CA1076720A

CA1076720A - Method and apparatus for composting refuse/sewage sludge mixtures

Info

Publication number: CA1076720A
Application number: CA260,565A
Authority: CA
Inventors: Hannes Willisch
Original assignee: Individual
Current assignee: Individual
Priority date: 1975-10-21
Filing date: 1976-09-03
Publication date: 1980-04-29
Also published as: NL7609986A; AU506654B2; ES451811A1; CH624083A5; AU1785476A; LU75731A1; ATA659276A; US4146382A; GB1561902A; SE415250B; FR2328680A1; JPS5252481A; FR2328680B1; SE7611643L; AT347977B; DK401076A

Abstract

A B S T R A C T

An improvement in the treatment and purification of waste materials or refuse/sewage sludge mixtures by composting and also by thermal retting, whereby the waste material is crushed and the non-compostable constituents are extracted by sifting of the reduced waste. The material, ready-treated for composting and of a predetermined particle size, is heaped layer upon layer to form a stack. In the interior of the stack, longitudinal tunnel-like hollow courses are provided at floor level, possibly with further channel-like passages above. Spaced vertical flue-like vents 5 are provided at various points and the hollow courses and channel-like passages are open at least at one extremity. The stacked material is left undisturbed until the compost has matured.

Description

~0767Z0 The present invention relates to a method of and apparatus for the treatment and purification of refuse, such as domestic refuse, industrial waste and the like, in particular of refuse-sewage sludge mixtures by the composting method, especially thermal retting.
Of the various ways of disposing of quantities of waste, that is to say of solid waste materials, such as domestic refuse, bulk waste, organic industrial by-products and industrial waste, also liquid waste, especially digested sludge from sewerage works, the composting process i8 to be preferred because in this way not inconsiderable quantities of the material can be recycled.
For the purpose of composting the waste material, or refuse/
sludge mixture, the procedure is that the domestic and industrial waste with sewage sludge is reduced by milling action in suitably balanced quantities. Portions of the reduced mixture which exceed a predetermined dimension are then extracted by sifting, the mate-rials concerned being glass, paper, plastic materials, rubber and metals. Small quantities of compostable materials in this dlameter range may be returned to the milling stage. The through-material is then conveyed to a second finer sieve which accepts particles ' of predetermined dimension, for example under 10 mm, or possibly 15 mm. Fractions larger than the predetermined dimens-on may again be returned to the milling stage, at which any iron is again extracted from the mass by magnets. When the through-material has reached the desired fineness, it is ready for composting. The - proportion of sewage sludge is so adjusted that a relatively moist 'J product is obtained which has a water content of approximately 45%
to 55%.

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- . :-~,.0767Zo The composting of waste material treated in the manner described still offers difficulty in obtaining complete and thorough purification by bedding the material. By the composting process an internal heat is generated in the material which may reach a temperature of approximately 75C, said heating being initiated by aerobic bacterial activity. The material is set up in clamps or stacks for composting. In this connection it has been found that the stacks cannot be built very high. Even with a height of approximately 1.30 m the so-called "black feet" occur, that is to say the material begins to rot because the air does not have sufficient access. Consequently, when waste material is stacked thu~, it requires to be frequently turned over in order to ensure that the interior of the stack is also brought sufficiently into contact with the outer air. Turning over of the stack thus in-volves additional labour, time and expense. The turning over opera-tion also has the disadvantage that the necessary heating of the material requires time on each occasion for the aerobic bacterial activity. Even with heights of 1.30 m to 1.50 m, a considerable surface area is required to cope with the daily accumulations of waste material. If the lesser heights o stack are employed, for dispersal of the treated material, the space requirement is so enormous that composting becomes uneconomical. Attempts have also been made to ventilate the material, ready tréated for composting, by artificial means, that is to say, by erecting fans which produce suction and pressure flows of air to aerate the stacks in order to prevent rotting of the waste material. Apart from the fact that ;'` .

- 2 -' the employment of blowers involves considerable additional costs and that these require to be constantly moved from area to area, it is never possible to produce odourless composting of the material and prevent the occurrence of rotting patches in the stacks. Arti-ficial ventilating cannot either be so contrived that the bacterial activity in the compost heap proceeds undisturbed. Another attempt to employ natural aeration of the compost heat consists in placing the compost material in cages which are placed at a certain height so that the surrounding air can reach the cage and consequentl~ also the material from all sides. This method of aeration is not satis-factory either since, beyond certain dimensions of cage, pockets of rot occur which ruin the entire compost heap. In addition, a great deal of mechanical handling is required in filling and emptying the cages, and also for turning over the material.
The object of the present invention is to arrange the ready-treated waste material in stacks in such a manner that there is con-tinuous feed and possibly also continuous output without the occur-rence of rotting or of pockets of decay, whereby the finished product is obtained by exposing the stack merely to the surrounding 20 air. The method of treating and purifying the waste material, or j~
refuse/sewage sludge mixtures, by means of thermal retting whereby the material is crushed and the non-compostable constituents are segregated by sif~ing of the crushed material, is according to the invention characterised in that the waste material which has been brought to a predetermined particle size for composting, is bedded out in stacks in such a manner ~hat, along the inside of the stack run longitudinal tunnel-like courses at floor level, with possibly longitudinal channel-like passages arranged above these and vertical flue-like vents disposed at intervals, the tunnel- and channel-like . . .
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' '' ~ '' ;'~ '', , 10767~0 passages remaining open at least at one end, whilst the waste material in the stack is left to itself until the compost has matured, that is to say until the finished product is obtained.
By employing stacks so constructed with longitudinal tunnel-like courses passing directly along the floor and with vertical flue-like vents, the stack becomes self-aerating, which results in complete and homogeneous retting and purification of the stack material. This honeycomb ventilation system within the stack pro-duces self-aeration at all points in the stack, whereby the very large quantities of air required for odour-free, aerobic fermenta-tion are drawn in and expelled continuously and at a low speed of flow, By means of the thermal updraught occasioned by the fermenta-tion itself, a continuous exchange of gases is made possible without the material being moved or the air being set in motion by fans.
The hollow courses and vents provided in the compost mass serve as circulatory channels and ensure excellent ventilation and also the required exchange of gases in the entire material in process of composting. The necessary generation of heat up to approximately 75C due to aerobic bacterial activity is produced and maintained by natural means. As this progresses,-the entire mass of compost becomes fungous in texture throughout. Since the compost body can left completely undisturbed, the bacterial activity continues unimpeded during the entire period of composting and thus becomes fully effective. After a suitable time, for example approximately three months, the stack material is completely retted through and can be removed for sale, or, if the time is not suited to the sale of compost, the product may be allowed to remain as long as is necessary in stack form without further manipulation, The matured , ' .
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107f~7~0 compost is growth-promoting, stable in moisture-retention and thoroughly mineralized. The self-aeration of the stacks occurring without unpleasant odours. The final product obtained is of con-sistent quality and has the biological phase fully completed, The longitudinal, tunnle-like courses should reach a height of approximately one half, or possibly two thirds of the height of the stacks. They should be spaced preferably at intervals of approximately 1 m to 1.5 m laterally within the stack. The remain-ing channel-like passages should preferably be offset in relation to the tunnel-like courses, so that the cross-section of the stack i8 seen to be provided with sufficient longitudinal ventilating passages.
The vertical flue-like vents should be dispersed longitudinally in the stack, preferably above the tunnel-like courses, with a fixed inter~al between.- The stack itself is preferably so constructed that it is flanked by relatively firm lateral walls. The fungous texture within the material, due to the bacterial activity, very quickly imparts to it an inner solidity. The large lateral surfaces contribute beneficially to the cross-ventilation.
According to a further feature of the invention, the horizon-tal and vertical passages in the stack are produced by means oftemplates. For the funnel-like courses templates of a certain length are employed whose lateral walls are perforated in the manner of a sieve. The template is constructed so that it is movable longitudi-nally and is adjustable vertically. This may be achieved by the use of rollers which have provision for height adjustment In par-ticular, the tunnel template should be of pointed-arch construction in cross-section. The width of the tunnel should be approximately one third to one quarter of its height By means of the movable _ 5 _ -10'~;72() tunnel template a stack honeycombed with tunnels i8 created which is able to accept the continuous stream of treated refuse/
sludge mixture at a steady rate and without interruption. In this way aerobic hacterial activity is generated without delay, resulting in creation of an entirely fungous structure in the com-post body. The warmth required for purification of the product may begin immediately. Thus, a stack is obtained which is self-supporting and has an internal freely-supported circulation system comprising tunnel-like courses, additional channel-like passages, and also vents. Thus, the inner channelled structure of the stack is self-supporting and maintains its structural form without assis-tance throughout the entire retting process. The tunnelled stack can also accept the continuously arriving stream of ready-treated -refuse/sludge mixture continuously and without interruption. This arrangement ensures that there are no bottlenecks at the treatment plant in the output of treated waste material, Since the tem-plates are continuously withdrawn from the stack as the composting mass increases after the stack is completed over a certain length the templates can be employed once more on the site for the con-structure of a new stack. A high degree of flexibility is obtainedin the course of the operation, The requirements in power and man-hours are very modest.
A further feature of the invention resides in the fact that the lateral walls of the tunnel termplate taper in longitudinal direction and to the rear. A slightly wedge-shaped formation of the tunnel template, with tapering to the rear, facilitates con-siderably the withdrawing of the template from the compost body, without the possible necessity of raising or lowering of the , . - ~ - - - : .
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'' ' 10'76720 template pa~tly or wholly during operation of the plant. On the other hand, the formation of the longitudinal tunnel-like courses is not in any way adversely affected or rendered more difficult.
Due to the relatively rapid and thorough fungous texture created by the bacterial activity, the stack material acquires a firm inner structure, so that, as the stream of continuously treated refuse/sludge mixture arrives, the tunnel template can be withdrawn relatively quickly from the stack as the material alongside and above the tunnel-like template becomes relatively quickly self-supporting. Since it is possi~le to dispense with the loweringmovement of the tunnel template to move it further forward, this represents a considerable economy in labour, apart from the fact that the template itself is easier to erect.
The tepering of the tunnel template from front to rear should amount on average to approximately 10%, In general, the tapering should be such that the resulting reduction in width of the tunnel template is greater than that occurring in the height. Thus, for example, the width of the tunnel template over its entire length may amount to approximately 30% whereas the ehgith of the tunnel template over its entire length may be reduced by only 2% to 5%.
In this way, the height of the tunnel-like courses in the stack is basically unaltered, which, in the forming of the stack in conjunc-tion with the further channel-like passages and flue-like ventila-tion shafts, is of advantage in the self-aeration of the stack.
Since the lateral walls of the tunnel template are tapered longitudi-nally towares the rear, the template is released relatively easily from the material heaped up around it. It is thus also possible to initiate the withdrawal of the tunnel template rather earlier .: , ' than was formerly the case.
A suitable arrangement is that the tunnel template is provided with a means of transportation which may have foupling devices for a plurality of tunnel templates arranged in spaced relationship side by side. The transporter may also be so constructed that it carrier further coupling means for the ventilation tubes provided about the tunnel templates. These tubes are extracted from the consolidated stack together with the tunnel template. The tunnel template may be sealed off at its rear end by a wall in which slides are preferably fitted for the purpose of regulating the incoming current of air.
Where stack has relatively steep lateral walls, a type of shuttering may be employed during construction which is in the form of a series of supports. As soon as the composting mass has become self-supporting, the shuttering can be removed. It can then be easily transferred. For this purpose, these supports can also be rendered mobile.
The invention will now be described in more detail with refer-ence to the accompanying drawings, in which:
Fig. 1 is a cross-section through a tunnel stack according to the invention, shown diagrammatically;
Fig, 2 shows part of the cross-section of Fig. 1, on a larger scale;
Fig. 3 is a longitudinal section through the tunnel stack of Fig. 1, on a larger scale and employing the templates for producing the hollow spaces in the compost body;
Fig. 4 is a plan view in diagrammatic form of the tunnel tem-plates with transporters;

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: '. ' `' ;:' Fig. 5 shows a method of execution of the lateral wall elements for the compost body;
Figs. 6 and 7 are diagrammatic views of a tapering tunnel tem-plate according to the invention, in plan and in longitudinal section.
The compost body comprising the ready-treated mixture of refuse and sludge assumes the form of a stack of any desired length, through which pass in longitudinal direction tunnel-like courses 2. Said courses 2 are preferably of pointed-arch cross-section and begin immediately from the ground 3 or floor of the site. Within the compost body of the stack 1 channels 4 are also provided which also extend along the entire length of the stack. The channels 4 should preferably be located above the tunnel courses 2 but are ~ffset in relation to these across their length. In addition there are pro-vided in the compost body of the stack 1 vertical flue-like vents 5 which assume the form of suitably constructed tubes having an open outlet at their upper extremity. The vents 5 may be located direc-tly on the axis of the tunnel courses and at a suitable distance therefrom. The vents 5 are arranged regularly or irregularly spaced in longitudinal and also in lateral direction throughout the stack 1. Such a tunnel system, with associated channels and vents serves to supply the interior of the compost body with sufficient quanti-ties of the outer air, whilst, at the same time, the longitudinal and vertical passages in the compost body ensure efficient self-aeration of the stack, with active exchange of gases from the com-post material. This self-aeration with low rate of flow re-liably stimulates aerobic bacterial activity which is evenly distributed throughout the compost, whereby very soon a certain heat is generated which may reach as high as 75C, as a result of which the entire compost body acquires _ g _ ..... .
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in a short time a fungous texture in the material. Since a compost stack with such a tunnel-, channel- and vent system can be left relatively unattended without the occurrence of patches of rot, excessive damp, "black feet" or the like, bacterial activity over the period of lying is completely undisturbed and i9 thus highly effective. After a suitable time, for example, approximately three months, the compost is fully retted through and purified. The material is now storable and may be used for appropriate purposes.
It is very suitable as soil-conditioner for agriculture and for the reclamation of land for agricultural purposes.
To form the tunnel-like courses 2, template elements 6 are used, the walls 7 and 8 of which carry perforations or are preferably of sieve-like construction. The templates 6 have preferably a cross-section of pointed-arch form and are mounted on rollers 9 so as to be movable. Moreover, the templates 6 can be raised or lowered relative to the rollers 9. This can be done by employing hydraulic raising means 9a in which the axles 10 of the rollers are adjustable in height relative to the walls 7 and 8 of the tunnel templates 6.
When the compost is being stacked, the tunnel template 6 is raised relative to the rollers 9. It is therefore in the high position. When it is required to withdraw the tunnel template from the compost stack, it is lowered. This produces a gap between the pointed arch shaped walls 7, 8 and the compost, so that the tunnel template can be pulled along without the compost material being drawn along with it. This gap may be approximately 5 cm. At the end of the tunnel template 6 is a rear wall 11 which closes off the template. Slides 12 may be provided on the wall 11 which can - .

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be adjusted in either direction in order to regulate the admission of air.
The long channel-like passages 4 are preferably formed from tubes 13 which extend over the length of the tunnel templates 6.
The circumferential surfaces of tubes 13 are not perforated suitably in order to ensure an easy withdrawal from the compost stack 1.
However, in suitable case,s, perforations can be also provided in the tubes 13.
The flue-like vents 5 are formed by the tubes 14 which are in-serted vertically into the compost stack 1. The tubes 14 can bewithdrawn from the compost stac~c as"soon as it has become self-suppor,ting. They may also remain in the compost stack until the final product clamp is removed.
With a height of stac~ 1 of about 4 to S m the tunnel template 6 has an advantageous ogival height of about 2 to 2,50 m, it being possible that the,breadth of the tunnel template is about O.S0 to 0.60 m. The length of the tunnel template and also the length of .
the horizontal tubes,13 is advantageously about 5 to 6'm. The distance of the tunnel templates of'each other shall be about 1 m to l.S0 m.' 'The flue'pipes may have a length of about 1 m to l.S0 m.
A diameter of 0.20 to 0.30 m will do generally for the horizontal tubes 13. The flues may have a di'ameter of 0.10 to O.lS.
For applying the tunnel templates 6, it is advantageous to use a transporter 15 provided with wheels 16 and with a hitch loop 17 for being coupled to a tractor or the like. It is advantageous for~ the transporter lS to be as broad as to permit to trail there-with several tunnel templates 6 by means,of corresponding coupling ' means 18. With a transporter 15, any desired number of tunnel ~ , . .

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107~;720 templates are drawn continuously along as the erection of the com-post stack 1 proceeds and are withdrawn ~rom the stack as soon as it has become self-supporting. The roller~ 9 of the tunnel template 6 are mounted within the body 6 in order to prevent them from in any way damaging the tunnel 2 which has been formed. The horizontal tubes 13 are preferably also connected to the transporter 15 by coupling means 19, so that the tubes 13 can also be withdraw~ from the compost stack 1 at the same time as the tunnel templates 6 move forward.
In order to support the lateral walls of the compost stack 1 lateral wall support elements 20, 21 are preferably employed which are so constructed as to provide practically complete access-of the surrounding air to the compost material. Accordingly, the lateral wall elements have slats 22 distributed over their height and secured to uprights 23. These slats consist preferably of planks secured between posts, The slats are preferably inclined downwards towards the side adjacent to the compost stack, the angle of incli-nation being capable of adjustment if necessary. For this purpose the slats may be rotatably mounted. The surface inclined downards towards the compost stack ensures that rain etc. is not allowed to run down the exposed side of the lateral walls, which might lead to the gathering of water at the base, with the consequent risk of "black feet" occurring in the compost stack. The rainwater directed towards the stack is absorbed into the stack itself and the effi- ' cient ventilation system ensures that the moisture abosrbed into the walls is once again quickly vapourised by the generation of heat in the stack.

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' ' 107~7~0 The lateral walls preferably assume the form of upright supports 24, Their length should correspond to the length of the tunnel template 6. The height of the lateral walls should be that of the intended compost stack 1 to be formed. The lateral walls 20, 21 may be withdrawn from the compost stack 1 as soon as the stack, due to the fungous structure resulting from bacterial activity, has become self-supporting and has formed a body of fixed shape.
In the case of the embodiment according to Figs. 6 and 7, the tunnel templates 6a are so constructed that they taper longitudi-nally, vertically and laterally. The decrease in height of thetunnel template 6a over its length (which is, for example, in the .. ~
region of some 5m to 6 m) may preferably be maintained between ap-proximately 2% to 5%. If the height of the tunnel template at the forward end is for example 2.50 m, the height at the rear end of the template might amount to approximately 2.40 m. By employing such a very slight variation in height, the pointed arch shaped hollow course 2 within the stack remains practically unaltered in height.
The width of the tunnel template is intended to decrease over its length to a greater degree. This decrease should be up to approximately 30% and possibly a little over. If, for example, the tunnel template 6a has a width at the forward end of approxi-mately 0.6 m the width at the rear end should be only approximately 0.4 m. This applied especially to a tunnel template approximately 5 m to 6 m long, By this form of construction, forward displace-ment of the template is facilitated without the necessity of lower-ing it somewhat.
On average, the slightly wedge-shape of the tunnel template should be achieved satisfactorily with a taper of approximately 8% to 20% with a mean of some 10%, :
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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for the treatment and purification of waste materials, or refuse/sewage sludge mixtures, by composting through thermal retting, comprising crushing the waste material and extracting the non-compostable constituents by sifting the reduced waste, heaping the material, ready-treated for compos-ting and of a predetermined particle size, layer upon layer to form a stack whilst leaving in the interior of said stack, through the use of removable formers, at ground level, laterally-spaced, longitudinal tunnel-like cavities of height at least half that of the stack, the tunnel-like cavities remaining open at least at one end of the stack, and leaving the stack material undisturbed until the compost has matured.

2. A method according to claim 1 comprising leaving in the stack, above said tunnel-like cavities, and also through the use of removable formers, longitudinally-extending duct-like cavities remaining open at least at one end of the stack and mutually-spaced, vertical chimney-like spaces opening upwardly from the stack.

3. A method according to claim 1 in which the tunnel-like cavities reach to a height of one half to two thirds the height of the stack.

4. A method according to claim 1 in which the tunnel-like cavities are spaced 1 m to 1.50 m apart laterally.

5. A method according to claim 2 in which the duct-like cavities are offset laterally in relation to the tunnel-like cavities.

6. A method according to claim 2 in which the vertical chimney-like spaces are spaced apart from one another longi-tudinally of the tunnel-like cavities.

7. A method according to claim 1 in which the compost body of the stack has steep sides.

8. Apparatus for stacking waste materials, or refuse/
sewage sludge mixtures in crushed and prepared condition for composting through thermal retting comprising longitudinal tunnel-like formers which have perforated walls, are of pre-determined length, are of height at least half of that of the stack to be formed, are to be disposed in laterally-spaced relationship at ground level for the stack to be built there-between and in layers thereover, and are adapted to be moved lengthwise to withdraw same from the stack when the stack material acquires a firm inner structure.

9. Apparatus according to claim 8, including longitudinal duct-forming tubes to be disposed above said tunnel-like formers as the stack is built up, and chimney-space-defining tubes to be located in vertical dispositions above said tunnel-like formers as the stack is built up.

10. Apparatus according to claim 8 in which each tunnel-like former is of pointed-arch-shaped cross-section and the width thereof corresponds to approximately one third to one quarter of the height thereof.

11. Apparatus according to claim 8 in which each tunnel-like former tapers longitudinally, vertically and laterally.

12. Apparatus according to claim 11, in which the height of each tunnel-like former decreases over its entire length by approximately 2% to 5%.

13. Apparatus according to claim 11 in which the width of each tunnel-like former decreases over its entire length by up to approximately 30%.

14. Apparatus according to claim 11 in which the tapering of each tunnel-like former vertically and/or laterally from the forward end to the rear end thereof in the intended direction of lengthwise movement is within the range of approximately 8%
to 20%.

15. Apparatus according to claim 8 in which each tunnel-like former is closed at its rear end by a wall in which is an adjustable slide to regulate the opening for admission of air into the tunnel-like former from said rear end.

16. Apparatus according to claim 8 in which each tunnel-like former has provision for raising and lowering of same for which purposes each former is provided with wheels the axles of which are adjustable in height relative to the walls of the former.

17. Apparatus according to claim 16 in which said wheels are located in the interior of each tunnel-like former.

18. Apparatus according to claim 8 including a carriage provided with coupling means for a plurality of tunnel-like formers.

19. Apparatus according to claim 18 in which said carriage has further coupling means for the duct-forming tubes.

20. Apparatus according to claim 8 in which lateral wall support elements are provided for the compost body or stack and have vertically-spaced bars secured to uprights.

21. Apparatus according to claim 20 in which the bars are inclined downwardly at their sides adjacent the compost body or stack.

22. Apparatus according to claim 20 in which the lateral wall support elements are kept upright by braces.