WO1997001519A1

WO1997001519A1 - Window curing and odor control system

Info

Publication number: WO1997001519A1
Application number: PCT/US1996/010752
Authority: WO
Inventors: Bioconversion Corporation Bedminster; Larry James Finn
Original assignee: Bedminster Bioconversion Corp
Priority date: 1995-06-29
Filing date: 1996-06-24
Publication date: 1997-01-16
Also published as: EP0778818A1; AU6338596A

Abstract

A window system for curing and deodorizing compost in which compost is deposited on an air floor (28) underlaid by a plenum (30) operationally divided into first and second treatment zones (Zones #1 and #2) by a blower (32) with baffle (33) disposed within the plenum (30) such that air is drawn through compost overlying the first zone and dispersed through compost overlying the second zone and a partition (33) forming a third zone within the plenum through which outside air is passed upwardly through compost overlying the third zone (Zone 3) whereby compost progressing along the windrow (26) by automatic turning means (36) is transformed from a raw state as it enters the windrow at zone one to a cured and deodorized state as it exits the windrow at zone three.

Description

WINDROW CURING AND ODOR CONTROL SYSTEM

This invention is directed to the curing and odor control phases of the composting process. More particularly, the invention comprises apparatus and a method of operation which enables the two functions of curing and odor control to be carried out by a unique windrow assembly.

BACKGROUND OF THE INVENTION Prior art systems for composting solid waste and sewage sludge typically employ one or more multi-stage digesters in which material being treated undergoes staged microbial decomposition. The conventional digester is divided into two or more compartments or stages and during material processing is rotated while air is circulated through the digester at controlled rates at predetermined conditions in a flow direction counter to the material flow. The climate in each stage is maintained to achieve the optimum development of the type and species of microorganism predominant in that stage. Spent air is vented from the digester as needed to maintain optimum climatic conditions in each of the operating stages. Temperatures are kept between 40°C and 55°C to ensure the maximum rate of composting consistent with maintenance of the microbial population. Typical of such prior art systems and methodology of operation are those set out and described in U.S. Patents 3,245,759 and 3,138,447 assigned to the assignee of the present invention, the teachings of which are hereby incorporated by reference. The method and apparatus for manufacture of compost described in those patents are designed to produce aerobic decomposition of 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. 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 horizonal. The interior of the digester is divided into a series of compartments or chambers by a plurality of traverse partitions spaced along the axis of rotation. Each partition is provided with transfer . buckets which are selectively opened and which when opened transfer material from compartment to compartment from the higher to the lower end of the drum, the waste material being fed into the digester at the higher end and partially cured or raw compost being withdrawn at the lower end. The output of the digester must undergo final curing and deodorizing before it is suitable for use in commercial applications. It is to this phase of the composting process that the present invention is directed.

SUMMARY OF THE INVENTION The compost curing and odor control system comprising the present invention utilizes windrows to provide a unique duality of function, to provide both curing of the compost and deodorizing of compost emissions. The system comprises a series of elongated compost piles or windrows. Each pile overlays a floor adapted for passage of air therethrough. The floor overlies a trough or plenum. The plenum and windrow are operationally divided into a number of treatment zones. In the example to be described and illustrated there are three such zones. The compost forming the windrow is turned and moved along the windrow periodically. Raw compost enters the system at the first treatment zone and is systematically moved through the several treatment zones by manually operated or automatic turning machines. Cured and deodorized compost is discharged from the third treatment zone. A blower is disposed within or adjacent to the plenum which forms the first and second treatment zones. In operation, the blower draws air through compost overlying the first treatment zone and disperses it through compost overlying the second treatment zone. A third section of the plenum is isolated from the other sections by a physical or backflow preventor barrier to form the third treatment zone. Air is drawn from the outside atmosphere and blown through compost overlying the third treatment zone. By proper adjustment of the rate of movement of compost through the various zones and the rate of air movement, the amount of oxygen and temperature within the several zones can be controlled to achieve curing and deodorizing of the compost. BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other aspects of the invention will be more fully understood by reference to the following drawings.

For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

Referring now more particularly to the drawings;

Fig. 1 is an overview of a composting facility showing the overall composting system and compost curing area to which the present invention has specific application;

Fig. 2 is a perspective showing details of one bay of the compost curing and odor control system comprising the present invention; Fig. 3 is a cross-sectional detail of the system shown in Fig. 2 including one type of turning apparatus;

Figs. 4 "A" and 4 "B" are sectional showings of alternate floor plank designs;

Figs. 5 and 6 are sectional details of the blower system forming the first and second treatment zones; and

Fig. 7 illustrates a computer controlled, retractable thermo-couple means for monitoring the compost pile temperature. DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT

Rapid rate aerobic composting is dependent on a number of factors. The most important are the ready supply of oxygenated air, optimization of temperature, optimization of compost moisture, and maximization of surface area through particulation of the partially cured compost. In order to achieve the above factors the compost must be aerated, agitated and moisturized on a regular basis.

By way of example, the invention will be described in connection with the windrow curing of raw compost previously processed through rotary digesters and passed through a 1 " trommel screen. It will be understood, however, that the principles of operation described have application to the curing and odor control of biodegradable material from whatever source derived.

Referring now to the drawings and more particularly to Fig. 1 thereof, there is shown a composting facility comprised of three major areas; the tipping area 10 a processing area 12 and an aeration or curing area 14. Solid waste is dumped and sorted in the tipping area 10. Unacceptable waste, such as white goods, car batteries, tires, large pieces of wood, etc., is rejected and sent to a land fill. Acceptable waste is then fed into digesters 16. Sewage sludge delivered to the plant is stored in a liquid sludge tank from where it is pumped by liquid sludge pumps directly into the digester 16 as needed to maintain the proper carbon/nitrogen ratio essential to efficient composting. Material is discharged from the digester after approximately 3 days of residence time. Upon removal from the digester, the material, now partially cured or raw compost plus non degradables, is transported by belt conveyors 18 and 20 to a 1 " trommel screen 22 where is it rough screened into two fractions. One is residue, which fails to pass through the screen. This residue is discharged back onto the tipping floor from where it is transported to a landfill for disposal. The second fraction is rough, or partially cured compost which has passed through the 1 W screen. The raw compost is transported to the curing area 14 by a tripping conveyor 24 or front-end loader. As previously noted, it is the curing area to which the present invention has specific application.

As seen in Fig. 1, the curing area 14 is comprised of a series of elongated windrows or bays 26 located outdoors. Each ,bay is approximately 400" in length and 8' wide. The bays may be of varying length depending on the specific application. As viewed in Fig. 1 the raw compost is fed into the bay at the right end and cured and deodorized compost discharged at the opposite end. Underlying each bay on which the compost is piled, as seen in Figs 2 and 3, is an aeration floor 28. Constructional details of one form of air floor construction are shown in Fig 4 "A". An alternate form of air floor is shown in Fig. 4 "B". The air floor overlies a plenum 30. The plenum and overlying windrow are operationally divided into a number of treatment zones. In the embodiment illustrated, the plenum and windrow are operationally divided into three such zones. Depending on the particular application, the process to be described can be repeated, extended, or the number of treatment zones increased or reduced to produce the desired result. As seen in Fig. 3 each zone is approximately 1/3 the total length of the bay. Located between zones one and two is a blower 32 which acts to draw ambient air through compost overlying the first treatment zone through the aeration floor into the plenum and to disperse the somewhat malodorous air upward through compost overlying the second treatment zone. By this procedure the compost is fully aerated accelerating the curing process while concomitantly deodorizing gasses emanating from the early stages of the composting process which are redirected through the more mature compost in the second treatment zone. The compost in zone two thus acts in the dual capacity of a curing medium and as a biofilter. To complete the process, a physical barrier 33 is placed in the plenum to form a third treatment zone. This section of the plenum as shown is physically isolated from the remainder of the plenum. A fresh air fan 34 blows ambient air into this section of the plenum forcing clean ambient air through the aeration floor up through compost overlying the third treatment zone. This step completes the final curing stage. Compost forming the windrow is periodically turned and moved along the windrow by a turning machine 36 (Fig. 3) at a rate to facilitate curing and deodorizing of the compost. During traverse of a bay by turning machine 36 the compost is moved between 10 to 15 feet toward the discharge end. At the end of each traverse the turning machine is returned to its starting position to repeat the next cycle of operation. This procedure can be accomplished manually or automatically. The length of each channel is determined by the specific characteristics of a particular application.

After each traverse of the length of the windrow by the turner, the compost is moved a distance sufficient to accommodate a fresh load of raw compost added at the feed end. The rawest compost is at the feed end and the most mature or fully treated compost is at the discharge end. Compost which has traversed the full length of the bay is fully cured and ready for final screening. The floor 38 on which the compost is deposited is of sufficient strength to support a diesel compost turner of the type illustrated. Compost turners are well known in the trade and are per se not a feature of the present invention. The windrows as illustrated are formed to facilitate automatic turning by such machines. The construction of the aeration floor is as shown and described in co-pending application SN #08/379,896 assigned to the assignee of the subject invention the teachings of which are hereby incorporated by reference. Briefly stated, this unique floor is comprised of a series of structural concrete elements or planks 40 from eight to ten feet in length having the general cross-sectional configuration shown in Fig. 4. The planks are placed in abutting relation as seen in that Fig. This arrangement provides for a very thin point of contact between adjacent elements. To create a narrow slit 42 through which air can pass, a thin rotary saw blade or rake is passed along the point of contact. The slit is narrow enough to prevent most compost stacked on the floor from falling through the slits. Such an arrangement in combination with the plenum 30 provides uniform distribution of air through the overlying compost and is substantially clog free. The planks shown are made from pre-cast concrete reinforced with steel bars as reguired. A typical plank is 12" wide at the top and 8" thick. The plenum 30 underlying the floor is formed using a high density polyethylene liner 44. To optimize operation of the biological systems the plenums may be converted to oxidation ditches or ponds by partially filling the plenum with water which acts to collect leachate from the biofiltering and compost curing units. The plenum also serves as a retention device for water runoff from the overlying compost. The runoff may be used to irrigate the windrows to prevent dryout of the material. As previously noted the biological objectives of aeration during curing are to provide optimal temperature and oxygen content within the compost pile to meet the biological needs of the composting microorganisms. Temperature should not exceed 65° Celsius. The oxygen content as expressed as a percentage of oxygen among gases present in the atmosphere being tested should desirably be in excess of 15%.

A blower is selected having an output sufficient to meet these operational parameters. To insure adequate air flow the thickness of the compost pile should preferably be between six and eight feet. To permit longitudinal adjustment of blower 32 within and along the plenum 30 the fan is suspended on rail 48. The fan is powered by motor 50 and with its separation baffle moveable along rail 48 by an independent motor drive system 52. The drive motor is connected by a flexible power cord 54 to external control means. This arrangement permits balancing of the air flows through the first and second treatment zones.

A maximum temperature for compost curing is 65°C. A higher temperature inhibits the growth of mesophilic organisisms and lowers decomposition. To maintain optimum operating temperatures and oxygen concentrations above 15% the blower systems are connected to temperature monitoring devices 50 located in the compost pile and timing devices

(not shown) to modulate operation of the blowers. To determine the relationship between aeration cycles, pile sizes, pile composition and oxygen content the piles are tested for oxygen content and the aeration cycles adjusted to prevent oxygen depletion. Temperature is a critical biological factor. Accordingly, temperature probes 56 are located at points throughout the composting material deemed essential to maintaining proper control. One effective means for measuring temperature is to use thermo-couples inserted into the curing pile at strategic locations as diagrammatically illustrated in Fig 2. One technique for automatic monitoring of the compost pile temperature is illustrated in Figure 7. A computer controlled retractable thermocouple probe 58 is selectably inserted into the compost pile by means of solenoid 60 connected to computer 62 programmed to achieve optimum operation. Oxygen concentrations can be determined by use of oxygen probes 64 to insure that the oxygen content of the piles does not fall below 15%. Information on temperature and oxygen content can be used to adjust the aeration rate as needed. This information is fed to computer 62 for automatic control of blowers 32 and 34. In instances in which atmospheric air temperatures are layered, a condition known as thermal inversion occurs. To counteract this problem, the use of a wind machine 66 is employed as taught in the aforementioned application. The wind machine is capable of dispersing the filtered air at elevations as high as 700 feet, well above normal inversion levels, resulting in an environmentally acceptable operation under the most adverse conditions.

It will be understood that structural and dimensional modifications differing from those described and illustrated will be required to meet varying circumstances and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, accordingly, reference should be made to the appended claims rather than to the foregoing specification as indicating the scope of the invention.

Claims

I claim:

1. A compost curing and odor control system comprising a windrow of compost; an air floor on which said compost is piled; a plenum underlying and in communication with said floor; means for periodically turning and moving the compost along the windrow; means for drawing air through selected portions of the compost pile and for redirecting air upward through other selected portions of the compost pile whereby both to facilitate curing of the compost and deodorizing of gaseous emanations from the compost pile.

2. A system for curing compost and for deodorizing compost gases, comprising an elongated windrow of compost; an air floor on which said compost is piled; a plenum underlying and in pneumatic communication with said floor; air delivery means disposed in said plenum operationally forming first and second treatment zones for pulling air through compost overlying said first treatment zone and pushing air upwardly through compost overlying said second treatment zone; means forming a third treatment zone within the plenum isolated from said first and second treatment zones; blower means for delivering ambient air to said third treatment zone whereby air is passed upward through compost overlying said third treatment zone; means for periodically turning and moving compost along the windrow such that raw compost enters the windrow at zone one and exits at zone three in a cured and deodorized state.

3. A windrow system for curing compost and deodorizing compost emissions, comprising: an air floor; a windrow of compost disposed on said floor; a plenum underlying said floor in pneumatic communication therewith; a blower operationally dividing said plenum into first and second treatment zones whereby ambient air can be drawn through compost disposed in overlying relation to said first treatment zone and dispersed via said plenum and air floor upwardly through compost overlying said second treatment zone; means forming a third treatment zone within said plenum operationally separated from said first and second treatment zones; and blower means for delivering ambient air to said plenum for dispersion through compost overlying said third treatment zone; means for periodically turning and moving compost along the windrow such that raw compost enters the windrow at zone one and exits at zone three whereby said windrow serves both as a curing medium and as a biofilter for deodorizing compost emissions.

4. An outdoor windrow system for curing compost and deodorizing compost emissions, comprising: an air floor; a windrow of compost disposed on said floor; a plenum underlying and in communication with said floor; a blower operationally dividing said plenum into first and second treatment zones whereby operation thereof draws air through compost disposed in overlying relation to said first treatment zone and disperses that air via said plenum and air floor through compost overlying said second treatment zone; means forming a third treatment zone within the plenum separated from said other treatment zones; and blower means for delivering outside air to said third treatment zone for dispersion through compost disposed in overlying relation thereto; means for periodically turning and moving compost along the windrow such that raw compost enters the windrow at zone one and exits at zone three whereby said windrow serves both as a curing medium and as a biofilter for deodorizing compost emissions. The method of curing and deodorizing compost, which comprises: providing an air floor; depositing on said floor a windrow of compost; disposing beneath said floor a plenum in pneumatic communication with said floor; providing within the plenum a blower system for pulling ambient air through selected portions of the windrow and for pushing that air through other selected portions of the windrow overlying a second section of the plenum; providing means separating a third section of the plenum from said first and second section; providing a second air-delivery system for furnishing fresh ambient air to said third section of the plenum for passage through compost overlying said third section and periodically turning and moving compost through the treatment zones whereby cumulatively to effect curing of the compost and deodorizing of effluent gasses. 6. The method of curing and deodorizing compost, which comprises; providing an elongated air floor; depositing on said floor a windrow of compost; disposing beneath said floor a plenum in pneumatic communication with said floor; dividing said plenum into first, second, and third treatment zones; providing within the plenum a first air delivery system for pulling ambient air through portions of the windrow overlying said first treatment zone and for pushing air through other portions of the windrow overlying said second treatment zone; providing means forming a third section of the plenum separated from said second section; providing a second air-delivery system for furnishing fresh ambient air to said third section of the plenum to effect passage of air through the windrow overlying said third treatment zone; periodically turning and moving compost along said windrow whereby the process cumulatively effects curing of the compost and deodorizing of effluent gasses.