Mixing Apparatus for Biochemical Treatment of Fluids With Oxygen

This invention relates to a mixing vessel for biochemical treatment of substances with cultures of bacteria, and more particularly to processes such as treatment of wastes, sewage digestion, purification of water and fermentation. The invention relates more particularly to a closed mixing system operable either in a batch or a continuous mode in which turbulent action is induced by injection of partially treated, recirculated waste material and of fluid additives supportive of bacterial-culture growth.

In the past and today in many existing waste treatment plants digestion by aerobic bacteria was and is conducted in large installations in a series of massive holding tanks each having long dwell times and various mixing and aeration devices associated therewith. More recently Venturi aerators have been utilized such as those shown in U.S. Pat. Nos. 3,271,304; 3,334,868 and 3,497,164.

In such prior art apparatuses the arrangement shown do not have the intimate mixing of partially treated waste with aeration fluid prior to and upon injection of the recirculation wastes. The recirculation of the present invention provides active digester operation during required time for digestion and reduces overall time for obtaining effluent purity desired.

Thus the present invention covers a closed digester or mixing vessel into which sewage or waste slurries are introduced through a feed pump that maintains the total volumetric content of the system. The feed is induced through a centrally disposed inflow pipe which is closed at lowermost end, but includes a series of orifices distributed over the length of the pipe so as to break the inflowing fluid into a plurality of smaller radially emitted streams. After filling the vessel to be within the efficient operational range and until sufficient bacterial digestion has been initiated, the digester contents are recirculated with air-or an oxygen-containing fluid combined therewith to support a high-rate growth of bacteria.

The recirculation is effected by withdrawing the waste under treatment through an annular, perforated collector concentric the inflow pipe. The outlet of the annular collector is connected to the suction of a second pump or recirculation pump. Into the recirculated fluid, a third pump or aeration pump injects air or any other bacterial-growth supporting fluid. The combined mixture of recirculated fluid and air is injected into the mixing vessel through an injection nozzle that directs the inflow against a baffle. The baffle performs a two-fold function of directing the mixture towards the inner walls of the vessel resulting in high turbulence and breaking the jet flow into a multiplicity of streamlines. The significance of the latter action is to increase the surface area of gas thereby increasing the surface contact area between the air and the bacteria with a resultant increase in the bacterial growth rate.

As digestion occurs, the treated waste is monitored at a point downstream from the recirculation pump outlet and, upon reaching an acceptable level for discharge, a portion of the treated waste is diverted therefrom to the system discharge outlet. The material discharged is replaced by an equivalent volume of feed at the initial system inlet.

Accordingly it is an object of the present invention to provide an improved mixing apparatus for biochemical treatment of waste fluids with oxygen.

It is another object of the present invention to provide a high turbulence mixer by use of jet injection of recirculated waste.

It is a feature of the present invention to utilize a deflector plate in the recirculation system for producing a multiplicity of streamlines to achieve increased surface contact between the materials under treatment and additive fluids.

It is yet another object of the present invention to inject a gaseous fluid into the recirculating waste so as to accelerate bacterial growth and to hasten digestion of waste.

It is yet another object of this invention to reduce time for chemical or biochemical processes as reaction time in such chemical or biochemical processes are directly proportional to the surface of contact of the reagents.

It is a feature of the present invention to utilize a sparger disposed on the longitudinal axis of the mixing vessel for feed introduction and in association therewith an annular collector concentric to the sparger.

It is yet another feature of the present invention that the pattern of flow generated, flow intensity and the level of turbulence are predictable and are easily controllable.

It is another feature of the present invention to provide an improved biochemical treatment mixing vessel which is readily used in batch or continuous modes of operation.

Other objects and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings in which:

FIG. 1 is a side view of a mixing system having an improved mixer-digester tank in accordance with the present invention.

FIG. 2 is a top view of the mixing system shown in FIG. 1.

FIG. 3 is a vertical section through the mixer-digester tank taken on line 3--3 of FIG. 2.

FIG. 4 is a cross-section taken on line 4--4 of FIG. 3.

FIG. 5 is a fragmentary inside plan view of the jet inlet device taken on line 5--5 of FIG. 3.

FIG. 6 is an enlarge perspective view of the jet inlet device as shown in FIG. 5 partly broken away.

FIG. 7 is a more detailed cross-section of the jet inlet device of FIG. 3.

Referring now to FIGS. 1 and 2 schematic representations of the mixing vessel for the biochemical treatment of sewage together with associated fluid flow control elements. The mixing vessel MV of the preferred embodiment has associated therewith a primary and a secondary inlet control means. The primary inlet control means, valve V1 and pump P1, provides feed of untreated sewage. The secondary inlet control means provides for recirculation (through recirculation control loop RCL) of partially treated sewage and injection therein of digestion-supportive additives. The recirculation control loop RCL is provided with pump P2 for withdrawing partially treated sewage, system outlet valve V2 (normally closed during batch operation), pump P3 for adding to recirculated material digestion-supportive additives such as air or other oxygen containing fluids, and valve V3 for controlling direction of flow from pump P3.

The structure of the mixing vessel (MV), generally designated as 10, is shown in detail in FIGS. 2 through 7. The interior of the mixing vessel forms a closed, aerobic waste-treatment chamber 12 having a generally circular side wall 14 with a substantially flat bottom 16 and top 18. Waste feed material 20, such as raw sewage or industrial waste, is introduced into the mixing vessel until such vessel is substantially filled preferably completely filled or slightly pressurized. The influence of feed 30, as shown in the preferred embodiment, is provided by passage through sewage pump (P1) 22 under the control of valve (V1) 24 and passage through feed line 28 to sparger (or distributor) 28. The sparger 28 is a closed end cylinder that depends from the central portion of top 18 almost the entire length of longitudinal axis of mixing vessel 10. The sparger is stabilized by supporting struts 32 and collar 34 at a point medial said top 18 and bottom 16. Proximal to the collar 34 and on either side thereof, a plurality of orifices 36 is located throughout the central portion of the chamber for providing discharge outlet means. Located concentric to sparger 28 and also supported by struts 32 is an annular or toroidal collector 28 disposed so that the plane in which lies the circular centerline 40 thereof is substantially normal to longitudinal axis 30.

Referring particularly to FIG. 4, the concentric relationship between sparger 38 and collector 38 is clearly shown. The effluence of partially treated waste for either recirculation or system discharge is obtained through uniformly distributed collector perforations 42 and is urged through discharge outlet line 44 by connection to the suction side of recirculation pump (P2) 46 which is in turn driven by pump motor 48.

For continuous operation, the mixing vessel is equipped with system discharge valve (V2) 50. To maintain efficient continuous operations, the system may be equipped with volumetric control means (not shown) for the purpose of metering the rate of production--the system output through valve 50--and for ensuring an equivalent inlet or make-up rate through valve 24.

The discharge or recirculation line 52 is arranged for cooperative functioning with an injection nozzle 54 to deliver recirculation and additive fluids as described in the discussion of the schematic diagram above. In the preferred embodiment, the injection nozzle connects to centrally located inlet 56 of mixing vessel bottom 16. Depending upon the nature of the waste under treatment, the degree of treatment already received by the waste, and the oxygen utilization of the aerobic bacterial culture, the recirculated fluid is joined at the injection nozzle 54 by a supply of digestion-supportive additive 58, usually, but not limited to a fluid such as air. The additive fluid 58 is entrained in the recirculated medium and is metered thereto by supply pump (P3) 60 under the control influence of relief/check valve (V3) 62. In batch operation, the additive supply means structure may be adapted to be at high volume levels at initial stages of digestion and at low volume levels at final stages thereof, and by contrast, in the continuous operation, the structure may be simplified for constant addition of air based on exponential factors. The jet injector or injection nozzle 54 is disposed in an upwardly discharging position, as illustrated in FIG. 6, and is arranged to discharge recirculation and additive fluids in a direction substantially tangential to inlet of fluids from sparger 28. The jet nozzle 54 of this invention is designed to accelerate fluid flow from pipeline 52. Rapid acceleration which is subsequently followed by a deceleration outside of the nozzle, both associated with high degree of internal shear, produce strong breaking up effect. The sizing and form of the nozzle is related to pump characteristics, to the size of the vessel, to the nature of the liquid treated and to the type of the process in question. By properly designing the jet injectors, a predictable and highly turbulent flow pattern is generated. This ensures that the whole volume of the vessel contents will uniformly participate in the mixing process, so that no "dead" zones where little or no exchange of phases takes place. To enhance turbulence, desirable for optimizing contact of waste with the bacterial culture, a baffle or deflector vane 66 is disposed adjacent the injector outlet or discharge mouth 65 and substantially parallel to vessel bottom 16. The baffle 66, which is supported on bottom 16 by legs 67, deflects the fluid flow outwardly. The deflected flow from nozzle 54 results in turbulent flow indicated by flow arrows shown in FIGS. 3 and 7. The fluid is shown as being deflected outwardly to the side wall of the chamber, thence upwardly to the upper portion of the chamber, and thence cascading from the side wall to the central portion. The baffle 66 is also adapted to forming a multiplicity of streamlines and thereby increasing the surface area presented to the aerobic bacterial culture.

In operation on a batch basis, the diversion of the treated waste occurs upon the completion of treatment and the system is practically drained, but for a small portion thereof to retain the bacterial culture for the next subsequent batch. The system inlet is then not ulilized in the "make-up" sense, but rather as a batch loading means. On a continuous basis the total system inlet flow of recirculated partially treated waste and of inlet make-up untreated waste is kept substantially consistent so that the rate of production of treated wastes, after treatment initiation, is also substantially constant. The continuous-basis system is adaptable to biochemical oxygen demand (B.O.D.) and chemical oxygen demand (C.O.D.) monitoring feedback instrumentation. Such instrumentation may be, when applied to ordinary sewage wastes, as simple as volumetric metering control of pumpage with constant air injection, or, when applied to hard-to-treat industrial wastes, as sophisticated as feedback control loops to supply more or less oxygen to the system.

The above discussion of the operation of this invention has been drawn in terms of bacterial treatment of sewage and other wastes; however, it is envisioned that the high-turbulence, rapid-mixing action is adaptable to other uses, such as the neutralization of treated water wherein other fluids besides air are injected. While the foregoing description illustrates the preferred embodiment of the present invention, it will be appreciated that certain changes and modifications may be made without departing from the spirit and scope of the invention and that same is defined by the claims as hereinafter set forth.