AU7748698A - A method for treating liquid waste - Google Patents

Description

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AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicants:

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o PALMER TECHNOLOGIES PTY LTD QUEENSLAND RAIL GREGORY BERTRAM PALMER WILFRED DAVID TANSLEY Actual Inventors: Address for Service: Invention Title: CULLEN CO., Patent Trade Mark Attorneys, 240 Queen Street, Brisbane, Qld. 4000, Australia.

A METHOD FOR TREATING LIQUID

WASTE

Details of Associated Provisional Application: No. P08192 filed 23 July 1997 The following statement is a full description of this invention, including the best method of performing it known to us: 2N The present invention relates to a method and apparatus for treating liquid waste and in particular relates to treating liquid waste which is contaminated with solids and oils Liquid waste is generated by most industrial processes, cleaning operations and municipal sewage systems. The liquid waste must be treated to at least partially remove pollutants and contaminants before discharge into the environment. Such pollutants and contaminants include suspended and dissolved solids, o. metals, salts, petroleum waste, greases, oils and organics.

Suspended solids 'are typically removed from liquid waste by sedimentation and/or filtration in the initial stages of waste treatment processes. Sand bed filters are well known for removing suspended solids. The filtered water from the sand bed filter is then subjected to further or secondary processing. Periodically, the filter bed must be either regenerated by back flushing to 20 remove the collected sludge or by simply replacing with fresh sand. A disadvantage of both these processes is that they produce either separated sludge in the case of backwashing or contaminated sand in the case of replacement. These waste solids must then be disposed of- Typically the solids are removed and disposed of as landfill. Removal and disposal of the waste materials to landfill sites is expensive. Further, such disposal exposes the environment to any pollutants which may leach from the waste. This is also undesirable.

Mixed filter media which include a combination of sand and coal are also known. Typically, a layer of coal having a fine particle size is spread over a sand filter bed. Typically the coal and sand layers have different particle sizes and densities. In some applications two or more layers of sand having different particle sizes and densities are used. For effective separation, and in pArticular separation of solids, it is considered necessary to have a gradient of particle size 3 and density from the upper to the lower portions of the filter bed. These mixed media filter beds must also be either regenerated or replaced in a manner similar to the sand filter beds. An added disadvantage of the mixed media filter beds is that the particle size and density gradient of the bed is subject to disruption during backwashing. In any case, the separated sludge or the contaminated filter media must still be disposed of and this is typically done as landfill.

After removal of solids from the liquid waste by filtration, the waste water is then subjected to further processing. Activated carbon is commonly used to absorb odours and residual contaminants in the final or tertiary stages of waste treatment. Activated carbon is prepared from coal which is "activated" by heating to a high temperature, preferably with steam or carbon dioxide to produce an internal porous structure. In order for the carbon to be effective in adsorbing contaminants it must have a large surface area. This is achieved by a 20 combination of the internal porous structure and a fine S.particle size.

Activated carbon is normally not considered suitable for filtering wastes having a large solids content as the solids, together with any oily or greasy material contained therein tend to coat the particles and/or block the pores of the carbon. This significantly reduces the effectiveness of the activated carbon. Another feature of using activated carbon is that its fine particle size introduces difficulties with material handling. This makes disposal of contaminated carbon difficult. In practice it has been found that because of this fine particle size and associated handling difficulties it is not possible to dispose of the contaminated carbon by combustion in most commercial incinerators.

It is therefore desirable to be able to develop a method for treating solid containing liquid wastes by 4 filtration in which the filter medium may be disposed of in an effective and environmentally friendly manner.

The present invention is directed towards the surprising discovery that coarse coal particles may be effective in filtering solids and other contaminants such as greases and oils from liquid waste. In particular it S has been surprisingly discovered that liquid wastes having a high solids content may be filtered. Further, the coal when loaded with the solids and other contaminants may have an enhanced calorific value and is suitable for use as an energy source. Thus the coal filter media may be recycled of by being burnt as a fuel in a power station or the like.

According to a first broad form of the present 15 invention there is provided a method of treating a liquid waste which comprises suspended solids, oil, grease or a mixture thereof, said method comprising providing a filter medium of coarse coal particles, filtering the waste through the coal such that at least part of said solids, 20 oil or grease are retained by the coal.

According to a second broad form of the invention there is provided a filter apparatus for treating a liquid waste which comprises suspended solids, oil, grease or a mixture thereof, the filter apparatus including a filter bed comprising coarse coal particles.

The method and apparatus of the present invention is particularly suited to treatment of liquid waste or water sludge having a moisture content of between about 30 and about 95% and typically between about 35 and 60% (corresponding to a solids content of between about to about typically 65 to The sludge may contain suspended solids and emulsified liquids such as hydrocarbons, oils and greases. This type of waste material may be generated by processes in the petroleum refining and chemical industries and commercial cleaning processes such as the cleaning of rail and road vehicles.

In some applications such as the treatment of liquid waste from the cleaning of rail vehicles the suspended solids in the waste may include suspended particles having a very fine particle size. These particles may include coal particles which have been washed from the vehicles. When liquid waste incorporating these types of particles is filtered using the filter media of the present invention, the fine particles may be entrapped in the lower regions of the filter media. This can create a bottom layer of fine particles on the filter bed. This difference in particle size between upper and lower layers may facilitate the filtration process.

Alternatively or in addition to the fine particles .i captured from the waste stream, a bottom layer of fine coal particles or activated carbon may be placed beneath the coal layer.

15 Thus, in an especially preferred embodiment of the present invention a bottom layer of a fine particle .size may be located over the coal layer. This fine layer may be obtained from the waste liquid itself such as in the case of treating waste from washing rail vehicles or .20 may be provided by adding fine coal or activated carbon to the coal filter media.

The present inventors have also surprisingly discovered that the effluent from a coal filter bed of .this preferred embodiment may have less pollutants and contaminants than corresponding effluent obtained from the known sand bed filters. In some cases, the effluent obtained from this preferred method of the present invention may be suitable for discharge directly to sewage or to be used as irrigation water without the further processing which is necessary to treat the effluent from the sand bed filters.

The coal which may be used in the present invention is of a type and particle size which is suitable for downstream materials handling. Preferably the coal is suitable for use as a fuel in the cement manufacturing, steam generation or power industries. Preferred types of coals are coking or steaming coal. Preferably the coal has a minimum particle size of about 0.075mm and typically =3~p-cP rrrrpp-ea~ yp ;y I about 2mm. The coal may have a maximum particle size of about 100mm. A preferred particle size is between about and about 65mm. Coal having a particle size distribution in which there is a high percentage of particles less than about 2mm are impractical for materials handling in industrial furnaces or dryers.

Further, coal having a high amount of fines has been found to become easily clcgged when used to filter waste having a high solids content. Very small particle sizes, such as the particle sizes of activated carbon have been found to be quite unsuitable. In the cases where the filter media includes a top layer of a fine material as described above, these fine particles are typically entrapped by the coarse coal particles during handling and the presence of these fine particles would not normally adversely affect the suitability of the filter media for combustion.

The filter media may be supported in filter beds or columns of known type. The filter media may also be contained in mobile containers. These containers typically may be filled with coal and rolled or otherwise moved into a desired location in the waste treatment plant. After use, the container may be rolled or otherwise moved to a drying area and then transported off site to a location where the coal may be combusted. The original container is simply replaced in the treatment plant with a new container with fresh coal.

By way of example only, the present invention 1will be described with reference to the Figures in which: Figure 1 is a flow sheet illustrating schematically the steps of a preferred method and filter bed of the present invention and Figure 2 illustrates particle size distribution of preferred coal particles.

The process illustrated in figure 1 may be used to treat contaminated water from a train washing process.

The waste water from this process contains residues from the cleaning process and includes suspended and dissolved solids, metals, greases, oils and organic materials. The

I

7 waste material is receivese n the receiving tank 1. The solids separate from the waste and the tank is regularly Sdesludged by running the solids to a sludge drying bed 2.

The average solids content of the sludge from the receiving tank is about 57% but may be as high as 70 to Oil/water flows from the receiving tank to an oil/water separator 3. The separator 3 removes excess oil by known means and the oil is passed via settling tank 8 i to storage tank 4. Solids from the separator 3 may then flow through outlet 3a to filter bed 2. The water from S* the separator may flow through to holding tank 5 and then to clarification tank 6. The clarification tank 6 further treats the water by conventional means and the water is discharged through outlet 6a to the sewer or stormwater.

Solids which settle in the clarification tank 6 are separated out and a waste fraction is pumped to a second filter bed 7. The solids content of this waste fraction is about 10%. Any solids which settle in the separator and settling tank are also pumped to the filter beds. The solids content of the effluent from the filter beds is typically less than about Alternatively oil from the separator 3 may flow to either one of the filter beds.

Filter beds 2, 7 contain coal filter media. The particle size of the coal in the beds is between about 0.075 to -65mm. Typically no more than about 20%-25%(w/w) of the particles have a particle size of less than about 1mm. Typical particle size distributions for preferred coal filter media is illustrated in Figure 2. The coal filters out solids and oily liquids. The filtered water is optionally returned to the clarifier. The filter containers are a roll-on-roll-off type. After a period of use, the filter beds are sun dried to remove moisture.

The coal in the filter beds has an improved calorific value and is suitable for use as an energy source in a power station or the like.

The above process may also be modified to a continuous process in which case tanks 5 and 6 will be 8 removed and the water from separator 3 will flow directly to the filter beds It can be seen that the method of the present invention provides a process for removing solids, oils and greases from a liquid waste. The coal is suitable for recycled by incineration. This avoids disposal of contaminated materials to landfill. Further, the filtration process may enhance the calorific value of the coal, which makes it particularly suitable for use as a fuel.

Claims (15)

1. A method of treating a liquid waste which comprises suspended solids, oil, grease or a mixture thereof, said method comprising providing a filter medium of coarse coal filter particles, filtering the waste through the coal such that at least part of said solids, oil or grease are retained by the coal.

2. The method of claim 1, wherein the coal particles have a particle size distribution from about +0.075mm to about

3. The method of claim 2 in which no more than about 25%(w/w) of the particles has a particle size less than about 1mm.

4. The method of claim 3 in which no more than about 20%(w/w) of the particles has a particle size less than about Imm. The method of claim 2, wherein the particle size distribution falls within the upper and lower curves of Figure 2.

6. The method of any one of claims 1 to 5, wherein the waste has a solids content of between about 5 and about

7. The method of claim 5, wherein the waste has a solids content is between about 40 and about

8. The method of claim 5, wherein the solids content is between about 70 and about

9. The method of any one of claims 1 to 8 which further comprises at least partially drying the coal after filtration.

10. The method of claim 9, wherein the at least partially dried filter media is combusted.

11. The method of any one of claims 1 to 10, wherein the filter media includes a bottom layer of fine coal particles.

12. The method of claim 11, wherein the fine particles have been filtered from the waste.

13. A filter apparatus for treating a liquid waste which comprises suspended solids, oil, grease or a mixture thereof, the filter apparatus including a filter bed comprising coarse coal particles.

14. The apparatus of claim 13, wherein the coal particles have a particle size distribution from about +0.075mm to about The apparatus of claim 13, wherein no more than about 25%(w/w) of the particles has a particle size of less than about 1mm.

16. The apparatus of claim 13, wherein no more than about 20%(w/w) of the particles has a particle size of less than about 1mm.

17. The apparatus of any one of claims 1 to 16, wherein the filter bed includes a bottom layer of fine coal particles. 15 18. A method of treating a liquid waste, substantially as hereinbefore described with reference to the Figures. PALMER TECHNOLOGIES PTY LTD and QUEENSLAND RAIL DATED this 23rd day of July 1998 25 By their Patent Attorneys CULLEN CO. -i 3