AU724038B2 - Device and method for treating waste water - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant(s): Actual Inventor(s): Address for Service: Invention Title: ROY TUDOR BREWER ROY TUDOR BREWER CULLEN CO., Patent Trade Mark Attorneys, 240 Queen Street, Brisbane, Qld. 4000, Australia.

DEVICE AND METHOD FOR TREATING WASTE WATER Details of Associated Provisional Applications: Nos. PP4761 21.07.98 The following statement is a full description of this invention, including the best method of performing it known to me: 2 The present invention relates to a filter bed and method for treating waste water and in particular is directed towards a method of recycling waste water.

Industry and municipalities generate vast amounts of waste water which are typically released into waterways or oceans. In order to minimise the environmental impact of releasing such water, it is desirable to treat such waste waters prior to their release into the environment. Municipal wastes are typically treated at one or two levels known as primary and secondary treatment. In primary treatment, the waste water is filtered through 10 a screen which removes large floating objects. The waste water then flows into a sedimentation tank and suspended solids are allowed to settle. The settled mass of solids is known as raw sludge which must eventually be removed for further treatment or disposal. The effluent from the sedimentation tanks may then be discharged into receiving waters or may be 15 further treated. Primary treatment is considered to be inadequate in most cases and further treatments are desirable.

In secondary treatment, the effluent from the primary treatment is further treated to remove organic matter. Secondary treatment makes use of the bacteria contained in the waste water to remove a substantial 20 proportion of the organic material. However, release of effluent from secondary treatment processes still has adverse environmental effects.

Further treatment is therefore desirable before release into the environment and is essential if the water is to be purified to drinking water standards.

Such further treatment is known as tertiary treatment and includes filtration through activated charcoal and/or chlorination.

The costs involved in the above water treatments are considerable. These costs are considered prohibitive in many countries and communities. For example, few cities have better than secondary treatment for their sewerage and many cities have only primary treatment. Still further, raw sewage, agricultural, industrial and sewage effluents are still being released into streams, rivers and coastal waters. Such release leads to pollution of the environment, damage degradation and death of marine and fluvine biota.

Water is a valuable resource and there are large costs associated with the procurement and supply of potable water. Recycling of waste water is desirable so as to be able to reduce the demand on existing water supplies. This is especially relevant in low rainfall areas and in communities experiencing large increase in water demand due to increased population and/or industrial requirements. However as discussed above, the cost of further treating effluent such that it approaches drinking water standards is prohibitive. A further disadvantage of the known primary and secondary treatment processes is that because of their cost and complexity, S 10 they are unsuitable for small scale applications. Such applications include treating wastes generated by isolated or discrete habitations including single dwellings, offshore living, island resorts and small communities.

It is therefore an object of the present invention to provide a method for treating waste water which may at least partially overcome the 15 above disadvantages or provide the public with a useful choice.

According to a first broad form of the invention there is provided a filter bed for treating waste water, the filter bed including a coarse filter "•media wherein interstices between coarse filter media particles are at least partially filled with a soil mixture comprising sand, clay and humus.

20 According to a second broad form of the invention there is ao..

:provided a device for treating waste water, the device including the filter bed of the first broad form, a waste water inlet for introducing the waste water to the filter bed and a water outlet.

According to a third broad form of the invention there is provided a method for treating waste water comprising passing waste water through the filter bed of the first broad form and collecting the water which has passed therethrough.

The filter bed, device and method of the present invention may be used in the treatment of any suitable type of waste water. Typically the waste water comprises primary or secondary effluent discharges emanating from industry and from municipal sewage treatment plants. Effluent from domestic septic tanks may also be treated.

The course filter media for use in the filter bed of the present invention media may be any suitable filter media including gravel and in particular round river gravel, glass or plastic marbles or ceramic balls.

Preferably, the filter media particles have a substantially uniform particle size.

Typically the coarse filter media particles have a diameter of between about and 30mm and preferably about 20mm. The depth of the filter bed may vary, depending upon the volume, application rate and nature of the waste water to be treated and other peripheral considerations. Typically the filter bed has a depth of between about 1 metre to 2 metres.

The interstices between the coarse filter media particles are at least partially filled with a soil mixture comprising sand, clay and humus. The soil mixture may be obtained from natural sources or may be an artificial soil.

A typical soil mixture comprises between about 5 to about 15% humus, about 10 to about 30% clay and about 55 to about 85% sand. Preferably the mixture comprises about 10% humus, about 20% clay and about 70% sand.

Preferably the filter bed includes a lower layer of coarse filter 15 media which does not have any added material in the interstices. The voids created by the empty interstices allows the relatively free flow of water and air through this layer. This layer acts as a drainage system for water passing through the filter bed. Typically the layer has a sloping bottom to facilitate water flow. The lower layer is typically separated from the upper layer by an air and water permeable barrier layer which prevents the humus, sand and clay entering the lower layer. Typical barriers are made from nonbiodegradable fabrics. A preferred material is a shade cloth material.

Typically the lower layer has a depth of between about 50 and about 200mm and preferably about 100mm.

Typically the filter bed is contained within an impervious barrier which may be formed from plastic sheeting, reinforced concrete or other suitable material.

Preferably the filter bed has an upper layer comprising a soil mixture without any course filter media mixed therein. This soil mixture may be the same or different to that admixed with the course filter particles. The soil may be natural or artificial. Preferably the soil mixture for the upper layer comprises sand, clay and humus in the ranges specified above. Typically the top layer has a depth of about 100 to 1400mm and is preferably about 300mm. The top layer depth typically is chosen to cater for the root depth of the flora chosen for nutrient extraction cycle. The top layer is typically separated from the main body of the filter bed by a water and air permeable barrier. The top layer is typically able to support the rapid growth of flora which can absorb nutrients from the waste water. The top soil layer may also support the growth of soil based organisms such as nematodes, fungi and microorganisms which are capable of digesting waste organic material and sewage organisms.

By way of example only, the present invention will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic cross sectional view of a preferred device of the present invention; Figure 2 is a schematic cross sectional view of a further preferred device of the present invention in association with a septic tank of 15 an isolated dwelling; Figure 3 is a plan view of the device of Figure 2 and Figures 4 to 7 are details A, B, C, and D respectively of features Figures 2 and 3.

Figure 1 illustrates a waste water treatment device 11. The 20 device has a filter bed 12 which comprises gravel and a soil mixture. The 999* mixture may be a natural or artificial soil. Typically the soil mixture contains humus, 20% clay and 70% sand. The filter bed 12 has an upper layer 13 which is separated from the filter bed by a non-biodegradable water and air permeable material 9 such as a shade cloth or fabric. The upper layer 13 comprises three sublayers 13a, 13b and 13c comprising soil, sand and soil respectively. Upper layer 13 supports the growth of plants.

The filter bed 12 includes a lower layer 14 which comprises gravel without any additional soil mixed therein. The lower layer 14 is separated from the filter bed 12 by a non-biodegradable water and air permeable material 9 such as a shade cloth or fabric. The base 15 of the filter bed includes a number of sloping stepped portions 16. Each stepped portion has a water outlet 17, 18, 19, The lower surface and walls of the device are lined with an air and water impervious barrier such as plastic or concrete.

The device has a series of first waste water inlets 21 which are located above the filter bed 12 but below top layer 13. A layer of gravel 25 is located about inlets 21. Second 22, third 23 and fourth 24 water inlets are provided in the forms of sprinklers.

The device of the present invention functions as follows: Waste water is introduced into the filter bed 12 through inlets 21. The waste water is typically effluent from primary or secondary treatments or from domestic septic tanks. Waste water effluents typically contain plant nutrients including nitrogen which is generally in the form of ammonia, phosphorous, potassium, calcium, magnesium, sulphur, chlorine, iron, copper, manganese, molybdenum, zinc and boron; pathogens including pathogenic bacteria, spores, protozoa, tapeworms, disease causing micro-organisms and viruses, dissolved and suspended organic material.

The waste water percolates through the layer 25 of gravel before entering the gravel and soil matrix. The soil mixture contains micro-organisms which are normally present in natural soils. Such microorganisms include nitrifying bacteria. Nitrifying bacteria are able to convert ammonia into nitrite and then through to nitrate. In this way, the ammonia in 20 the waste water is converted into nitrates. Other microorganisms digest the organic material in the waste water.

The pathogenic organisms in the waste water may be destroyed by predatory biota from the soil, which include bacteriophages, viruses, protozoa, amoeba, nematodes and fungi. The pathogenic organisms may also be destroyed by competition with the soil based organisms. Removal of pathogenic organisms such as viruses may be facilitated by the presence of the clay. In the aqueous environment of the filter bed, the viruses have an electric charge and migrate towards the oppositely charged clay particles.

The viruses are then captured by the clay particles and eventually destroyed.

After the waste water has percolated through the filter bed 12 it passes into the lower gravel layer 14 and runs into outlet 20. A pump (not illustrated) pumps the water from the outlet to a sprinkler system which distributes the water through sprinkler 23 over a different section of the filter bed. Alternatively, the water may be pumped and sprinkled onto a second filter bed. The top layer 13 of the filter bed supports the growth of plants and other effluent decomposing microorganisms. These plants are able to absorb the aforementioned plant nutrients from the waste water. Heavy metals in low concentrations may also be absorbed by the plants. In cases where the levels of certain heavy metals is considered excessive, these contaminants may be removed in a separate step using a high rate biological filter utilising blue green algae as the capture medium. Plants are generally unable to assimilate ammoniacal nitrogen. However, as described above, ammoniacal nitrogen in the waste water has been converted into nitrate form, which can be absorbed by the plants. Typically, the plants are selected from rapid growing species such as grasses and crops. The plants are selectively harvested to remove nutrients from the system. The plants may be suitable for use as animal or human foodstuffs.

S 15 The soil bacteria which convert the ammonia into nitrite and nitrate nitrogen and other micro-organisms which participate in the destruction of pathogens and in the decomposition of the organic components of waste water are aerobic. Air is introduced into the system as a result of the intermittent flushing and draining of the treated water through the system and 20 by aeration of the water during sprinkling. In cases where the water is not introduced by sprinklers it may be desirable to pre-aerate the water in an aerator prior to introduction into the system. Aeration of the system may also be facilitated by fauna within the system. For example, the tunnelling movement of nematodes and other soil based organisms through the filter bed 12 and upper layer 13 facilitate aeration of the system. The lower gravel :layer 16 has empty voids between the interstices, which also facilitates circulation of air.

After the waste water has percolated through the filter bed a second time it passes through the outlets 18, 19. If desired, the water can be recycled and passed through the sprinkler system a second or third time.

Alternatively, if the water quality is acceptable, the water may be discharged or reused at this stage. Typically, an acceptable water quality will be reached after three cycles. The water may then be released into the environment or 8 recycled. The sprinklers on the 2nd, 3rd, (and 4th) cycles distribute equally over adjoining sections of the filter beds so that 50% of water of each cycle is double-treated in each filter bed and progressively dilutes the cycling waste water. For example in the second cycle, the waste water is sprayed over first and second sections of the filter bed. In a third cycle, the water is sprayed over second and third sections of the bed. Distributing the waste water in the filter beds in this manner has a number of advantages. This distribution enables the micro-organisms feeding on the organic and mineral contaminants in the waste water to be seeded into oncoming water on each of the filter bed cycles; the incoming waste water to be progressively diluted; the period of time during which the waste water is exposed to treatment in the filter beds to be extended by 50%; the oxygenation of the filter beds by aerated water to be significantly increased; the size of the installation required to treat a given volume and character of waste water to be substantially reduced; the rate of intermittent cycling through the filter beds to be doubled; the exposure of the nutrient extracting flora on the filter beds, to the nutrients in the waste water to be substantially increased; and the activity of the symbiotic micro-organisms breaking down the organic matter and modifying "the heavy metals in the waste water to be stimulated.

20 The effluent from the filter bed of the present invention will 0 typically be of a quality that it does not constitute a health hazard or a hazard to the environment. Up to about 20% of available water may be lost during the water treatment process through a combination of evaporation and transpiration by the plants. If desired, this water may be retained by erecting and enclosing a greenhouse type structure over the device, thus enabling recovery of a substantial portion of the water lost by condensation.

Figures 2 to 7 illustrate another preferred device 30 of the present invention shown in association with an isolated dwelling having a septic tank 31 and a rain water tank 32. The device 30 is similar to that illustrated in Figure 1 and like parts have been given the same reference numbers. Effluent from the septic tank 3 passes through an alternating dosage apparatus 33 (more clearly illustrated in Figure 5) to a series of inlets 21. A detail of an inlet 21 is illustrated in Figure 4. The inlet 21 is surrounded by a layer 24 of river gravel having a diameter of about 15 to about Surrounding the river gravel is a layer of shade cloth 34.

Figure 5 is a detail C of the alternating dosage apparatus 33.

The dosage application has an inlet 35 and two outlets 36, 37. A W shaped alternating tipper 38 is pivotally mounted within apparatus 33 at pivot point 39.

Figure 6 is a detail B of outlet 19. The outlet 19 has a slotted PVC irrigation pipe 40. The pipe 40 is embedded in lower layer 14 which is made up of a lower level 41 of 15/20mm round river gravel and an upper 75mm gravel blanket 42. The outlet is surrounded by a layer 43 of plastic sheeting or shade cloth 44.

Figure 7 is a detail D of elbow joint 50 in which a 75mm pipe 51 is joined to a 50mm nozzle 52.

The effluent percolates intermittently through the filter bed 12 15 and is recycled and redistributed through sprinklers 22 as described with .oo.oi reference to Figure 1. After the second or third cycle, the water passes though outlet 18 and passes to storage tank 35 for future use.

It can be seen that the device of the present invention is relatively simple and easy to install and run when compared with the known methods of water treatment. The filter bed imitates the processes which *occur naturally in soil. Such processes include nitrification, extraction of nutrients and metals from water, oxidation and digestion of suspended and dissolved organic and mineral waste components, filtration and destruction of protozoa, spores, pathogenic bacteria and viruses and capture of inorganic particles.

The preferred filter bed of the present invention may also accelerate and magnify the natural processes, which occur in the soil. Such acceleration and magnification may be achieved by optimising the conditions desirable for a synergistic relationship between the surface flora and fauna, soil bacteria and other microorganisms, clay and humus. Optimisation of filtration is achieved by use of a selected mix of course filter media and soil mixture. The matrix of course filter media particles in the filter bed enhances water drainage and aeration of the system.

In the present specification and claims, the word "comprising" and its derivatives including "comprises" and "comprise" include each of the stated integers but does not exclude the inclusion of one or more further integers.

It should be appreciated that various other changes and modifications may be made to the embodiment described without departing from the spirit and scope of the invention as claimed.

S. eeo e~

Claims (16)

1. A filter bed for treating waste water, the filter bed including a coarse filter media wherein interstices between course filter media particles are at least partially filled with a soil mixture comprising sand, clay and humus.

2. The filter bed of claim 1, wherein the coarse filter media has an average particle size of between about 10 to about 30 mm.

3. The filter bed of claim 1 or claim 2, wherein the coarse filter media is selected from gravel, marbles, ceramic balls or a mixture thereof. l0

4. The filter bed of any one of claims 1 to 3, wherein the filter bed has a depth of between about 1 to about 2 metres.

The filter bed of any one of claims 1 to 4, wherein the soil mixture comprises between about 5 to about 15% humus, about 10 to about clay and about 55 to about 85% sand.

6. The filter bed of any one of claims 1 to 5, which further includes a lower layer of coarse filter media which does not have any added material in the interstices.

7. The filter bed of any one of claims 1 to 6, which further includes an upper layer of a soil material.

8. A filter bed for treating waste water, substantially as hereinbefore described with reference to Figure 1.

9. A device for treating waste water, the device including a filter bed of any one of claims 1 to 8, a waste water inlet for introducing the waste water to the filter bed and a water outlet. 25

10. The device of claim 9, which further includes means for recycling the water from the outlet such that the recycled water is re-introduced onto the filter bed and can pass through the filter bed at least twice.

11. The device of claim 10, wherein the waste water is first introduced to a first section of the filter bed and the recycled water is re- introduced onto a second section of the filter bed.

12. The device of claim 10 or claim 11, which includes sprinklers for Q re-introducing the recycled water onto the filter bed. 12

13. The device of any one of claims 9 to 12, wherein the filter bed has an upper layer which can support the growth of plants.

14. A device for treating waste water, substantially as hereinbefore described with reference to the Figures.

15. A method for treating waste water comprising passing waste water through a filter bed of any one of claims 1 to 8 and collecting the water which has passed therethrough.

16. The method of claim 15, wherein the waste water is recycled and passes through the filter bed at least twice. DATED this 20th day of July 1999 ROY TUDOR BREWER By his Patent Attorneys CULLEN CO. **e *°ee