Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F1/5263—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using natural chemical compounds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/14—Ultrafiltration; Microfiltration
  • B01D61/145—Ultrafiltration
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
  • B01D61/14—Ultrafiltration; Microfiltration
  • B01D61/16—Feed pretreatment
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F1/54—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using organic material
  • C02F1/56—Macromolecular compounds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2311/00—Details relating to membrane separation process operations and control
  • B01D2311/04—Specific process operations in the feed stream; Feed pretreatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2311/00—Details relating to membrane separation process operations and control
  • B01D2311/16—Flow or flux control
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/28—Treatment of water, waste water, or sewage by sorption
  • C02F1/283—Treatment of water, waste water, or sewage by sorption using coal, charred products, or inorganic mixtures containing them
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
  • C02F1/444—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by ultrafiltration or microfiltration
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2305/00—Use of specific compounds during water treatment
  • C02F2305/12—Inert solids used as ballast for improving sedimentation

Definitions

• the field of the invention is that of the treatment of any type of water with a view to its purification or its potabilization.
• the invention relates to a water treatment technique including a weighted flocculation step.
• Processes of this type consist in adding to the waters to be treated one or more reagents for flocculating, that is to say, in the form of flocs, at least a large part of the pollutants present in the water, then to separate these flocs of pollutants from purified water.
• Flocculation is usually preceded by coagulation.
• Coagulation consists of injecting at least one coagulating reagent into the water to be treated in order to reduce or cancel the electrical charges carried by the pollutants present in the water in the form of colloidal particles in suspension, in order to favor their subsequent agglomeration in the form of flocs.
• the flocculation consists in injecting at least one flocculating reagent into the water, which is preferably pre-coagulated, so as to form large easily separable particles or flocs, by agglomeration of the colloidal particles in suspension in water. Flocculation is facilitated by the prior implementation of coagulation.
• Purified water is then obtained by separating the flocs suspended therein by settling.
• a granular material denser than water such as sand preferably having a particle size of between 60 and 300 microns, may be injected into the water to be treated upstream or during flocculation so as to ballast the flocks and thus promote and speed up their settling.
• a flocculation step during which, or upstream of which, a granular material denser than water, or ballast, is injected into the water is commonly called weighted flocculation.
• the weighted flocculation is carried out with stirring.
• the flocculation step thus takes place inside a flocculation tank which usually houses a mechanical agitator of the paddle stirrer type.
• the specific velocity be greater than 0.1 ms -1 in the vessel within which the weighted flocculation is carried out.
• the specific speed is equal to the ratio between the pumping rate Q p according to which the treated water is stirred in the flocculation tank and the ground surface of this tank.
• N P characterizes the coefficient of drag of the stirrer in the fluid
• the average speed gradient G can thus be calculated according to the following formula: where: Qp is the pumping rate (m .s " ) Np is the power number
• N is the rotational speed of the agitator (tr.mn 1 )
• p is the fluid density (kg .m 3)
• ⁇ is the kinematic viscosity of the fluid (kg.s ⁇ .m 1 )
• V is the volume of the tank (m 3 )
• P is the power of the stirrer (kg.m 2 .s 3 )
• G is the average speed gradient (s 1 )
• the average speed gradient prevailing inside the flocculation tank generates shear stresses on the flocs that are in suspension there.
• the flocs must therefore have good mechanical strength so as not to disintegrate under the effect of these shear forces.
• the flocculating agents also called flocculation adjuvants, used must give the flocs sufficient mechanical strength.
• the flocculating agents currently used for the purpose of satisfying these constraints are organic in nature. These are most often synthetic oil derivatives.
• organic flocculating agents such as for example polyacrylamide
• polyacrylamide are currently suspected of being carcinogenic. Therefore, their implementation might not be totally neutral about the state of health of the operators who handle them or consumers who use the treated water produced by processes using such organic flocculants.
• these organic flocculating agents which are found in the sludge obtained after separation of the flocs, are not biodegradable. This sludge is collected generally for incineration or as a fertilizer. The organic flocculants they contain can then be sources of pollution of the atmosphere or soils.
• the organic flocculants constitute a source of clogging of the filtration membranes used for this purpose.
• the invention particularly aims to overcome these disadvantages of the prior art.
• an object of the invention is to provide a weighted flocculation water treatment technique whose implementation has a reduced or no ecological impact.
• the invention aims to provide such a technique that has no effect on the state of health of the operators who implement them or consumers who use the treated water produced by such a technique.
• Another objective of the invention is to implement such a technique which has a level of efficiency equivalent if not close to that of current water treatment techniques by weighted flocculation.
• the invention also aims to provide such a technique whose implementation is at least no more expensive than current water treatment techniques weighted flocculation.
• the invention aims to provide such a technique which leads to limiting the clogging of membranes that can be implemented to filter treated water produced by ballasted flocculation.
• a weighted flocculation water treatment method comprising a step of injection into said water of at least one flocculating agent, a step of injecting into said water at least one particulate material denser than water, and a step of recovering a treated water, said weighted flocculation being carried out with stirring in a mean speed gradient of between 100 and 1,400 s -1 and said flocculant being at least one naturally occurring carbohydrate polymer having an anionic charge density of from -900 to -4,000 eq / g.
• carbohydrate polymer of natural origin having an anionic charge density is understood to mean:
• any carbohydrate polymer extracted from plants such as in particular starch, functionalized by grafting anionic reaction groups according to conventional techniques known to the chemist specialized in this field,
• the general principle of the invention is therefore based on the implementation of carbohydrate polymers of natural origin functionalized as flocculants in a weighted flocculation water treatment under high average gradient conditions, said polymer having a selected filler in a particular range.
• the invention makes it possible to produce a treated water having a quality equivalent to a water treated by weighted flocculation using a conventional synthetic organic flocculant polymer while being more respectful of the environment and having a limited impact on the health of individuals since the anionic flocculants based on natural carbohydrate polymer functionalized according to the invention are biodegradable.
• Said flocculating agent is preferably composed of substituted starch.
• the substituted starches are preferred because less expensive and more easily available on the market.
• the range of anionicity ranging from -900 ⁇ 4 -4000 ⁇ of a substituted starch corresponds to a degree of substitution of between about 0.1 and 0.5.
• the substituent or substituents of said substituted starch are preferably selected from the group consisting of carboxylate groups, sulfonates, phosphates, phosphonates.
• a method according to the invention comprises a coagulation step upstream of said weighted flocculation step.
• weighted flocculation step is followed by a decantation step.
• a method according to the invention comprises a step of injecting activated carbon into said water upstream of said weighted flocculation step.
• a process according to the invention preferably comprises a filtration step, in particular by membranes, in succession to said decantation step.
• a method according to the invention comprises in this case an additional coagulation step implemented immediately before said filtration step.
• the additional coagulation causes the formation of flocs with the excess of polymer contained in the water from the decantation. These flocs are larger in size than the particles initially present in the water coming from the settling. These flocs are deposited on the surface of the membranes of the filtration unit while the particles initially present in the water from the flocculation penetrate deeper.
• the implementation of the second coagulation is therefore advantageous because it limits the clogging of the filtration unit or at least makes it easier to unclogging.
• the ionic charge thereof should preferably be chosen as a function of the alkalinity of the water. In practice, the harder the water to be treated, the more the anionic charge density will be close to -4,000 eq / g. The less hard the water, the more the anionic charge density will be close to -900 ⁇ eq / g.
• the process according to the invention comprises a preliminary step of choosing said flocculating agent as a function of the hardness of the water to be treated, the harder the water, the more flocculant being anionic.
• said step of injecting into said water at least one flocculating agent is carried out by adding said flocculating agent to water previously coagulated at a content of between 0.1 and 5 ppm, preferably between 0.1 and 2 ppm depending on the load of the water to be treated flocculating pollutants.
• said weighted flocculation is carried out with stirring in accordance with a mean velocity gradient of between 200 and 800 s -1 This range of speed gradient is that used in the majority of reactors flocculation.
• FIG. 1 illustrates an installation for implementing a first embodiment of a method according to the invention
• FIG. 2 illustrates an installation for implementing a second embodiment of a method according to the invention
• FIGS. 3 and 4 are graphs showing comparisons of organic wastewater treatment performance in a plant of the type shown in FIG. 1, using on the one hand a synthetic organic flocculation agent, state of the art and secondly implementing a flocculating agent of natural origin according to the present invention;
• Fig. 5 is a graph illustrating that the flocculant used according to the present invention is less clogging than conventional flocculation adjuvants.
• the general principle of the invention is based on the use of anionic flocculating agent consisting of carbohydrate polymer of natural origin in a weighted flocculation water treatment conducted at a high average rate gradient.
• Such an implementation makes it possible to produce a treated water having a quality equivalent to a water treated by weighted flocculation using a synthetic organic flocculant polymer while being more respectful of the environment and individuals because the flocculants constituted of carbohydrate polymer of natural origin are biodegradable.
• this type of flocculating agent has the advantage, compared with organic flocculant agents of synthetic origin, to allow the production of treated water whose clogging power is lower. This can then be filtered while limiting the constraints associated with unclogging filtration units implemented for this purpose. 7.2.
• FIG. 1 a first embodiment of a weighted flocculation water treatment method according to the invention is presented.
• Such a process consists in introducing a water to be treated 10, which is, for example, previously clarified or floated, in a coagulation tank 11 in which a coagulating agent 12 is injected, which in this embodiment consists of ferric chloride (FeCl 3 ), commercial product.
• a coagulating agent 12 which in this embodiment consists of ferric chloride (FeCl 3 ), commercial product.
• the water thus coagulated 13 is introduced into a stirred ball of weighted flocculation 14 inside which are injected a flocculating agent 15 and a particulate material denser than water 16, or ballast, which in this embodiment is microsable.
• the flocculation tank 14 houses a paddle stirrer 20 which is implemented in such a way that there prevails inside this tank a mean velocity gradient of between 300 and 1400 s -1 .
• the flocculating agent 15 consists of a carbohydrate polymer of natural origin, preferably of substituted starch, and has an anionic charge density preferably of between -900 and -4,000 eq / g. In the case of substituted starch, such a range of anionic charge density corresponds to a degree of substitution of between 0.1 and 0.5.
• the substituents are then advantageously chosen from the group comprising carboxylates, sulphonates, phosphates and phosphonates.
• the coagulated and flocculated water 17 is introduced into a decanter 18 in the bottom of which are deposited sludge consisting of weighted flocs separated from a clarified water which is extracted overflow 19.
• the sludge 21 is extracted from the decanter 18 by means of, for example, a recirculation pump 22 and is introduced, via a pipe 23, into a hydrocyclone 24 into which service water 25 is injected.
• a mixture of sludge and microsand loaded with microsand 16 is poured under the hydrocyclone 24 into the weighted flocculation tank 14.
• a mixture of sludge and microsand heavily loaded with sludge 27 is discharged overflow of ⁇ hydrocyclone 24 in a spillway channel 26.
• a partly dehydrated mixture is extracted from the chute 26 by means of an extraction pump 28 and the effluent 29 from this dehydration is injected into the coagulation tank 11.
• it may be provided to implement no coagulation.
• FIG. 2 a second embodiment of a weighted flocculation water treatment method according to the invention is presented.
• the water to be treated 10 is introduced into a stirred pre-contact tank 31 into which powdered activated carbon 32 (CAP) is injected via a pump 33, and that
• CAP powdered activated carbon
• the mixture of water to be treated and CAP 34 is then introduced into the coagulation tank 11.
• This second embodiment is further distinguished from the first by the fact that the produced treated water 19 is introduced into a coagulation chamber 40 in which a coagulating agent is introduced, then into a filtration unit composed of a pre-filter 42 having a cut-off threshold at 150 microns and a membrane ultrafiltration module 41 having a cutoff threshold at 25 nm.
• the coagulation implemented in the coagulation zone immediately preceding the filtration unit causes the formation of flocs with the excess of flocculating agent contained in the water leaving the decanter. These flocs present a larger size than the particles initially present in the water from the settling. These flocs are deposited on the surface of the membranes of the ultrafiltration unit while the particles initially present in the water coming from the settling penetrate the ultrafiltration unit further.
• the implementation of this coagulation is therefore advantageous because it makes unclogging of the ultrafiltration unit easier.
• a method according to this second embodiment comprises cleaning phases of the ultrafiltration unit.
• These cleaning phases are of two types: the hydraulic cleaning which consists of backwashing, and the chemical cleaning which implements chemical cleaning solutions.
• a first test consisted of treating a raw water with a content of DOC (dissolved organic carbon) equal to 10.6 mg / l and an alkalinity of 5 ° f (ie 50 mg / l of CaCO 3 ) by the implementation a ballasted coagulation-flocculation process according to the first embodiment described above with the following characteristics:
• the anionic charge of this starch was measured using a device ("zametameter") MUTEK PCD 04 travel marketed in France by the company Noviprofibre under the reference X20128.
• test results described above also show that the use of flocculent polymers of natural origin (in this case a substituted starch) in proportions of water in the form of weighted flocculation-coagulation-flocculation processes.
• flocculent polymers of natural origin in this case a substituted starch
• Ten times higher than that of synthetic organic flocculant polymer makes it possible to produce treated water with levels of qualities that are fairly similar in terms of DOC content, turbidity and UV absorbance at 254 nm.
• the water treated using a dose of 2 ppm of C * PLUS 35704 does not have a significantly greater biological COD than that treated using a dose of 0.2.
• adding 10 times more organic flocculation adjuvant in a water was obviously feared that the latter a risk of seeing the biological COD of the treated water increase significantly.
• Those skilled in the art were therefore in no way prompted to add to a water to be treated organic flocculation agent at dosages significantly higher than those used with adjuvants consisting of synthetic organic polymers.
• polymers of natural origin are biodegradable. Their use therefore has no adverse effect on the environment or the state of health of individuals.
• Two other tests were reproduced under the same conditions as those of the two tests described above, but with a raw water less loaded with organic matter and having an alkalinity of 5 ° f (ie 50 mg / l CaCO 3 ) with doses of coagulant and different flocculating agents as shown in Table 2 below.
• the loss of permeability was 20.7 L / (h.bar.m 2 ) for a dose of 0.05 ppm FeCl 3 . It was equal to 4.5 L / (h.bar.m 2 ) for a dose of 0.1 ppm FeCl 3 . It was equal to 2.8 L / (h.bar.m 2 ) for a dose of 0.15 ppm FeCl 3 .
• FIG. 5 is a graph illustrating the variation of permeability at the level of the ultrafiltration unit during the implementation of the process according to FIG. second embodiment on the one hand with the use of polymer of anionic synthetic origin of charge density equal to -1400 // eq / g and secondly with use of the polymer C * plus 35704 of natural origin (substituted starch) whose anionic charge density is -900 eq / g)). During these tests, washing phases of the ultrafiltration unit were implemented.
• maintenance cleaning including injection of soda for 25 seconds, soaking (maintaining sodium hydroxide in the ultrafiltration unit) for 10 minutes, rinsing for 80 seconds, filtration for 40 minutes, injection of acid during
• maintenance cleaning including injection of soda for 25 seconds, soaking (maintaining sodium hydroxide in the ultrafiltration unit) for 10 minutes, rinsing for 80 seconds.
• the graph of FIG. 5 shows that the starch-based polymer which accumulates on the membrane surface of the ultrafiltration unit is more easily removed than the polymer of synthetic origin because:
• the washes used during the use of the flocculant polymer of natural origin are less powerful and less frequent than those used when using polymer of synthetic origin, and that the difference in permeability of the ultrafiltration module between the end of a filtration cycle and the beginning The cycle following a maintenance cleaning is more important when using the flocculant polymer of natural origin (arrow A) than that of the polymer of synthetic origin (arrow B).
• the starch-based polymer is therefore less viscous and less clogging than the organic polymer. Its implementation makes it possible to reduce the washing frequency of the ultrafiltration unit. This is particularly because it is biodegradable.
• Flocculants consisting of natural carbohydrate polymers functionalized with anionic functional groups, such as substituted starches, having an anionic charge density of between -900 and -4000 eq / g have the following advantages in particular:

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• Engineering & Computer Science (AREA)
• Water Supply & Treatment (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Life Sciences & Earth Sciences (AREA)
• Hydrology & Water Resources (AREA)
• Environmental & Geological Engineering (AREA)
• Organic Chemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Separation Of Suspended Particles By Flocculating Agents (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Water Treatment By Sorption (AREA)

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• 2010
  • 2010-04-20 FR FR1053012A patent/FR2958927B1/fr not_active Expired - Fee Related
• 2011
  • 2011-04-18 NZ NZ603683A patent/NZ603683A/en not_active IP Right Cessation
  • 2011-04-18 CA CA2796713A patent/CA2796713A1/en not_active Abandoned
  • 2011-04-18 CN CN201180030555.5A patent/CN103108688B/zh not_active Expired - Fee Related
  • 2011-04-18 WO PCT/EP2011/056164 patent/WO2011131632A1/fr not_active Ceased
  • 2011-04-18 AU AU2011244352A patent/AU2011244352B2/en not_active Ceased
  • 2011-04-18 EP EP11714584A patent/EP2560744A1/de not_active Withdrawn
  • 2011-04-18 JP JP2013505438A patent/JP5770830B2/ja not_active Expired - Fee Related
  • 2011-04-18 US US13/641,745 patent/US20130168318A1/en not_active Abandoned
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