WO2004046037A2

WO2004046037A2 - Purification of contaminated water

Info

Publication number: WO2004046037A2
Application number: PCT/GB2003/003049
Authority: WO
Inventors: Stephen Skill; Lee F. Robinson
Original assignee: Photosynthesis Jersey Ltd
Priority date: 2002-07-16
Filing date: 2003-07-15
Publication date: 2004-06-03
Also published as: AU2003248940A8; WO2004046037A3; AU2003248940A1; GB0216476D0

Abstract

An apparatus for treating contaminated water is described, The apparatus comprises a water permeable matrix of a transparent or translucent substrate and a bio-film comprising at least one photosynthetic micro-organism supported on the substrate. Also described is a method for treating contaminated water that uses the apparatus.

Description

PURIFICATION OF CONTAMINATED WATER

This invention relates to the purification of contaminated water and to installations for purifying contaminated water. More particularly, the present invention relates to the purification of waste waters generated by agricultural, livestock, aqua-culture, industrial and urban activities.

Industry, intensive agriculture, aqua-culture and livestock farming as well as large urban settlements all produce large volumes of effluent which pollute the environment if badly managed. In certain parts of the world, there is an urgent need to address these pollution problems.

Several methods to process wastes generated by livestock and using photosynthetic organisms are known.

US-3,955,318 discloses a system for treating sewage or cannery waste using unicellular algae. This system uses colonies of algae and aerobic bacteria to treat the waste. However, high strength agricultural wastes containing high levels of total organic carbon (TOC) and a high biological oxygen demand (BOD) are unable to be processed by this method due to the narrow culture conditions ofthe algae.

GB-2,320,031 discloses a bio-reactor for the culture of micro-organisms. In one embodiment, wastewater is used as a nutrient source and a bio-film or slime layer comprising a mixed colony or consortium of photosynthetic micro-organisms is formed. The different micro-organisms tend to occupy distinct zones within the bio-film which allows the bio-reactor to provide a multi-stage water treatment process in which the wastewater is treated progressively by a series of different micro-organism communities that can assimilate different wastes. Typically, the bio-film at the inlet end of the reactor tends to be predominantly colonised by photosynthetic, anaerobic bacteria followed by photosynthetic, oxygen evolving, aerobic organisms.

The photosynthetic anaerobic bacteria can degrade complex organic molecules providing simple molecules as substrates for algal growth.

The system disclosed in GB-2,320,031 is suitable for urban areas where the land area for processing waste water is limited.

There is a need for an efficient and cost-effective method of processing agricultural, livestock and other waste waters. A method that results in the production of commercially valuable by-products is particularly desirable.

The present invention provides a water purification process that utilises a bio-film of photosynthetic micro-organisms to assimilate and remove organic and/or inorganic contaminants. The bio-film is supported on a transparent, water permeable matrix. The process can have a low capital cost and can be used on a large scale, e.g. to treat wastes from pig, cattle, poultry, sheep and fish farms and from stables; to treat household sewage and landfill leachate; to treat food and industrial effluents, such as electroplating effluents, oil refinery effluents and abattoir wastewater; and to prevent algal bloom in lakes, rivers and ponds.

According to a first aspect of the present invention there is provided an apparatus for treating contaminated water comprising a water permeable matrix of a transparent or translucent substrate and a bio-film comprising at least one photosynthetic micro-organism supported on the substrate.

According to a second aspect of the present invention there is provided a method for treating contaminated water comprising the step of contacting the water with a bio-film comprising at least one photosynthetic micro- organism supported on a water permeable matrix of a transparent or translucent substrate.

The term "bio-film" refers to the layer which forms upon the surface of the transparent or translucent substrate forming the matrix. These films typically comprise a mixed colony or consortium of different photosynthetic micro-organisms and other non-photosynthetic bacteria and fungi. The micro-organisms typically secrete polysaccharide like compounds which permeate and stabilise the bio-film and give rise to a slimy surface. The light required for the photosynthetic micro-organisms is preferably natural sunlight, but may be artificial.

The water will typically be contaminated with both organic and inorganic materials and preferably results from agricultural, livestock, industrial or urban activities.

The apparatus and method of the present invention can provide for the efficient processing of waste waters containing, inter alia, total organic carbons (TOC), contaminants that give rise to a biological oxygen demand (BOD), nitrogen (N) containing contaminants, including ammonia (NH₃), and phosphorus (P) containing contaminants, including phosphates, polyphosphates, organic phosphates and acid-digestible phosphorous. They can also provide for the removal of suspended solids as well as the removal of heavy metals or radionuclides including, but not limited to, cadmium, zinc, copper, lead, chromium, caesium and nickel.

In a preferred embodiment of the present invention, greater than 99 weight percent of the waste materials, including suspended solids that contaminate the water are removed. In a further preferred embodiment of the present invention, the bio-film of photosynthetic micro-organisms is able to effectively treat waste water streams that have a contaminant level that is over 40 times more concentrated than typical urban waste water streams that are processed by conventional water treatment systems.

The processing capacity of the process of the present invention is generally unlimited. However, a typical capacity ranges from 1 to 1,000,000 m³ of water per day.

The waste materials contaminating the water are utilised as nutrient sources by the photosynthetic micro-organisms which assimilate the materials in the presence of light and grow.

By "assimilation" we are referring to the biological transformation and'or uptake ofthe waste materials by the micro-organisms.

By "photosynthetic micro-organisms" we include unicellular and multi- cellular organisms that utilise light to generate at least part of the energy needed for survival. Examples of photosynthetic micro-organisms that may populate the bio-film include, inter alia, photosynthetic and/or facultative bacteria, e.g. purple, non-sulphur bacteria (archaebacteria), such as Rhodospirillium, Rhodopsuedomonas, Rhodobacter, Chromatium, Thiocapsia, and Rubrivivaz and cyanobacteria (blue-green algae), green algae, euglenophytes, heterokontophytes and red algae. Algal species that may populate the bio-film include, inter alia, microalgae such as Chlorella, Occilatoria, Scenedesmus, Anabaena, Nostoc and Calothrix. These microorganisms all occur naturally. When the transparent matrix is first exposed to the contaminated water, it will not ordinarily comprise a bio-film. Instead, this film develops on the surface of the transparent substrate from which the matrix is formed as the contaminated water is passed through the matrix. The photosynthetic micro- organisms that first deposit on the matrix or that have been used to seed the matrix assimilate the waste materials and this leads to the growth of the micro-organisms and the development of the bio-film. In a preferred embodiment, the matrix is seeded with some of the micro-organisms that will ultimately form the bio-film in order to encourage the growth of that film upon the matrix.

An advantage of the present invention is that the grown micro-organisms making up the bio-film can be harvested subsequently and processed into products which possess high levels of crude protein, crude fat, and amino acids, and which can therefore be used as commercial agricultural products or fuel. As a result, the costs that are incurred on disposal of the waste sludges that are generated by many conventional waste treatment processes can be avoided.

The purified water effluent can be used for crop irrigation or other uses.

The water permeable matrix may be made of any transparent or translucent material. Transparent materials are preferred, and normally the matrix will consist of transparent plastic pieces or clear glass shards that have been compacted into bags, bales or baskets for ease of handling.

The matrix will preferably have a surface area in the range of from 5 m²/m³ to 1000 m²/m³, more preferably in the range of from 20 m²/m³ to 500 rn²/m³ and particularly in the range of from 25 m²/m³ to 100 m²/m³. All of this area is, in principle,~available for growth ofthe bio-film. Typically, the matrix will comprise one or more compacted bales of the transparent substrate. These bales may be arranged in a longitudinally extending channel through which the contaminated water is passed or they may be simply suspended in a contaminated body of water.

Pieces of transparent plastic materials, e.g. produced by shredding, are a particularly suitable substrate for the bio-film. The plastic material may be a recycled material and it is a particular aspect of the present invention that recycled plastic materials are used for the matrix.

Polyvinyl chloride (PVC), the polycarbonates, the polyethylenes and polyethylene terephthalate (PET) are particularly preferred substrates for the matrix as certain species of photosynthetic micro-organisms which thrive in anoxic environments are capable of degrading these materials. This can result in the generation of carbon dioxide which can be consumed by the aerobic micro-organisms in the bio-film thereby improving the efficiency ofthe purification process.

This generation of carbon dioxide can be of particular benefit when the contaminated water contains high levels of ammonia and/or nitrates with a low BOD. Effluent streams arising from petroleum refineries are typical examples. In order to assimilate ammonia and nitrates, aerobic photosynthetic micro-organisms must have a source of carbon either in the form of carbon dioxide or organic acids (e.g. acetic acid). With the process of the present invention, the photosynthetic micro-organisms may, in the absence of a suitable carbon source in the contaminated water, derive additional carbon from the degradation of the plastic materials forming the matrix. A particularly preferred substrate material for the matrix is PET. The

PET may be translucent or transparent, but is preferably transparent.

Accordingly, another aspect of the present invention provides for the use of translucent or transparent PET in the treatment of contaminated water. The water treatment process preferably comprises contacting the contaminated water with a bio-film of at least one photosynthetic micro-organism supported on a water permeable matrix comprising an agglomeration of pieces of a translucent or transparent PET substrate. The pieces of PET are preferably compacted together to form the matrix. Preferably the matrix comprises one or more compacted bales or bags of PET.

PET containers create a large disposal problem and can occupy a substantial volume of landfill sites. Furthermore, PET biodegrades very slowly under landfill conditions. Thus, matrices made by compacting pieces of PET derived from the shredding or other comminution of waste PET products are particularly preferred. Furthermore, degradation of the PET brought about by photosynthetic micro-organisms living on its surface may offer a means to finally dispose of the waste material.

The plastic that is used is normally chopped into pieces averaging from 10 to 500 mm in size, preferably from 20 to 400 mm, using conventional shredding machinery.

The shreds are then preferably compacted to form a bale. Bales of any shape and dimension may be used in the present invention, but typically the bales are rectangular in cross-section and have dimensions of from 10 cm x 10 cm x 20 cm to 100 cm x 100 cm x 200 cm, preferably around 50 cm x 50 cm x 100 cm. The shreds that are used to form the bales typically have a size of around 200 mm. Alternatively, plastic shreds ranging from 10 to 50 mm in size can be compacted into bags. The bags preferably consist of a mesh type material which allows the passage of at least 80 % of ambient light into the bag.

Bags manufactured from polypropylene mesh are particularly suitable for this purpose.

The density ofthe matrix and, therefore, the size of the openings within the matrix that are available for water flow can be varied and depend on the degree of compaction of the material forming the matrix. Conventional agricultural balers can be used to make plastic bails.

In a preferred embodiment, the transparent/translucent water permeable matrix is positioned within a channel through which the contaminated water is directed. The channel will have an inlet end for receiving the contaminated water and an outlet end for removing the treated water and may be constructed of brick, concrete, treated timber or plastic materials, including reinforced plastic materials. Timber, plastic and glass reinforced plastic materials, being lighter in weight, allow the channels to be constructed upon a building roof or other elevated structure where land space is a premium. The channel may be covered with a translucent and preferably a transparent cover to maintain anaerobic conditions in the channel.

Typically, the matrix will comprise one or more compacted bales of the transparent/translucent substrate arranged in a longitudinally extending channel through which the contaminated water is passed.

The passage of water through the matrix results in the growth of the bio- film with different types of micro-organisms tending to grow in distinct zones of the matrix. In a preferred embodiment, the photosynthetic, anaerobic micro-organisms tend to dominate the bio-film at the inlet end ofthe matrix and there is a progressive change along the matrix to the outlet end which tends to be colonised predominantly by photosynthetic, aerobic micro-organisms. Furthermore, although the transparent/translucent nature of the matrix allows light to travel into the matrix, the intensity of the light diminishes progressively so that photosynthetic micro-organisms preferring dim light tend to dominate the bio-film in the regions of the matrix that are distanced from the light.

The natural bio-film that is generated as the process ofthe present invention is operated also tends to develop a 'sticky' surface as a result of polysaccharides that are generated. This allows the bio-film to capture suspended solids in the water which adhere to the bio-film as the contaminated water flows through the matrix.

Over a period of time, bio-film growth and suspended solids accumulation eventually clog the matrix at the inlet end. This clogging tends to be characterised by a green algal growth on the outer surface ofthe matrix. As a result, incoming wastewater will tend to bypass the inlet end ofthe matrix and enter an unclogged region of the matrix further up the water channel. For example, when the matrix comprises a plurality of bales arranged in a longitudinally extending water channel, the bales at the inlet end of the channel become clogged first of all, preventing water flow through the bales. The waste water then tends to flow over or around the clogged bales until it encounters a bale with an unclogged matrix. Over time, bales further down the channel become progressively impermeable to water flow and eventually all the bales will need to be replaced. The biomass in the clogged bails may then be harvested as described more particularly below. By "biomass" we are referring to the consortium of photosynthetic micro- organisms, principally bacteria and algae, forming the bio-film. In another embodiment of the present invention, the transparent matrix that supports the bio-film, rather than being arranged in a water channel through which the water to be treated is directed, is used to purify a large body of still or flowing water, such as a lake, lagoon, river or stream, by being suspended in that body of water. This embodiment of the present invention may be used to purify bodies of water that have been polluted by organic and inorganic contaminants by discharges of industrial, municipal or agricultural wastes. The body of water may be covered with a translucent and preferably a transparent cover to maintain anaerobic conditions.

Many lakes and rivers are polluted and if untreated can develop toxic, photosynthetic algal blooms which consume the pollutants, especially in the summer. With the present invention, the algae can be encouraged to grow within the confines of the matrix providing a nutrient sink which discourages a suspension of algal growth in the body of water itself.

In a preferred embodiment, the matrix will comprise an array of suitably tethered matrix bales which are suspended in the body of water requiring remediation.

The matrix may incorporate a device to maintain buoyancy when the matrix is suspended in deep water.

The buoyancy device may be controlled to submerge or raise the matrix in the water. In this way, water can be encouraged to flow through the matrix by sequentially raising the matrix above the surface of the water and then submerging the matrix below the water level. The buoyancy device may be controlled manually or automatically, e.g. by circulating a gas into and out of buoyancy tanks that are attached to the matrix. The gas for operating the buoyancy tanks may be held within suitable storage devices.

The raising and lowering of the matrix may also be achieved mechanically. In this embodiment, the matrix is attached to a mechanically driven support which can raise or lower the matrix relative to the water level.

A continuous cycle of raising and lowering the matrix relative to the water level is preferable for effective water remediation by the matrix. The cycle of raising and submerging the matrix preferably has a duration of from 10 seconds to 24 hours, more preferably from 30 seconds to 60 minutes.

The matrix may also be rotated within the body of water to be treated to encourage the flow of water over the bio-film. For example, mechanical devices driven by electrical-, wind or solar power can be used to rotate the matrix.

In one particular embodiment, the matrix comprises one or more cylindrically shaped bales or bags, e.g. with a diameter in the range of from 100 mm to 5000 mm and a length in the range of from 1000 mm to 100 m, that are attached to an axial drive shaft which passes through the matrix bales or bags and is in turn attached to a suitable drive means for rotating the shaft and the matrix bales or bags that it carries. Preferably 5 to 60 % by volume of the matrix should sit above the surface of the water. Rotation of the drive shaft will rotate the matrix bales/bags within the body of water and encourage water to flow over the bio-film.

A particular aspect of the present invention relates to the use of the buoyed matrix in deep water lagoons, e.g. having a depth of from 0.5 m to 6 m. More especially, the matrix may be used in facultative wastewater lagoon systems such as the Advanced Integrated Ponding System (AIPS). The major drawback with facultative wastewater lagoon systems is the large land area requirement. To overcome this problem, mechanical aerators which float on the lagoon surface are used to assist with the biological oxidation of the contaminants remaining in the wastewater. However, mechanical aerators are costly to run and require constant maintenance.

With the present invention, the matrix may be used to replace mechanical aerators in the AIPS and other facultative lagoon systems since the photosynthetic biomass supported on the matrix can provide the necessary oxygen for wastewater oxidation. Furthermore, by varying the depth of the matrix within the lagoon, e.g. using the buoyancy device described above, it is also possible to collect methane and other gases generated at the lagoon bottom.

Over time, the matrix may become clogged with biomass and will need to be removed from the body of water and allowed to drain. The biomass in the matrix may then be harvested and used as detailed below and a new matrix suspended in the body of water being treated.

Another aspect of the present invention relates to the harvesting and recovery of the accumulated bio-film from the matrix. The bio-film can either be recovered as a dry powder or alternatively as a concentrated soup containing the photosynthetic biomass along with the captured suspended solids.

When the matrix has been arranged in a water channel, the recovery of a dry powder normally involves draining the channel and allowing residual water retained within the matrix to seep out from within the matrix. After this process is complete, normally after several days, the matrix containing the partially dry bio-film can be removed from the channel either mechanically or by hand. The matrix may then be stacked preferably under cover for further drying. Conventional agricultural bale handling machinery is ideal for this task when the matrix comprises one or more bales. The drying rate largely depends upon the ambient weather conditions, but may take as long as 14 days in the UK.

The matrix is then opened onto a suitable agitating device which causes detachment of the dry bio-film from the matrix as a powder. Suitable agitation devices include trommel screens and vibrating screens.

When the matrix has been suspended in a contaminated body of water, the recovery of a dry powdered material involves draining and drying the matrix, preferably under cover. The matrix is then opened and the bio-film recovered as before using a suitable agitating device.

The dry powder biomass that is collected, optionally after further grinding, may be stored in sacks for use as a fertiliser, as a fuel for diesel engines or as a high protein supplement for animal and fish feed. The biomass may also be used for combustion in fluidised bed boilers in which steam is generated to produce electricity in conventional turbines.

One method for recovering a wet concentrate of the bio-film from a matrix positioned within a water flow channel, involves stopping the flow of contaminated water through the channel and compressing the bio-film loaded matrix with an agricultural roller or similar device. This results in the release of the bio-film from the matrix into solution. Following a series of compression cycles, a concentrated slurry of biomass surrounds the matrix, which can be recovered by draining the channel. This cycle may be repeated in order to recover the majority of the bio-film contained within the matrix by refilling the water channel with fresh effluent and then repeating the compression process.

The resulting biomass concentrate may be used directly as a liquid fertiliser or as a fish or animal feed.

Bio-films that have been used to treat wastewater containing radionuclides and heavy metals such as cadmium, chromium, mercury, zinc, uranium and plutonium will become contaminated with these materials. The radionuclides and heavy metals may be recovered by stopping the flow of water through the channel and then adjusting the pH of the water that remains in the channel with an acid. The acidic conditions allow the radionuclides and heavy metals to be washed from the bio-film and the acidic solution containing these materials can then be recovered by draining the channel. The flow of contaminated water through the channel can then be resumed providing the matrix is not clogged or the biomass may be recovered as described above.

Another embodiment of the present invention relates to the reuse of the cleaned matrix material following the removal of the bio-film. A small percentage of the bio-film tends to remain on the surface of the transparent substrate. This material can be reformed into new matrices, optionally together with previously unused substrate material, e.g. by compaction to form bales. Agricultural hay and straw bailing machinery and solid waste compactors are particularly suitable for making bales. The resulting matrices contain sufficient attached biomass to serve as a seed when the matrices are used to purify contaminated water in accordance with the present invention. The present invention will now be described by way of example and with reference to the enclosed drawings in which:

Figure 1 is a schematic diagram showing a preferred apparatus of the present invention.

Figure 2 is a flow diagram showing in schematic form how the method of the invention is operated in a preferred embodiment.

Figure 3 is a colour diagram showing a waste purification installation ofthe present invention.

Figure 4 is a colour diagram showing an alternative waste purification installation ofthe present invention.

In Figure 1 the apparatus for piirifying the water comprises a channel for water that is bounded by a pair of walls (4) disposed in a spaced-apart, parallel relationship. The channel has an inlet end (1) and an outlet end (3) that is disposed below the inlet so that gravity flow occurs toward the outlet end. Bales (2) comprising a matrix of a transparent substrate, particularly PET, are placed between the walls so that photosynthetic micro-organisms can grow and form a bio-film within the body of the matrix. A transparent cover may be installed above the channel to maintain anaerobic conditions and reduce odours if required.

A waste water stream is caused to flow along the channel through the bales from the inlet end to the outlet end. The micro-organisms assimilate the organic and inorganic pollutants in the water and as result grow and develop into a bio-film. The bio-film that develops tends to have different populations of microorganisms along the length of the matrix, beginning with substantially photosynthetic, anaerobic micro-organisms at the inlet end (1) of the channel, changing to a mixed anaerobic/aerobic or facultative consortium of photosynthetic micro-organisms in the middle region of the channel and finally substantially photosynthetic, aerobic micro-organisms at the outlet end (3), where aerobic conditions substantially predominate. Photosynthetic micro-organisms such as purple, non-sulphur photosynthetic bacteria including Rhodospirillium, Rhodopsuedomonas, Rhodobacter, Chromatium, Thiocapsia, and Rubrivivaz tend to thrive within the bio-film at the waste inlet end (1) ofthe channel, while microalgae such as Chlorella, Occilatoria, Scenedesmus, Anabaena, Nostoc, Calothrix tend to dominate the bio-film towards the outlet end (3) ofthe channel.

In addition, the bio-film develops a sticky surface as a result of polysaccharide excretions and this allows suspended particulates within the water to be trapped.

Over a period of time, bio-film growth and suspended solids accumulation eventually clog the matrix in the bales at the inlet end of the channel, preventing wastewater flow through the bales. Wastewater then flows over the clogged bails until it encounters a bale with an unclogged matrix. Over time, bales further down the channel will also become progressively impermeable to water flow. The clogging manifests itself by a green algal growth developing on the upper surface of the bales as a result of waste water flowing over the bales.

The clogged bales can then be treated as described previously to harvest the bio-film. It will be appreciated that more than one bale filled channel may be utilised in the apparatus and method of the invention. This is shown in

Figure 3.

The waste water material may be from any source and may be any of the waste waters discussed above. A typical waste water might contain from 1 to 40,000 mg/1 of contaminants that create a BOD, from 1 to 40,000 mg/1 of TOC, from 1 to 6,000 mg/1 of NH₃ bound nitrogen and from 1 to 1200 mg/1 total phosphorous. Particularly preferred sources of raw waste are livestock sources including poultry, cattle, pigs and combinations thereof.

Figure 2 is a schematic showing the operation of a preferred working installation ofthe present invention.

Clear PET plastic bottles (10) and the like are chopped into fragments using conventional waste shredding equipment (11). The new plastic fragments (12) are then compacted into bales (15), e.g. using standard bailing machinery which is widely available (13). The bales (15) are placed within a channel (16), typically constructed from reinforced concrete or the like, and extend between the walls ofthe channel so that wastewater is prevented from bypassing the bales.

When the channel is occupied by a suitable array of bails, waste water is introduced at the inlet end of the channel at a reduced rate until the channel fills up to the level of the discharge weir (20). The waste water input rate is regulated through the process so that only properly treated water discharges from the outlet end of the .channel. Over a period of time, as the bio-film develops upon the matrix within the bales, the waste water input rate is increased as the 'capture' capacity of the bio-film increases.

As explained previously, bio-film growth and suspended solids accumulation eventually clog the matrix in the bales along the channel starting at the inlet end.

When clogging of the bales substantially diminishes the capture capacity of the bio-film through a lack of working surface area, e.g. when 90% or more ofthe bales in the channel have become clogged, the waste stream flow into the channels is stopped and the channels are drained. The matrix within the bails is allowed to drain for a further period before the partially dry bails are removed from the channels for further drying, preferably under cover. The bails may be stacked to improve air circulation during drying. Artificial drying methods may be used.

When the bio-film is suitably dry, the bales may be opened and the dry biomass removed from the matrix fragments (19) by agitation, e.g. using a trommel or vibratory screen (18). The biomass powder (17) is then collected.

The used plastic fragments (14) still retain a small proportion of the dry biomass on their surfaces following agitation. This biomass can serve as seed for establishing a new bio-film by reforming the used fragments into bales. In this way, the commissioning time for the attainment of an optimal waste stream treatment is minimised. The used plastic fragments (14) may be recombined with new plastic fragments (12) to compensate for the slow decomposition of the plastic fragments by the anoxic micro-organisms present in the bio-film.

Figure 3 shows a digital artists impression of a large scale installation ofthe present invention. The installation comprises a plurality of channels (31). Each channel is bounded by walls (32) and comprises an inlet end (30) and an outlet end (not shown). The channels accommodate bails of compacted transparent matrix material (33a, 33b).

Figure 4 shows a transparent matrix integrated into a facultative lagoon wastewater treatment process.

The matrix comprises matrix modules (44, 45) that can be suspended above or submerged in the facultative lagoon (40). Reference numeral 44 shows the matrix modules above the lagoon and reference numeral 45 shows the modules submerged in the lagoon.

The height of the matrix modules relative to the lagoon is controlled by buoyancy devices (46). The buoyancy devices are conveniently made from recycled 50 gallon polypropylene barrels which have been cut in half. The half barrels are attached to a support frame (47) upon which the matrix modules (53), in either bale or bag form are supported. In use, each buoyancy device with its attached matrix module is oriented in the lagoon so that the open ends ofthe barrels face downwards. Each buoyancy device is connected by gas pipe work (48) so that gas may be pumped into or out of the buoyancy devices therefore making the matrix modules sink or float within the lagoon. The gas pipes (48) from a series of buoyancy devices may be connected together so that a number of matrix modules may be maintained at the same level within the water.

Interconnection between buoyancy devices also allows gas contained in one complement of buoyancy devices to be transferred to another complement of buoyancy devices. For example, the gas contained in the buoyancy devices that are keeping the matrix modules (44) afloat on the surface ofthe lagoon may be transferred to the buoyancy devices that are supporting the matrix modules (45). As a result, the matrix modules (44) sink in the lagoon while the modules (45) are raised to float on the surface of the lagoon. In this way, water is forced to flow through and around the matrix modules and, therefore, the bio-film. This can substantially increase the performance ofthe system.

The cycling of gas from one complement of buoyancy devices to the next can be easily automated and any excess gas conveyed to storage elsewhere.

It is also possible to make use of methane gas formed by digesting organic matter at the base (43, 50) of the lagoon (40) in the operation of the buoyancy devices. This gas bubbles towards the surface of the lagoon and can be collected in the upturned barrels of each buoyancy device. Excess gas can be conveyed from the buoyancy devices for storage.

Claims

Claims:

1. An apparatus for treating contaminated water comprising a water permeable matrix of a transparent or translucent substrate and a bio-film comprising at least one photosynthetic micro-organism supported on the substrate.

2. The apparatus according to claim 1, wherein the bio-film was developed on the surface of the transparent substrate from which the matrix is formed as contaminated water was passed through the matrix.

3. The apparatus according to claim 1 or claim 2, wherein the water permeable matrix comprises a transparent material.

4. The apparatus according to any one ofthe preceding claims, wherein the water permeable matrix has a surface area in the range of from 5 m²/m³ to 1000 m²/m³.

5. The apparatus according to any one of the preceding claims, wherein the water permeable matrix comprises an agglomeration of plastic pieces or glass shards.

6. The apparatus according to claim 5, wherein the water permeable matrix comprises recycled plastic materials.

7. The apparatus according to claim 5 or claim 6, wherein the water permeable matrix comprises at least one plastic material selected from the group consisting of polyvinyl chloride (PVC), the polycarbonates, the polyethylenes and polyethylene terephthalate (PET).

8. The apparatus according to claim 7, wherein the water permeable matrix comprises polyethylene terephthalate (PET).

9. The apparatus according to any one of claims 5 to 8, wherein the plastic pieces or glass shards have been compacted together to form the matrix.

10. The apparatus according to claim 9, wherein the plastic pieces or glass shards have been compacted into bags, bales or baskets.

11. The apparatus according to any one ofthe preceding claims, wherein the water permeable matrix is arranged in a longitudinally extending channel through which the contaminated water is passed, said channel having an inlet end for receiving the contaminated water and an outlet end for removing the treated water.

12. The apparatus according to claim 11, wherein the channel is covered with a translucent or transparent cover.

13. The apparatus according to claim 11 or claim 12, wherein the water permeable matrix comprises a plurality of compacted bales.

14. The apparatus according to any one of claims 11 to 13, wherein photosynthetic, anaerobic micro-organisms dominate the bio-film at an inlet end ofthe matrix and photosynthetic, aerobic micro-organisms dominate the bio-film at an outlet end ofthe matrix.

15. The apparatus according to any one of claims 1 to 10, wherein the water permeable matrix is adapted to be suspended in a contaminated body of water.

16. The apparatus according to claim 15, wherein the body of water is covered with a translucent or transparent cover.

17. The apparatus according to claim 15 or claim 16, wherein the water permeable matrix comprises a plurality of compacted bales.

18. The apparatus according to any one of claims 15 to 17, wherein the water permeable matrix is equipped with buoyancy means.

19. The apparatus according to claim 18, wherein the buoyancy means can be controlled to raise or lower the water permeable matrix in the body of water.

20. The apparatus according to claim 18 or claim 19, wherein the buoyancy means comprises buoyancy tanks for receiving a gas.

21. The apparatus according to claim 18 or claim 19, wherein the water permeable matrix is arranged on a support frame and the buoyancy means comprises at least one plastic container which has an opening to receive a gas and which is attached to the support frame so that in use the opening of the plastic container can face downwards in the contaminated body of water.

22. The apparatus according to any one of claims 15 to 21, further comprising rotation means for rotating the water permeable matrix within the body of water to be treated.

23. A method for treating contaminated water comprising the step of contacting the water with a bio-film comprising at least one photosynthetic micro-organism supported on a water permeable matrix of a transparent or translucent substrate.

24. A method for treating contaminated water comprising the step of placing a water permeable matrix of a transparent or translucent substrate seeded with at least one photosynthetic micro-organism in contact with the water to be treated.

25. The method according to claim 23, wherein the bio-film was developed on the surface ofthe transparent substrate from which the matrix is formed as contaminated water was passed through the matrix.

26. The method according to any one of claims 23 to 25, wherein the water permeable matrix comprises a transparent material.

27. The method according to any one of claims 23 to 26, wherein the water permeable matrix has a surface area in the range of from 5 m²/m^J to 1000 m²/m³.

28. The method according to any one of claims 23 to 27, wherein the water permeable matrix comprises an agglomeration of plastic pieces or glass shards.

29. The method according to claim 28, wherein the water permeable matrix comprises recycled plastic materials.

30. The method according to claim 28 or claim 29, wherein the water permeable matrix comprises at least one plastic material selected from the group consisting of polyvinyl chloride (PVC), the polycarbonates, the polyethylenes and polyethylene terephthalate (PET).

31. The method according to claim 30, wherein the water permeable matrix comprises polyethylene terephthalate (PET).

32. The method according to any one of claims 28 to 31, wherein the plastic pieces or glass shards have been compacted together to form the matrix.

33. The method according to claim 32, wherein the plastic pieces or glass shards have been compacted into bags, bales or baskets.

34. The method according to any one of claims 23 to 33, wherein the water permeable matrix is arranged in a longitudinally extending channel through which the contaminated water is passed, said channel having an inlet end for receiving the contaminated water and an outlet end for removing the treated water.

35. The method according to claim 34, wherein the channel is covered with a translucent or transparent cover.

36. The method according to claim 34 or claim 35, wherein the water permeable matrix comprises a plurality of compacted bales.

37. The method according to any one of claims 34 to 36, wherein photosynthetic, anaerobic micro-organisms dominate the bio-film at an inlet end ofthe matrix and photosynthetic, aerobic micro-organisms dominate the bio-film at an outlet end ofthe matrix.

38. The method according to any one of claims 23 to 33, wherein the water permeable matrix is suspended in a contaminated body of water.

39. The method according to claim 38, wherein the body of water is covered with a translucent or transparent cover.

40. The method according to claim 38 or claim 39, wherein the water permeable matrix comprises a plurality of compacted bales.

41. The method according to any one of claims 38 to 40, wherein the water permeable matrix is equipped with buoyancy means.

42. The method according to claim 41, wherein the buoyancy means is controlled to raise or lower the water permeable matrix in the body of water.

43. The method according to claim 41 or claim 42, wherein the buoyancy means comprises buoyancy tanks for receiving a gas.

44. The method according to any one of claims 38 to 43, wherein the water permeable matrix is rotated within the body of water to be treated.

45. The method according to any one of claims 23 to 44, further comprising the step of harvesting the biomass constituting the bio-film once water flow through the water permeable matrix is impaired.

46. The method according to claim 45, further comprising the step of reusing the material of the water permeable matrix to treat contaminated water following harvesting of the biomass.

47. The use of a water permeable matrix of a transparent or translucent substrate for the purification of water.

48. The use of a water permeable matrix of a transparent or translucent substrate to support a bio-film comprising at least one photosynthetic microorganism for the purification of water.

49. The use according to claim 47 or claim 48, wherein the water permeable matrix comprises an agglomeration of plastic pieces or glass shards.

50. The use according to claim 49, wherein the water permeable matrix comprises recycled plastic materials.

51. The use according to claim 49 or claim 50, wherein the water permeable matrix comprises at least one plastic material selected from the group consisting of polyvinyl chloride (PVC), the polycarbonates, the polyethylenes and polyethylene terephthalate (PET).

52. The use according to claim 51, wherein the water permeable matrix comprises polyethylene terephthalate (PET).

53. The use according to any one of claims 49 to 52, wherein the plastic pieces or glass shards have been compacted together to form the matrix.

54. The use according to claim 53, wherein the plastic pieces or glass shards have been compacted into bags, bales or baskets.

55. The use of a translucent or transparent plastic material in the treatment of contaminated water.

56. The use according to claim 55, wherein the plastic material comprises recycled plastic material.

57. The use according to claim 55 or claim 56, wherein the plastic material comprises at least one material selected from the group consisting of polyvinyl chloride (PVC), the polycarbonates, the polyethylenes and polyethylene terephthalate (PET).

58. The use according to claim 55 or claim 56, wherein the plastic material comprises polyethylene terephthalate (PET).

59. A method of degrading translucent or transparent plastic material comprising placing the material in contact with a contaminated body of water to allow a bio-film comprising at least one photosynthetic microorganism that degrades the plastic to develop on the surface ofthe plastic.

60. The method according to claim 59, wherein the plastic material comprises recycled plastic material.

61. The method according to claim 59 or claim 60, wherein the plastic material comprises at least one material selected from the group consisting of polyvinyl chloride (PVC), the polycarbonates, the polyethylenes and polyethylene terephthalate (PET).

62. The method according to claim 59 or claim 60, wherein the plastic material comprises polyethylene terephthalate (PET).

63. The method according to any one of claims 59 to 62, wherein the plastic material is comminuted into pieces.

64. The method according to claim 63, wherein the plastic pieces are compacted together to form a matrix.

65. The method according to claim 64, wherein the plastic pieces are compacted into bags, bales or baskets.