Method for water treatment by adsorption and filtration on a granular material bed

Abstract

Method for treating water by filtration on a bed of granular material in order to reduce its content in contaminants, said method comprising the steps for: making said water travel in transit in a reactor containing said bed in a upward flow at a speed that does not permit the fluidization of said bed but permits said material to migrate, as and when the filtration takes place, towards the lower part of said reactor, continuously removing a fouled granular material at the foot of the reactor, by means of a piping into which a gas is insufflated, said fouled granular material being constituted by granular material and contaminants adsorbed on said granular material; continuously or intermittently carrying out the physical cleansing of said fouled granular material thus removed, so as to obtain a cleansed granular material essentially rid of said contaminants; reinjecting the granular material thus cleansed into an upper part of said bed; characterized in that the granular material is an adsorbent granular material and in that it comprises: a continuous or intermittent step for the discharging, during the filtration, of a part of the fouled granular material removed at the foot of the reactor; and a continuous or intermittent step for the introduction into the reactor, during the filtration, of fresh granular material in a quantity sufficient to compensate for the part of granular material discharged.

Claims

1. A method of removing particles and organic matter from water by employing a bed of adsorbent granular material disposed in a reactor, the method comprising: directing the water into the reactor and upwardly from a bottom portion of the reactor through the bed of adsorbent granular material and to a top portion of the reactor; as the water flows upwardly through the bed of adsorbent granular material, continuously flowing the adsorbent granular material downwardly to the bottom portion of the reactor; as the water moves upwardly through the bed of the adsorbent granular material, filtering the water with the adsorbent granular material to remove particles from the water, resulting in the bed of adsorbent granular material retaining the particles; in addition, as the water moves upwardly through the bed of adsorbent granular material, adsorbing the organic matter in the water onto the adsorbent granular material; wherein filtering the water with the adsorbent granular material and absorbing the organic matter from the water onto the adsorbent granular material yields a treated water; conveying the adsorbent granular material and the retained particles from the bottom portion of the reactor to a cleaning station disposed over the bed of adsorbent granular material; wherein a portion of the treated water is used as a cleaning water to clean the adsorbent granular material by contacting the adsorbent granular material with the cleaning water and separating the particles from the adsorbent granular material; discharging the cleaning water and the particles separated from the adsorbent granular material from the reactor; continuously or intermittently purging a portion of the adsorbent granular material having organic matter absorbed therefrom from the reactor and injecting fresh adsorbent granular material into the reactor; discharging the treated water from the reactor; and wherein the cleaning station includes a helical ramp having an upper portion and a lower portion and the method includes discharging the adsorbent granular material and retained particles into the upper portion of the helical ramp and directing treated water into the lower portion of the helical ramp such that the adsorbent granular material and retained particles move counter to the treated water and wherein the treated water is effective to separate the retained particles from the adsorbent granular material.

2. The method of claim 1 wherein the adsorbent granular material comprises agglomerates of adsorbent granular material.

3. The method of claim 1 wherein the adsorbent granular material comprises agglomerates of adsorbent granular material having an average size of 200 micron to 1000 micron.

4. The method of claim 1 wherein the adsorbent granular material comprises agglomerates of activated carbon particles with said agglomerates having an average size of 200 micron to 1000 micron and wherein the agglomerates of the activated carbon particles have a smaller size than that of granular activated carbon and a greater grain size than powdered activated carbon.

5. The method of claim 1 including conveying the adsorbent granular material through a conduit to the cleaning station and injecting a gas into the conduit and employing the gas to lift the adsorbent granular material and filtered particles upwardly through the conduit towards the cleaning station.

6. The method of claim 5 wherein the conduit includes a portion that is disposed exteriorly of the reactor.

7. The method of claim 1 including thermally regenerating at least a portion of the purged adsorbent granular material.

8. The method of claim 1 including the step of mixing ozone with the adsorbent granular material prior to the adsorbent granular material reaching the cleaning station.

9. The method of claim 1 wherein the adsorbent granular material and retained particles are directed from the bottom portion of the reactor into a conduit that directs the adsorbent granular material upwardly towards the cleaning station; the method including injecting a gas into the conduit and air lifting the adsorbent granular material and retained particles upwardly through the conduit towards the cleaning station; and wherein purging the adsorbent granular material includes removing a portion of the adsorbent granular material from the conduit at a point in the conduit between a point where the gas is injected and the cleaning station.

10. The method of claim 1 including directing the water upwardly through the bed of adsorbent granular material at a speed that does not permit the fluidization of said bed but which allows the adsorbent granular material to flow downwardly in the reactor as filtration occurs.

11. The method of claim 1 including conveying the adsorbent granular material through a conduit to the cleaning station and injecting a gas into the conduit and employing the gas to lift the adsorbent granular material and filtered particles upwardly through the conduit towards the cleaning station; purging at least a portion of the adsorbent granular material by removing a portion of the adsorbent granular material from the conduit at a point in the conduit between a point where the gas is injected and the cleaning station; and directing the water upwardly through the bed of adsorbent granular material at a speed that does not permit the fluidization of said bed but which allows the adsorbent granular material to flow downwardly in the reactor as filtration occurs.

12. The method of claim 1 including conveying the adsorbent granular material having adsorbed organic matter through a conduit to the cleaning station; oxidizing and degrading the organic matter adsorbed on the adsorbent granular material as the adsorbent granular material moves through the conduit; wherein oxidizing and degrading the organic matter adsorbed on the adsorbent granular material includes injecting a gas containing ozone into the conduit; and wherein the gas containing ozone carries out both an air lift operation and at the same time functions to oxidize and degrade the organic matter adsorbed onto the adsorbent granular material.

13. The method of claim 1 further including: renewing the adsorbent granular material without interrupting the treatment of the water moving through the reactor such that filtration of the water and removing organic matter from the water continues while renewing the adsorbent granular material; directing the water upwardly through the bed of adsorbent granular material at a speed that does not permit the fluidation of said bed but which allows the adsorbent granular material to flow downwardly in the reactor as filtration occurs; and constantly cleaning the adsorbent granular material and constantly renewing the adsorbent granular material.

14. The method of claim 13 wherein the adsorbent granular material comprises activating carbon that is not a powdered activated carbon nor a granular activated carbon, and wherein the activated carbon assumes the form of agglomerates of activated carbon having an average size of 400 ?m to 600 ?m.

Description

5. LIST OF FIGURES

(1) The invention as well as its different advantages will be understood more clearly from the following description of a non-exhaustive embodiment of the invention given with reference to the appended drawings, of which:

(2) FIG. 1 is a schematic view of a plant for implementing the method according to the invention;

(3) FIG. 2 also presents a schematic view of the means for dispensing raw water in the body of the reactor represented in FIG. 1;

(4) FIG. 3 also schematically represents a view in section of the reactor of the plant represented in FIG. 1, presenting a detailed view especially of the means for cleansing the fouled granular material removed from the foot of the reactor;

(5) FIG. 4 is a graph representing the reduction of the organic material (chemical organic demand or COD) over time by means of the invention.

6. DETAILED DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION

(6) Referring to FIGS. 1 and 3, the method of the invention is implemented in a plant which includes a reactor 1 comprising a reactor body 2 within which there is disposed a filtering bed of adsorbent granular material 3.

(7) This reactor body 2 has a cylindrical upper part 2a and a conical lower part 2b forming a reactor bed.

(8) This reactor 1 is provided in its upper part with 4 means for introducing water to be treated and means 5 for extracting treated water.

(9) This reactor also comprises a piping 6 mounted externally to the body 2 of the reactor 1. One of the ends of this piping 6 is connected to an aperture provided in the conical lower part 2b of the reactor body 2. The other end of this piping 6 joins the reactor body 2 in its cylindrical upper part 2a. This piping 6 cooperates with means 7 for conveying gas, in this case air, supplied through a compressor (not shown).

(10) Draining means 9 for draining the content of the reactor are also provided in the lower part of the reactor.

(11) Means 4 for introducing raw water into the reactor are extended by a piping 14 leading raw water to a device 11 for equidistribution of water within the filter bed 3.

(12) Inside the reactor, a baffle 10 is also provided. This baffle 10 takes the form of a cone anchored to the center of the reactor.

(13) Finally, the reactor also comprises means 20 for cleansing the granular material provided in the upper part of the reactor 1. The end of the piping 16 arrives at the level of these means 20. These cleansing means include a helical ramp 21, the lower end of which leads into the interior of the reactor while its upper end cooperates with a box 22 connected to a piping for discharging fouled water 23.

(14) Referring to FIG. 2, the equidistribution device 11 for raw water to be treated within the filter bed takes the form of a plurality of radial ramps 12 pierced with holes and connected to each other by a circular piping 13 also pierced with holes.

(15) The slope of the helical ramp is designed to allow the descent by gravity of this granular material along the ramp in a counterflow to filtered water rising in this ramp. The filtered water then constitutes washing water that gradually gets charged with organic matter and thus cleanses the granular material. The fouled water is retrieved in the box 22 provided in the upper part of the cleansing means 20 and discharged by a piping 23.

(16) A baffle 10 constituted by a metal cone is provided in the lower part of the reactor. This baffle 10 prevents the treated water from taking preferred paths of travel within the filter bed 3.

(17) In compliance with the implementation of the method according to the invention, the filter bed is constituted by agglomerates of activated carbon particles.

(18) The agglomerates in question have an average diameter of 396 ?m. The coefficient of uniformity of this material is 1.4 Its apparent density is 510 g/I.

(19) Referring to FIG. 1, the working of the plant represented for implementing the method was the following.

(20) During trials, the filtering speed was 3.7 m/h for a residence time of the water in the granular material of 9 min, corresponding to an overall residence time of the water in the reactor of 15 min, the flow rate of the airlift for its part being fixed at 0.1 m.sup.3/h.

(21) The water to be treated arrives by the piping 4 and is conveyed by the piping 14 up to the equidistribution means 11. For experimental needs, this supply is done at a flow rate of 1 m.sup.3/h. However, far higher feed flow rates, of the order of 10 m.sup.3/h to 15 m.sup.3/h, or even more, can be used at the industrial stage.

(22) The water travels in the filter bed 3 of adsorbent granular material. This travel enables both its filtration and the adsorption on the granular material in question of the organic matter and of the micropollutants that it contains. This travel is done in an upward flow as shown by the unshaded or blank arrows 15. The water thus filtered is discharged by the means 5 for extracting treated water which include an overflow element 17 and a discharge piping 18.

(23) Within the reactor, as and when it gets charged with organic matter, the adsorbent granular material migrates towards the upper part of the reactor demarcated by the conical part 2b of its body 2. This migration is symbolized by the solid arrows 16. This fouled granular material is finally captured by the airlift, prompted by the input of air through the means 7 in the piping 6, and sent back into the upper part of the body 2 of the reactor in the cleansing means 20.

(24) Referring to FIG. 1, on the piping 16 there are provided discharging means 25 including a piping 24. These discharging means 25 enable the discharge, during the filtration, i.e. during the working of the reactor, of a part of the fouled granular material that has been picked up at the foot of the reactor and is being conveyed towards the cleansing means 20. In practice, during trials performed, the flow rate of matter discharged was fixed at 0.08 m/h, or 8% of the treatment flow rate.

(25) To compensate for the discharge of this fouled granular material, which can be done continuously or intermittently, fresh granular material is introduced into the device as symbolized by the arrow 26.

(26) By means of the airlift, the fouled granular material reaches the cleansing means 20 through the piping 6. During its path in the helical ramp 21, it meets filtered water rising by this very same ramp, thus enabling it to be cleansed. The advantage of the use of such a helical ramp is that of increasing the contact between the fouled material and the washing water constituted by filtered water. Indeed, in the prior art, there are cleansing means for this type of reactor according to which only one part of the fouled granular material meets the wash water, leading to imperfect cleansing of this water.

(27) Water constituted by water to be potabilized, coming from a dam and having undergone a clarification step, was treated by the method according to the invention from Jan. 15 to Feb. 17, 2014. Before clarification, the water depending on the period had a relatively stable temperature varying from 11? C. to 13? C. and an organic matter content (COD) of 4 mg/l to 5.5 mg/l.

(28) At exit from the clarification process, the raw water had a COD content of 3 mg/l to 4 mg/l depending on the period.

(29) This clarified water was conveyed towards the device represented and described with reference to FIGS. 1 to 3.

(30) Referring to FIG. 4, the method of the invention enables this COD value to be made to pass from 3 mg/l-4 mg/l to 1.7-2.5 mg/l approximately.