CA2096175C - Wastewater treatment method and apparatus - Google Patents

Abstract

A water treatment system is described, for use with potent wastewaters such as septic tank effluent, the system including single-pass aerobic filtration in a small contained transportable volume, using a special water-absorbent and air-permeable filter medium such as polyurethane foam particles, and including optional ensuing water-saturated treatment for removal of additional undesirable constituents before discharging to the environment. The high-rate aerobic biofilter has low maintenance requirements, is independent of soil and drainage conditions, and can be pre-manufactured for predictable performance.

Description

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FIELD OF THE IN~ENTION
This invention relates to aerobic and ensuing treatments of domestic sewage and wastewater, and certain types of industrial wastewaters, and to the renovation of polluted water in ganeral.

BACKGROUND ART
The most common method for on-site treatment of domestic sewage and wastewater is a conventional septic system using a septic tank for anaerobic treatment and a tile bed, raised hed, or sand filter for aerobic biofiltration. These solid particle aerobic filters are readily constructed, and are passive, single-pass biofilters which require little maintenance. However, even in ideal conditions, nitrate and phosphorus are released to the groundwater because the treated water cannot be collected for further treatment. Loading rates of potent wastewater such as sept:ic tank effluent in solid particle media are low, usually 1 5 cm/day (cm3 volume/cm2 area~, and treatment beds therefore require large volumes of filter media. A tile bed requires ~0-400 m3 of unsaturated soil, and a sand filter requires about 25-35 m3 of sand and gravel. Signi~icantly higher loading rates are required for the biofilter to be transportable. The physical characteristics of natural filter media such as soil and sand are highly variable.
The large volumes and natural variations preclude pre-manufacturing the biofilters to consistent specifications so that performance can be guaranteed at any site.
Aerobic package plants that are manufactured off-site are generally highly mechanical units with high capital cost and h gh maintenance requirements.
There is a need for a low-maintenance single-pass aerobic biofilter with a filter medium that has predictable physical properties and therefora predictable

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treatment performance. It shou:Ld withstand high loading rates so it can be pre-manufactured to consistent specifications in a small volume and transported to site.
Burial of the system and removal of nitrate and other undesirable contaminants after aerobic treatment is also advantageous.
In certain countries, polluted water is used directly for human consumption and cooking, resulting in sickness and death from water--borne diseases. There is a need for a low-cost, low-technology, and transportable aerobic treatment system which removes substantial amounts of biological pathogens.
An at-grade peat system uses natural peat as the filter medium and removes nutrients such as nitrogen and phosphorus. It requires a very specific peat and the loading rate for septic tank effluent is only 4-5 cm/day, thereby precluding central manufacture and transport of the ~50-m3 volume. The peat also requires special handling to avoid over-compaction. The syst:em cannot be buried and it removes a significant area of t:he property (-200-300 m2) from use.
United States patent no. 5,049,265 (Boyd et al.), granted in 1991, uses biologically active young sphagnum peat in containers which can be buried. The increased water-holding capacity enables treatment to occur at what are stated to be "very high loading rates".
~he peat is mixed with a non-specific amount of peat fibre to reduce the tendency to clog and pond on the surface. It is compacted by a non-specific amount to prevent channelling i~ undercompacted, and clogging if over-compacted. Because the medium is inconsistent, treatment performance cannot be assured. Loading rates of only 7-15 cm/day are cit~d with a preferred rate of <11 cm/day, which is insufficient to allow pre-construction and transport of the 20-30 m3 volume to site.

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Synthetic filter media have heen used for treating relatively clear water. In U.S. patent no.
4,427,5~ uick), granted in 1984, a slab of polyurethane foam is used as a physical and biological filter to remove solids and ammonium from aquarium water.
The slab filter must be removed and cleaned frequently and does not constitute an alternative biofilter for treating potent wastewater with high solids and biochemical oxygen demand. Under high loading rates of potent wast~water, solid foam soon plugs up and becomes anaerobic, similar to a solid particle biofilter.

DISCLOSURE OF INVENTION
It is an object of the invention to provide a single-pass aerobic treatment method and apparatus for potent wastewater in a small contained volume, in view of the above deficiencies of the prior art. Another object is to collect the aerobically treated water for removal of other undesirable contaminants.
The invention includes a high-efficiency biofiltration module which provides thorough wastewater treatment in a relatively small contained volume, because of the distinctive physical properties of a special absorbent filter medium. It also includes preferably at least one water-saturated module which further renovates wastewater while isolated from the natural environment.
Each module generally has a specific treatment function, including aeration, nitrate or phosphorus removal, organi~ solvent removal, etc. Modules of similar function (e.g., two or more aerobic modules and/or two or more saturated modules) may be combined for larger capacity.
Wastewater such as septic tank effluent, or any water which contains biodegradable matter, is introduced into a free-draining aerobic module which contains the ~ 3 i~ 3~

special absorbent biofilter medium. The aerobic filter medium is a material with superior water retention and air-permeability properties, such as polyurethane foam particles or a foam slab with aeration conduits formed through it. The particles have open cellular interiors so that the wastewater is transferred through the interiors of the particles or through the foam slab, while the large voids between the particles or the aeration conduits remain open, precluding plugging by biomat development and allowing for simultaneous wastewater loading and air ventilation. By contrast, solid particle media must be loaded intermittently, then allowed to drain free to be ventilated. They cannot be loaded and ventilated at the same time, and therefore have much ~5 lower potential loading rates. In the invention, the combination of water retention and ventilation allows for greatly increased loading rates (consistently 10 times or more higher) over that of solid particle media such as sand or a solid slab of foam without aeration conduits.
The small voids between solid particles are readily bridged by biomat. No plugging of the foam particles in the invention has occurred in laboratory and field experiments even after 10 months of ~0 cm/day loading rates and 18 months of continuous use~ Field units have incurred 10 months of loading at 55 cm/day of potent wastewater, with 95-9~% removal of total suspended solids and BOD, and with no sign of plugging (Table 1).
They have incurred surges of 170 cm/day for several days with insignificant effect on performance. On the other hand, peat and sand filters plugged up within one month of use at these high loading rates. In the invention, the superior physical properties of high surfa~e area, high water retention, and permeability to air allow treatment within a small contained volume in a single pass.

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TABl,e 1: Avcra~ecd r~ s Or i~o~ml ficl~l unit trcating pr;mary clarificr crf1ucnl(T = 5-14 ~) ~low r~tcs avc~g~ 2(l()0 L/day, or a very high l~ading rale of 54 cm/day.
n Inrlll~nt Efflu~nt ~/o Rcmov~l BO~7 (mg/L) 9 123 2.~ 97-99 TS~; 10 ~2 2.X 9~ )8 NH4-N 7 5.9 I.-I -NO3-N 1() 0.2 22.5 Total coliform ~CFU/lO()mL) lO -1.6c7 7.lc4 99.3-99. 7 10 ~ec~ll colifo~m -lO 5.6ct) 3.4c4 99.5-99.7 The wastewater percolates slowly downwardly through the unsaturated filter medium in the aerobic module, during which time it is renovated by microbial activity. Natural air convection through vents in the 15 container wall ordinarily provides ade~uate treatment of organic matter, solids, and pathogens. However, to achieve full nitrification and ammonia removal at low temperatures, the air flow through the medium should be increased by means of larger voids between particles or hy artificial forced air means. If the wastewater contains adequate dissolved oxygen for the treatment process, simple vents through th~ container provide adequate aeration by natural convection.
The aerobically treated water collects at the bottom of the aerobic module and passes to the next treatment module in series, usually a saturated module with a reactive medium for removal of nitrate, phosphorus, or other constituents. ~lternatively the aerobically treated water may be discharged directly to the environment in some cases.
The use of contained volumes enables the wastewater to be nitrified, collected, and then denitrified before discharge. Denitrification and further biological filter treatment can be provided by one or more saturated modules containing a suitable 2 ~ ~ 6 ~

filter medium. In the water-saturaked module(sl~ non-reactive media such as synthetic foam particles provide a protected attachment means for microhes to biodegrade nitrate or chemicals. Reactive or absorbing media such as coal, limestone, cellulose, or iron oxides provide a variety of treatments for removal of unde~irable constituents.
The invention works effectively in drainage and soil conditions which are otherwise inappropriate for conventional, engineered, or peat tile beds. The modules can be place~ above or below ground and can be designed to operate with or without electricity.
The invention provides a high rate, single-pass aerobic biofilter for potent wastewater treatment which has low main~enance demands, and which can be pre-manufac~ured off-site and transported to the site for consistent performance. The invention replaces and improves upon tile beds and sand filters, and has fewer maintenance re~uirements than mechanized aeration systems.
Additional features of t:he invention will become apparent from a consideration of the drawings and the ensuing detailed description.

BRIEF DESCRIPTION OF DRAWINGS
Preferred and alternative embodiments of the invention will now be described in detail, with reference to the accompanying drawings, in which:
Fig. 1 is a schematic cross-section of the modular treatment invention which replaces the conventional tile bed with an aerobic biofilter, and removes additional constituents in subsequent treatment modules;
Fig. 2 shows the invention in a vertical configuration for above-ground installation. Ventilation

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pipes enhance the aerobic treatment, especially to provide thorough nitrification at low temperatures;
Fig. 3 is a perspective drawing of an unsaturated aerobic module with a low profile des~gned specifically for burial. Wastewater and ventilation air flow paths through the treatment medium are indicated;
Fig. 4 is a perspective drawing of a water-saturated module for burial or surface instal'ation.
Water flow paths are circuitous through the module to 10 r~;mi ze contact with the treatment medium;
Fig. 5 is a schematic cross-section showing a prior art medium such as sand, and Fig. 6 is a schematic cross-section showing an example of the medium in the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION
A detailed description of the best mode for carrying out the invention/ and of variations on the invention, is as set out below:

Basic structure of the aerobic moclule The aerobic module 100 (shown schematically in Figs. l and 2 and in detail in Fig. 3) is the key element in the treatment process and preferably includes a container 100, a distribution header llO, a treatment medium 115, and a ventilation means 175. The structure 25 of the container 100 includes a wastewater inlet 105, a treated water outlet 125, and an optional inspection or access port 150. It may be buried, as illustrated in Fig. 1, if the water table is sufficiently low, or installed on the surface.
The distribution header 110 is embedded proximate the top of the treatment medium 115 and is connected to the wastewater inlet 105. The distribution header 110 is supported by any suitable means.

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The air ventilation means 175 preferably includes an air collection header 155 embedded proximate the hottom of the medium 115, an air inlet 150, an air outlet 170, and an air ventilation fan 165. The air collection header 155 is supported by any suitable means.
In another embodiment in which adequate aeration can be provided by natural convection, the air ventilation means 175 includes the air inlet 150 or air outlet 170. In another embodiment, ventilation air may be introduced through the distribution header 110 along with the wastewater by means of a pump using compressed air as a driving means.
The treatment med~um 115 substantially fills the module 100.

Function/process of the aerobic module Wastewater 130 is introduced to the aerobic module 100 through the inlet 105, into the distribution header 110. The water percolates slowly downwardly through the absorbent medium 115 where treatment is efEected, and is discharged through the outlet 125 to another treatment module, such as a water-saturated module 200 as shown in Figs. 1 and 4, or to the environment.
Ventilation air 145 is preferably brought in through the inlet ~50 and is drawn through the permeable medium 115 to the collection header 155, and is discharged through the outlet 170. Alternatively, air may be introduced by a fan or with the wastewater by means of an air-driven pump.

Details of the aerobic module elements - Container The container used for the aerobic module 100 is enclosed and made of any suitable material which is preferably impermeable, non-reactive, durable, and structurally sound, such as plastic or concrete.
Tha container may be of any reasonable shape, and the size of the container is typically approximately 3-5 m3 for a flow of 2000 L/day of potent wastewa~er.
Larger or more numerous modules can be used for larger flows.
The water and air inlets and outlets 105, 125, 150, 170 are through-wall fittings of durable materials such as plastic, are appropriately sized, and are connected by any suitable means.
The inlet 105 is preferably located proximate the top oE the module and the outlet 125 is located proximate the bottom, ensuring free drainage of the wastewater through the module 100. When pump dosed, the inlet 105 may be proximate the bottom for convenience or to prevent freezing, although the distribution header will of course still be proximate th~ top.
The access port 150 should allow for inspection and maintenance and can double as the air inlet for ventilation air 145.

Details of aerobic module elements - Distribution header As seen in Fig. 3, the distribution header 110 is a means to distribute the wastewater evenly and directly into the upper portions of the medium 115. The header 1~0 can be made of perforated tubes of durable plastic such as PVC, appropriately sized, connected by any suitable means and supported by any suitable means.
If dosing is by pump or siphon surge, the header 110 can be a series of spray nozzles, preferably discharging onto splash plates (not shown).
The distribution header 110 is shaped and perforations therein are sized and positioned so that the wastewater is evenly distributed onto the medium 115. In another embodiment, the spray nozzles and splash plates '. 7 ~ 3 in header 110 are arranged to spray evenly onto the medium 115.

Details of aerobic module elements -Structure of ventilation means The air ventilation means 175 preferably includes a ventilation air inlet 150 (previously described), an air collection header 155, a ~an 165, and an air outlet 170 (previously described).
The air collection header 155 is preferably made of perforated plastic tubes of appropriate size, connected by any suitable means, and support~d by any suitable means~ Appropriate perforations are positioned uniformly along the tubes, such as every 10-20 cm, for example. Durable screen preferably covers the perforated tubes to prevent clogging by the medium 115 which preferably surrounds the header 155.
The air collection header 155 is shaped so that the ventilation air is distributed as evenly as possible through the medium 115. For example, in field trials of the configuration shown in Fig. 2l a long, narrow rectangular loop of perforated tube was found to be effective in ventilating a long narrow tank.
In one embodiment, a fan 165 is located proximate the air outlet 170 to facilitate ventilation of the module 100. The fan 165 can be electric or wind-driven.
In another embodiment, the air ventilation means 175 includes the air inlet 150 or air outlet 170.
In another embodiment, the air ventilation means 175 includes an air-driven pump and the air outlet 170.

Function - air flow through media and ventilation system The ventilation air is brought into the module 1~
100 to sustain aerobic biotic activity within the medium 115 and to aerate the water.
Flow can be directed upwardly or downwardly through the medium 115, but odour in the vented air 148 is minimized if the air flow follows the path of the wastewater. Odour removal can also be effected by passing the discharged air 148 through a de-odourizing media such as natural peat or activated charcoal (not shown).

Details of aerobic module elements - Structure of media The treatment medium 115 is a means for conveying the wastewater 510wly downwardly through the aerobic module 100 and promoting aeration. Water treatment within a module of reasonable size is possible only with the use of medium 115 which has superior water retention and air permeability properties. Preferred materials for the medium 115 incl~lde particles of open cellular synthetic ~oam such as flexible polyurethane foam, modified synthetic foam, sponge, or other similar materials. These absorbent particles transmit water through their interiors by way of the open cells, and also have high water-retention capacity. The particles remain water-saturated, but air ventilation occurs simultaneously through the open voids between t~e particles. For example, excellent aerobic treatment was attained in laboratory and field experiments with particles of polyurethane foam of mixed sizes ranging generally between about 0.5 and 5 cmO A narrow size distribution of larger particles provides larger and more open void spaces between the particles for ease of aeration, whereas a distribution of small and large particles provides smaller void spaces and more restricted air flow.
The medium 115 does not necessarily require a 5~

particulate form, but could rather be a solid slab of plastic foam, for example, with aeration conduits formed substantially through it to allow diffusion of oxygen from the conduits to the water contained in the foam interior. This format would ease the fabrication of the aerobic module 100. The size and separation of the aeration conduits would depend on the loading rate and wastewater potency hut could be 2 cm in diameter, and distributed through the slab every 10 to 20 cm, for example. To promote ventilation, the conduits would preferably be oriented approximately vertically with optional hori~ontal interconnections.
The medium material preferably should be durable enough to retain these superior properties over the expected life span of the system (e.g., 20-30 years)~

Function of the media The unsaturated aerobic module 100 reproduces the processes of a conventional tile bed in a small, aerobic container 100 (e.g., 3-5 m3 for a typical domicile).
The medium 115 sustains diverse populations of beneficial biota by providing protection from desiccation, extreme temperatures, and washouts by increased flow of wastewater. As can be seen from Fig.
6, the medium 115 allows entry of ventilation air through the large air-filled ~oid spaces 116 between the water-filled foam particles 117 (or through the aeration conduits in the case of solid foam blocks), provides nutrient-rich wastewater to sustain the biotic populations, and retains it long enough to be thoroughly treated in the biofilter. In Fig. 6~ the large arrows illustrate air flow through the voids, and the small arrows illustrate wastewater flow through the particles.
By contrast, as can be seen from Fig. 5 (prior ~ ~ r~ ~ 3 7 ~

art), ventilation air cannot flow, since the space between particles is filled with the wastewater.

Basic structure of the saturated module The saturated module, shown in Fig. 4, includes a container 200~ and a treatment medium 215 and preferably, vertical flow baffles 210. The structure of the container 200 includes a water inlet 205 and a water outlet 225.
The flow ba~fles 210 are preferably fastened to the interior walls.
The treatment medium 215 substantially fills the module.
Th~ module 200 can be placed either adjacent to or under the aerobic module 100 as desired or as space limitations demand.

Function/process of the saturated module The saturated module 200, if used, receives aerobically treated water through the water inlet 205 and guides it through the treatment medium 215 around the flow baffles 210, and discharqes it through the outlet 225. The circuitous flow path ~i izes exposure of the water to the medium 215.
The saturated module 200 promotes anaerobic biological activity to remove additional undesirable constituents discharged from the aerobic module 100.
The saturated module 200 is convenient for abiotic removal of phosphate and other contaminants, although an anaerobic environment is not a requirement.
The saturated module 200 is a self-contained, water-saturated module containing media conducive to the growth and maintenance of beneficial anaerobic bacteria and biota. Water is passed to it at a rate sufficient to allow the media to retaln the effluent to further treat 7 ~

the water before displacement by additional aerobic effluent.

Details of the saturated module elements - Container The container used for the saturated modul~ 200 is made of any suitable material which is preferably impermeable, non-reactive, durable, and structurally sound, such as plastic or concrete.
The container may be of any reasonable shape, and the size of the container should be adequate for a residence time of a~out 1 day.
The containers require an access port (not shown) with a removable cover for filling and inspection.
The water inlet and outlets 205, 225 are through-wall fittings of durable materials such as plastic, are appropriately sized, and are connected by any suitable means.
The inlet and outlets 205, 225 are proximate the top of the container to maintain saturated conditions. The inlet 205 brings aerobically treated water into the saturated module 200.
Durable screen preferably covers the inside of the inlet and outlet 20~, 225 to keep the medium 215 inside module 200.

Details of the saturated module elements Structure and function of the media The treatment medium 215 includes any natural or artificial material which promotes biotic and abiotic treatment under water-saturated conditions, and which is sustainable over the expected life of the system (e.g., 20-30 years).
Removal of phosphorus from wastewater is an abiotic chemical reaction process which occurs when dissolved phosphorus reacts with calcium carbonate to 2 ~ . '7 ~

create a calcium phosphate mineral. Crushed limestone can therefore be used as a treatmen-t medium 215 to remove phosphorus. Phosphorus is also adsorbed onto iron oxy-hydroxides in aci~ic conditions, and therefore certain crushed iron ores, pellets~ or similar material can ~e used as treatment media. Organic solvents can be absorbed onto media such as coal particles which may be mixed with other media in the saturated modules. Foam particles may be mixed in with the reactive media to promote microbial populations.

Polluted water treatment This is an additional use using the same apparatus.
The aerobic module 100, with or without the saturated mvdule 200, can be used to renova~e polluted water for domestic consumption. Inorganic matter such as clay and mud is first removed by any suitable conventional filtration means. Laboratory experiments show that at 20 C, coliform bacteria are reduced by 5-6 orders of magnitude in <1 m thickness of polyurethane foam medium 115. The medium 115 acts as a physical filter as well as a biological filter, and is able to retain and remove larger harmful biota, such as Giardia cysts. Tropical climates are ideal for this invention and are the areas where water-borne diseases are most prevalent.

Summary The invention provides a means for single-pass aerobic treatment of potent wastewater at high loading rates in a small, contained and transportable volume, by way of a special absorbent filter medium and ventilation means. The aerobically treated water can be collected and further treated in water-saturated modules to remove .7 ~

undesirable constituents such as nitrate and phosphorusO
The invention i5 independent of the natural environment and does not re~uire high maintenance mechanical devices.
Anaerobic septic tank effluent i5 an obvious wastewater source for the invention, but any water containing undesirable biodegradable matter can be treated, such as polluted surface water. The apparatus can be placed above or below ground and is equally effective in all drainage and soil or rock conditions, even conditions which are inappropriate for conventional or engineered tile beds.
Accordingly, advanta~es of the invention are possibly that the wastewater treatment system may:
(1) allow thorough and flexible treatment of domestic wastewater and certain industrial wastewaters, including aerobic and ensuing treatments in successive modules, independently of soil type, precipitation, and drainage conditions;
(2) treat polluted surface water or groundwater for disposal or for subsequent use;
(3) treat the wastewater in a small~volume aerobic module by using absorbent particles instead of solid particles;

(4) not require a large lot, and not remove any land from use when buried;

(5) be low-technology, low~maintenance, and easily installed by semi-skilled workers, and not rely on mechanical devices or chemical additives, although either could be included;
(~) not depend on a particular tank shape, size, or composition for the treatment modules t and may use common, sustaina~le, and inexpensive materials for the modules and for the aerobic and saturated treatment media;
(7) be customized to treat a particular type or ~ '7l~3 volume of wastewater by adding a particular treatment module or by linking modules together;
(8~ be connected directly to a conventional septic tank for easy retrofitting and not require special plumbing in the house or building;
(9) be a factory-made standardized product for predictable performance, ease of inspection and approval, and is easily transportable; and (10) be installed above ground or below ground, may be disguised with attractive panelling or wall cavering, may be shaded easily from the sun, and may be insulated and heated easily in permafrost areas.
It should be recognized that not all of the above advantages will necessarily be achieved simultaneously in any given installation.
It will be appreciated that the above description relates to the preferred embodiment by way of example only. Many variations on the invantion will be obvious to those knowledgeable in the field, and such obvious variations are within the scope of the invention as described and claimed, whether or not expressly described.
For example, although the above description refers to the aerobic and saturated modules being defined by containers, it should be readily appreciated that in some soil conditions, it may be acceptable to simply excavate a containment volume, defined by the walls of the excavation, and position and support the various components within that excavated containment volume, with a suitable cover or lid being provided.
It should also be appreciated that although the preferred embodiment of the invention contemplates combining aerobic and ensuing treatment stages, an aerobic stage only may be sufficient for certain applications.

Claims (16)

Claims

1. Water treatment apparatus, for the treatment of polluted water, wherein:
the apparatus comprises a treatment station, which includes a container, in which is contained a body of a foam material;
the treatment station includes a water-throughflow-control-means, including an inlet and an outlet, for conveying water through the container;
the apparatus includes a means admitting polluted water into the container, through the inlet, and onto the body of foam material;
the treatment station includes means for enabling the polluted water, so admitted, to percolate gradually down through the body of foam material;
the foam material is of a sponge-like, open, cellular structure, in which the cells are mutually interconnected;
the cells are so small that water present in the cells is retained in the cells by sponge action;
the foam material is elastomeric, flexible, soft, and resiliently deformable;
the foam material in the container is in the form of many separate blocks;
the blocks are arranged in a loose, open, heap in the container, and the blocks in the heap touch each other at places of contact;
the blocks in the heap form large, free, open, interconnected voids and spaces, through which air can circulate smoothly and freely, around and between the blocks;
the voids are so large that water cannot, in substance, support itself in the voids by surface tension, whereby water in the voids drains from the voids, leaving the voids substantially freely open and clear to the circulation of air therethrough;
the water-throughflow-control-means includes means for moving water through the container in such a way that the said voids and spaces are maintained substantially open and clear of water;
the blocks are so resilient and sponge-like that, at the said places of contact between the blocks, the material of the blocks deforms and spreads resiliently, whereby, at the places of contact, the blocks lie in water-transmitting contact with each other over a substantial contact area;
whereby the blocks form a means for retaining, between dosings, a body of water, to undergo further biological treatment, inside the block, between dosings.

2. As in claim 1, wherein the arrangement of the water-throughflow-control-means is such that the polluted water is dosed periodically into the container, and is such that the voids and spaces become substantially open and free of water shortly after the body of foam material has been dosed, whereby the voids and spaces are filled with water for no more than a small portion of the dosing period.

3. As in claim 1, wherein the body of foam material conforms resiliently to the container.

4. As in claim 3, which includes means for constraining the air to pass through the voids.

5. As in claim 1, wherein the foam is of the kind in which the cells of the cellular structure have an average diameter of less than 0.5 mm.

6. As in claim 1, wherein the arrangement of the apparatus is such that the polluted water substantially cannot pass from the inlet to the outlet other than by passing though the blocks in the heap.

7. As in claim 1, wherein the material of the foam blocks is polyurethane.

8. As in claim 1, wherein the apparatus includes an operable means for forcefully drawing air or oxygen into and through the voids and spaces, whereby in respect of substantially every block in the heap, when the means is in operation, air is constantly in motion over and around the block.

9. As in claim 8, wherein the said means comprises a powered fan or air-pump.

10. As in claim 1, wherein the inlet includes a means for spreading the polluted water admitted into the container evenly over the whole heap of blocks.

11. As in claim 1, wherein the whole heap consists exclusively of physically seperable and separate blocks of foam.

12. As in claim 1, where said container is an excavated in-ground container, having a volume defined by the walls and floor of said excavation.

13. As in claim 1, where said container has substantially fluid-impervious walls, floor and lid.

14. As in claim 1, which includes a ventilation means comprising an air inlet (150) in an upper area of said container, an air collection header (155) in a lower area of said container, an air outlet (170) connected to said air collection header, andmeans (165) connected to draw air from said container via said air collection header and said air outlet.

15. Wastewater treatment apparatus, for the treatment of polluted water, wherein:
the apparatus comprises a first treatment station, which includes a container, in which is contained a body of a foam material;
the 1st treatment station includes a water-throughflow-control-means, including an inlet and an outlet, for conveying water through the container;
the apparatus includes a means admitting polluted water into the container, through the inlet, and onto the body of foam material;
the 1 st treatment station includes means for enabling the polluted water, so admitted, to percolate gradually down through the body of foam material;
the 1 st treatment station includes a water-absorbent and air-permeable medium substantially throughout the container, to provide a suitable environment for promoting aerobic contaminant-breakdown reactions;
the 1 st treatment station includes ventilation means whereby air may pass through at least a substantial portion of the container;
the apparatus includes a second treatment station;
the 2nd treatment station includes a water-saturated containment volume (200), and means for connecting same to receive water from the water outlet (125) of the first container (100);
the 2nd treatment station includes a water inlet (205) for receiving water from the 1 st treatment station into one upper end of said water-saturated containment volume;the 2nd treatment station includes a water outlet (225) at the other upper end of said volume;
the 2nd treatment station includes water-permeable media (215) substantially throughout said containment volume, to provide a suitable environment for promoting anaerobic contaminant-breakdown reactions.

16. As in claim 15, in which said water-saturated containment volume includes a plurality of baffles (210) within said volume for forcing said wastewater to follow a circuitous path from said water inlet to said water outlet.