GB1594619A

GB1594619A - Treatment of effluents containing colloidal material

Info

Publication number: GB1594619A
Application number: GB51168/77A
Authority: GB
Original assignee: ANPRESS Pty Ltd
Current assignee: ANPRESS Pty Ltd
Priority date: 1976-12-10
Filing date: 1977-12-08
Publication date: 1981-08-05
Also published as: FR2373318A1; HK28182A; MY8200183A; DE2754769A1; NZ185896A; AU3128277A; JPS5381478A; FR2373318B3

Description

(54) TREATMENT OF EFFLUENTS CONTAINING COLLOIDAL MATERIAL (71) We, ANPRESS PTY. LTD., a Company incorporated in Western Australia, of Corner Price Street, and Marine Terrace, Fremantle, in the State of Western Australia, Commonwealth of Australia, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to the treatment of effluents containing colloidal material.

Effluents comprising a mixture of two or more immiscible liquids, one of which is usually water, are difficult to treat to bring them to a condition in which they can be safely discharged into a sewerage or drainage system or re-cycled. The treatment of mixtures of water with oil, grease, wax, fats and the like (hereinafter referred to as oils) using conventional methods such as dissolved air-flotation and gravity settling are only effective for the primary separation of the free particles of oil and are not effective for removing the particles of oil dispersed in a colloidal form in the water. Various other methods such as the addition of inorganic or organic coagulants, heat treatment centrifugation, electrostatic precipitation, electro-flotation and flow-through porous beds have been used with varying degrees of success.

It has now been found that if such effluents from which the free particles of oil have been removed are passed through a coalescing bed of activated carbon in contact with a metal, which will having a standard electrode potential different from that of the carbon, the colloid can be substantially broken and the dispersed particles caused to floculate so that they can be readily removed by filtration or like treatment. Thus in its broadest form the invention resides in a method of treating effluents containing colloidal material which comprises passing the effluent through a coalescing bed of activated carbon having therein a metal, which will have a standard electrode potential different from that of the carbon, said metal being in the form of rods or plates embedded in or projecting into the carbon or in the form of small particles mixed with the carbon.

The invention also resides in apparatus for the treatment of colloid-containing effluents comprising a container formed of conducting material, a bed of activated carbon within the casing and one or more electrodes in the form of rods or plates formed of a metal projecting into or embedded in the bed of activated carbon, or in the form of small particles mixed with the carbon, and electrically insulated from the casing, said casing having an inlet and an outlet.

Preferably the casing is provided with means for back washing the bed of activated carbon.

The particle size of the carbon should preferably be such that the material being treated can flow freely through the bed with a maximum of contact with the carbon particles and retention of the flocculated particles. For most purposes a particle size of the order of 510 British Standard mesh has been found to be suitable.

The most suitable electrode is aluminium but other metals such as iron, magnesium, manganese, titanium and alloys thereof may be used.

For most practical purposes electrodes in the form of rods or plates are the most suitable. Alternatively the electrodes may be in the form of small particles of metal mixed in with the coalescing material but in this form back washing of the bed may cause difficulties through stratification of the particles of metal and activated carbon.

The invention will be better understood by reference to the following description of one specific embodiment of the apparatus shown in the accompanying drawings wherein: Fig. I is an elevation; Fig. 2 is a section elevation; Fig. 3 is a plan view of the distributor; and Fig. 4 is a fragmentary elevation showing the mounting of the electrodes.

As shown in the drawings a cylindrical casing 1 formed of a conducting material such as steel is closed at the bottom and fitted with a removable top 2. A coalescing bed 3 formed of granules of activated carbon is supported on a supporting bed 4 of gravel or other inert material in particulate form within the casing. The upper level of the bed 3 is indicated by the broken line A in Fig. 2 whilst the upper level of the supporting bed 4 is indicated by the broken line B. The unit is fitted with a pump 5 connected to the upper and lower portions of the casing through pipe 6 and valves 7, 8, 9 and 10. The casing is fitted with an outlet 11 and a drain valve 12. A venturi type air inlet 13 is provided in the pipe 6. A slotted flow distributor 14 is embedded in the supporting bed 4 and is connected to pipe 15 through valve 10. A series of aluminium electrodes 16 in the form of rods are suspended from the top 2 so that they project into the bed 3. As shown in Fig. 4 of the drawings the upper ends of the rods 16 are supported in insulating bushes 17.

When the unit Is operated as a down flow unit the valves 6 and 1U are closed and the valves 7 and 9 are open. The fluid to be treated flows through valve 7 into the top of the unit, down through the beds 3 and 4 into the slotted distributor 14 and through valve 10 to the pipe 15. To back wash the unit valves 8 and 9 are opened to allow back wash water to flow through pipe 15, slotted distributor 14, up through beds 4 and 3 and out through valve 8 to outlet 11. During the back wash operation air is drawn into the back wash fluid through air inlet 13 to assist in removal of the flocculated particles from the beds 3 and 4.

The arrangement of the valves for up flow operation of the unit is similar to that for back washing.

The flow rate of liquid to be treated through the coalescing bed 3 should be fast enough to avoid contamination of the electrode surfaces but slow enough to allow the colloidal particles to coagulate.

The liquid interface volume C above the coalescing bed 3 is related to the size of the carbon granules used in the bed and the liquid flow rates required. It is especially critical when the apparatus is used as an upflow coalescer in which the coalescing bed is constantly fluidised and therefore the apparatus must be designed to allow for bed expansion related to the emulsion flowrates in order not to waste any carbon medium. In a downflow coalescer the relation between the carbon bed expansion and the emulsion flow rate is not so critical as the flow rate required to fluidise the bed in a backwash can be controlled by a flow control valve.

If desired, the suspended electrodes 16 may be replaced by electrodes mixed in with the carbon granules of the coalescing bed.

The liquid to be treated containing a large proportion of suspended solids is pre-treated in a conventional settling tank or the like before entering the coalescing apparatus. The liquid in combination with the activated carbon of the bed 3 and the electrodes 16 is believed to produce an electrochemical action which causes migration of the colloidal particles towards either the activated carbon granules or aluminium electrodes and subsequently coagulation of the colloidal particles in the emulsion.

A portion of the coagulated particles are absorbed by the supporting bed; the liquid and remaining coagulated particles are passed out through the outlet and subsequently treated by conventional means to remove the remaining particles from the liauid.

The treated liquid may be recycled through the coalescer to ensure effective treatment. Preferably the rate of recycling is twice the inflow rate.

The cubic capacities, mesh sizes and the bulk densities of the bed are directly related to the type of colloidal precipitate to be treated and the flowrates required.

The time of residence is a critical factor in a carbon-metal bed. Higher residence times permit efficient operation for longer periods and a minimum residence time of 60 seconds is desirable.

The performance of the coalescer inversely relates to the porosity of the coalescing bed. Porosity depends on the size and shapes of the granules and on the method of packing. Less porous beds encourage faster coalescence by increasing the electric field strength. However, the choice of small porosities are limited to the higher head losses encountered, especially in a downflow coalescer.

Flow rates should be fast enough to avoid the contamination of the metal surfaces caused by the concentration of coalesced particles and metal irons and their hydroxides but slow enough to allow the colloidal particles to flocculate.

The effectiveness of the coalescer unit is illustrated by the following test results:- Test Result No. 1 Treatment of effluent from oil distribution depot After After Raw Preliminary Coalescer Units Effluent Treatment Treatment Total oil and grease (includes petroleum hydrocarbons and mixed oil mgm/Kgm 34600 95 < 5 Total solids (180 C) mgm/Kgm 3700 460 t 380 Suspended solids mgm/Kgm 2060 41 < 5 Lead mgm/l < 0.5 < 0.5 < 0.5 Aluminium mgm/le < 2 PH 6.7 7.1 8.0 B.O.D. (5 day) mgm/l 172 57 6.5 Note-The coalescer unit was operated with a continuous recycle through the final effluent at twice the flow rate of the incoming effluent.

Test Result No. 2 Treatment of Wool Scouring Rinse Water Re-cycle through After One pass coalescer at Raw preliminary through twice the Effluent treatment coalescer incoming flow Total solids (ppm) 1390 970 555 513 Suspended solids (ppm) 685 335 64 11 Grease (ppm) 220 165 67 27 PH. 6.4 6.4 7.3 7.5 The treated water was suitable for recycling as rinse water.

WHAT WE CLAIM IS: 1. A method of treating effluents containing colloidal material which comprises passing the effluent through a coalescing bed of activated carbon having a metal therein, said metal being in the form of rods or plates embedded in or projecting into the carbon or in the form of small particles mixed with the carbon.

2. A method as claimed in claim 1 wherein the metal is aluminium.

3. A method as claimed in claim 1 or claim 2 wherein the metal is in the form of electrodes projecting into the activated carbon.

4. A method as claimed in claim 1 or claim 2 wherein the metal is in the form of particles dispersed through.out the activated carbon.

5. A method of treating effluents containing colloidal material, substantially as herein described.

6. Apparatus for the treatment of effluents containing colloidal material comprising a container formed of conducting material, a coalescing bed of activated carbon within the casing and one or more electrodes formed of a metal projecting into or embedded in the bed of activated carbon or in the form of small particles mixed with the carbon, and electrically insulated from the casing, said casing having an inlet and an outlet.

7. Apparatus as claimed in claim 6 wherein the bed of activated carbon is supported on a bed of supporting material.

8. Apparatus as claimed in claim 7 wherein the supporting material is gravel.

9. Apparatus as claimed in any one of claims 6, 7 and 8 wherein the electrodes are formed of aluminium.

10. Apparatus as claimed in any one of claims 6 to 9 wherein the electrodes are

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. higher head losses encountered, especially in a downflow coalescer. Flow rates should be fast enough to avoid the contamination of the metal surfaces caused by the concentration of coalesced particles and metal irons and their hydroxides but slow enough to allow the colloidal particles to flocculate. The effectiveness of the coalescer unit is illustrated by the following test results:- Test Result No. 1 Treatment of effluent from oil distribution depot After After Raw Preliminary Coalescer Units Effluent Treatment Treatment Total oil and grease (includes petroleum hydrocarbons and mixed oil mgm/Kgm 34600 95 < 5 Total solids (180 C) mgm/Kgm 3700 460 t 380 Suspended solids mgm/Kgm 2060 41 < 5 Lead mgm/l < 0.5 < 0.5 < 0.5 Aluminium mgm/le < 2 PH 6.7 7.1 8.0 B.O.D. (5 day) mgm/l 172 57 6.5 Note-The coalescer unit was operated with a continuous recycle through the final effluent at twice the flow rate of the incoming effluent. Test Result No. 2 Treatment of Wool Scouring Rinse Water Re-cycle through After One pass coalescer at Raw preliminary through twice the Effluent treatment coalescer incoming flow Total solids (ppm) 1390 970 555 513 Suspended solids (ppm) 685 335 64 11 Grease (ppm) 220 165 67 27 PH. 6.4 6.4 7.3 7.5 The treated water was suitable for recycling as rinse water. WHAT WE CLAIM IS:

1. A method of treating effluents containing colloidal material which comprises passing the effluent through a coalescing bed of activated carbon having a metal therein, said metal being in the form of rods or plates embedded in or projecting into the carbon or in the form of small particles mixed with the carbon.

2. A method as claimed in claim 1 wherein the metal is aluminium.

8. Apparatus as claimed in claim 7 wherein the supporting material is gravel.

10. Apparatus as claimed in any one of claims 6 to 9 wherein the electrodes are

mounted on the top of the container and project downwardly into the coalescing bed.

11. Apparatus as claimed in any one of claims 6 to 10 wherein the container is fitted with valves to enable the unit to be operated as a down flow unit or an upflow unit and backwash.

12. Apparatus as claimed in claim 11 wherein an air inlet valve is provided to assist in back washing.

13. Apparatus for the treatment of colloid-containing effluents substantially as herein described with reference to the accompanying drawings.