Method of deodorizing sludge and device for performing said method

Abstract

The continuous treatment of a flow of organic liquid sludge is disclosed. Following the optional addition of granular mineral matter to the flow, the sludge is injected at a rate q into a column of air which is at overpressure relative to atmospheric pressure. The air column is circulating at a rate Q>5q in a chamber extending over a specific length in order to create a fluidized bed, in which the sludge is aerolized, between air supply piping upstream of the sludge injection and an outlet reservoir downstream of the fluidized bed, the reservoir being substantially at atmospheric pressure. A flocculant is introduced continuously downstream of the chamber into the fluidized bed in order to aggregate the organic matter before the solid part obtained in this way is separated from the liquid part, the resulting solid part thus being deodorized.

Claims

1. A method for producing a deodorized cake of sludge by continuously treating a flow of liquid sludge, wherein the flow is injected at a flow rate q into a chamber at an increased pressure compared with atmospheric pressure, while also injecting air at a flow rate Q5 q into said chamber, prior to evacuation and separation between solid and liquid parts obtained, downstream of the chamber, wherein the liquid sludge is an organic sludge, the method being applied to the deodorization of the solid part obtained, in that the sludge is injected into a column of air at an increased pressure that is itself injected at said flow rate Q5 q, said column extending over a given length L along a longitudinal axis, said length L, the flow rate and the increased pressure of said column of air being designed to create in the chamber a fluidized bed wherein the sludge is aerolized, between a pipe for feeding the air and a line or a reservoir downstream of the fluidized bed obtained, in that said fluidized bed including air bubbles is evacuated into said line or said reservoir that is pressurized to atmospheric pressure or substantially to atmospheric pressure, and in that a flocculant is continuously introduced into said fluidized bed downstream of the chamber, under conditions designed to aggregate and/or coagulate the organic matter whereby the flocculant traps said bubbles of air in contact with the sludge producing micro-meter scale and millimeter scale microporous cake of sludge so that a dewatering and complete deodorization of the solid part obtained after separation are obtained, and further comprising the step of structuring said de watered cake so that deodorization is maintained on a long term basis.

2. The method as claimed in claim 1, wherein the flow of sludge is injected into the chamber opposite and at a distance d of less than a given value from a wall and/or from a screen of said chamber.

3. The method as claimed in claim 2, wherein d is less than 50 mm.

4. The method as claimed in claim 1, wherein the absolute pressure P of the column of air is greater than 1.5 bar.

5. The method as claimed in claim 1, wherein, with the chamber vertical, the flow is evacuated continuously or intermittently from the top part of said chamber by way of a pressure relief valve that triggers above a given threshold value defining the increased pressure of the column of air.

6. The method as claimed in claim 1, wherein the solid matter is separated continuously from the liquid by filtration through successive bags that are changed as they are filled with the filtered solid matter.

7. The method as claimed in claim 1, wherein a granular inorganic matter is added to the flow, this granular inorganic matter being sand.

8. The method as claimed in claim 1, wherein a granular inorganic matter is added to the flow, the granular inorganic matter being used in a proportion of greater than 5% of the dry matter content of the sludge.

9. The method as claimed in claim 1, wherein the air flows through the chamber at a flow rate Q20q.

10. The method as claimed in claim 1, wherein the flow rate q is greater than or equal to 100 Nm.sup.3/h, and in that the relative pressure in the chamber is greater than or equal to 1 bar.

11. The method as claimed in claim 10, wherein the flow rate q is greater than or equal to 200 Nm.sup.3/h and the relative pressure in the chamber is greater than or equal to 1.2 bar.

12. The method as claimed in claim 1, wherein the flocculant is added in a proportion of between 0.5% and 3% of the dry matter content contained in the sludge.

13. The method as claimed in claim 1, wherein the flocculant is a cationic polymer.

14. The method as claimed in claim 1, wherein the effluents are degassed at the outlet of the chamber and the gases obtained are used to feed the injection of air in the bottom part.

15. The method as claimed in claim 1, wherein the cake obtained is recovered and dewatered by drying, pressing or centrifuging in order to obtain a solidified pancake.

16. A solidified organic sludge pancake obtained from the method as claimed in claim 15, wherein it has a porosity of greater than 40%.

17. The pancake as claimed in claim 16, wherein it is formed of layers and/or strips of sludge disposed one on top of another.

18. A device for treating a flow of liquid sludge fed continuously at a flow rate q, comprising: means for feeding air at a flow rate Q5 q, a chamber extending over a given length L and along a longitudinal axis, designed to be fed by the air feeding means in the bottom part and comprising at least one tube for feeding sludge, said tube being located in the lower half of said chamber, means for injecting the sludge at said flow rate q into the chamber through said tube, an outlet line or reservoir of the flow of aerolized sludge downstream of the chamber, and means for separation between the solid part and the liquid part of the treated sludge, wherein, since the liquid sludge is organic, the length L, the flow rate Q and the increased pressure in the chamber are designed to create a fluidized bed, in that said line or said reservoir comprise means for pressurizing to atmospheric pressure or substantially to atmospheric pressure, and means for introducing a flocculant continuously into said line or said reservoir in order to aggregate/coagulate the organic matter in said line or said reservoir while deodorizing it, before the introduction into said separation means.

19. The device as claimed in claim 18, wherein at least one tube for feeding sludge to be deodorized is provided, said tube being located in the lower half of said chamber, the end of said tube projecting into the chamber and being located above the air feed and at a distance d from the opposite wall such that d50 mm.

20. The device as claimed in claim 18, wherein the flow is evacuated from the top part by way of a pressure relief valve that triggers above a given threshold value.

21. The device as claimed in claim 18, wherein the chamber is formed by a cylindrical column of diameter D, the given length L being greater than or equal to 10 times D.

22. The device as claimed in claim 18, wherein the outlet line has a diameter d.sub.0 of between 0.5 D and 0.9 D.

23. The device as claimed in claim 18, comprising means for feeding a liquid oxygenation or coagulation reagent at a given flow rate.

24. The device as claimed in claim 18, comprising means for recovering the dewatered treated sludge that are formed by at least one filtration bag.

25. The device as claimed in claim 18, comprising means for extruding the treated sludge in separate rolls.

Description

(1) The invention will be understood better from reading the following description of embodiments that are given hereinafter by way of nonlimiting example. The description refers to the accompanying drawings, in which:

(2) FIG. 1 is an operating diagram of one embodiment of a device according to the invention.

(3) FIG. 2 illustrates a variant of the end of treatment of the sludge, according to another embodiment of the invention.

(4) FIG. 1 shows a device or reactor 1 formed by an elongate chamber 2 that extends about an axis 3, for example formed by a vertical cylindrical column 4 of small diameter, for example 20 centimeters. The sludge is injected (arrow 5) through a port 6 at a flow rate q, for example 5 m.sup.3/h.

(5) The port is located in the bottom part of the chamber, for example at a distance h from the bottom 7 of the chamber of between a tenth and a fifth of the height H of the chamber.

(6) This port is located and opens out at a distance of a few centimeters from the opposite wall 8 and allows the flow of sludge to be fed under pressure, causing a significant impact on contact with the wall.

(7) In other words, the pumping of waters from the outside (not shown) that are introduced into the chamber of the reactor 1 of small diameter allows an impact of the flow of sludge in the zone 9 on account of the outlet pressure of the feed pump(s) (not shown), this depending on the height of water in said feed pumps upstream of the ports and the head losses in the circuit.

(8) Conventionally, using commercial industrial pumps and a circuit without excessive aberrations, a pressure of 2 bar at the outlet 9 of the port in the chamber is easily achievable.

(9) The kinetic energy of pumping is then converted into impact energy, which is maximized by increasing the speed of introduction into the chamber for the outlet from the port through a regulator 10 which has a size that is reduced but compatible with the maximum granulometry of the sludge.

(10) Furthermore, and according to the embodiment of the invention that is described more particularly here, a quantity of air at a raised pressure is introduced (arrow 11) below the zone 9 at a very high flow rate Q much greater than 5 Q, for example 20 Q (in Nm.sup.3/h).

(11) The expression at a raised pressure is understood to mean a slight increase in pressure which may be between 0.1 bar relative and 1 bar relative compared with the pressure of introduction of the sludges, for example 0.8 bar relative.

(12) This introduction of air takes place through a port 12 and creates a significant flow of compressed air in which the drops of sludge 13 will split up, allowing bad odors to be stripped by contact.

(13) The port 12 is located below the meeting point with the effluents in zone 9, for example between a hundredth and a tenth of the height H of the chamber. This introduction of air also increases the energy level of the chamber, at increased pressure compared with its outlet 14 for evacuation of the effluents after treatment.

(14) In the bottom part of the reactor (bottom 7), provision is made, in a manner known per se, of a blow off (not shown) for excessively dense products which do not escape via the top of the reactor, said blow off being emptied sequentially.

(15) At the outlet 14 of the reactor, the emulsion of air and sludges 15 escape into an outlet line or reservoir R designed to be at atmospheric pressure (vent E), for example formed by a line of small size (for example 20 cm) which, following decanting at 16, provides transparent water 17 that is physically separated from the solid matter 18, which a very low solid matter content, in particular less than 30 mg/l, or even than 10 mg/l, whereas initially it could be close to 500 mg/l.

(16) The decolloidized solid matter 18 obtained at this level is more porous and consequently easily compactable. It may even, depending on its initial organic matter content, be directly pelletizable on leaving the reactor.

(17) The gas extracted from the reactor emerges with the water and the sludge at the rate of the increased pressure and can be recovered, treated and, if appropriate, recycled in order to be reused in the bottom part of the reactor.

(18) It should be noted that the presence of coarse matter of the type of sand, gravel, etc., increases the number of impacts and as a result improves the process.

(19) The pressure P in the chamber 2 is for its part designed and/or regulated so as to optimize the internal energy by generating a very rapid ascending flow 19 (for example 30 m/s or 40 m/s), emerging at the top.

(20) Such a pressure is thus determined in accordance with the functional characteristics of the circuit (height of water in the pumps) but also on the type of effluents and the desired treatment rates.

(21) The size finally chosen for the reactor will also be determined by a person skilled in the art in accordance with the basic knowledge of an engineer in the field of chemical engineering, and with the diagram of the flows.

(22) The pressure and the outlet are ensured for example by way of a slide valve 20 which releases the flow when the given pressure is exceeded.

(23) Since the method according to the invention employs agitation in three phases, solid, liquid and gaseous, it is necessary to implement separation at the outlet, taking into account the degassing, the solid phase that is denser than water, and the evacuation of the water.

(24) In the embodiment more particularly described, a flocculant is added (arrow 21) at the outlet of the slide valve by way of a metering device that is known per se (not shown).

(25) This addition takes place for example in the zone 22 at the continuous outlet from the evacuation means (slide valve or other valve 20) of liquid that has passed through the chamber, the slide valve or other valve 20, which opens above a given pressure in the chamber, for example 1.3 bar.

(26) It is also possible not to provide a valve, the downstream circuit itself forming the head loss necessary to maintain the relative increased pressure in the chamber, for example by way of a venturi.

(27) The emulsion 15 is then evacuated in the top part in order to arrive in a filtration bag 23 which is known per se.

(28) However, this bag may be replaced by a vessel 24 (see FIG. 2).

(29) For example, this decanting vessel 24 is formed by a cylindrical tank 25 into which the evacuation pipe 26 leads above the operating lever 27, in order to be at atmospheric pressure.

(30) The vessel 24 for its part empties via an overflow 28, through a non-turbulent lateral tank portion 29 that is separated from the rest of the tank by a wall 30 that is perforated in locations.

(31) The decanted solid matter 31 (FIG. 2) or filtered solid mater 18 (FIG. 1) is evacuated in the bottom part 32, or once the bag 23 is full in order to be able to be subsequently treated.

(32) The emulsion thus agitated and fed with air remains in the reactor for a period of time corresponding to the relative ratio between the flow rates, the volume and the pressure.

(33) It is thus kept for example for a residence time of a few seconds, for example less than one 1 minute before being evacuated.

(34) This time may even be much less, since, with a flow rate of effluent of greater than 20 m.sup.3/h, it is possible for example to remain in the chamber for a period of less than 10 seconds.

(35) The feed rate of sludges has for its part a direct action on the percussion velocity, bearing in mind that the contact time and residence time in the reactor under pressure also acts on the speed of formation of the flocs and the decanting thereof.

(36) The flow rate of air and the influence of the pressure in the reactor are furthermore elements which, in view of the desired result, will be adapted in a manner which is within the abilities of a person skilled in the art.

(37) The supernatant or filtered water obtained has high purity and is itself evacuated continuously.

(38) The sludge 31 obtained in the bottom part of the decanting vessel is evacuated either continuously or discontinuously, at given intervals, for example once per day.

(39) Re-evacuating this sludge very quickly increases its quality in particular as far as its good porosity is concerned.

(40) In the embodiment more particularly described here, the sludge 31, drained in a mobile vessel B, is then introduced for example by pumping into an extruder 33 formed by a closed cylindrical tube 34 that is perforated with orifices 35 through which the sludge is pushed for example by the introduction of compressed air at 36 via a tube 37 that dips into the tube 34. The sludge thus emerges in the form of rolls or batons 38 which are deposited by gravity in layers 39, 39 for example in a container 40 or, in the case of moving plant, directly onto spreading land. The residual water 41 flows and is evacuated easily on account of the high aeration of the layers 39, 39 which thus dry even more rapidly.

(41) In a general manner, and with the above-described device being employed, a significant modification of the level of oxidation can be observed, the stripping of the sludge making it possible to pass from a redox of 250 mV to +250 mV.

(42) Furthermore, the odor measurements carried out on the NH.sub.3, mercaptans and the H.sub.2S show that with the invention, the organic sludge (80% organic matter) which originates from a conventional treatment station for a residential community and has passed through the device described above with reference to FIG. 1, at a flow rate of 10 m.sup.3/h with a flow rate of compressed air of 100 Nm.sup.3/h and the addition of a conventional flocculant (polymer), has the following characteristics: No odor of ammonia (measured <10 ppm) No odor of H.sub.2S (measured <10 ppm) No odor of mercaptans (but measured >100 ppm).

(43) An acceleration in biodegradation is also observed: in one month the organic matter content passes from MV=76.8% to MV=53.2%.

(44) The treatment carried out by virtue of the method and reactor according to the invention thus makes it possible to obtain a porous and dewatered cake, the sludge recovered being empty, dry and manipulable. A few hours are sufficient as opposed to three months in the context of the use of what is known as conventional drying, in order to obtain a comparable result, the sludge obtained being odorless or smelling of humus, and thus being more easily recyclable.

(45) As will be obvious, and as also results from the preceding text, the present invention is not limited to the embodiments more particularly described. By contrast, it encompasses all the variants and in particular those in which the orifices may be regulators, tubes passing into the interior of the chamber in order to minimize the distance between the outlets and to increase the force of the impacts, use is made of upstream reagents such as sand, calcium carbonate, slaked lime, the extruder is different and/or replaced by means for example having blades, in order to further aerate the sludge obtained and to further facilitate its rapidity of drying.