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 polluants and contaminants before discharge into the environment. Such polluants and contaminants include suspended and dissolved solids, metals, salts, petroleum waste, greases, oils and organics, such as surfactants.

A wide variety of processes have been described for the treatment of liquid waste in order to remove contaminants and pollutants.

Highly contaminated liquid waste is generally subjected to a number of preliminary steps to remove a substantial portion of any suspended solids and oil.

Suspended solids are typically removed from liquid waste by sedimentation and/or filtration in the initial stages of waste treatment processes. Suspended solids are generally removed in the form a sludge.

Australian Patent No. 728309 describes a process whereby the sludge is filtered and dried in a bed of a coal filter medium.

Oil may be removed using a variety of known separation techniques.

Liquid waste such as highly contaminated liquid waste that has been treat to remove a substantial portion of suspended solids and oil, or lightly contaminated liquid waste still presents a potential environmental problem with respect to its disposal.

We have now found an efficient and cost effective process to treat contaminated liquid waste to remove contaminants therefrom.

According to one aspect of the present invention there is provided a process for the treatment of liquid waste comprising passing the liquid waste through a filter wherein the filter comprises particulate coal as a filter medium and wherein the approach velocity of the liquid waste is less than 10cm/min.

We have also found that in highly contaminated and/or polluted

liquid wastes the process of the first aspect of the present invention may be used in combination with pretreatment steps that remove a proportion of suspended solids and oils. Accordingly, in a second aspect of the present invention there is provided a process for the treatment of liquid waste comprising the steps of: a) removing suspended solids from the liquid waste; b) removing oil from the liquid waste; and c) subsequently passing the liquid waste through a filter wherein the filter comprises particulate coal as a filter medium and wherein the approach velocity of the liquid waste is less than 10cm/min or 1 OOL/min/m2.

The process of the first aspect of the present invention is particularly suited for the treatment of liquid waste including liquid containing suspended solids and contaminates, eg. aluminium, cadmium, copper, nickel, lead, zinc, oil/grease.

The process of the first aspect of the present invention is preferably conducted in a pressure filter, that is a filter having an elevated pressure on the upstream side of the filter.

This may be readily achieved by pumping the liquid waste through the filter. The filter we prefer is generally lower in pressure as the velocity through the bed is slower than standard filters. The differential pressure is typically less than 100kPa.

The filter medium of the present invention is coal. A variety of different coal types may be used in the present invention. It is preferred that black coal, or anthracite, be used as the filter medium. The coal is preferably crushed to have a particle size of-1.8mm to +0.6mm.

The filtration process of the first aspect of the present invention employs a relatively slow approach velocity. The approach velocity is the velocity of the liquid waste as it approaches the filter medium. The approach velocity is less than 10cm/min. The flow rate is divided by the cross sectional area of the filter bed to determine the approach velocity. It is preferred that the approach velocity is in the range of from 5cm/min to 10cm/min. Without wishing to be bound by theory, it is believed that by employing coal as the

filter medium the filtration process operates by the simple mechanical entrapment of suspended solids and oils as well adsorbing heavy metals from the liquid waste.

The process of the first aspect of the present invention may be employed with preliminary treatment steps to treat heavily contaminated liquid waste. In the second aspect of the present invention such a process is described. In the treatment of heavily contaminated liquid waste suspended solids are removed. Preferably suspended solids are removed using a sedimentation, or setting, process. Liquid waste may be pumped into a setting tank of suitable dimensions and clarified liquid waste removed from the top of the settling tank and a sludge containing a substantial proportion of the suspended solids removed from the bottom of the settling tank.

Other separation techniques may be used to remove a substantial portion of the suspended solids.

The sludge may be further treated in accordance with Australian Patent No. 728309. The sludge generally has 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 70 to about 5%, typically 65 to 40%). The sludge may contain suspended solids and emulsified liquids such as hydrocarbons, oils and greases. The sludge is filtered through a course coal filter with the filtrate returned to the settling tank for further processing as clarified liquid waste.

The filter cake of sludge retained in the filter bed may be dried with the coal filter medium and used as a fuel such as in power generation, steam production or cement manufacture.

The coal used as a filter medium for the treatment of the sludge preferably has a minimum particle size of about 0.075mm and typically about 2mm. The coal may have a maximum particle size of about 100mm. A preferred particle size is between about 20 and about 65mm. Coal having a particle size distribution in which there is a high percentage of particles less than about 2mm is undesirable for materials handling in industrial furnaces or dryers. Further, coal having a high amount of fines becomes easily clogged when used to filter waste having a high solids content.

The filter medium for use in the first and second aspects of the present invention 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.

The clarified liquid waste, in the second aspect of the present invention, is then subjected to a process for removing a substantial proportion of oil therefrom. Preferably oil is removed from the liquid waste using an oil- water separator. Oil removed from the liquid waste may be collected for subsequent disposal.

The aqueous component of the clarified liquid waste may then be continuously filtered in accordance with the process of the first aspect of the present invention described above.

We have found that liquid waste treated in accordance with the second aspect of the present invention has improved quality, in particular with respect to heavy metal contaminants.

Advantageously the filter medium can be discharged from the filter to the sludge dump directly or fed into the process of the second aspect of the present invention as liquid waste.

The filtration step is particularly suited for any chemical dosing of the liquid waste that may be required. The liquid waste may be dosed with chlorine for sanitization. Acid or base (such as lime) may be used to control the pH of the liquid waste.

We have advantageously found that even heavily contaminated liquid waste, when treated in accordance with the second aspect of the present invention, is suitable for discharge to town sewerage and may even be used as grey water.

Liquid waste generated by processes in the petroleum refining and chemical industries and commercial cleaning processes such as the cleaning of rail and road vehicles once treated in accordance with the second

aspect of the present invention may be recycled for use in the original process. For example in rail vehicle cleaning applications the treated water derived from the liquid waste may be used for cleaning rail vehicles substantially reducing the water requirements of the process.

The present invention will now be described with reference to the following examples and accompanying drawings. The examples and drawings are provided for illustrative purposes and do not limit the scope of the present invention.

Figure 1 is a process control diagram of one embodiment of the present invention.

Figure 1 shows a process according to one embodiment of the present invention. Waste water from locomotive wash down from steam cleaning bays from maintenance buildings and from other sources including drying beds is collected in a black-well (sump). Waste water from the black- well is pumped to a receiving tank. The waste water in the receiving tank settles and sludge is removed from the base of the receiving tanks and pumped to sludge dumps. Clarified waste water from the receiving tanks is pumped to an oil water separator. The oil water separator includes sumps for the collection of any sediment. The sumps are drained to the black-well.

Oil collected from the oil water separator is transferred to an oil receiving tank for disposal. The oil receiving tank has an overflow to an oil transport holding tank. The oil transport holding tank has an overflow that returns excess oil to the black-well. The base of the oil receiving tank also has an outlet for the removal of oil either to a load out or to the black-well.

9 The water removed from the oil water separator is transferred to a pair of effluent holding tanks through which the effluent is reticulated.

Sediment from the base of the effluent holding tanks may be returned to the black-well for reprocessing. The clarified liquid waste is pumped through a high pressure primary filter.

The primary filter is a high pressure filter having coal as the filter medium. The approach velocity of the influent is maintained in the range of from 5cm/min to 20cm/min. The filtered water is then pumped to a batch clarifier tank from which the filtered water may be disposed through a

sewerage pit to the town sewerage or may be used as grey water for flushing toilets, for use in the steam cleaners room or for use in the maintenance building.

The influent to the primary filter is partially diverted through a pH dosing circuit where the pH of the influent is determined and the influent is dosed with acid or lime as the case may be. Chlorine may be dosed into the filtered water prior to pumping to the batch clarifier.

The primary filter has a media ejection from which the used coal may be pumped to the black-well. The used coal in the black-well may then be subjected to the process described herein.

Example 1 In a rail vehicle washing facility the process shown in Figure 1 was employed. Typically the black-well waste water had the properties shown in Table 1 below.

Table 1 Blackwell 10 June 1998 13 October 1998 TSS 78600 94900 PH 6. 89 6.78 Oil and Grease 76500 52100 Cr (total) 0.29 0.35 Cu (total) 20.1 25.9 Pb (total) Al (total) 113 93. 1 Zn (total) 18 15.9 Mo (total) 0.85 0.45 Ni (total) 0.17 0.19 Table 2 shows the content of waste water treated by a process without the use of a high pressure coal filter.

Table 2 Comparative Jul 01 Jan 02 Apr 02 Jul 02 Average SD BOD5 mg/l 8 5 7 11 7.75 2.50 Suspended 6 9 11 12 9.50 4.44 Solids mg/) H 7. 2 7.2 7.6 6.9 7.23 0.25 Oil & Grease mg/ ! <10 <10 <10 <10 <10 Chromium mg/ ! 0.02 0. 15 0. 001 0.057 0.081 Copper mg/) 0.03 0. 04 0. 052 0.041 0.011 Lead mull 0.05 0.01 <0.001 0.001 0.020 0.026 Aluminium mgn 0.11 4.7 0.31 0. 91 1.508 1.97 Zinc mg/l 0. 16 0.49 0.036 0.02 0.177 0.20 Iron mg/l 0. 28 7 0.41 0.95 2.16 3.24 Cadmium mull <0. 01 <0.01 0.004 0.004 0.004 Anionic 1.6 0.4 0.7 1.5 1. 05 0. 60 Surfactants mg/l

Table 3 shows the final water quality results of the use of a coal filter in accordance with the process shown in Figure 1.

Table 3 Invention Oct 02 Nov 02 Dec 02 Average SD % improvement on average BODs mg/l 6 7 9 7.33 1.53 6 Suspended 1 7 21 9.67 10.26-2 Solids mg/i pH 7. 1 7.1 7.3 7.17 0.12 Oil & Grease <10 <10 <10 <10 mg/l Chromium mg/l 0.001 0.001 0.002 0.001 0.001 4175 Copper mg/ ! 0.021 0.03 0.036 0.029 0.008 40 Lead mg/l <0.001 <0.001 <0.001 0. 001 1933 Aluminium mon 0.025 0.015 0.02 0.020 0.005 7438 Zinc mg/l 0. 014 0.022 0.03 0.022 0.008 702 Iron mg/l 0.69 0.67 1.5 0.95 0. 47 127 Cadmium mg/l 0.002 0.002 0.003 0.002 0.001 71 Anionic 0.5 1.9 1.4 1.27 0.71-17 Surfactants mg/) Table 4 shows the final water quality results before and after the final filter.

February 2003 Results

Parameter Limit Pre-Filter Post-Filter Iron < 100 mg/L 29 1. 1 Aluminium < 100 mg/L 5. 9 0. 059 Cadmium < 2 mg/L 0. 008 < 0.005 Chromium < 20 mg/L 0. 26 < 0.005 Copper < 10 mg/L 5. 7 0. 018 Lead < 10 mg/L 0. 079 < 0.005 Zinc < 10 mg/L 3. 1 0. 054 Oil & Grease < 200 mg/L 66 45 pH 6. 0-10.0 6. 8 6. 9 Suspended Solids < 300 mg/L 270 <5 Anionic Surfactants < 500 mg/L 0. 4 0. 4 Persons skilled in the art will appreciate that the invention described above may be subject to improvements and modifications that will be apparent without departing from the spirit and scope of the invention described herein.