The present invention also relates to apparatus and methods for rupturing microbial cells (lysis) and separating the cellular membrane from the cytoplasm in the production of cell-free extracts, serum and nutriments from fermentations, cell cultures and tissue. Further, the present invention relates to apparatus and methods for disintegrating solid particles in the production of liposomes and submicron dispersions.

Background Art In recent years, the demand for more effective and efficient sewage treatment facilities has grown. One of the most important aspects of sewage treatment is the removal and disposal of biosolids. It has long been recognized that biological respiration and synthesis occurring in the aeration system of a secondary biological wastewater treatment plant converts the organic material it receives in the sewerage it treats to carbon dioxide, water and new cells. The amount of biodegradable organic material in the

sewerage treated can be indirectly determined as biological oxygen demand (BOD). Much of this BOD (40 to 60%) is transformed into new cells as a result of the aerobic respiration occurring in the treatment plant's aeration system. These new cells (biosolids), which are produced daily, must be removed for the proper operation of the treatment plant. This waste stream is known as waste activated sludge. Merely separating and removing the biosolids translates to a substantial solid waste disposal problem, with a large portion of the mass of the biosolids being attributable to intracellular water.

Accordingly, if the cell solids could be isolated and removed from the biomass leaving cellular water content to be returned to the processed wastewater, such separation would constitute a large reduction in the mass and volume of biosolids requiring disposal, e. g., in a landfill.

In the past, rotor and stator colloidal dispersion mills have been used for mechanically disintegrating suspended solid and liquid components of, e. g., wastewater sludge, paint, ink and the like to produce liquid suspensions with finely divided components. In U. S. Patent No. 5,240,599, liquid containing immiscible liquid (s) and/or partially dispersed solid particulate component (s), are propelled by a rotor against the interior surface of a concentric stator ring having a plurality of radial passageways or slots intermittently spaced around its circumference. The slots have a constant, relative narrow width compared to the circumference of the stator. The rotor is typically propelled at a very high velocity, e. g., usually between 5,000 to

12,000 feet per minute. As a result, the fluid and entrained immiscibles to be processed are subjected to strong centrifugal forces which induce an outward flow through the narrow slots of the stator. When the rotor and stator slots come into alignment, the fluid is ejected from the rotor slots into the stator slots. All components carried in the ejected fluid have an initial resultant velocity attributable to the radial and tangential velocity imparted by the rotor.

Predominantly tangential motion causes some portion of the immiscibles carried in the flow through the rotor slot to impinge on the interior radial surface of the stator slot emanating from the trailing edge of the slot, fracturing them into smaller sub-parts. This action is applicable to particles or to globules of undissolved fluids which can be broken down by impinging them against the stator slot walls.

Workers in the field of cell disruption have shown that pressures on the order of 5,000 to 20,000 psia are necessary to rupture bacterial cell membranes. Traditional lysing processes rely on brute-force techniques to generate high-pressures. For example, hydraulic cylinders raise the pressure of a flow stream up to the required pressure of 5,000 to 20,000 psia. The liquid is then forced through an orifice, split into two streams which are brought back together, and made to impinge against one another. This technique is far more energy intensive then comparable lysing with a dispersion mill, which produces these high pressures for a brief instant with each impact.

U. S. Patent No. 5,522,553 sought to improve the lysing capacity of a dispersion mill of the type with a slotted rotor and stator by changing the design of the slots in the stator. The'553 patent describes chamfers on the leading edges of the stator slots to permit fluid flow from the rotor into the stator which is of longer duration, of greater volume, and along a path resulting in a impact angle of 90°. The impact angle of 90° of U. S. Patent No.

5,522,533 generates greater stagnation forces that result in cavitation when the fluid accelerates away from the impact zone. Subsequent discharges into the stator slot increase ambient pressure around vapor cavities created by prior fluid injections into the slot and accelerate cavity collapse. This generates higher pressures through accelerated collapse and also through reentrant jet effects. The tremendous pressures associated with cavitation and reentrant jet effects result in shock waves which are transmitted through the fluid and lead to a disintegration of entrained particulates, such as cells.

While the prior art referred to above is highly effective in cell lysing, improvements are always desirable to increase the efficiency and effectiveness of cell lysing apparatus, which is an objective of the present invention.

It is a further object of the present invention to incorporate a cell lysing apparatus into a wastewater processing train to produce a more efficient wastewater processing system. Another objective of the invention's cellular disruption is the elimination of the occurrence of bulking arising from

the production of excess filamentous organisms in an aerobic wastewater treatment system.

It is another objective of this invention to provide an efficient apparatus for microbial lysis and particle disintegration which is sufficiently small so as to be easily installed into existing wastewater treatment facilities with little or no modification of such facilities being required.

Disclosure of the Invention The present invention provides a novel means of operating an activated sludge wastewater treatment facility without the need to remove excess biological sludge. The present invention, through the induction of robust cavitation and impingement, ruptures the cells and fragments the particles in the waste activated sludge stream and recycles this processed/lysed material as food to the microorganisms that reside in the aeration system of the wastewater treatment plant. The recycling of the disintegrated waste activated sludge is not sufficient alone to eliminate the production of excess biosolids due to the composite metabolism of all the microorganisms residing in the wastewater treatment system. Therefore it is also part of the claimed invention that the continuous operation of the embodied apparatus generates conditions, where only specific species of microorganisms can exist and thrive. This method of operation artificially creates an endogenous phase of respiration, where the growth of cells does

not cease, but where the rate, by which, microorganisms reproduce (biological respiration) is exceeded by the combination of natural cellular degradation and the rate of cellular disruption and lysis generated by the present invention. The invention's capacity to produce cellular disruption also eliminates bulking, which arises from the production of excess filamentous organisms in an aerobic wastewater treatment system. The present invention, while providing an efficient and effective means of microbial lysis and particle disintegration, is physically modest in size and suitable for installation into existing wastewater treatment facilities without substantial modification thereof.

Brief Description of the Drawings For a more complete understanding of the present invention, reference may be had to the following detailed description considered in conjunction with the accompanying drawings, in which : FIG. 1 is a partially schematic cross-sectional view of a dispersion mill in accordance with the prior art, more specifically as shown in FIG. 1 of U. S. Patent No. 5,522,553; FIG. 2 is an enlarged, cross-sectional view of the prior art rotor and stator utilized in the dispersion mill of FIG. 1; FIG. 3 is an elevational view of a lysing mill in accordance with the present invention;

FIG. 4 is a side view of the lysing mill of FIG. 3; FIG. 5 is a top view of the lysing mill of FIGS. 3 and 4; FIG. 6 is an enlarged cross-sectional view of the lysing mill shown in FIGS. 3-5 taken along section line VI-VI and looking in the direction of the arrows; FIG. 7 is a plan view of a rotor from the lysing mill of FIG. 6; FIG. 8 is a cross-sectional view of the rotor of FIG. 7 taken along section line VIII-VIII and looking in the direction of the arrows; FIG. 9 is a plan view of a stator as would be utilized in the lysing mill of FIG. 6; FIG. 10 is a cross-sectional view of the stator shown in FIG. 9 taken along section line X-X and looking in the direction of the arrows; FIG. 11 is an enlarged fragmentary view of the rotor of FIG. 9 in the area identified as XI; FIG. 12 is a plan view of a wear plate for incorporation in the lysing mill of FIG. 6; FIG. 13 is a cross-sectional view of the wear plate of FIG. 12 taken along section line XIII-XIII and looking in the direction of the arrows; FIG. 14 is a schematic diagram of a wastewater treatment plant incorporating a lysing mill in accordance with the present invention; and FIG. 15 is a more detailed schematic diagram of a portion of the wastewater treatment plant depicted in FIG. 14.

Best Mode for Carrying Out the Invention FIGS. 1 and 2 illustrate a prior art dispersion mill which can be utilized, inter alia, for treatment of sewage. The mill includes a tank having a rotor/stator assembly disposed in the bottom thereof. A shaft extends from the rotor inside the tank to the exterior where a source of rotary power is coupled to the shaft for rotating the rotor. In order to increase the occurrences of entrained particulates striking the surface of the stator as fluid is pumped through the stator, the slots in the stator shown in FIG. 2 are chamfered on the leading edge. The chamfer permits a greater volume of fluid to enter the stator slots and increases the number of 90° impacts against the stator slot. A 90° impact angle results in greater stagnation forces and cavitation, as well as giving rise to the reentrant jet effect which generates shock waves to disintegrate entrained particulates. The prior art device shown in FIGS. 1 and 2 is suitable for batch processing wherein a volume of fluid to be processed is introduced into the tank, processed, then drained from the tank.

FIGS. 3,4 and 5 show a lysing mill 10 in accordance with the present invention and having a tank 12 in which the process of particulate comminution occurs. The lysing mill 10 inclues a motor 14 for driving the mill works within the lysing tank 12 via a transmission 16. The transmission can be any conventional power transmitting device such as a belt and pulleys, chain and sprockets, gears, etc. Typically, the lysing mill 10 will include a

stand 18 for holding the mill components at a suitable height. Because the tysing mill 10 is driven at very high speeds, it is important to provide an uncontaminated supply of oil to the bearings. A lubrication system is therefore provided and preferably includes an oil filter 20. Tank 12 is preferably provided with a cooling jacket 22 to remove heat generated through operation of the mill. The! ysing mitt 10 of the present invention may be used as an in-line mill due to its high processing capacity and the efficiency/thoroughness of its two-stage processing as described below. The in-line functionality of the mill 10 is indicated by inlet 24 and outlet 26 on the lysing tank 12.

FIG. 6 illustrates a two-stage mill assembly 28 within tank 12.

The bottom portion of the mill assembly 28 is inserted through an opening in the bottom of the tank 12 such that a shaft 30 thereof may be coupled to a suitable means for turning the mill, such as a pulley and belt, direct drive or other known mechanical transmission means for connecting a motor to a driven shaft. Shaft housing 32 accommodates roller or ball bearings and seals for supporting the shaft 30 securely and in a manner allowing the shaft to be rotated at very high speeds. The shaft housing 32 is bolted and sealed to the bottom of the tank 12 and receives a support spider 34 having a plurality of spaced arms that extend upwardly and receive at the upper ends thereof a bottom divider plate 36. The bottom divider plate 36 creates a lower chamber L within the tank 12 that receives the fluid inflow from inlet 24. The

bottom divider plate 36 has an orifice therein for receiving an orifice/wear plate 38 which is essentially a flanged disk that rests upon a portion of the spider support arms coaxially with the bottom divider plate 36. The orifice/wear plate 38 has an axial bore 40 which, in cooperation with spacer 42, defines a fluid inlet to the first stage rotor 44. The rotor 44 is keyed to the shaft 30 and rotates conjointly therewith. The fluid entering the lower chamber of the tank 12 passes between the arms of the spider support 34 and its flow is restricted by bore 40 in the orifice/wear plate 38 before it enters the rotor 44. A first stage stator 46 is coaxially associated with the rotor 44 such that fluid propelled from the rotor 44 by centrifugal force passes through the stator 46 into an intermediate chamber I above the bottom divider plate 36. An intermediate spacer 48 spaces the first stage rotor 44 from the second stage rotor 50 which, like the first stage rotor 44, is keyed to the shaft 30 and turns in unison with the shaft and the first stage rotor. A top divider plate 52 completes the intermediate chamber and further divides the tank 12 into three separate chambers, the upper-most, T, being vented by outlet 26. The top divider plate 52 is mounted on a flow cage 54 that permits fluid to flow from the intermediate chamber through the flow cage and the top divider plate 52 into the second stage rotor 50. The top divider plate 52 supports the second stage stator 56 through which fluid is forced via the centrifugal action of the second stage rotor 50. As is evident from a comparison of the bottom divider plate 36 and the top divider plate 52 shown in FIG. 6, the orifice wear plate 38

is optional and can be omitted in lieu of a divider plate having a selected orifice. An independent orifice/wear plate 38 is desirable however, in that the plate can be replaced to reestablish tolerances after wear occurs, namely between the rotors 44,50 and a corresponding orifice/wear plate 38. It should be appreciated that the orifice 40,41 defined by an orifice/wear plate 38 or by a divider plate 36,52 has an important effect on the operation of the lysing mill 10. More specifically, the orifice determines the rate of flow therethrough and the pressure differential between the inlet and outlet sides of each rotor. It should further be appreciated that each stage of the mill preferably has an optimized orifice 40 feeding the respective stage in the mill.

This promotes efficiency in that each stage has its own optimal pressure differential across the respective rotors for producing maximum cavitation.

A cap plate 58 completes the two stage mill assembly 28 via bolts that are received within the spider support 34. A rotor spacer 60 permits a bolt threaded into the end of the shaft 30 to clamp the rotor assemblies onto the shaft 30 in their proper positions. The divider plates 36 and 52 are sealed against the walls of the tank 12 via seal rings 62 that bolt to the divider plates 36,52 and urge cooperating, resilient o-rings 64 into sealing engagement with the walls of the tank 12.

FIGS. 7 and 8 illustrate the rotor 44 of the present invention in greater detail. A central depressed area 66 functions as an inlet area for fluid when the rotor is sealed against a wear plate 38 or one of the divider plates

36,52. FIG. 7 illustrates a unique feature of the present invention, namely, tapered rotor slots 68 which are designed to enhance the cavitation effect within the lysis mill by increasing the pressure differential across the rotor/stator gap. As can be appreciated from FIG. 7, the rotor slots are comprised of a first slot wall in the range of approximately 23° from the radial position and a second wall approximately 34° from the radial. Cavitation enhancement is due to an increased fluid pressure at the tip of the tapered rotor slot relative to a straight rotor slot. Namely, when a given volume of fluid is passed through the rotor slot, as the rotor slot, converges, the pressure increases. The sudden release of fluid pressure at the end of the rotor slot as the fluid enters the chamfered stator slots results in an increase in the frequency of vapor cavity formation or cavitation, as well as the violent collapse of vapor cavities at the stator slot. The effects of vapor cavity formation are further enhanced by varying the diameter of the orificelwear plate 38 in accordance with the cavitation index number desired. Namely, by lowering the suction head at the inside throat of the rotor slot, the frequency of vapor cavity formation will be increased. It has been determined that a suction head of approximately 3.5 to 7.5 pounds per square inch absolute pressure is preferable for obtaining maximum cavitation effects.

Robust cavitation can be induced more easily for liquid suspensions with varying concentrations of solids and/or low viscosities by increasing the differential area between the inside rotor slot opening and the

opening at the outside rotor slot opening. That is, for liquid suspensions with solids concentrations of 1% (10,000 mg/L) to 4% (40,000 mg/L) a ratio of 2: 1 between the area of the inside slot opening to the outside or tip is desired.

Where the concentration of solids in liquid suspensions are greater than 4% (40,000 mg/L), a ratio of 1: 1 between the area of the inside slot opening to the outside or tip is desired. When the concentration of solids in liquid suspensions are 0.5% (5,000 mg/L) to 1% (10,000 mg/L), a ratio of 4: 1 between the area of the inside slot opening to the outside or tip is desired.

When the concentration of solids in liquid suspensions are 0.01% (100 mg/L) to 0.5% (5,000 mg/L), a ratio of 8: 1 between the area of the inside slot opening to the outside or tip is desired.

FIGS. 9,10 and 11 show the configuration of the stators used in the lysing mill 10 of the present invention. More particularly, the stators utilize chamfered statored slots 70 as proposed in U. S. Patent No. 5, 522,553, a patent which has been assigned to the Assignee herein and which is incorporated herein by reference, for its teachings relative to the formation of rotors, stators and dispersion mills in general.

FIGS. 12 and 13 show in more detail the orifice/wear plate 38 of the present invention.

FIGS. 14 and 15 show the use of the present invention lysing mill within a wastewater treatment facility. The present invention can be employed in a conventional activated sludge treatment plant having one or

more processing trains. In FIG. 14, the wastewater treatment facility includes a primary clarifier 74, aeration basin 76 and a secondary clarifier 78.

Although, the diagram shows a primary clarifier/settling tank as part of the treatment process, it is not an operational requirement of the present invention. As can be appreciated from FIG. 14, the lysing mill 10 of the present invention may be installed in the waste activated sludge line leading from the secondary clarifier 78. The present invention withdraws some or all of a selected portion of the waste activated sludge, processes it and outputs the processed/lysed material to the aeration basin 76 thereby reintroducing the processed/lysed waste activated sludge as an additional food source for the microorganisms residing in the aeration system. Through microbial respiration, this processed/lysed sludge is converted to carbon dioxide, water and new cells. The introduction of the disintegrated waste activated sludge is not sufficient alone to eliminate the production of excess biosolids due to the composite metabolism of all the microorganisms residing in the wastewater treatment system. However, through the continuous operation of the present invention, conditions are generated whereby only a certain subset of species of microorganisms can exist and thrive. These species exist in an endogenous phase of respiration artificially created by the present invention, where the growth of cells does not cease, but where biological respiration is exceeded by the combination of natural cellular degradation and the cellular disruption generated by the present invention.

In the present invention, the intense localized pressure and temperature generated by the repeated collapse of vapor cavities at the stator from cavitation oxidizes a portion of the solubilized cytoplasm and disintegrated particulate to form carbon dioxide (C02), sulfur dioxide (SO2), and nitrate (NO3) compounds. The portion of carbonaceous material so oxidized no longer represents a demand on the aeration system of an activated sludge wastewater treatment plant in that such oxidized compounds are not readily utilized by microbes as nutrients. Yet another beneficial aspect of the present invention resides in its capacity to eliminate odiferous compounds from the processed waste stream. More specifically, hydrogen sulfide, a common, foul smelling compound present in sewage is converted to a non-odiferous bisulfate by exposure to a wastewater treatment train configured in accordance with the present invention.

A variable flow control valve 82 is desirable for regulating the inlet fluid pressure/volume to the lysing mill. The valve 82 permits adjustments to be made to achieve maximum cavitation effects by adjusting the differential input/output pressures. It should also be appreciated that the duty cycle of the lysing mill should be adjusted to meet the loading of the wastewater treatment facility. For example, in periods of peak usage of a regional sewage system, the duty cycle can be increased to meet the demand of the loading of the wastewater treatment facility.

While the present invention has been described as relating to an apparatus and method for lysing biological sludges, biological floc and mixed liquor, and dewatering sludge, it can also be used to rupture microbial cells (lysis) to separate the cellular membrane from the cytoplasm in the production of cell-free extracts, serum and nutriments from fermentations, cell cultures and tissue. Further, the present invention can also be used for disintegrating solid particles in the production of liposomes and submicron dispersions for injectable pharmaceuticals or other pharmacological, medicinal and therapeutic substances.