Method for treating water containing organic matter using ion exchange and ballasted flocculation

Abstract

Method for treating water, containing organic matter characterized in that it comprises a step of adsorption of the organic matter contained in said water, in which this water is put into contact with an amagnetic ion-exchanging resin in an infinitely stirred tank (1); the filtering of the mixture of water and resin within the tank (1) and the discharging of filtered water from this tank, the filtering being implemented through at least one screen (4) provided within the tank (1) enabling the resin to be contained in the infinitely stirred tank; the periodic cleansing of the screen (4) consisting of the separation, from this screen, of the saturated resin that has collected thereon; the drawing off (18) of saturated resin from the tank (1); the regenerating (6) of at least a part of the saturated resin thus drawn off; the recycling (7) of said resin thus regenerated in the tank (1); a step of ballasted coagulation/flocculation (12, 13) and separation (14) comprising the addition of coagulant reagent (12b), flocculent reagent (13b) and microballast (21) to the filtered water coming from the tank (1) leading to the formation of flocs; the separation of the formed flocs from a clarified water (16); and the discharging (16) of the clarified water; and the discharging (17) of the sludges formed by the separated flocs.

Claims

1. A method for treating water containing organic matter comprising: contacting the organic matter contained in the water with an amagnetic ion exchange resin in a stirred tank and adsorbing the organic matter onto the resin; filtering the mixture of water and resin within the tank and discharging the filtered water from the tank; said filtering being implemented through at least one screen in the tank and wherein the filtering of the water in the tank is such that the resin is contained within the tank and some used resin is collected on the screen; periodically cleaning the at least one screen and separating from the screen used resin that is collected on the screen; removing the used resin from the tank; regenerating at least a portion of the used resin removed from the tank; recycling at least a portion of the regenerated resin to the tank; directing the filtered water to a downstream ballasted flocculation and separation system; in the ballasted flocculation and separation system, adding a coagulant reagent, a flocculant reagent and a microballast to the filtered water which causes the formation of flocs; separating the formed flocs from a clarified water; discharging the clarified water from the ballast flocculation and separation system; and wherein the flocs form a part of sludge and the method includes discharging the sludge from the ballasted flocculation and separation system.

2. The method of claim 1 wherein cleaning the screen includes injecting a fluid into and through the screen where the injected fluid flows in a direction generally counter to the direction of flow of the filtered water.

3. The method of claim 1 wherein the regeneration of the used resin comprises the elution of the organic matter adsorbed on this resin by passage of an eluent on said resin and the recovery of an eluate, said eluate being fractioned into at least one fraction highly charged with organic matter and at least one fraction not highly charged with organic matter, said fraction highly charged with organic matter being discharged and said fraction not highly charged with organic matter being recycled as an eluent.

4. The method according to claim 1, characterized in that the separation of said flocs is done by flotation.

5. The method according to claim 1, characterized in that the separation of said flocs is done by lamellar or non-lamellar decantation.

6. The method according to claim 1, characterized in that said resin is an anionic resin.

7. The method of claim 1 further including maintaining the concentration of resin in the water in the tank in the range of 100-200 ml of resin per liter of water.

8. The method of claim 1 wherein regenerating the resin includes employing a brine as an eluent.

9. The method of claim 8 wherein the eluent is NaCl.

10. The method of claim 1 wherein recycling the regenerated resin includes providing a resin renewal rate in the tank of 2-4 ml of resin per liter of water.

11. The method of claim 1 wherein organic matter and suspended solids are removed from the water through the processes in the tank and the ballasted flocculation and separation system such that the clarified water leaving the ballasted flocculation and separation system includes an organic matter content expressed in TOC of 1 mgC/L and a turbidity in NTU below 1.

Description

LIST OF FIGURES

(1) The invention as well as its different advantages will be more easily understood from the description of an embodiment of the installation and the method according to the invention, given by way of non-restrictive examples and with reference to the figures, of which:

(2) FIG. 1 is a schematic representation of an example of an embodiment of a plant according to the invention for implementing the method according to the invention;

(3) FIG. 2 is a schematic representation of an infinitely stirred tank provided with means for regenerating resin and means for recycling regenerated resin in said tank that can be implemented in the framework of the invention; and

(4) FIG. 3 represents a schematic view in perspective of one embodiment of a screen that can be implemented in a plant according to the present invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(5) Plant

(6) Referring to FIG. 1 and FIG. 2, the plant according to the invention schematically represented comprises an infinitely stirred tank 1. This tank 1 is provided with means 2 for conveying raw water provided in the lower part and means 5 for discharging filtered water provided in the upper part. It is also equipped with stirring means 3 comprising a blade-fitted stirrer moved by a motor. In other embodiments, these stirring means could be constituted by other types of stirring means, especially a device as described in the patent application FR2971436.

(7) In accordance with the present invention, the tank 1 is provided with one or more screens 4, which shall be described in detail here below with reference to FIG. 3. These screens in the present embodiment are provided in the upper part of the tank 1. However, in other embodiments they could be provided in any other part of the tank, the important point being that they can be submerged by the mixture of water and resin received by the infinitely stirred tank 1. This mixture is shaded in FIG. 1.

(8) Finally, the infinitely stirred tank 1 is also provided with means for extracting resin 18.

(9) As can be seen in FIG. 2, and according to the present invention, the plant also comprises means 30 for cleansing the screens 4. These cleansing means 30 include a conduit 31 of compressed air flowing in a counter flow to the sense of filtration of the mixture of resin and water by the screens. This sense of filtration is symbolized by the arrow A in FIG. 2.

(10) Also in compliance with the present invention, the means for extracting resin 18 include a recovery unit 19 designed to recover the essential part of the matter detached from the screens 4 through the means 30 for cleansing these screens. This recovery unit 19 is connected to a pipe 32 provided with a pump which extracts this matter to convey it towards the resin regeneration means 6.

(11) The plant indeed also comprises such resin regeneration means 6 in fluid communication with the infinitely stirred tank 1. These resin regeneration means 6 include a regeneration tank 10, means 9 for conveying eluent to said regeneration tank and means 8 for separating the eluent into fractions. A common pipe 8a conveys the totality of the eluate coming from the regeneration 10 towards the separating means 8, and a pipe 8c is dedicated to the recycling of eluate fractions meagerly charged with organic matter, as eluent towards the eluent conveying means 9 while a pipe 8b is dedicated to discharging fractions of eluate more highly charged with organic matter and non-reusable as eluent.

(12) The plant also comprises means 7b for recycling regenerated resin through the resin regeneration means 6. These recycling means include a pipe connecting the lower part of the regeneration tank 10 to the infinitely stirred tank 1 and enable the re-routing of the regenerated resin into the tank 10.

(13) The plant also includes a coagulation reactor 12 in fluid communication with the means 5 for discharging filtered water into the infinitely stirred tank. This reactor 12 is provided with the blade-fitted stirrer 12a and means 12b for distributing coagulating reagent.

(14) The plant also includes a flocculation reactor 12 in fluid communication with said coagulation reactor 12. This reactor 13 is provided with a blade-fitted stirrer 13a, means for distributing coagulant reagent 13b and means for distributing a ballast intended to increase the density of the flocs and therefore to facilitate the subsequent separation by decantation.

(15) Finally, the plant comprises separation means 14 comprising means 16 for discharging clarified water and means 17 for discharging sludges. In the present embodiment, these separation means include a decanter 15 provided with inclined blades (not shown) helping in the decantation process. The sludge discharging means 17 include a pipe 17a for transferring a part of these sludges to a hydrocyclone 21, the underflow of which communicates with the ballast distribution means 20 and the overflow of which discharges dirty water. These means recycle the ballast and therefore reduce its consumption.

(16) Referring to FIG. 3, the screens 4 are constituted in the form of a box, the side walls 4a, 4b, 4c, 4d, 4e and the bottom 4f of which are constituted by thick plates, 3 to 10 mm, made of porous PEHD, the pores of which have a cut-off threshold of 40 m to 120 m. The mixture of resin and water present in the infinitely stirred tank is filtered as symbolized by the arrows A in the sense going from outside the box to its interior. The means for discharging filtered water communicate with this interior.

(17) Method

(18) The plant described here is implemented to treat water having an organic matter content expressed in TOC (total organic carbon) of about 2.5 to 5 mg C/L and the turbidity varies from 1 to 50 NTU.

(19) As a coagulant reagent, ferrous chloride FeCl.sub.3 was used.

(20) As a flocculent reagent, an AN 934 type anionic polymer was used.

(21) As ballast, micro-sand was used.

(22) The resin used was an amagnetic anionic resin commercially distributed as Purolite.

(23) The water was treated in the plant at a flow rate of 3 m.sup.3/h, and the volume of water treated corresponded to 24 m.sup.3/day.

(24) The concentration of resin in the water within the infinitely stirred tank was fixed and maintained in the range of 100 to 200 ml of resin/L typically 150 ml of resin/L.

(25) A speed of clarification in the settling tank of 60 m/h was implemented.

(26) For the regeneration of the resin, brine, (120 to 300 g NaCl/l) was used as eluent. The eluate was fractioned into several fractions. The fractions having an organic matter concentration above a predetermined threshold were discharged while the fractions having a concentration below this threshold were reutilized as eluent. This method enabled savings in brine.

(27) The recycling of regenerated resin was implemented so as to observe a resin renewal rate within the infinitely stirred tank of 2 to 4 ml of resin/L.

(28) The water obtained at the exit from the plant had an organic matter content expressed in TOC of 1 mg C/L and a turbidity in NTU below 1.

(29) To obtain this excellent result, only 10 g/m.sup.3 of FeCl.sub.3 and only 0.2 g/m.sup.3 of flocculent polymer was used. Almost the entire portion of ballast (micro-sand) was also recycled.

(30) Table 1 gives a synthetic view of the costs entailed in the implementation of the method according to the invention and two prior-art techniques to process one cubic meter of the same water in order to obtain treated water of similar quality.

(31) These results confirm the advantage of the present invention over the prior art in terms of economy of chemical reagents, the invention permitting savings of about 50% to 75% in the total cost of reagents used.

(32) Finally, it will be noted that the invention has the advantage of removing the need for using magnetized resins and therefore for producing resin fines.

(33) TABLE-US-00001 INVENTION Price Price (/m3) (/m3) Reagent FR2973794 EP162867 with with prices Dose Price Dose Price Dose regeneration regeneration Price) (g/m3) (/m3) (g/m3) (/m3) (g/m3) of resin 2 mL/L of resin 4 mL/ Added resin 4 0.1 0.01 0.01 (/L) Brine (NaCl) 100 /ton 0.015 0.03 Cost of electricity 0,0002 0.0004 needed at the resin regeneration step () FeCl3 150 /ton 10 0.0015 10 0.0015 0.0015 Carbon active 2500 /ton 20 0.0500 30 0.075 powder Polymer 2000 /ton 0.5 0.001 0.2 0.0004 0.0004 Sand 150 /ton 5 0.00075 5 0.00075 0.00075 Citric acid 1000 /ton 0.0006 Bleach 0.001 Total treated water 0.053 0.077 0.028 0.043 in /m3