid entrapment, and effectively de-stratify solids and fluid stratification layers that may be contained in the liquid body, especially floatable matter, while controlling the entraining of a fluid at atmospheric pressure, so that alternating process conditions can be accommodated in an energy efficient way by means of a single and universal equipment. For example, one embodiment of apparatus of the present invention may use an oxygen-containing gas (such as atmospheric air) as the fluid to be entrained. By controlling the rate of the gas entrainment the following process conditions can be alternately provided in the same reactor: when air is off then anaerobic conditions prevail, when air feed is at a minimum level then anoxic conditions prevail, when air feed is at an average level then aerobic conditions prevail, when air feed is at a maximum level (or alternatively feeding a high purity oxygen containing fluid) then oxic conditions prevail. This type of process flexibility facilitates a unique process application for biological nutrient removal in activated sludge systems. One embodiment of the apparatus of the present invention may be adapted to suit some existing pumping stations and use pumped liquid energy to mix and provide alternating conditions mentioned above, to produce an energy efficient process application. 
     As a result, the present invention can provide improved biological nutrient removal efficiency in activated sludge systems comprising MBR, MBBR, and IFAS systems. The advantages comprise: right and steady degree of agitation (eliminating adverse affects of excess agitation on biological removal efficiency), energy savings, less complexity for installation, process and operation flexibility, hassle-free maintenance (by using in-situ cleaning mechanisms and easy access to the critical equipment), and noise-mitigation (by eliminating any loud equipment such as air blowers). 
    
    
     
       BRIEF REFERENCE TO THE DRAWINGS 
       In the drawings, closely related figures have the same number but different suffixes. 
         FIG. 1  is a diagrammatic sectional view of a liquid-jet-means and liquid-jet-ejector-means illustrating two embodiments  FIG. 1(   a ), and  FIG. 1(   b ). 
         FIG. 2  is a diagrammatic sectional view of two further embodiments of liquid-jet-ejector-means according to the invention,  FIG. 2(   a ) and  FIG. 2(   b ); 
         FIG. 3  is an exploded isometric view of the liquid-jet-ejector-means embodiment of  FIG. 2(   a ); 
         FIG. 4  is an isometric-view of a container as the liquid reactor to receive liquid jet means and liquid jet ejector means of  FIGS. 1 to 3 ; 
         FIG. 5  is a diagrammatic sectional view of a preferred apparatus embodiment of the invention, with a bi-directional mixing pattern; 
         FIG. 6  is a section-view of a similar apparatus embodiment to that of  FIG. 5 , but with a unidirectional mixing pattern; 
         FIG. 7  is a diagrammatic isometric view of a set of rectangular reactors according to  FIG. 4 , illustrating different mixing patterns and liquid jet means arrangements; 
         FIG. 8  is a diagrammatic view of a preferred liquid-inlet-routing-control-means and a liquid-transfer-routing-means according to  FIG. 5 , illustrating a an optional and complex arrangements; 
         FIG. 9  is a diagrammatic view of one interconnection system of an apparatus according to an embodiment of the invention; 
         FIG. 10  is a diagrammatic view of a preferred embodiment of an overall process according to a preferred embodiment of the invention; 
         FIG. 11  is a perspective view, partially in section, of an apparatus for conducting preferred process embodiments of the invention. 
     
    
    
     In the drawings, like reference numerals indicate like parts. 
     DETAILED DESCRIPTION 
       FIG. 1(   a ) is a diagrammatic view, in section, of the preferred embodiment of the liquid inlet jet means (liquid jet mixer)  40  of the invention, illustrating the principle of operation. The jet comprises a vertically downwardly extending pipe terminating at its lower extremity in a constricted liquid jet nozzle  48  (or liquid jet slot), the outlet  49  being adapted to be disposed a short distance  55  below the liquid surface  36  ( FIG. 5) . Below the outlet  49  is provided a baffle mechanism  80 , comprising plurality of annular plates inclined at acute angles to the liquid surface  36 , and angularly adjustable to provide appropriate flow patterns as the liquid from outlet  49  enters the body of liquid. Plurality of baffle plates  82 ,  86  making up the baffle mechanism  80  are attached to the lower portion of the liquid inlet jet means. 
       FIG. 1(   b ) is a similar illustration of another embodiment of liquid inlet jet means,  40 A, in which the inlet line to the liquid nozzle  48  includes a fluid injection mechanism  115  in the form of a venturi, a fluid feeding control means  71 A through which a fluid such as air (or methanol) can be controllably supplied to the wastewater and activated sludge liquid flowing to the liquid jet nozzle  48  via the venturi, and a control valve  117  on a flow by-pass line to effectively control fluid entraining. 
       FIG. 2(   a ) and  FIG. 2  ( b ) are similar illustrations of further embodiments of liquid inlet jet means, but also including controllable fluid inlet means. The embodiment of  FIG. 2(   a ) has a fluid inlet means in the form of a sleeve  60  surrounding the liquid jet nozzle  48  and separated to leave an annular space therebetween. The sleeve  60  also terminates at its lower extremity in a frusto-conical fluid inlet nozzle  50  (or a fluid inlet slot) and its outlet  51 , leaving an annular gap  62  between the sleeve  60  and the liquid jet nozzle  48 . By raising and lowering the fluid inlet nozzle  50  by use of inter-fitting screw threads  58 M and  58 F, the size of the gap  62  between the nozzles  48  and  50  can be adjusted. Upper extremity of liquid jet ejector  40 C is also made telescopic by use of inter-fitting screw threads  44 F and  44 M, ( FIG. 2(   a ) and  FIG. 3) , so that the submergence depth  55  into the liquid body can be adjusted. Two separate fluid inlets  63  and  67  are provided in sleeve  60 , communicating with gap  62 . Through inlet  63 , fluid such as oxygen-containing fluid is supplied, under flow control of valve  71  and backflow prevention mechanism (a check valve)  65 . This allows for controlled addition of air or the like to the incoming wastewater and activated sludge liquid, for controlled aerobic, oxic or anoxic fermentation. Through inlet means (a pipe)  67 , liquid can be supplied under control of inlet control valve  72  and backflow prevention mechanism (a check valve)  65 L. This serves as a means for introducing flushing and cleaning liquid to service the gap  62  and negative pressure reliving mechanism ( 64 ,  66 ,  68 ), or for addition of other liquids to assist the fermentation, or even as a supplementary, controlled inflow of additional wastewater or activated sludge. 
       FIG. 2(   b ) shows an alternative embodiment, in which the wastewater in the liquid jet nozzle  48  surrounds the fluid inlet nozzle  50 E, which is in the form of a tube  41 , terminating at its lower end in a frusto-conical tip. An upper chamber  60 E communicates both with the tube  41  via holes  70  in the top-end and with liquid inlet  67  and fluid inlet  63 , as previously described. In both embodiments a safety feature  66 ,  68  is provided to control negative pressures and prevent cavitation in sleeve  60  or liquid suck-back into the gap  62 . In both embodiments also, it will be noted that the outlets  51 ,  49  project downwardly into the liquid body and terminate a short distance  55  below the surface. 
       FIG. 3  shows an exploded perspective of the  FIG. 2(   a ) embodiment  40 C, with like reference numerals indicating like parts. Relative vertical positioning of screw inter-fitting tubular elements  44 F and  44 M of the inner sleeve  60  provides for vertical, telescopic adjustment of the height of the outlet  49  from the sleeve. 
     By raising and lowering the fluid inlet nozzle  50  by use of inter-fitting screw threads  58 M and  58 F, the size of the gap  62  between the nozzles  48  and  50  can be adjusted. When a gas such as air is supplied through sleeve  60 , the size of this gap and lower peripheral edges  49  and  51  largely control the bubble size of the gas entraining with the liquid issuing from liquid jet nozzle  48 . 
       FIG. 4  diagrammatically illustrates a rectangular tank  30  of liquid  90  (wastewater and activated sludge as mixed-liquor) with side walls  31 ,  35 , and containing solids, some of which  92  are floating and others  94  of which are settling. With no mixing or agitation in the tank  30 , stratification results. This is undesirable, since in most instances the solids (especially the floating solids that are artificially added to improve process performance in MBBR and IFAS systems), have substantial amounts of the required fermentation bacteria adhered to them. These need to be distributed through the body of liquid for efficient fermentation. For an embodiment adapted to MBBR and IFAS systems, artificially added floatable solids will not be removed from the tank  30  via outlets  39  and  39 A as the process is conducted continuously. 
     With reference to accompanying  FIG. 5 , a preferred embodiment of an apparatus according to the invention shows the container (tank)  30  as liquid reactor, with inlet liquid jet ejector  40 C according to the embodiments previously described operating therein. A liquid-inlet-routing-control-means  110  (a valved intake or set of flow routing control valves as shown in  FIG. 8 ) is adapted to draw liquid from a plurality of liquid containers (optionally including the container  30  as described below via outlet  39 A at the bottom of container  30 ). 
     A liquid-transfer-routing-control-means  120  (comprised of multi-port flow control valves for flow routing and interconnecting pipelines as shown in  FIG. 8 ) connects to and is adapted to transfer liquid into a plurality of liquid containers, including the container  30 , via a plurality of liquid jet nozzles  48  or liquid jet ejector  40 C previously described, the jets being disposed just below the liquid surfaces  36  of the respective containers. This plurality of containers aspect is further described below, with reference to  FIG. 7  to  FIG. 11 . 
     A liquid pump  101 , connected to the liquid-inlet-routing-control-means  110  and the liquid-transfer-routing-control-means  120  transfers liquid from one to the other. 
     A fluid injection mechanism (e.g. venturi)  115  is connected to the liquid-transfer-routing-control-means  120  via branch piping to a back-flow preventing device (e.g. a check valve)  65 A and a fluid entraining flow control means (e.g. a control valve and a solenoid valve)  71 A (all off-the-shelf, conventional non-proprietary items), and a bypass-line with a flow control valve  117 , and to a liquid distribution means  150  (e.g. a sparge bar or manifold). The manifold  150  communicates to a plurality of liquid jet ejector devices  40 C that protrude vertically downwardly, terminating at their lower ends in a constricted liquid jet nozzle  48  with a lowermost throttled outlet  49 , disposed a short distance below the surface  36  of the body of liquid  90  in the container  30 . 
     The apparatus also includes a central fluid feeding system disposed generally above the container and comprising, connected in series by fluid delivery pipes, a central fluid feeding control means (e.g. a flow control panel comprising a valve and a flow monitoring device)  200 , a fluid feeding header or manifold  220 , a plurality of local fluid feeding control means (e.g. a valve)  71 , and a back flow preventing device  65 . This is normally used for supplying controlled amounts of oxygen containing fluid for aerobic fermentation, recycled activated sludge and nitrate-recycle for anoxic fermentation, methanol for anaerobic fermentation and any combination the above fluids to improve biological nutrient removal. A plurality of fluid output pipes  63  communicates with the interior of a plurality of depending annular sleeves  60 , one for each liquid jet nozzle  48  (or liquid jet slot), arranged concentrically around the vertically downwardly protruding portion of liquid jet ejector  40 C ( FIG. 2(   a )), to deliver fluid thereto. Sleeve  60  terminates at its lower end in the frusto-conical fluid inlet nozzle  50  described in connection with  FIG. 2(   a ) and constituting a fluid entraining slot (or nozzle) and forming a fluid inlet means. The outlet from the sleeve  60  defines an adjustable contact gap  62  between the fluid inlet nozzle  50  formed by lower extremity portion  51  ( FIG. 02(   a )) and the throttled liquid outlet  49 , and disposed at about the same level as, in fact slightly lower than, throttled outlet  49  of the liquid inlet means. The nozzles (or slots)  50  and  48  are custom designed for each application defining the liquid flowrate, degree of mixing energy and desired (optimum) fluid entraining rate (a optimum bubble size for gas feed). The gap  62  is adjustable by means of telescopic positioning mechanism (inter-fitting screw threads)  58 F and  58 M. The submergence depth  55  of the liquid nozzle throat  49  into the liquid body can also be adjusted by means of similar telescopic mechanism (inter-fitting screw threads)  44 F and  44 M, to generate small bubbles when a gas such as air is fed as the fluid, for the purpose of optimizing the amount of gas entrapping so that increasing gas transfer rate into the liquid (wastewater and activated sludge). There are at least 4 types of fluid entrapping control which can be used in embodiments of the invention: custom design liquid jet throat  49  and fluid outlet throat  51  of predetermined cross-sectional areas, a gap  62  adjustment mechanism such as an inter-fitting screw threads  58 F and  58 M; alternating the both cross-sectional area of throttled outlets  49  and  51  accommodated by means of a flexible spout (or slot) shape control mechanism; a local flow control valve comprised in control assembly  71 ; and a central flow control valve comprised in global flow control panel  200 . 
     Also provided generally above the container  30  is a central liquid feeding system comprising a central control means (a control panel)  230 , an interconnecting pipeline  240  and liquid feeding pipeline (header or manifold)  250 . This also communicates with sleeve  60 , via a local inlet control valve  72 , a check valve  65 L and a negative pressure prevention mechanism  66  adapted to relieve any excess negative pressure occurrence in tube  60  to prevent possible cavitation when fluid feeding controls  71  and  72  are both closed, all as described above with reference to  FIG. 5 . In the event of excess negative pressure, liquid (wastewater) is sucked from the container  30  by means of pipeline  68  through control means  66  (a valve) and connecting pipeline  64  into sleeve  60  and therefrom recycled back to the container  30  by means of gap  62 . 
     The container  30  also includes an optional second influent mechanism  38  by which liquid is fed to the container  30 , and two effluent mechanisms  39  and  39 A, by which liquid can be removed from the container. The liquid pump  101  is adapted to draw liquid via a liquid-inlet-routing-control-means  110  and transfer liquid to the liquid-transfer-routing-control-means  120 . The liquid-inlet-routing-control-means  110  (in the form of a valved intake) is provided with an optional inlet-routing-means (in the form of multi-port set of valves and depending pipelines, one embodiment shown in  FIG. 8 ) adapted to draw liquid from plurality of liquid containers including the liquid reactor  30 , to be mixed therein. The liquid-transfer-routing-control-means  120  (in the form of a valved discharge) with an optional outlet-routing-means (in the form of multi-port set of valves and depending pipelines, one embodiment shown in  FIG. 8 ) is adapted to pump liquid into a plurality of liquid containers including said reactor  30 , as illustrated in  FIG. 7  and  FIG. 10 , by means of a plurality of flow distribution manifolds  150  which are adapted to distribute liquid into plurality of liquid jet mix ejectors  40 C of the type illustrated in  FIG. 2(   a ). 
     A further outlet pipe  64  leads from the tube  60 , via a negative pressure preventing mechanism (e.g. control valve)  66 , into the container  30 , terminating at its lower end  68  at about the same level as outlet  49 , but laterally offset therefrom. This serves to relieve excess negative pressure to prevent possible cavitation and back-flow into the sleeve  60  via gap  62 , according to good engineering practice. 
       FIG. 6  illustrates an apparatus according to another embodiment of the invention. It is similar to  FIG. 5 , except that the plurality of liquid jet ejectors  40 C are disposed to one side of the container  30  instead of centrally. All other apparatus items are essentially the same. The delivery of liquid to container  30  from each liquid jet nozzle  48  is still essentially vertically downward, at a location just below the liquid surface. Similar flow patterns are obtained, but to one side of the container only. Effective de-stratification is still achieved. 
     The liquid jet ejectors  40 C and  40 E (in  FIG. 2 ) are adapted to mix a body of liquid  90  in the reactor  30  that may contain one or both of floatable matter such as floatable solids  92  and settleable matter such as settleable solids  94 , effectively to de-stratify floatable-matter-layer by means of a floating-matter-routing-baffle-means (baffles)  80  and settleable-solids-layer in the body of liquid. This is achieved by vertically downward delivery of liquid just below the surface  36  of the body of liquid, so that the flow penetrates to the bottom  33  of the container  30  with a sufficient hydraulic force, resulting in homogeneous mixing throughout said reactor  30 , while concomitantly achieving in-situ and controlled entraining, dispersing or dissolving of a fluid  91  in the body of said liquid  90 . 
     The operation of the process of the present invention, using an apparatus such as that illustrated in  FIG. 5  or  FIG. 6 , will be apparent from a consideration of the drawings. The liquid pump  101  transfers liquid such as wastewater at a desired liquid flow-rate and at a certain pressure, thereby providing a steady agitation rate to a body of liquid  90  contained in the reactor  30 . The pumped liquid is fed through liquid-transfer-routing-control mechanism  120  and optional fluid injection mechanism “J” or  115  (in the form of a venturi) to sparge-bar-manifold  150  and distributed into evenly disposed liquid jet nozzles  48  exposing said liquid jet nozzles or liquid jet ejectors  40 C to the body of said liquid  90  at a certain vertical submergence level  55  preferably just under the liquid surface  36  to provide constant mixing independently from entraining a fluid or gas, progressing substantially vertically downward into the body of liquid, and creating vertically plunging parallel trajectory jet streams on a line located adjacent to liquid surface  36 , at the mid-point along the reactor width  36  (liquid surface and reactor width are represented by the same number:  36 ), parallel to side walls ( 31  or  35 ) and lining along the reactor length ( 37 ). 
     The fluid inlet nozzle  50  is adapted to each liquid jet nozzle  48  to accommodate controlled entraining, dispersing and dissolving a fluid  91  into the body of liquid  90 . The contact-gap  62  between liquid jet nozzle  48  and fluid inlet nozzle  50  is adjusted to control—especially for gas entraining—the rate-of-gas-flow and gas bubble size for optimizing gas dissolution and transfer rate. 
     The optional fluid injection venturi  115  is adapted to accommodate controlled entraining, dispersing or dissolving a fluid into body of liquid by means of a control valve  117  on by a pass pipeline. This optional fluid injection means  115  is used as an alternative fluid inlet for further improvement especially in gas dissolution and gas transfer rates into the body of liquid. 
     The kinetic energy of each individual vertically plunging liquid jet (dependent on cross-section  49 ) is adjusted to penetrate a certain thickness of floatable solids layer at the liquid surface  36  and to entrain the floatable solids  92  into the plunging jet stream by means of assistance from the baffle mechanism  80 ; the mixture of liquid-solid-gas-fluid is then carried downwards, to reach the reactor bottom with an adequate energy to keep settleable solids also in suspension. The flowing mixture then diverges into two, and produces bi-directional streams along the reactor bottom across to the each side walls  31  and  35  ( FIG. 5 ). Then the streams move upwards along the side walls  31  and  35  and reach the liquid surface  36 . Then the streams move along the surface  36  pushing the floatable solids  94  towards the plurality of liquid jet ejectors  40 C induction area and finally to converge at the mid point where liquid jet-mix-ejectors are located, thus completing a full cycle. When the body of liquid comprises artificially added floatable solids  92  (such as in MBBR and IFAS systems), the liquid jets are designed to provide adequate kinetic energy to carry some of the floatable solids vertically downwardly to and along the bottom portion of the container  30 , with subsequent upward movement of the floatable solids to contribute to the liquid mixing pattern and efficiency. Minimizing the kinetic energy provided by liquid jets and taking advantage of floating solids to contribute subsequently upward liquid mixing pattern will significantly reduce energy utilization. 
     The present invention of apparatus in  FIG. 5  is shown as including a single inlet liquid jet mixer  40  arrangement ( FIG. 1 ), but it can readily be adapted to include a plurality thereof, all feeding into a single container  30  or into a plurality of such containers.  FIG. 7  of the accompanying drawings illustrates three embodiments in which several inlet jet means feed into a single container  30 . In  FIG. 7(   a ), the arrangement is as shown in more detail in  FIG. 5 , with the inlet jets located centrally in the container and creating circular flow patterns in two sides of the container. In  FIG. 7(   b ), the arrangement is as shown in detail in  FIG. 6 , with the liquid jet nozzles  48  (as a portion of  40  or  40 C) at one side and creating a single circulation system in the container. In  FIG. 7(   c ), two sets of liquid jet nozzles  48  are provided at opposed sides of the container  30 , creating a flow pattern similar to that of the  FIG. 7(   a ) arrangement, but in the reverse directions. 
       FIG. 8  of the accompanying drawings diagrammatically illustrates one interconnecting arrangement of a plurality of apparatus as described in  FIG. 5 . This shows in more detail the liquid-inlet-routing-control-means  110 , which is in the form of interconnecting pipeline associated controls “C”, each feeding liquid from selectively one (or more) of set of containers, e.g. anaerobic container  380 , anoxic container  382 , aerobic container  386 , and solids separator  388 , by means of pump  101 , to the liquid-transfer-routing-control-means  120 . This provides far feed or recycle of liquid to an additional set of containers e.g. anaerobic container  390 , anoxic container  392 , aerobic container  394 . Also transferring from liquid-transfer-routing-control-means  120  back to containers  380 ,  382 , and  386  can be arranged. All containers are equipped with inlet arrangements such as liquid jet mixer  40  or liquid jet ejector  40 A,  40 C, or  40 E as previously described. 
     For these and similar arrangements, a fluid-feeding-system comprising one or more fluid-flow-control-mechanisms  200  can be adopted, feeding to a manifold  220  with several separate pipelines and valves  71  feeding to different liquid jet ejectors  40 C, as diagrammatically illustrated in  FIG. 9 . Also included are the liquid inlet system  230  for the cleaning, flushing and optional chemical addition, and the liquid-transfer-routing-control-means  120  for the inlet of wastewater or activated sludge, as described in  FIG. 6 . Each feeds a respective manifold and thence to the different liquid jet ejector  40 C. Local liquid and fluid feeding control systems  71  and  72  can be eliminated for small systems where individual liquid-jet-ejector  40 C flow adjustment is not critical and required. 
     For one embodiment of the present invention of apparatus  100  as illustrated in  FIG. 5 , liquid jet mix ejector  40 C (in  FIG. 2(   a )) direction is substantially vertically downward, with an essential angle of 90° with horizontal XY-plane represented by liquid surface  36 . In other words it is essentially vertical to both horizontal X-axes and horizontal Y-axes and those angles depicted by angles  45  and  47  in  FIG. 5 . Suitable jet penetration angles range between 81° to 99° degrees with respect to horizontal-Y-axis (angle  45 ) and also make an optional angle range between 81° to 99° degrees with respect to horizontal-X-axis (angle  47 ), resulting in optional ±10% deviation from 90°-degree-vertical-line to the XY-horizontal-plane which represents quiescent liquid surface  36 . 
     Liquid jet nozzle ( 48 ) exposure in to the body of said liquid ( 90 ) is a certain vertical submergence level ( 55 ) with a general range of 0.001 meter to 1.0 meter, further ranging from 0.04 meter to 0.30 meter, preferably 0.06 meter to 0.15 meter from the surface. 
     The degree of hydraulic force created by the liquid jet nozzles ( 48 ) are dependent of Reynolds Number, “Re” (a dimensionless fluid flow measure defined as the ratio of dynamic pressure and shearing stress) with a general range between 16,000 and 90,000 (observed during model study for the present invention) however, calculated general range for actual size embodiment “Re” is between 100,000 and 500,000. It will be noted that, there is no optimum “Re” or hydraulic agitation energy per unit volume for all scenarios. Optimum “Re” is calculated by considering many design factors such as tank dimensions (depth, width, shape), characteristics of body of liquid to be agitated, required amounts of fluid (or gas) to be entrained, percent solids content and other key characteristics of the body of liquid. Therefore, for specific cases the present invention can be designed to have lower or higher “Re” as disclosed above. The higher “Re” the less energy-efficiency, so the object is to aim low “Re” values as possible but high enough “Re” values accommodating the required adequate agitation and fluid entraining. The liquid jet nozzle ( 48 ) jet also has a preferred “mean cross-sectional velocity” with a general range tested during the model study between 5.0 m/second and 24 m/second. Again, the higher the jet velocity the less the energy-efficiency, so the object is to aim low velocities as possible, but high enough to provide adequate agitation and fluid entraining requirement for an individual case. 
     Liquid-inlet-routing-control-means has an optional routing-control-means ( 110 ) comprising a plurality of pipelines, valves, open/close control mechanisms, and screens (one embodiment shown in  FIG. 8 ). 
     Liquid-transfer-routing-control-means ( 120 ) has an optional routing control mechanism comprising a plurality of pipelines, valves, open/close control mechanisms, pressure and temperature monitoring devices (one embodiment shown in  FIG. 8 ). 
     The liquid-jet-ejector ( 40 C), liquid-jet-nozzle ( 48 ) and fluid-inlet-nozzle(s) ( 50 ,  50 A) have cross-sectional shape preferably circular or oval, alternatively a custom designed geometric shape where a custom designed spout is made up of a flexible material to alternate its cross-sectional shape and area to control fluid entraining rate and gas bubble size created. 
     A preferred container for a most energy efficient embodiment of the present invention is custom designed for individual cases. As a rule of thumb, the container can be hydraulically idealized by custom Width (W)-Length (L)-Height (H) ratios to provide ideal hydraulic conditions for substantially vertical downward (tumbling) mixing, where those are defined as ratio H/W is between 1 and 3 and the ratio of L/H between 1 to 10. It will be noted that the present invention will be suited to work in existing containers with a higher or lower H/W and L/H ratios than provided above with a potential less energy-efficient means. 
     The operation of a preferred embodiment of the process of the invention will now be described with reference to  FIG. 10 . A process for the treatment of wastewater and biological nutrient removal, in particularly for integrated fixed-film activated sludge system uses a plurality of the apparatus described above, as universal equipment to provide adequate mixing required in a set of reactors  310 ,  320 ,  330 ,  340 ,  350 , and  360 , followed by a downstream solids separator  370 . In each of the reactors, desired process conditions such as anaerobic, anoxic, aerobic and oxic (advanced oxidation) can be concomitantly arranged while agitation is being provided. Alternatively the conditions can be varied or alternated in one reactor. As depicted in  FIG. 10 , the process includes a first step of introducing raw wastewater to an equalization tank or container  300 . The raw wastewater is drawn from the equalization tank or container  300  via pipeline  152 , and transferred into an anoxic reactor  320  or alternatively into an anaerobic reactor  310  under control of liquid-flow-control-mechanism (valve)  311 F. The energy of the pumped liquid is used for the mixing in the anoxic reactor  320  while concomitantly-controlling the entraining (by means of flow control system  322 F), dispersing and dissolving of air at atmospheric pressure or alternatively another fluid such as methanol as required for process, using the previously described jets  40  to maintain desired anoxic conditions in said reactor  320 . Delivery of liquid in each case is substantially vertically downwardly, at a location just below the liquid surface as previously described, optionally but preferably using baffle plates to create the desired flow patterns. 
     In one method, activated sludge is drawn from the underflow of a solid-separation unit  370  located downstream of the reactors  320 , etc., and transferred into an anaerobic reactor  310  upstream of the aforementioned anoxic reactor  320 , and into another anoxic reactor  350  located upstream of an aerobic reactor  360 . Again, the pumped liquid energy is used for the mixing in the reactors  310  and  350 , while concomitantly-controlled-entraining or feeding of raw wastewater from the pipeline  152  is effected by means of liquid-flow-control-mechanisms  311 F and  356 F into the corresponding liquid jet mix apparatuses  311 ,  356 , which are liquid jet ejectors  40 C as previously described. 
     Activated sludge mixed-liquor may be drawn from an aerobic reactor  360  or  340  in which nitrification (biological oxidation of ammonia to nitrate and nitrite using specialized bacteria) taking place, and recycling into a preceding anoxic reactor  320  or alternatively into a preceding anaerobic reactor  310  (not shown for the embodiment in  FIG. 10 ) for denitrification (biological reduction of nitrate and nitrite to nitrogen gas). Again, the pumped liquid energy is preferably used for the mixing in the respective anoxic or anaerobic reactor  320  or  310 , further reducing energy consumption. At the same time, concomitantly-controlled-entraining and dispersing of returned activated sludge from a header or pipeline  151  or  156  is effected by means of a sludge-flow-control-mechanism  323 F into a mixing apparatus  323  involving a jet of the type  40 C previously described. 
     In another method according to the embodiments of the invention, activated sludge mixed-liquor is drawn from an aerobic reactor  340  and transferred to an upstream aerobic reactor  330 , again using the pumped liquid energy for the mixing while concomitantly-controlled-entraining dispersing and dissolving of an oxygen containing fluid (such as air, oxygen gas, or hydrogen-peroxide) is effected to maintain desired aerobic conditions in the aerobic reactor  330  for mixing and aeration. Recycling of activated sludge mixed-liquor from a nitrifying reactor to an upstream aerobic reactor facilitates more robust nitrifiying bacteria culture throughout the disclosed process of invention. 
     In another method in accordance with the invention, activated sludge mixed-liquor is drawn from an aerobic reactor  340 ,  360  and recycled to the same aerobic reactor  340 ,  360 , using the pumped liquid energy for mixing while concomitantly-controlled-entraining dispersing and dissolving of an oxygen containing fluid (such as air, oxygen gas, or hydrogen-peroxide) is conducted to maintain desired aerobic conditions in said aerobic reactor  340 ,  360 . 
     Embodiments of the present invention provide a mixing apparatus with a capability of entraining, dispersing and dissolving fluids that may be necessary for the activated sludge system and biological nutrient removal. 
     When the present invention is incorporated to entrain an oxygen containing fluid, it serves as aeration equipment; therefore it provides a system in which the degree of mixing and degree of aeration are not dependent each other. 
     The present invention incorporates an immersed-plunging liquid jet which does not entrain ambient air due to surface impingement. On the contrary, the vertical jet is deliberately created just under liquid surface to provide steady mixing energy to the liquid body and concomitantly but independently from the rate of mixing accommodating in-situ and controllable entraining, dispersing and dissolving a fluid (such as atmospheric air) in the body of liquid contained in a reactor. Submersed jets do not create any significant surface impingement and therefore cause less likely foam problems associated with. The degree of mixing provided by the liquid jet is kept relatively constant, while entrained rate of fluid (air) is independently adjustable from zero to a maximum value to meet desired conditions and optimum bubble size for improved gas transfer and dissolution efficiency. Fluid (air) entrainment can be turned off completely to provide mixing only for anaerobic and anoxic reactors. 
     One embodiment of this invention not only incorporates steady mixing versus independently variable aeration in one apparatus, but also facilitates energy efficient biological nutrient removal in activated sludge systems and its improved versions (often called hybrid systems such as MBR, MBBR and IFAS). 
     The invention incorporates a vertically plunging jet created just under the liquid surface in order to have a steady mixing concomitantly but independently achieving in-situ and controllable entraining, dispersing and dissolving of not only atmospheric air but any other fluids that may be necessary for the process. 
     One embodiment of this invention has been adapted so that no major equipment, device, or pipeline has to be totally submerged into a reactor to do either or both of mix and aerate. All equipment can be located outside of the liquid reactor, except the plurality of liquid-jet-ejectors  40 C that need to be semi-submerged or just submersed under the liquid surface to provide in-situ-controllable fluid entrainment including atmospheric air. The liquid-jet-ejectors are located at a very convenient distance from the liquid surface so that, in case of a potential clogging occurrence, they can easily be inspected and cleaned without stopping the operation. If an ejector ever needs to be serviced outside for maintenance, then it can be retrieved individually while the remaining ejectors that are unplugged can keep running. 
     The apparatus of the present invention comprises well known components such as pumps, pipelines, manifolds, valves, fluid-control systems etc. that can be easily mastered by any ordinary operation technician. There is no major proprietary equipment other than the custom designed jet-ejectors which can be cost effectively stored as spare parts. The design of the jet-mixing-apparatus may be complicated for some cases; however, the final product is relatively simple, energy-efficient and user friendly to operate and maintain, and significantly less noisy compared to air compressors or blowers. 
     Desired air bubbles size ( 93  in  FIG. 5 ) is created by means of plurality of concentric frusto-conical nozzle arrangement (such as in  40 C) and the control surface at the gap  62  between the nozzles  48  and  50 .