EP1165462A1 - Waste treatment apparatus and methods - Google Patents

Abstract

A waste treatment plant comprises a fermentation structure (10, 56) including two rows of closable cells (12) for processing of waste therein to produce biogas. The two rows are separated by at least two vertically spaced passageways (32, 34, 36). For each cell (12), waste in the cell (12) at the respective heights of the passageways can be monitored, respectively, from the corresponding passageway (32, 34, 36). Additionally, one of the passageways can be used to house fluid distribution means (46, 48, 49) communicating with each cell (12) for collection of biogas and distribution of leachate. Alternatively, a single row of cells (12) can be built adjacent a greenhouse (20) (or other building) so that biogas from the cells can be used to heat the greenhouse (70) (or power processes in the other building).

Description

WASTE TREATMENT APPARATUS AND METHODS

The invention relates to waste treatment apparatus and methods.

Hitherto putrescible waste has largely been disposed of in landfill sites but it is also

known to ferment waste in closed cells so as to reduce the volume of the waste and

collect inflammable biogas derived from the fermentation. The invention relates to

improved apparatus and methods of this latter kind.

According to a first aspect of the invention there is provided an apparatus for treating

waste and a building, the apparatus comprising a closeable cell for processing of waste

therein to produce biogas, the cell bearing at least part of the weight of the building.

According to a second aspect of the invention there is provided an apparatus for

treating waste, comprising a closeable cell for processing of waste therein to produce

biogas, the cell comprising a floor, a wall and a roof, the roof being immoveable

relative to the floor and the wall.

According to a third aspect of the invention there is provided a method of treating

waste comprising processing waste in a closed cell to produce biogas and drying the

processed waste using heat generated from the biogas or from the processing. According to a fourth aspect of the invention, there is provided an apparatus for

treating waste, comprising a plurality of closable cells for processing of waste therein

to produce biogas and an accessway, the accessway extending alongside each cell and

being separated from waste being processed in the cells by at least one wall, and

means allowing, for each cell, when waste is being processed in said each cell to

produce biogas, monitoring of a variable of said processing in said each cell from the

accessway.

According to a fifth aspect of the invention, there is provided an apparatus for treating

waste, comprising first and second parallel rows of closable cells for processing of

waste therein to produce biogas, a space extending between the rows and fluid

distribution means being provided in the space and communicating with each cell.

According to a sixth aspect of the invention, there is provided a method of treating

waste comprising, processing waste to produce biogas, collecting leachate from said

waste, adding the leachate to waste, the wherein during said addition the leachate is

at a temperature to hasten production of biogas from the waste to which the leachate

is added.

According to a seventh aspect of the invention, there is provided a method of treating

waste comprising; providing a plurality of closable cells and a supply of waste;

treating the supplied waste in a cycle including: loading the supplied waste successively into individual cells of the plurality; processing the waste in the loaded

cells so as to produce biogas; preparing the loaded cells for loading of supplied waste;

the number of cells of the plurality and the supply of waste being such that each cell

of the plurality is in the cycle, and at least one further cell being provided.

According to a eighth aspect of the invention, there is provided an apparatus for

treating waste, comprising a closable cell for processing of waste therein to produce

biogas, and a system for introducing a fluid, especially a liquid, into the cell to at least

partially submerge waste in the cell.

According to a ninth aspect of the invention, there is provided a method of treating

waste, comprising processing the waste in a closed cell so as to produce biogas, and

introducing a fluid, especially a liquid, into the cell to submerge at least partially the

waste so as to stop substantially the process.

According to a tenth aspect of the invention, there is provided an apparatus for treating

waste, comprising a plurality of closable cells for processing of waste therein to

produce biogas, and a building, the cells being located adjacent the building and

energy generated from the biogas being used in the building in a process unrelated to

said waste processing. According to an eleventh aspect of the invention, there is provided a method of

treating waste, comprising processing the waste to produce biogas, and using the

biogas to generate energy for heating a greenhouse.

According to a twelfth aspect of the invention, there is provided a method for treating

waste, comprising processing fish farm waste in a closed cell to produce biogas.

The following is a more detailed description of embodiments of the invention, by way

of example, reference being made to the appended schematic drawings in which:-

Figure 1 is a perspective view of waste treatment apparatus in the form of a

fermentation structure that is suitable for use in waste treatment apparatus formed by

a waste treatment plant;

Figure 2 is a cross-sectional view of the fermentation structure of Figure 1 ;

Figure 3 is an enlarged view of part of Figure 2;

Figure 4 is a plan view of the fermentation structure;

Figure 5 shows a first waste treatment plant including a fermentation structure similar

to the structure of Figures 1 to 4; Figure 6 is a cross-sectional view of a second waste treatment plant including a

greenhouse;

Figure 7 is a partial longitudinal sectional view of a third waste treatment plant;

Figure 8 is a partial cross-sectional view of the third waste treatment plant taken on

the line 8 - 8 in Figure 7;

Figure 9 is a partial cross-sectional view of the third waste treatment plant taken on

the line 9 - 9 in Figure 7; and

Figure 10 is a plan view of part of a fermentation structure of the third waste treatment

plant.

Referring firstly to Figures 1 to 3, the fermentation structure 10 includes two identical,

elongate and mutually parallel side sections 14. Each side section 14 is subdivided,

respectively, into six cells 12 arranged in a row extending along the length of the side

section 14. Only one of the side sections 14 will be described in detail below.

Corresponding features of the two side sections 14 will be given the same reference

numerals. The described side section 14 is formed by a vertical wall 16, an inclined wall 18

spaced from the vertical wall 16 by a floor 20 and by two end walls 22, and is formed

into the cells 12 by dividing walls 24. The vertical wall 16 is rectangular and extends

for the full length of the side section 14. The inclined wall 18 is rectangular and also

extends for the full length of the side section 14. The floor 20 is horizontal and

rectangular and also extends for the full length of the side section 14 between a base

of the vertical wall 16 to a base of the inclined wall 18. The inclined wall 18 has a

gradient of 1 in 2 (or thereabouts) and the top of the inclined wall 18 is further from

the vertical wall 16 than the bottom of the inclined wall 18.

Each end wall 22 is trapezoidal and extends vertically upwards from the

corresponding end of the horizontal floor 20 and connects the corresponding ends of

the vertical wall 16 and the inclined wall 18. Hence the vertical wall 16, the inclined

wall 18, the floor 20 and the two end walls 22 together form a trough. There are five

trapezoidal dividing walls 24 - each of which extends vertically from the floor 20 and

connects the vertical wall 16 with the inclined wall 18 to form the six cells 12. As

shown in Figure 1 , the dividing walls 24 are equally spaced along the length of the

side section 14 so that the cells 12 are of equal size.

As seen best in Figures 2 and 3, the two side sections 14 are arranged relative to one

another such that the vertical walls 16 lie innermost and parallel to one another and the inclined walls 18 lie outermost so that one side section 14 is laterally reversed

relative to the other about a vertical plane between the vertical walls 16.

An elongate U-shaped base 40 connects the lower edges of the vertical walls 16 and

extends the full length of the side sections 14 so as to form a channel 42 between and

below the vertical walls 16. The channel 42 communicates with each cell 12 for a

purpose described below.

The horizontal floors 20, the vertical walls 16, the inclined walls 18, the end walls 22,

the dividing walls 24 and the U-shaped member 40 may be constructed of reinforced

concrete.

Each cell 14 is sealed by a flexible, thermally insulated, impermeable cover 25 (one

per cell - see Figure 3) that is preferably made from an elastic, plastics material, and

that can be stretched across the top of the cell 12.

As seen best in Figure 3, the two vertical walls 16 of the two side sections 14 are

connected by three vertically spaced floors 26,28,30 that extend the full length of the

two side sections 14. The lower floor 26 is co-planar with the horizontal floors 20 of

the side sections 14. The lower floor 26 may be formed with gaps (one of which is

shown at 44) to allow access to and inspection of the channel 42. The middle floor 28

is positioned above the lower floor 26 by a height corresponding to approximately one third the height of the cells 12. The upper floor 30 is positioned at a height above the

lower floor 26 corresponding to approximately two thirds of the height of the cells 12.

Hence, the lower, middle and upper floors 26,28,30, together with the vertical walls

16, define, respectively, lower, middle and upper passageways 32,34,36. Each

passageway is sufficiently high for human access - for example 2.5m high. As will

be appreciated from the above, the lower passageway 32 spans the lower third of each

cell 12, the middle passageway 34 spans the middle third of each cell 12 and the upper

passageway 36 spans the upper third of each cell 12. Each passageway 32,34,36 is

divided into a number of rooms or compartments, arranged along the length of the

passageway 32,34,36, by partition walls 35.

Each vertical wall 16 is provided with a plurality of airtight windows represented by

the arrows 37 in Figure 3. The windows are arranged in the vertical walls 16 such that

the interior of each cell 12 can be seen from each of the passageways 32,34,36

through an associated window or windows 37. Additionally, each vertical wall 16 is

provided with a plurality of monitoring conduits (not shown) that extend through the

wall 16. Each cell is associated, respectively, with three conduits, one in each-

passageway (there may be more than one conduit per passageway per cell). Each

conduit that opens in the upper passageway 36 opens into the upper third of the

associated cell 12. Each conduit that opens into the middle passageway 35 opens into

the middle third of the associated cell. Each conduit that opens into the lower

passageway 32 opens into the lower third of the associated cell 12. A roof 38 extends between respective tops of the two vertical walls 16 and closes the

upper passageway 36.

The upper passageway 36 houses a fluid distribution system (not shown in detail)

comprising two liquid distribution networks and a gas distribution network. The first

liquid distribution network, shown schematically at 46 in Figure 3, allows liquid

collected in the channel 42 (leachate as described below) to be introduced, selectively,

into any one or any subset of the cells 12. The first liquid distribution network 46

introduces the liquid at the tops of the cells 12. The gas collection network, shown

schematically at 48 in Figure 3, allows gas to be collected from any one or from any

subset of the cells 12 (as described below). The gas is collected from the tops of the

cells 12. The second liquid distribution network is shown schematically at 49 in

Figure 3 and serves to collect rainwater that falls on the impermeable, flexible covers

25 of those cells that are sealed (see below). The second liquid distribution network

also allows water to be passed into, selectively, any one or subset of the cells 12 (as

discussed below).

As will be appreciated from the above the fluid distribution system is provided in a

space between two parallel rows of cells 12 and communicates with each cell 12. This

is particularly convenient and can be implemented in waste treatment apparatus

independently of the other features of the fermentation structure 10. As shown in Figure 2, the fermentation structure 10 may be built in an excavation in

the underlying ground 50 so that the tops of the vertical walls 16, the inclined walls

18, the trapezoidal end walls 22 and the dividing walls 24 lie generally at ground

level.

The fermentation structure 10 also includes thermal insulation 52 provided between

the undersides of the horizontal floors 20 and the ground 50 and between the

undersides of the inclined walls 18 and the ground 50. The vertical walls 16, the end

walls 22 and the dividing walls 24 are also preferably provided with thermal insulation

(not shown).

As shown in Figures 2 and 4, a respective area of "hard standing" 54 is provided, at

ground level, adjacent the top of the inclined wall 18 of each row 14. The cells 12 can

be filled and emptied by mechanical means positioned on the hard standing 54 or by

waste carrying vehicles as described below.

Having now described a fermentation structure 10 suitable for use in a waste

treatment plant, a waste treatment plant including such a structure 56 will now be

described with reference to Figure 5. The waste treatment plant comprises, in addition

to the fermentation structure 56, a reservoir 58 for a liquid, an energy generation unit

60, a waste receipt area 62, a waste separation area 64 and a storage area 66 for storing

certain types of separated waste. The fermentation structure 56 is similar to the fermentation structure 10 shown in

Figures 1 to 4 and described above, but has six trapezoidal dividing walls 24 in each

side section 14 (instead of five in the fermentation structure 10) so as to form seven

cells 12 in each side section 14 (instead of six cells of the fermentation structure 10).

The component parts of the fermentation structure 56 will thus not be described in

detail below and will be given the same reference numerals as the corresponding parts

of the fermentation structure 10.

The reservoir 58 is connected to the second liquid distribution network 49. Rainwater

collected in the second liquid distribution network 49 (as discussed above) passes

through the network 49 to the reservoir 58 where it is stored. The level in the

reservoir 58 is maintained at a predetermined, desired level. If insufficient rain water

is collected to maintain water at this level in the reservoir 58, the reservoir can be

topped up with water from another source. The second liquid distribution network

49 also allows water held in the reservoir 58 to be passed, selectively, to any one or

more of the cells 12 so as to fill the or each selected cell 12. This procedure can be

desirable in any one of a number of contingencies, as discussed below.

The energy generation unit 60 contains machinery (not shown) suitable for generating

both electricity and heat energy from inflammable gas. The machinery is connected

to the gas collection network 48. Alternatively the machinery could be situated in the

passageways 32,34,36. The waste receipt area 62 is preferably covered, and is used for receiving waste

delivered to the waste treatment plant.

The waste separation area 64 contains machinery suitable for separating waste that

comprises of organic, putrescible components and also non-putrescible components such as metal, plastics, etc. The storage area 66 is used to store recovered non-

putrescible components, such as metals and plastics. The recovery of metals, plastics etc on site, possibly utilising the thermal and electrical energy generated from the biogas is advantageous compared to methods in which recovery is performed at

disparate locations without the advantages of using on-site generated energy.

Operation of the waste treatment plant to treat Municipal Solid Waste is now

described. Municipal Solid Waste is delivered to the waste treatment plant and is

received in the waste receipt area 62 from where it is transferred, as required, to the

waste separation area 64. Municipal Solid Waste includes, in a mixture, organic,

putrescible components and non-putrescible components such as metals, plastics, etc.

The Municipal Solid Waste is separated by the machinery in the waste separate area

64 to give an organic, putrescible component that is shredded (shredding is optional),

and separated non-putrescible components that are stored in the storage area 66. The

shredded putrescible component may be mixed with sewage sludge. Sewage sludge

has a relatively high content of the anaerobic micro-organisms that are required for

the fermentation process and so the addition of sewage sludge tends to hasten the initiation of fermentation (and, during the processing, the sewage sludge is

neutralised).

The shredded organic component forms a continuously generated supply of waste that

is treated in a cycle. During the cycle, waste is loaded into, and, in due course,

emptied from, twelve of the fourteen cells 12 (where it undergoes biodegradation

including fermentation), in a sequence. The sequential loading and unloading is

repeated in each phase of the cycle. Before the sequence is described, the treatment

procedure, as it occurs in any single cell 12, will be described.

The shredded putrescible waste (with or without sewage sludge) is loaded into the cell

12 over a period that is sufficiently short so that substantial fermentation does not

occur. In general, this period will be approximately 50 days or less. During loading

of the cell 12, the cell is covered by an inflatable cover 68 (shown in Figure 1 ). The

inflatable cover 68 does not reduce the entry of oxygen into the cell, but acts to reduce

entry of wind and rain into the cell 12 and to reduce the entry of birds and animals that

might otherwise carry putrescible material from the cell 12. The 1 in 2 gradient of the

inclined walls 18 allows the cell 12 to be filled using vehicular waste carrying

machinery that can drive into and out of the cells 12 on the inclined walls 18 (the

inflatable cover 68 does not obstruct this). When loading of the cell 12 is completed,

the inflatable cover 68 is removed (for use in loading another cell) and the cell is

sealed using a flexible, impermeable cover 25, as described above. When in the cell 12, the waste undergoes processing to produce biogas. The seal or

closure formed by the cover 25 is sufficiently airtight so that oxygen in the cell is used

up by aerobic processes so as to render the environment within the cell 12 anaerobic

(strict hermetic sealing may not be required). The anaerobic conditions lead to

biodegradation (including fermentation) of the waste by anaerobic micro-organisms

and this results in the production of methane-containing biogas. The biogas passes

from the cell 12 into the gas collection network 48 which carries the gas to the energy

generation unit 60 for the production of electrical and heat energy.

Additionally, the biodegradation results in the production of a liquid, which is referred

to herein as leachate, and which has a relatively high content of the anaerobic micro¬

organisms that perform the biodegradation. The leachate drains, via sealed traps, into

and collects in the channel 42. The sealed traps (not shown) allow leachate to pass

from the cells 12 to the channel 42 but prevent entry of air into the cells 12. Leachate

can be passed from the channel 42 into the liquid distribution network 46 from where

it can be dispensed, selectively, into any one of the cells 12. Additionally, if required

an enclosed reservoir for the leachate may be provided (not shown).

The dispensing of leachate onto waste in the cells 12 hastens the biodegradation of

the waste. Leachate may be dispensed into cells containing waste that is already

undergoing biodegradation - so as to accelerate the process, or it may be dispensed

into cells containing waste in which biodegradation has not yet started - in which case the leachate hastens the initiation of biodegradation. Before the leachate is dispensed

into the cells 12, the temperature of the leachate may be adjusted to a temperature at

which the leachate is most effective at hastening biodegradation. The leachate remains

at this temperature up to and during dispensing onto the waste. Generally, this will

involve heating the leachate, preferably to a temperature in the range of 50°-60°C, and

most preferably to about 55°C. The leachate may be heated using heat energy

generated from biogas in the energy generation unit 60. The addition of leachate to

waste when the leachate is at a temperature to hasten the production of biogas may be

particularly advantageous and can be applied to waste treatment methods

independently of the other features of the current method.

Excess leachate may be fed into reedbeds or biological (such as willow) dewatering

systems for detoxification of the leachate. Alternatively, the leachate may be treated

using conventional methods. As a further alternative, excess leachate can be dried to

produce a powder residue suitable for use as a fertiliser. Leachate can be dried using

energy generated during processing or from combustion of biogas. Leachate could

also be spread on fields as a fertiliser.

Heat is generated in the cell during biodegradation. The concrete walls 16, 18,22,24

act as a heat store. The insulation 52 helps to retain the heat in the concrete. The

concrete walls and the insulation 52 help to maintain the temperature of the cell 12 at

thermophyllic temperatures (50°C - 60°C, preferably 55°C), which are preferred for biodegradation as they enhance both the rate and nature of methanogenesis.

Biodegradation could also be carried out at mesophyllic temperatures.

The biodegradation results in a significant reduction in the volume of the waste over

a relatively short time scale - dependent on the constituents of the waste. On

substantial completion of biodegradation, which is marked by substantial reduction

in the production of biogas, the volume of the waste may be as little as one third of

its initial volume. After substantial completion of biodegradation, the cell is prepared

for receiving untreated putrescible waste. Firstly, addition of leachate is stopped.

Residual leachate is then drained from the cell 12 and the heat retained by the cell

walls 18,22,24 is advantageously used to dry residual waste. Any biogas that is

produced during this stage is collected by the gas distribution network. The

impermeable cover 25 is then removed and the dried residual waste is emptied. If

required, maintenance is performed on the cell 12. Removed waste can be used, for

example, as compost, soil dressings or conditioners. Removed waste may be inert.

Having now described the treatment procedures for a single cell 12, the use of the

fourteen cells 12 of the fermentation structure 56 and the sequence of loading and

unloading of the twelve cells 12 which are used for waste processing, will now be

described.

The fourteen cells 12 shown in Figure 5, are for the purposes of this description each

identified by a letter from the sequence A-N. As stated above, twelve of the cells 12, A-L, are used for biodegradation. The remaining two cells 12, M and N, are left

empty for use in contingencies. The twelve cells 12 A-L are used in a sequence that

is repeated cyclically.

Initially, before the cycle is commenced, the cells A-L are filled in succession and the

volume of waste treated is matched to the number of cells 12 so that as cell L is filled,

cell A finishes its treatment procedure and is emptied. Thus at the beginning of the

cycle, cell A is empty and cells B-L contain waste at different stages of

biodegradation. The waste in cell B will be completely biodegraded, while cell L has

just been sealed and the waste contained in cell L is just starting to biodegrade.

Shredded putrescible waste from the separation area 64 is loaded into cell A as

described above. At generally the same time, the flexible, impermeable cover is

removed from cell B, biodegraded waste is removed and any necessary maintenance

is carried out on cell B. By the time cell A has been filled, cell B is empty and any

necessary maintenance has been completed. Cell A is then closed with a flexible,

impermeable cover 25 and the process of loading cell B with shredded putrescible

waste is started. As cell B is loaded, the waste in cell C, which will now have

completed biodegradation, is removed and cell C is inspected and any necessary

maintenance undertaken. This process is repeated continuously.

Thus, in any phase of the cycle, the cells 12, A-L, are loaded in a sequence and

emptied in the same sequence, the sequential loading and emptying being repeated in each successive phase of the cycle such that while each cell 12, A-L, is being emptied

the cell 12, A-L that is the proceeding cell in the sequence is being loaded.

As will be appreciated from the above the supply of the shredded putrescible waste

is such that each cell 12, A-L is in the cycle (but not cells M and N). Additionally, at

any one time at least one cell, A-L, is available for receiving shredded putrescible

waste and biodegradation is taking place in nine or ten cells. These features can be

applied to waste treatment methods independently of one another and of the other

features of the current method and are particularly advantageous. In particular, there

will be a fairly continuous supply of biogas to the energy generation unit 60 and a

fairly continuous production of leachate. Additionally, the time that putrescible

organic waste remains in either the receipt area 62 or in the separation area 64 before

it is loaded into the cells is minimized - and this minimizes environmental

contamination. The sequence also has the advantage of maximizing the use of the

cells A-L.

During the processing of waste in the cells 12 to produce biogas, the windows 37 and

the monitoring channels allow monitoring of several variables of the processing from

the passageways 32,34,36. For example, the windows 37 allow monitoring, by visual

observation, of the visual appearance of the waste, the volume of the waste (as the

height of the waste is proportional to the volume and can be observed through the

windows) and the level of any leachate standing in the cells. The monitoring conduits allow monitoring of, e.g., fluid composition and content in the cells 12 (as samples

can be withdrawn through the channels) and temperature of the waste (as temperature

probes can be inserted into the cells 12 through the conduits). It will be appreciated

that each cell 12 is observable from each passageway 32,34,36 (through a respective

one, or more, of the windows 37 associated with that cell 12). Thus the appearance of

waste lying in the lower, middle and upper thirds of the cell 12 can be observed from,

respectively, the lower, middle and upper passageways 32,34,36. Similarly the

monitoring conduits allow monitoring, for each cell, of variables (e.g. temperature)

in the lower third of the cell 12 from the lower passageway 32, in the middle third of

the cell 12 from the middle passageway 34 and in the upper third of the cell 12 from

the upper passageway 36. The ability to monitor variables in any cell of a plurality of

cells from a passageway extending adjacent each cell is particularly convenient and

can be implemented in waste treatment apparatus independently of the other features

of the waste treatment plant. This feature is particularly advantageous when the cells

are arranged in a row and the passageway extends parallel to the row. The provision

of the three passageways 32,34,36 and the provision of windows 37 and conduits

between each passageway and each cell is a very convenient arrangement for allowing

variables at different heights in each cell 12 to be monitored.

The cells M and N can be used for biodegrading organic material should the waste

treatment plant have to cope with a short term increase in the amount of municipal

solid waste requiring treatment, should it be necessary to close down one of the cells A-L for extensive maintenance, or should it be necessary to shut down one of the cells

A-L in an emergency, such as a fire or contamination of the cell.

In certain emergencies such as, for example, the break out of fire in a particular cell

12, waste in the cell 12 can be submerged in water by filling the cell 12 with water

from the reservoir 58 via the second liquid distribution network 49. Similarly, should

it at any time become necessary to halt biodegradation in a cell 12, this can be done

by flooding the cell with water from the reservoir 58 so as to submerge the waste - the

oxygenated water stopping the fermentation process. Water in cells 12 flooded in this

way can be drained from the cells 12 into the channel 42 and from the channel 42 into

a mains drain system. The use of a liquid, such as water, to submerge waste is

particularly advantageous and can be applied independently to other waste treatment

apparatus and methods. Instead of water, aerated leachate may be added to the cells

to submerge waste so as to stop processing. Instead of liquids, fluids, e.g. steam, can

be injected into cells to stop the fermentation process. Steam can be generated from

water using heat from burning biogas.

When designing a waste treatment plant of this type, the number and capacity of the

cells 12 should, as indicated briefly above, be decided, for a given, anticipated rate of

supply of waste to be treated, so that the cells 12 can be operated cyclically, as

discussed above, such that the waste in any cell undergoes complete fermentation

before it is necessary to empty that cell. In this regard, the fermentation time can vary greatly, dependent on the constituents of the waste, the temperature and on the

conditions of leachate recirculation. It has been calculated that the fermentation

period can be from less than one year up to approximately three years. Preferably the

fermentation period will be from two months to eighteen months. The number of cells

will also be a function of the degradation characteristics of the waste and the optimum

production of biogas.

It will be appreciated that the waste treatment plant and the method of treating waste

described above can be varied in many aspects.

Firstly, the fermentation structure 56 need not be as described above. For example,

the waste treatment plant could have a fermentation structure having a single row of

cells which could, for example, be similar to one of the side sections 14 of the

fermentation structure 56. In this case, there would be only a single vertical wall 16

and the structure would not have the passageways 32,34,36 described above. The

fermentation process in the cells 12 could still be monitored using windows and

channels, from a suitable accessway extending adjacent the vertical wall 16.

Additionally, the first and second liquid distribution networks 46,49 and the gas

collection network 48 could be attached to the vertical wall 16 at the side of the wall

16 that lies outside of the cells 12. Where necessary, balconies could be provided on

the outside of the vertical walls 16 to allow access to higher windows, channels and

the distribution networks 46,49,48. Instead of the vertical wall 16, a plurality of walls, each forming a wall of a cell of the row, could be arranged edge to edge but spaced

in a line extending alongside the accessway.

Where two rows are provided, it is not necessary to have three passageways 32,34,36

between the two vertical walls 16. Any convenient number of floors 26,28,30 could

extend between the two vertical walls 16.

The cells need not be arranged in rows. When cells are arranged in rows, the rows

need not be such that the cells are arranged side by side with their sides parallel to one

another and their ends co-planar - cells could be arranged, for example, generally in

a curved (e.g. arcuate) row. The cells need not be at the same level. For example

cells can be constructed one on top of another.

It will be appreciated that the waste treatment plant need not be used to treat municipal

solid waste. Alternatively, the plant could be used to treat other putrescible wastes,

such as farm waste, vegetable waste, or waste from fish farms. In the case of farm

waste, vegetable waste or fish farm waste, the waste is almost entirely putrescible in

nature and such wastes may be loaded from the receipt area 62 directly into the cells

12 without separation. The processing of such wastes in one or more closed cells to

produce biogas may be particularly advantageous and applicable to waste treatment

methods independently of the other features of the current method. Additional

materials such as shredded forest waste (i.e. tree waste) and shredded paper may be added to the waste before, during or after processing. This can improve the compost

value of the waste residue remaining after processing.

The cells need not be operated in the cycle described above. The cells 12 may be used

in any cycle. This may depend on the rate of degradation. Preferably the cycle is such

that at any one time at least one cell of the cycle is available for receiving waste and

waste is being processed in more than half of the cells of the cycle. Moreover, the

waste treatment plant need not be operated in the same cycle for the whole life of the

plant. The cycle can be varied to suit changing circumstances.

It will be appreciated that the cells do not require an inclined wall. Additionally the

junctions between the walls 16,22,24 and the floors 20 could either be rounded or

splayed.

The fermentation structures 10 and 56 need not be sunk in the ground, in an

excavation as described above, but could be built so that the floors 20 lie at ground

level or above ground level. As an alternative to building the fermentation structures

in excavations, they can be built at ground level and earth can then be ramped up to

the tops of the inclined walls 18.

The covers 68 need not be inflatable. The windows 37 could be replaced by any other means allowing the interiors of the

cells to be observed from the passageways.

If required, the biodegradation process can be slowed (either by adding water, adding

oxygen, or by reducing the addition temperature of the leachate). The process can

then, if required, be accelerated by increasing the addition temperature of the leachate.

This could be useful to accommodate variations in the rate of supply of putrescible

waste.

In addition to collecting biogas, the gas collection network 48 can be used to extract

air during filling and emptying of the cells.

In the first waste treatment plant, separate liquid distribution networks 46,49 are used

for conveying leachate and water. However, a single distribution network could be

used for both purposes.

A second waste treatment plant is shown in Figure 6. The second waste treatment

plant is the same as the fermentation structure 10 described above with reference

Figures 1-4 but with one side section 14 omitted and replaced by a greenhouse 70 with

a rear vertical wall 72 of the greenhouse 70 located in the same position as the vertical

wall 16 of the omitted section 14. The features of the second waste treatment plant

that are common to the fermentation structure 10 and to the second waste treatment plant will not be described in detail below and will be given the same reference

numerals as the corresponding features of the fermentation structure 10.

The greenhouse 70 is thus constructed adjacent to and integrally with the remaining

side section 14. The rear vertical wall 72 lies adjacent and parallel to the vertical wall

16 of the side section 14, as described above. The rear wall 72 is composed largely

of a transparent material such as reinforced glass. A floor 74 of the greenhouse

extends horizontally from the base of the rear wall at the opposite side of the rear wall

72 to the vertical wall 16. An inclined wall 76, could be composed largely of glass,

extends from the greenhouse floor 74 to the top of the rear wall 72 and onwards to a

position above the top of the vertical wall 16. Another vertical wall 78 closes the gap

between the top of the vertical wall 16 and the inclined wall 76 of the greenhouse.

The floors 26,28,30 and the roof 46 extend between the vertical wall 16 and the rear

wall 72 of the greenhouse 70 and the arcuate base 40 connects the lower edges of the

vertical wall 16 and the rear wall 72.

A first balcony 80 extends from the rear wall 72 into the greenhouse 70 at a height

corresponding to the height of the middle floor 28 and a second balcony 82 extends

from the rear wall 72 into the greenhouse 70 at a height corresponding to the height

of the upper floor 28. In operation, the cells 12 are used for fermenting putrescible waste, as described

above. One or more of the cells 12 may be kept empty for contingencies and the

remainder of the cells may be filled and emptied in a cycle similar to the cycle in

which the cells A-L of Figure 5 are filled, as described above.

Biogas produced in the cells 12 is collected using the gas collection network 48 and

is used to heat the greenhouse 70. Thermal energy discharged from a combined heat

and power system during electricity generation is used to heat the greenhouse. All

other functions of the greenhouse may be powered by electricity generated from the

biogas. Once biogas production has substantially ceased, residual waste from the cells

12, after drainage of leachate and partial drying, may be used as compost in the

greenhouse 70. If desired, biomass from growth in the greenhouse 70 may be used

as waste to be fermented in the cells 12. Carbon dioxide resulting from the conversion

of biogas will be used to enhance biomass growth within the greenhouse.

It will be appreciated that the waste treatment plant shown in Figure 6 demonstrates

an inventive concept that is not limited to the use of fermentation cells 12 in

combination with a greenhouse 70. A waste treatment plant including closable cells

12 may include any suitable building or series of buildings in place of the greenhouse

70 such that energy generated from the biogas can be used in the building in processes

unrelated to the waste treatment. For example, the building could be a farm or a

dwelling. Alternatively, the building could be a research facility. This concept can be applied to waste treatment apparatus independently of the other features of the

second waste treatment plant. The use of biogas from waste to heat a greenhouse is

also of independent utility.

It will be understood that the fermentation structures 10 and 56 and the second

treatment plant could be built in stages, the cells 12 being constructed as and when

they become necessary for use in the first cycle of loading with waste. This concept

has the advantage of spreading out the capital cost outlay over a period in which the

process is being utilised.

Modifications may be made to the second waste treatment plant.

For example instead of the cells 12 being covered entirely by the impermeable flexible

covers 25 discussed above, they may be partially covered by an immovable concrete

roof. For example such a roof may extend partially over the cells from the vertical

wall 16. Impermeable flexible covers could be used to cover the remaining portions

of the cells 12.

The greenhouse may have water beds heated by energy derived from the processing

itself or from combustion of the biogas. The greenhouse may be divided to produce different temperature and humidity zones.

For example, it may be divided horizontally and/or vertically.

Figures 7 to 10 show a third waste treatment plant comprising a fermentation structure

90, that is largely situated in an excavation in the ground 91, and a building 92, that

lies over the fermentation structure 90.

As best seen in Figure 10, the fermentation structure 90 includes first and second

identical, elongate and mutually parallel side sections 94,95. Only the first side

section 94 will be described in detail below. Corresponding features of the two side

sections 94,95 will be given the same reference numerals.

The first side section 94 comprises an inner, rectangular vertical wall 96 and an outer,

rectangular vertical wall 98 that lies parallel to the inner vertical wall 96. A

rectangular, horizontal floor 100 connects the vertical walls 96,98 at their bases. Each

one of the vertical walls 96,98 and the floor 100 extends the full length of the first side

section 94.

At each end of the first side section 94, respective first and second end walls 102, 104

extend upwardly from the floor 100 and connect the inner vertical wall 96 and the

outer vertical wall 98. The inner vertical wall 96 is provided with a first rectangular opening 106 that is

located at a distance corresponding to a quarter of the length of the first side section

94 from the first end wall 102. The inner vertical wall 96 is also provided with a

second rectangular opening 108 that is located at a distance corresponding to one

quarter of the length of the first side section 94 from the second end wall 104. Each

of the first and second rectangular openings 106,108 extends upwardly from the base

of the inner vertical wall 96 but does not reach the top of the inner vertical wall 96.

Hence, the inner vertical wall 96, the outer vertical wall 98, the floor 100 and the first

and second end walls 102,104 together define a trough. This trough is divided into

four cells 126,128,130,132 of equal size by first, second and third dividing walls

112,1 14,116 that extend upwardly from the floor 100 and lie parallel to the first and

second end walls 102,104.

The first dividing wall 112 is spaced from the first end wall 102 by a distance

coπesponding to one quarter of the length of the first side section 94. The first

dividing wall 1 12 meets the outer vertical wall 98 all the way from the base of the

outer vertical wall 98 to the top of the outer vertical wall 98. However, at the other

side, the first dividing wall 1 12 has a vertical edge 1 18 that lies short of the inner

vertical wall 96 and that extends from the floor 100 to a level corresponding to the top

of the first opening 106 of the inner vertical wall 96. Above this level, the first dividing wall 1 12 meets the inner vertical wall 96 above the first opening 106 (not

shown).

The second dividing wall 1 14 is spaced from the second end wall 104 by a distance

coπesponding to one quarter of the length of the first side section 94. The second

dividing wall 1 14 is identical in shape to the first dividing wall 112 and extends

between the inner and outer vertical walls 96,98 in the same manner as the first

dividing wall 112. Hence, the second dividing wall 1 14 has a vertical edge 120 that

is spaced from and faces the second opening 108 of the inner vertical wall 96.

The third dividing wall 116 lies midway between the first and second end walls

102,104, is rectangular and connects the inner and outer vertical walls 96,98.

Hence, a first cell 126 lies between the vertical walls 96,98 and between the first end

wall 102 and the first dividing wall 1 12. A second cell 128 lies between the vertical

walls 96,98 and between the first and third dividing walls 1 12,1 16. A third cell 130

lies between the inner and outer vertical walls 96,98 and between the third dividing

wall 116 and the second dividing wall 1 14. A fourth cell 132 lies between the inner

and outer vertical walls 96,98 and between the second dividing wall 1 14 and the

second end wall 104. As seen in Figure 10, a first triangular space 122 lies between the first rectangular

opening 106 and the vertical edge 1 18 of the first dividing wall 1 12 and a second

triangular space 124 lies between the second rectangular opening 108 and the vertical

edge 120 of the second dividing wall 1 14. Each triangular space 122,124 is roofed by

a respective triangular roof (not shown) that extends from the top of the corresponding

opening 106,108 to the top of the coπesponding vertical edge 118,120. Each of the

first and second cells 126,128 is separated from the first triangular space 122 by a

respective door and each of the third and fourth cells 130,132 is separated from the

second triangular space 124 by a respective door.

Each cell 126,128,130,132 is provided with a respective ramp 134 that extends from

the floor 100 to the top of the outer vertical wall 98. The ramps 134 of the first and

second cells 126, 128 are located adjacent to one another and at opposite sides of the

first dividing wall 1 12. The ramps 134 of the third and fourth cells 130, 132 are

similarly located adjacent to one another and at opposite sides of the second dividing

wall 1 14.

As best seen in Figure 10, the two side sections 94,95 are aπanged relative to one

another such that the inner vertical walls 96 lie innermost and parallel to one another

and the outer vertical walls 98 lie outermost so that the first side section 94 is laterally

reversed relative to the second side section 95 about a vertical plane between the inner

vertical walls 96. The two inner vertical walls 96 are connected, at their bases, by an intermediate

rectangular floor 136 that is co-planar with the floors 100. The intermediate

rectangular floor 136 together with the two inner vertical walls 96 together define an

elongate space 138 that serves for human access and for other purposes described

below. Each end of the elongate space 138 is closed by a respective intermediate end

wall 140 that is co-planar with the end walls 102,104 of the coπesponding ends of the

side sections 94,95. An intermediate dividing wall 142, provided with a door for

human access, extends across the elongate space 138 at a point equidistant from the

two intermediate end walls 140.

It will be appreciated that the two floors 100 and the intermediate rectangular floor

136 may be formed integrally. Similarly, the first end walls 102 may be formed

integrally with the coπesponding intermediate end wall 140 and the second end walls

104 may be formed integrally with the coπesponding intermediate end wall 140. The

intermediate dividing wall 142 may also be formed integrally with the third dividing

walls 1 16.

As will be appreciated from the above, and as seen in Figure 10, the two first

triangular spaces 122 face one another and are separated by the elongate space 138

and the two second triangular spaces 124 also face one another and are separated by

the elongate space 138. As seen in Figures 7, 8 and 9, the two floors 100, the intermediate rectangular floor

136, the two inner vertical walls 96, the two outer vertical walls 98, the four end walls

102,104, the six dividing walls 1 12,114,1 16, the two intermediate end walls 140 and

the intermediate dividing wall 142 are disposed in the excavation in the ground 91.

The inner and outer vertical walls 96,98, the end walls 102, 104,140 and the dividing

walls 112,114,116,142 are all of the same height and these walls have their respective

tops at ground level.

The fermentation structure 90 includes a roof 146 that covers the two side sections

94,95 and the elongate space 138 (see Figures 7, 8 and 9). The roof 146 has a main

horizontal region 148 and four rectangular, inclined regions 150 (one of which is

shown in Figure 9). Each rectangular, inclined region 150 extends parallel to, and

covers, two adjacent ramps 134. Thus, one rectangular inclined region 150 covers the

ramp 134 of the first cell 126 of the first side section 94 and also the ramp 134 of the

second cell 128 of the first side section 94. The other inclined regions 150 cover the

other ramps 134. Each inclined edge of each rectangular inclined region 150 is

connected to the main horizontal region 148 by a respective triangular, vertical wall

(not shown). Additionally, each rectangular inclined region 150 is connected to the

underlying dividing wall 1 12, 1 14 by a triangular, vertical wall (not shown). Thus,

each rectangular inclined region 150, together with the three associated vertical

triangular walls, the two underlying ramps 134 and part of the underlying dividing

wall 1 12,1 14 define two accessways 152. Each accessway 152 lies over a respective ramp 134 and leads to the floor 100 of a respective one of the cells 126, 128, 130, 132.

Each accessway 152 is closed, at the top of the coπesponding ramp 134, by a

respective door 154 (shown in Figure 9). For each cell 126,128,130, 132, biogas

produced during processing can be conveniently collected at a point on the

coπesponding inclined region 150 adjacent the coπesponding door 154.

A sprinkler system (not shown) is mounted on the underside of the roof 146 for

introducing leachate or water into each cell 126,128, 130,132.

The main horizontal region 148 of the roof 146 also extends over the ground 91 for

a short distance at each end of the fermentation structure 90 (see Figure 7).

As seen in Figures 7,8 and 9, the roof 146 is supported by the inner and outer vertical

walls 96,98, by the end walls 102, 104, 140 and by the dividing walls 1 12, 1 14, 1 16, 142.

Additionally, if required, the roof 146 may be supported by columns provided in the

cells 126,128, 130, 132 and extending up from the floor 100.

The building 92 is built on the roof 146 of the fermentation structure 90. The

building 92 does not have its own floor or conventional foundations but, instead, the

weight of the building is borne by the fermentation structure 90 - the different

elements of the fermentation structure 90 being constructed with sufficient strength

so that the fermentation structure 90 is able to bear the weight of the building 92. The building 92 comprises, from one end to another (from left to right as shown in

Figure 7), a greenhouse section 158, a first three-storeyed section 160, a central

single-storeyed section 162 having a high roof, a second three-storeyed section 164

and a single-storeyed end section 166 having a high slopping roof. Machinery for

generating heat and electrical energy from biogas produced during fermentation in the

cells is located in the lower storeys of the first and second three-storeyed sections

160,164.

A first conveyor 168 leads from the elongate space 138, at a point intermediate the

first triangular spaces 122 to the central section 162. A second conveyor 170 leads

from the elongate space 138, at a point intermediate the second triangular spaces 124

to the central section 162.

An extractor 172 is provided to extract gas from the central section 162 to outside of

the building.

The cells 126,128,130,132 are used for processing biodegradable waste in a similar

manner to that described above for the first waste treatment plant. Waste to be

processed is introduced into the cells 126,128, 130, 132 through the doors 154 and via

the ramps 134. After biodegradation has ceased, the processed waste is dried more

thoroughly than the waste processed in the first waste treatment plant. In addition to

using heat retained by the structural elements of the cells 126,128,130,132 to dry the waste, as described above for the first waste treatment plant, additional heat generated

from biogas combustion is also used to dry the waste in the cells. The more thorough

drying of the waste leads to an even greater reduction in the weight and volume of the

waste and also leads to the waste being more easily handled. Additionally, the more

thorough drying leads to the waste being less odorous. This aspect of the invention

is independent from other aspects of the invention described herein.

After waste processing and appropriate drying has been completed in a particular cell

126, 128, 130, 132, the waste from that cell is emptied from the cell via the door

separating the cell from the adjacent triangular space 122,124. The waste is loaded

onto the nearest conveyor 168,170 and transported to a holding region in the central

section 162. The central section 162 also houses suitable machinery for recovering

residual, non-biodegradable components such as metals and plastics. Recovery of

such components is facilitated by the dry nature of the processed waste.

The transport of waste from a cell 126, 128,130,132 by a conveyor 168, 170 to the

central section 162 enables air from the cell to be drawn into the central section. This-

air is vented to the atmosphere via the extractor 172. In turn, air drawn from the cell

126, 128, 130, 132 is replaced by fresh air that enters through the door 154 of the cell

or through a suitable vent. The fresh air facilitates entry into the cell by workers

during emptying of the cell. Processing of waste in the cells 126,128,130,132 can be monitored from the elongate

space 138 using windows or conduits as described above for the first waste treatment

plant.

As the building 92 is built on the fermentation structure 90 and conventional

foundations for the building 92 are omitted, the cost of the building 92 may be

considerably reduced. This is an important aspect of the invention and is independent

of the other aspects of the inventions described herein. Even if a building is not built

on the fermentation structure 90, there are advantages in the form of the fermentation

structure 90. In particular, the provision of the immovable roof 146 may be cheaper

than providing moveable covers for the cells such as the flexible impermeable covers

25 of the first waste treatment plant described above. Again this feature is

independent of the other aspects of the invention described herein.

It will be appreciated that the third waste treatment plant may be varied in many ways.

For example, monitoring of waste processing could take place from above the cells

126,128,130,132 via monitoring means such as conduits or windows provided in the

roof 146.

It will be appreciated that features of the first, second and third waste treatment plants

are interchangeable. Thus a feature that is used in one of the treatment plants but not

in another may be applied to the plant that does not use the feature. As discussed above, processing of waste in the first, second and third waste treatment

plants gives rise to a residual, particulate, solid material. This residual material,

preferably after drying, can be compacted, either alone or with other materials, to

produce blocks. Such blocks have many uses.

For example, the residual material is relative inert and can be compacted, optionally

with other relatively inert waste materials, to produce blocks that can be used as day

cover for land-fill sites. Blocks of this type can also be used as fill material in

landscaping or other environmental projects.

The blocks can also be used to support plant growth. For example, the blocks may be

provided with seeds, bulbs or other plant propagative materials which will germinate

and grow in the blocks. Such blocks may be used to produce, relatively quickly, a

pleasing surface layer in landscaping, land reclamation, the forming of embankments

and other such environmental projects. In order to make blocks for such uses, the

residual solid material may be mixed, before compacting, with other materials, for

example compost, in order to improve the ability of the blocks to support plant

growth.

Alternatively, the blocks can be provided with a surface layer of a natural or artificial

plant growth medium. The surface layer could then be provided with seeds, bulbs or other plant propagative materials, which will germinate and grow in the growth

medium, the roots eventually growing into the blocks.

Depending on the cohesive properties of the blocks and on the intended use of the

blocks, they may be bound or covered so as to help retain the material of the blocks

together and in the required shape. Where the blocks are provided with a surface layer

of plant growth medium, the binding or covering would be provided on the outside of

the growth medium. One potential covering material is latex which can be applied in

a thin layer through which plants can grow.

Clearly, blocks can be formed in any desired shape or size to suit particular uses.

Claims

1. Apparatus for treating waste and a building, the apparatus comprising a

closeable cell for processing of waste therein to produce biogas, the cell bearing

at least part of the weight of the building.

2. Apparatus and a building according to claim 1 , wherein at least part of the

building is disposed on the cell.

3. Apparatus and a building according to claim 2, wherein the apparatus

comprises a plurality of closeable cells for processing of waste therein to produce

biogas, respective parts of the building being disposed on respective ones of the

plurality of cells.

4. Apparatus and a building according to claim 3, wherein each cell has a roof,

the roofs together forming a horizontal surface on which is disposed at least part

of the building.

5. Apparatus and a building according to any one of claims 1 to 4, wherein the

building comprises an area for receiving waste processed in the or each cell.

6. Apparatus and a building according to claim 5, wherein the area houses

equipment for further processing the processed waste.

7. Apparatus and a building according to claim 5 or claim 6, wherein means

are provided for conveying processed waste from the or each cell to the area,

conveying of processed waste by the conveying means from the or each cell to the

area causing gas flow from the or said each cell and the entry of fresh air into the

or said each cell.

8. Apparatus according to claim 7, wherein said gas flow from the or said each

cell comprises gas flow via the area to a vent for venting to outside of the building.

9. Apparatus for treating waste, comprising a closeable cell for processing of

waste therein to produce biogas, the cell comprising a floor, a wall and a roof, the

roof being immoveable relative to the floor and the wall.

10. Apparatus according to claim 9, wherein the wall is provided with an

opening for filling the cell.

1 1. Apparatus according to claim 10, wherein the cell includes a closure for

closing the opening.

12. Apparatus according to claim 10 or claim 1 1 , wherein the floor is below

ground, the opening being provided at ground level and a ramp extending between

the opening and the floor.

13. Apparatus according to any one of claims 9 to 12, wherein the roof is

constructed at least partially with concrete.

14. Method of treating waste comprising processing waste in a closed cell

to produce biogas and drying the processed waste using heat generated from the

biogas or from the processing.

15. Apparatus for treating waste, comprising a plurality of closable cells for

processing of waste therein to produce biogas and an accessway, the accessway

extending alongside each cell and being separated from waste being processed in

the cells by at least one wall, and means allowing, for each cell, when waste is

being processed in said each cell to produce biogas, monitoring of a variable of

said processing in said each cell from the accessway.

16. Apparatus according to claim 15 wherein the means is provided in the at

least one wall.

17. Apparatus according to claim 15 or claim 16, wherein the means allows

monitoring of the variable, separately, at different heights in said each cell.

18. Apparatus according to any one of claims 15 to 17, wherein the means

(which may, for example comprise one or more windows) allows monitoring of

the variable by visual observation from the accessway.

19. Apparatus according to any one of claims 15 to 18, wherein the means

comprises a plurality of conduits extending through the at least one wall, a

respective at least one channel communicating each cell with the accessway.

20. Apparatus according to any one of claims 15 to 19, wherein the cells are

disposed in a row and the accessway extends alongside the row.

21. Apparatus according to claim 20, wherein the apparatus comprises a further

row of closable cells for processing of waste therein to produce biogas, the further

row lying parallel to the first-mentioned row, the accessway being a passageway

lying between the first-mentioned and further rows, the passageway being

separated from waste being processed in the cells of the further row by a further

at least one wall, said means allowing, for each cell of both rows, when waste is

being processed in said each cell of both rows to produce biogas, monitoring of a

variable of said processing in said each cell of both rows from the passageway.

22. Apparatus according to claim 21, wherein the first-mentioned at least one

wall is a first continuous wall and the further at least one wall is a second

continuous wall, at least two vertically spaced floors extending between the first

and second walls to form, respectively, at least two vertically spaced passageways

between the walls, said means allowing monitoring of said variable of said

processing in said each cell of both rows at a plurality of different heights in said

each cell from, respectively, coπesponding ones of the passageways.

23. Apparatus according to any one of claims 15 to 22, wherein the or each at

least one wall forms a respective wall of each one of the cells separated from the

accessway by said the or each at least one wall.

24. Apparatus according to claim 20, wherein the at least one wall is a

continuous wall extending parallel to the row, a wall of a greenhouse extending

parallel to the continuous wall and the accessway being a passageway extending

between the continuous wall and the greenhouse wall.

25. Apparatus according to claim 24, wherein at least two vertically spaced

floors extend between the continuous wall and the greenhouse wall to form,

respectively, at least two vertically spaced passageways between the walls, and

wherein said means allows monitoring of said variable of said processing in said each cell at a plurality of different heights in said each cell from, respectively,

coπesponding ones of the passageways.

26. Apparatus according to any one of claims 15 to 25, wherein the or each at

least one wall is substantially vertical.

27. Apparatus according to any one of claims 15 to 26, wherein each cell has,

at a side thereof opposite to the accessway, an inclined wall.

28. Apparatus for treating waste, comprising first and second parallel rows of

closable cells for processing of waste therein to produce biogas, a space extending

between the rows and fluid distribution means being provided in the space and

communicating with each cell.

29. Apparatus according to claim 28, wherein the fluid distribution means

comprises one or more conduits for carrying biogas removed from the cells.

30. Apparatus according to claim 28 or claim 29, wherein the fluid distribution

means comprises one or more conduits for supplying leachate to the cells.

31. Apparatus according to any one of claims 28 to 30, wherein the space is

separated from waste being processed in the cells of the first row by a first wall and the space is separated from waste being processed in the cells of the second

row by a second wall, the first and second walls being connected at their bases by

an upwardly concave elongate member forming a channel which communicates

with each cell for receiving leachate therefrom.

32. Method of treating waste comprising, processing waste to produce biogas,

collecting leachate from said waste, adding the leachate to waste, the wherein

during said addition the leachate is at a temperature to hasten production of biogas

from the waste to which the leachate is added.

33. Method according to claim 32, wherein the waste to which the leachate is

added is not the waste from which the leachate was collected.

34. Method according to claim 32 or claim 33, wherein a temperature of the

leachate is adjusted prior to said addition so that the leachate is at said addition

temperature during said addition.

35. Method according to claim 34, wherein said adjusting consists of heating

the leachate.

36. Method according to any one of claims 32 to 35, wherein the leachate is at

50°-60°C, preferably 55°C, during said addition.

37. Method according to claim 36, when claim 36 is dependent on claim 35,

wherein said heating comprises heating the leachate to between 50-60°C.

38. Method of treating waste comprising; providing a plurality of closable cells

and a supply of waste; treating the supplied waste in a cycle including: loading the

supplied waste successively into individual cells of the plurality; processing the

waste in the loaded cells so as to produce biogas; preparing the loaded cells for

loading of supplied waste; the number of cells of the plurality and the supply of

waste being such that each cell of the plurality is in the cycle, and at least one

further cell being provided.

39. Method according to claim 38, wherein at any one time in the cycle, at least

one cell of the plurality is available for loading.

40. Method according to claim 38 or claim 39, wherein, at any one time in the

cycle, waste is being processed to produce biogas in more than half of the cells of

the plurality.

41. Method according to any one of claims 38 to 40, wherein during the cycle

the cells of the plurality are loaded in a sequence and emptied in the same

sequence, the sequential loading and emptying being repeated such that while each cell of the plurality is being emptied the cell of the plurality that precedes said each

cell in the sequence is being loaded.

42. Apparatus for treating waste, comprising a closable cell for processing of

waste therein to produce biogas, and a system for introducing a fluid, especially

a liquid into the cell to at least partially submerge waste in the cell.

43. Apparatus according to claim 42, wherein the apparatus includes a plurality

of closable cells for processing of waste therein to produce biogas, the system

allowing, selectively, introduction of fluid into each of the cells individually so as

to at least partially submerge waste in said each cell.

44. Apparatus according to claim 42 or claim 43, wherein the fluid is a liquid

and the system includes a reservoir for the liquid.

45. Method of treating waste, comprising processing the waste in a closed cell

so as to produce biogas, and introducing a fluid, especially a liquid, into the cell ^~

to submerge at least partially the waste so as to stop substantially the process.

46. Method according to claim 45, wherein the fluid is water or substantially

water.

47. Apparatus for treating waste, comprising a plurality of closable cells for

processing of waste therein to produce biogas, and a building, the cells being

located adjacent the building and energy generated from the biogas being used in

the building in a process unrelated to said waste processing.

48. Apparatus according to claim 47, wherein the building is integrally formed

with the cells.

49. Apparatus according to claim 47 or claim 48, wherein the building is a

greenhouse that is heated using said energy.

50. Method of treating waste, comprising processing the waste to produce

biogas, and using the biogas to generate energy for heating a greenhouse.

51. Method according to claim 50, wherein, after said processing, a solid

derived from the waste is used in the greenhouse as compost, soil dressing or soil

conditioner.

52. Method according to claim 50 or claim 51 , wherein the waste comprises

biomass from the greenhouse.

53. Method according to any one of claim 50 to 52, wherein carbon dioxide

from the conversion of biogas to energy is fed into the greenhouse.

54. Method for treating waste, comprising processing fish farm waste or

chicken manure in a closed cell to produce biogas.

55. A method of treating particulate waste comprising processing the waste in

a closed cell to produce biogas and a residual solid material, and compacting at

least the residual solid material so as to form a block from said at least the residual

solid material.

56. A method according to claim 55, further including wrapping or binding the

block.

57. A method according to claim 56, wherein the block is wrapped in latex.

58. A method according to claim 55, further including covering at least part

of the block with latex.

59. A method according to any one of claims 55 to 58, wherein the block is

provided with seeds, bulbs, or other plant propagative material for growth of plants

in the block.

60. A method according to any one of claims 55 to 59, further including

growing plants in the block.

61. A method according to claim 55, further including covering at least part

of the block with a plant growth medium.

62. A method according to claim 61 , wherein the growth medium is provided

with seeds, bulbs, or other plant propagative material for growth of plants in

the medium.

63. A method according to claim 61 or claim 62, further including growing

plants in the growth medium.

64. A method according to claim 55, wherein the block is used as a land-fill day

cover.

65. A method according to any one of claims 55 to 64, wherein the residual

solid material is dried before said compacting.