FR2628337A1 - Filtration and purificn.. of fluids e.g. water - by addn. of active carbon as adsorbent for organic material followed by membrane filtration and recirculation of retentate mixt. - Google Patents

Abstract

An appts. for filtration and purificn. of fluids, esp. liqs. such as water, by means of membranes or by tangential filtration and an adsorbent, esp. active carbon, operates as a sealed loop circuit, with the adsorbent being introduced into the stream of fluid to be treated and fed with this to a filtration unit comprising at least one membrane or a tangential filtration unit, through which part of the fluid to be treated passes, while the remainder of the mixt. of fluid to be treated and adsorbent is returned to the loop followed by additional fluid to be treated. USE/ADVANTAGE - The appts. provides a combination of membrane filtration (micro- or ultrafiltration) with an adsorbent treatment to remove dissolved organic materials which are not retained by the filtration. The process provides good removal of suspended solids (turbidity) and dissolved organic substances in water.

Description

 The invention relates to the field of treatment, with a view to their filtration and purification, of fluids, in particular of liquids, such as water and relates more particularly to membrane filtration (micro- or ultra filtration) and to purification by adsorbent of such fluids.

 It is common ground that, in a conventional water filtration installation, even using a membrane as a filtration medium, the dissolved organic materials are little or not retained. It is therefore essential to complete the installation with one or more refining treatments for the elimination of these materials, one of the most effective treatments for this elimination being adsorption on activated carbon.

 The invention makes it possible to couple, in the same installation, the advantages of using a membrane as a filtration means and that of an adsorbent, more particularly of activated carbon, to perfect the filtration effect obtained by the membrane. .

It relates to an installation essentially characterized in that it forms a "loop", that is to say that it operates in a circuit close the adsorbent being introduced into the stream of liquid to be treated and brought with it a pass over at least one filter membrane, and reintroduced into the circuit followed by the liquid to be treated;
The installation comprises an inlet for the liquid to be filtered, means for dosing the adsorbent injected into the liquid to be filtered, at least one filtering membrane downstream of which is provided an outlet for the filtered liquid, and means for bringing the residual liquid-adsorbent mixture upstream of the filter membrane and an outlet for the spent adsorbent.

 The adsorbent can be introduced into the loop either by mixing it with the fluid to be treated, or in the loop itself, in a continuous or discontinuous mode.

 The combination of the speed of filtration through the membrane and the speed of circulation of the fluid in the loop, allows the constitution of a layer of reagent on the surface of the filtration membrane, or an integral mixture of the reagent in the fluid circulating in the loop, or the combination of the two phenomena. In addition, the independent adjustment of the filtration speed, by the mean pressure of the loop, and of the circulation speed of the fluid by acting on the recirculation flow, makes it possible to control the thickness of the adsorbent layer and the concentration "free of adsorbent in the fluid vein. The total concentration of adsorbent in the loop can be controlled in two ways: either through the injection of fresh adsorbent or by the exhaustion of spent reagent. As for the layer of adsorbent formed on the membrane, it is renewed by periodic backwashing.

 The formation, in an installation according to the invention, of a precoat of the adsorbent, such as activated carbon, on the filter membrane has a number of important advantages.

 The use in water treatment of an adsorbent, such as powdered activated carbon, requires a prior treatment of flocculation of the water using metallic salts and / or flocculation additives to make settling and filterable. particles suspended in water But thanks to membrane filtration, this treatment is no longer necessary, which increases the adsorption capacity of the activated carbon since it is not covered with a hydroxide layer. metallic and / or flocculation aids from the flocculation treatment. In addition, the adsorption is improved due to the concentration of activated carbon in the circuit followed by the water in the loop according to the invention. This concentration effect does not exist in conventional applications of this reagent (filtration on sand or decantation). Activated carbon is, moreover, better used since its residence time in the loop is much longer than that of strip, this residence time being controlled by the adjustable rate of rejection of spent activated carbon.

 Furthermore, it is known that the organic materials contained in the water & BR <to treat play a very important role in the clogging of the membranes. In addition to its purifying power, the activated carbon plays vis-à-vis the membrane the role of "trap" of clogging materials, which reduces clogging of the membrane and therefore increases the performance of the filtration operation. . Finally, it has been shown that the addition of particles of controlled diameter proves effective in controlling the formation of the filter cake. This is the case with the activated carbon particles used.

 An installation according to the invention can take various boreholes, such as those, given solely by way of examples in the description which follows, given with reference to FIGS. 1 to 3 of the accompanying drawings which are diagrams of such installations.

 In the example treated in FIG. 1, a loop according to the invention comprises, as a filtering membrane, a tangential filtration module 1 supplied with water to be treated by a closed circuit to which the water is supplied by a pipe 2 provided with a pump 3 and a valve 4. The activated carbon, in powder form, is introduced at 5 into the line 2, by means of any metering system (not shown). In the filtration module and downstream of the filtration, a line 6 is taken intended for recycling, at the start of installation, the water-activated carbon mixture. On this pipe is provided, in 7, an adjustable purge for the outlet of the spent activated carbon. Finally, the outlet of the treated water is provided by a pipe 8.

 By varying the different parameters that constitute the speed of introduction of water into the installation, the filtration pressure exerted in the tangential filtration module, the flow rate of treated water and the flow rate of the exhausted activated carbon purge , the thickness of the coal pre-layer formed on the filtration unit of the module is influenced, the concentration of the coal mixed with water, therefore on the filtration capacity and the adsorption capacity.

 The installation shown in FIG. 2 presents two identical loops A and B & filtration on membrane 9, ga and placed in series-production. Activated carbon powder is introduced at 10 between the two loops in the pipe connecting them. In the upstream loop A emerges the line 12 for supplying water to be treated, the treated water leaves the downstream loop B via the line 17. The water-activated carbon mixture is returned to the upstream loop A by a line 13 , this mixture circulating against the current of the water to be treated. Pumps, respectively 14, 15, with their control valves (not shown) one equip loop B, the other loop A, to ensure respectively one, 14, the recycling of the water-activated carbon mixture, the other, 15, the supply of active carbon to loop A and the extraction by the purge 16, of spent activated carbon.

 In such an installation, powdered carbon, which circulates against the flow relative to the fluid to be treated, is better used since it is first in contact with a fluid already freed from the most adsorbable substances during its passage through the upstream loop A, the downstream loop B then refining the processing initiated in the upstream loop.

 In addition, the transfer of powdered carbon from the downstream loop to the upstream loop results in the fact that, since the powdered carbon has been in contact with a relatively low-concentrated fluid, it remains effective for adsorbing impurities at higher concentration.

 An installation as shown in FIG. 3, allows the use of an adsorbent consisting of granular activated carbon, the adsorption capacity of which is greater than that of powdered carbon but which has the drawback of being friable, this friability generating fines present in the liquid treated and must be separated from the latter.

 According to the embodiment shown in FIG. 3, the adsorber constituted by a fluidized bed of granular coal 18 is disposed between two membrane filtration loops A1, B1, similar to loops A and B of FIG. 2. The water to be treated is injected upstream of the loop Ai, into the pipe 19 supplying the water to be treated to the loop Ai and the water-activated carbon mixture returns, under the same conditions, in the opposite direction, by line 20 has that bringing the water to be treated & the upstream loop. The used activated carbon is purged at 21 from the upstream loop Ai and the treated water leaves, at 22, from the downstream loop A2.

Thanks to these arrangements according to the invention, the presence of the downstream loop, at the outlet of the adsorber, makes it possible to remove from the treated water the carbon fines produced during the treatment and, moreover, to refine the treatment. The Ai loop protects the adsorber from fine particles contained in the water to be treated. It is then possible to use in the adsorber, particles of adsorbent of finer particle size, which are consequently more effective, without thereby producing a significant clogging. In addition to this protective role, the arrangement adopted has the advantages already mentioned above for the combination of two membrane filtration loops, described in connection with the
Figure 2.

The following example shows the advantages provided by the invention
River water containing on average 6 mg / l of dissolved organic matter, and with a turbidity of 5 NTU was treated by 3 types of treatment 1 - Coagulation treatment on a filter with aluminum sulphate (10 mg / l ), activated silica (2 mg / l) and activated carbon (10 mg / l). Coal was added first, followed by mixing aluminum sulfate, and finally activated silica.

2 - Treatment by tangential microfiltration on membrane, at an initial flow of 100 l / m2 / h, a recirculation flow of 3m3 / m2 / h, and an initial purge of 5 l / h. The filtration yield is then 95/6.

3 - Treatment with powdered activated carbon (5 mg / l) followed by microfiltration on a membrane, according to the invention, and having the same settings as conventional microfiltration.

The compared results of these three treatments are illustrated in the following table
type of organic matter clogging time *
dissolved membrane treatment
1 4.5 mg / l
2 5.7 mg / l 2 hours
3 2.3 mgol 7 hours I Time required for a reduction in the flow rate of the membranes by 20 Z.

 The effectiveness of powdered activated carbon in the filtration loop is explained by the concentration carried out in this loop, which is multiplied by 20 compared to a simple mixing of the carbon with the water to be treated. In addition, we can see that the microfiltration membranes used clog 3.5 times slower than in conventional tangential microfiltration (treatment 22. The treatment also shows a saving of 50% of the reagent, for better efficiency.

Claims (5)

 1 - Installation for the filtration and purification of fluids, in particular liquids, such as water, by means of membranes or by tangential filtration and an adsorbent, such as in particular activated carbon, characterized in that it is present in the form of a "loop", that is to say that it operates in a closed circuit, the adsorbent being introduced into the stream of the fluid to be treated and brought with it to a filtration means constituted by at least one membrane or a tangential filtration unit through which a part of the fluid to be treated passes, the rest of the mixture: fluid to be treated-adsorbent, being reintroduced into the circuit followed by the fluid to be treated.  2 - Installation according to claim 1 characterized in that it is constituted by a single loop comprising an inlet (2) for the fluid & BR <treat, means for injecting, in an adjustable manner, the adsorbent in the fluid stream , at least one micro-filtration means, such as membrane (1) to which the mixture: fluid-adsorbent is brought, with evacuation of the treated fluid; at least one means (6) for bringing the residual mixture: fluid-adsorbent at the head of the installation, against the flow of the initial mixture; and a purge for the spent adsorbent.  3 - Installation according to claim 2 characterized in that the filtration means. is a tangential filtration module and the adsorbent of powdered activated carbon.  4 - Installation according to any one of the preceding claims, characterized in that it comprises two loops (A, B) with membrane filtration (9, 9a) placed in series-production and connected together by a pipe (11) into which is injected the adsorbent, consisting of powdered activated carbon, the upstream loop (A) receiving the fluid to be treated, the downstream loop (B) comprising an outlet for the treated fluid and the two loops being connected by a pipe (-13) bringing the fluid-adsorbent mixture, in the upstream loop (A) upstream of the membrane.  5 - Installation according to any one of the preceding claims, characterized in that it comprises two loops (A1 / B1) with membrane filtration between which is arranged an adsorber constituted by a fluidized bed of granular activated carbon, the upstream loop ( A1) receiving the fluid to be treated and the outgoing fluid-adsorbent mixture being injected into the stream of fluid to be treated before it enters the upstream loop.