Apparatus for the fermentation of organic materials

Abstract: A compartmentalized horizontally mounted rotatable cylindrical digester drum is provided with inter-compartment transfer buckets each having an inlet opening substantially congruent to a segment of the circular partition separating one compartment from the next. In addition one or more annular flanges are located in each treatment compartment extending radially inwardly from the cylindrical wall of the drum. The transfer buckets may be rectangular prismatic in contour with a bottom wall within the confines of the drum coincident with the chordal boundary of the segment and an upper wall spaced radially outwardly of the cylindrical wall of the drum.

Description: The present invention relates to apparatus for making organic fertilizer, sometimes referred to as compost, or other fermentation products from organic waste materials such as municipal garbage, sewage sludge, animal manure, canning factory wastes and the like. In prior US Patent Nos, 3,138,447 and 3,245,759, a method and apparatus for such manufacture have been described which are designed to produce an efficient and thorough aerobic decomposition of such organic waste materials by maintaining, within the apparatus in which the method is carried out, conditions suitable for optimum propagation of the different types of aerobic bacteria on which such decomposition depends. As described in said patents, the apparatus comprises a digester in the form of a cylindrical drum mounted for rotation on an axis which is slightly declined towards the discharge end relative to the horizontal. The interior of the digester is divided into a series of compartments or chambers by a plurality of transverse partitions spaced along the axis of rotation. Each partition is provided with transfer buckets which are selectably opened and which, when opened, transfer material from compartment to compartment from the higher to the lower end of the drum, the raw waste organic material being fed into the digester at the higher end and the finished product being withdrawn at the lower end. As used in the said patents the term "buckets" describes a small enclosure or chamber with inlet and outlet openings. The requisite inoculation of the charge in each compartment is effected by retaining a portion of the treated material in each compartment to mix with the material received from the adjacent upstream compartment. In said prior apparatus, the inoculation material is retained in each compartment by locating the openings in the partitions, which openings communicate with the transfer buckets, displaced a short distance from the periphery of the partition. Such openings are also relatively small compared to the size of the partitions. As explained in said patents, the method relies upon staging the fermentation process by maintaining optimum but different temperatures in each of the compartments for efficient promotion of the microbial activity. For this purpose air is forced through the entire digester from the discharge or lower end of the drum to the input or higher end, and spent air may be selectably and controllably vented from each compartment to maintain the climate therein that is optimum for the micro-organisms predominant in the stage associated with such compartment. Efficiency of such method and apparatus depends upon being able to effect rapid transfer of material between compartments causing minimum albeit inevitable interruption of the biological activity. Further important parameters are the speed with which a charge entering a compartment can be mixed with the inoculant retained in such compartment, as well as the capability of retaining at least the necessary minimum and, preferably, an optimum quantity of inoculant. While the apparatus described in said patents is suitable for carrying out said method, it has been discovered that the efficiency can be increased by increasing the speed with which inter-compartment transfer can be accomplished and, at the same time, modifying the means for automatically retaining the inoculant material in each compartment, whereby more immediate and thus more efficient mixing between the inoculant and incoming charge is effected. Accordingly, in its broadest sense, the present invention provides an apparatus for the fermentation of natural organic material by treatment with successive groups of aerobic microorganisms comprising: a digester drum mounted for rotation about its longitudinal axis and divided by at least one partition into a series of treatment compartments for successive groups of microorganisms; a transfer bucket associated with each partition, each transfer bucket having an inlet defined by side wall portions of the digester drum and by the partition for receiving material from a compartment and a discharge opening for transferring material between compartments; the apparatus characterised in that each transfer bucket further comprises a valve associated with the discharge opening for selectively operating the transfer bucket to permit the transfer of material between compartments and a link movably and permanently connected to the valve for opening and closing the valve and which link projects externally through the side wall of the drum to serve as an external visual indication of the position of the valve, and each compartment has means disposed therein for retaining an effective quantity of material as inoculant. Furthermore, in accordance with one aspect of the present invention there is provided an apparatus comprising a digester drum mounted for rotation about its longitudinal axis, one or more circular partitions positioned within said drum to divide the drum into a series of treatment compartments, an entry at one end of said drum for enabling said material to be introduced into the digester, a discharge port at the other end of said drum for permitting discharge of treated material, said axis of the drum being inclined from the horizontal with said entry elevated with respect to said discharge port, selectively operable transfer buckets adjacent each of said partitions to move material from a higher to a lower compartment, and means for forcing air into said digester and to cause said air to move through said drum from the lower to the higher end thereof, further characterized in that said transfer buckets are located on the downstream side of each partition in constant communication with the compartment on the upstream side of the respective partition through an inlet opening substantially congruent to a segment of the partition. The invention will be better understood after reading the following detailed description of the presently preferred embodiments thereof with reference to the appended drawings in which: Fig. 1 is a longitudinal vertical sectional view of an intermediate portion of a digester drum constructed in accordance with the present invention; Fig. 2 is a transverse sectional view taken along line 2-2 in Fig. 1 showing the access ports or openings in a partition for the transfer buckets or chambers; Fig. 3 is a transverse sectional view taken along line 3-3 in Fig. 1 showing the opposite side of the partition; Fig. 4 is a view similar to Fig. 1 but showing a modification thereof; Fig. 5 is a transverse sectional view taken along line 5-5 in Fig. 4 showing a partition from the side with the openings leading to the transfer buckets or chambers; and Fig. 6 is a transverse sectional view taken along line 6-6 in Fig. 4 showing the transfer buckets or chambers from the opposite side of the partition. The same reference numerals are used throughout the drawings to designate the same or similar parts. Referring to Figs. 1, 2 and 3 of the drawings, there is shown an intermediate portion of a digester comprising a drum 10 mounted in known manner (not shown) on bearing blocks for rotation about an axis 11 which is slightly inclined from the horizontal to allow gravity feed of the material through the length of the drum from the higher elevation to the lower elevation end. Details for mounting and rotating the drum as well as for supplying forced air thereto and both introducing and removing material therefrom can best be seen from the above-identified patents. As shown in the present drawings, the drum 10 is subdivided into compartments by circular partitions such as the partitions 12 and 13. While two partitions and the concomitant three compartments, 14, 15 and 45, are shown in the drawings, it is to be understood that the drum 10 is subdivided into as many compartments as are required to carry out the desired fermentation process. In the prior patents the drum is divided into four treatment compartments wherein a quantity of inoculant material is retained for propagating the fermentation process therein. However, two or more compartments are contemplated depending upon the particular processing parameters. Selectively operable transfer buckets or chambers 16 and 17 are provided adjacent each of the partitions such as 12 and 13 to move material from the higher elevation to a lower elevation compartment. As shown in the drawing, the transfer buckets are located on the downstream side of each partition in constant communication with the compartment on the upstream side of the respective partition through the inlet openings 18 and 19, respectively, which openings are bounded on one side by a chord of the circle that marks the perimeter of the respective partition and on the other side by the wall of the digester drum thus being congruent to a geometric segment of the circular partition. In the preferred embodiment, the transfer buckets and openings are enlarged to effect a more rapid flow rate of organic material through the apparatus, to ensure complete filling of the buckets with each rotation, and to permit entry of large pieces of sewage into the apparatus. Each transfer bucket is provided with a valve controlled discharge opening 20 controlled by the gravity operable valve 21. As best seen in Fig. 3, a link 22 is connected at one end 23 to the valve 21 while the other end of the link 22 projects at end 24 through the wall of drum 10. End 24 is operatively connected to discharge opening 20 through link 22 for selectively transferring material between compartments, as shown in Fig. 1. The link 22 may be provided with suitable apertures through which can be inserted a pin, bolt or other latch member 25 to selectively engage and hold the valve 21 in closed position as illustrated with respect to bucket 17 or in open position as illustrated with respect to bucket 16. When the latch pin 25 is removed to free the link 22, the valve 21 will be free to operate under the forces of gravity as the drum rotates. Each compartment in the drum is provided with flow inhibiting means in the form of an annular flange 26 for retaining in the compartment an effective quantity of material for inoculating material entering the compartment. The flange 26 extends radially inwardly from the cylindrical wall of the drum 10 and, preferably, has a height related to the diameter of the drum falling within the range of about 9% to 23%. In a drum having a diameter of about 3.35 m (11 feet), where the partitions are spaced about 11 m (36 feet) apart, a single retainer ring or annulus 26 having a height of about 46 cm (18 inches) and located about midway between the partitions or end walls defining the compartment, will retain a quantity of material in the compartment equal to about 5% of the quantity of incoming material that is to be inoculated. This is for a digester inclined at the rate of 0.3 m (1 foot) in 9 m (30 feet) from the horizontal. In order to assure about 10% of retained inoculant, a central ring (flange) in a compartment of the aforesaid dimensions should have a height of about 76 cm (30 inches). Alternatively, two rings (flanges) about 41 cm (16 inches) high with one located about midway between the partitions defining the compartment and a second one located about midway between the first flange and that one of the partitions that is upstream from the first flange will provide the same 10% rate of inoculation. It should be apparent that by making openings 18 and 19 congruent with geometrical segments of the circular partition, rapid filling of the transfer buckets can take place as the drum rotates. The links 22 movably and permanently connected to the valves 21 serve a number of functions. Because the end 24 is exposed outside of the drum, the link acts as an indicator regarding proper closing and opening of the respective valve member 21. Indication can be furnished by direct observation or indirectly by suitable telemetry apparatus under the control of the link. If the valve should be stuck or clogged for any reason the link 22 can be manipulated from the outside of the digester with reasonable likelihood that it will serve to free the valve. If for some reason this does not occur, access to the valve area can be had through a port such as that shown at 27. Further improvement can be obtained by resorting to the modification shown in Figs. 4, 5 and 6 to which attention should now be directed. As seen therein the transfer buckets (chambers) 30 and 31 are constructed as separate right rectangular prismatic containers having a bottom wall 32 within the confines of the drum 10, the interior surface of wall 32 defining a plane coincident with the chordal boundary 33 of the geometrical segment 34 of truncated circular partition 35. The upper wall 36 of each of the transfer buckets 30 and 31 is spaced radially outwardly of the cylindrical wall of the drum 10. In all other respects the construction of the digester shown in Figs. 4, 5 and 6 may be the same as that previously described with reference to Figs. 1, 2 and 3. It should be understood that the buckets 30 and 31 can be fabricated as separate components and inserted each through an opening in the cylindrical wall of the drum 10 where it is fastened in any suitable manner to the supporting partition such as 35 and/or to the cylindrical shell of the drum. This mode of construction, obviously, permits replacement and ready repair of the transfer bucket structure if any part of it should fail during the life of the digester. One of the advantages of the construction shown in Figs. 4, 5 and 6 is that when the bucket is at the low point with respect to the drum 10 the material in the associated drum compartment is acted upon by gravity and can fall into the radially outwardly (at this point downwardly) projecting portion of the bucket (chamber) rather than merely sliding into it as will occur with the embodiment of Figs. 1 to 3. It should be apparent that the enlarged bucket construction of Figs. 4 to 6 will effect more rapid transport of material from compartment to compartment than the buckets shown in Figs. 1 to 3. Of course, the buckets shown in any of the Figs. of the present application are capable of more rapid material transport than the buckets described in the aforesaid patents. In conclusion, it should be readily understood that by altering the dimensions of the annular flanges 26 and their location within the particular compartment of the digester, ready control can be obtained with regard to the quantity of inoculant that is held back to be mixed with the incoming charge. The effectiveness of the flanges 26 is independent of operator control and insures that a minimum quantity of inoculant is always retained to insure efficient microbial activity. Having described the present preferred embodiments of the invention with reference to the appended drawings, it should be understood by those skilled in the art that various changes in construction can be introduced without departing from the scope of the invention.

Claims: Apparatus for the fermentation of natural organic material by treatment with successive groups of aerobic microorganisms comprising: a digester drum (10) mounted for rotation about its longitudinal axis and divided by at least one partition (12,13,35) into a series of treatment compartments (14,15,45) for retention of successive groups of microorganisms; a transfer bucket (16,17,30,31) associated with each partition (12,13,35), each transfer bucket having an inlet (18,19,34) defined by side wall portions of the digester drum (10) and by the partition (12,13,35) for receiving material from a compartment and a discharge opening (20) for transferring material between compartments (14,15,45); the apparatus characterised in that each transfer bucket (16,17,30,31) further comprises a valve (21) associated with the discharge opening (20) for selectively operating the transfer bucket to permit the transfer of material between compartments (14,15,45) and a link (22) movably and permanently connected to the valve (21) for opening and closing the valve (21) and which link (22) projects externally through the side wall of the drum (10) to serve as an external visual indication of the position of the valve (21), and each compartment (14,15,45) has means (26) disposed therein for retaining an effective quantity of material as inoculant. Apparatus according to claim 1, further comprising a latch member (25) for selectively engaging each link (22) to hold the valve (21) in a closed position. Apparatus according to claim 1 or claim 2, characterised in that the inoculant retaining means (26) comprises at least one annular flange extending radially inwardly from the side wall of the drum (10). Apparatus according to claim 3, characterised in that the flange has a height of 9% to 23% of the diameter of the drum (10). Apparatus according to claim 4, characterised in that the drum (10) has a diameter of about 3.35 metres (11 feet) and the flange has a height of 46 to 76 cm (18 to 30 inches), the flange being positioned approximately midway between the partitions defining the respective compartment. Apparatus according to claim 3, characterised in that the inoculant retaining means (26) comprises a plurality of annular flanges extending radially inwardly from the side wall of the drum (10). Apparatus according to claim 6, characterised in that a first flange is positioned approximately midway between the partitions defining the respective compartment, and a second flange is positioned approximately midway between the first flange and the partition that is upstream from the first flange. Apparatus according to claim 7, characterised in that each flange is about 41 cm (16 inches) in height. Apparatus according to any preceding claim, characterised in that each transfer bucket (30,31) has walls located outwardly from the side wall of the drum (10). Apparatus according to claim 9, characterised in that each transfer bucket (30,31) is constructed as separate rectangular prismatic container which in use is inserted through an opening in the side wall of the drum (10). Apparatus according to any preceding claim, further comprising a valve communicating with each compartment (14,15,45) to exhaust a selectable portion of air in each compartment to the atmosphere.

Inventors: EWESON ERIC C O BEDMINSTER BIO, EWESON, ERIC, C/O BEDMINSTER BIOCONVERSION CORP.
Applicants: BEDMINSTER BIOCONVERSION CORP, BEDMINSTER BIOCONVERSION CORPORATION
Application year: 1990
Main classification: C05F17
IPC codes: C05F17