AU595491B2 - Process for the treatment and purification of water by the flocculation of suspended particles in a fluidized bed - Google Patents

Description

I

I

I

I

5 549A COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952-69 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: AP 9q 7q-1gC, Complete Specification Lodged: Accepted: Published: -4 L I T •Priority: ,Related Art 4.4 1

I

I

I

I

4.-I 440" 4 0 044 Name of Applicant: Adress of Applicant o, o s so cn X Actual 2nventor: 46 r fSv tAddress for Service 41g V MORNEX LIMITED 49 Conduit Street, London WIR 9FB, England SAMUEL ELMALEH and ALAIN GRASMICK EDWD. WATERS SONS, 50 QUEEN STREET, MELBOURNE, AUSTRALIA, 3000.

C604h v 0 4 Complete Specification for the invention entitled: PROCESS FOR THE TREATMENT AND PURIFICATION OF WATER BY THE FLOCCULATION OF SUSPENDED PARTICLES IN A FLUIDIZED BED The following statement is a full description of this invention, including the best method of performing it known to :.US 1.

a- 4 process for the treatment and purification of water y bthe floacIlation of susperded 2 articles in a fluidized bed.

The present invention involves a process for the treatment and purification of water by the floaulation in fluidized beds of suspended particles. More particularly, the invention concerns a process of this type which in some cases (suspensions of organic matter) can be used without the addition of chemical reagents Sto give results similar to those obtained by the usual physico-chemical processes.

Urban waste water, for example, is known to contain about 200-300 mg/l of suspended matter and has a total biologic oxygen demand BOD 5 the 5-day biologic oxygen demand) of about 200-400 mg/l, 100 to 200 mg/1 of which is the dissolved BOD 5 The polluting matter which such water contains can be roughly categorized as solid pollutants (about one-third) colloidal pollutants (another third) and dissolved pollutants (the final third).

20 The usual pathways of water purification involve the use of biologic or physico-chemical processes.

Although biologic processes do provide considerable reduction in the level of pollution, they respond poorly to variations in the level of pollution of the water 425 under treatment or to the inflow of toxic pollutants, such as may occur if the water-treatment plant receives industrial effluents.' About 10 or 20 years ago, great interest was aroused by physico-chemical processes and, in particular those processes in which a liquid/solid separator was installed upstream of the flocculator. This was, for instance the case in the clariflocalation processes which.combined a floamlator and a settler.

The advantage of units of this type is that they make it possible to treat a wide range of pollution 44 4 4 IImr' 444 d i i i 1 inflow, such as face. plants serving holiday-resorts with very varied population. Such processes provide to 90% reduction of the pollution influx and the residual pollution can, if neccessary, be subject to further treatment.

The main drawbacks to systems of this type result from the need to use large amounts of expensive reagents, which implies the production of large amounts of sludge with mediocre mineralization.

It has also been suggested (European Patent application (published as no 0 085 629) that processes could be used in which the liquid containing the suspended matter is passed through a granular medium in a fixed bed until the medium is saturated 15 (either partially or totally). The medium in the fixed bed is then at least partially de-clogged t t X and the liquid containing the suspended particles passed through-it once more, either with or without i l b O 4 4 o

I;

chem ca reagents, the e tfect eing the U LLformation oL flocclated aggregates. The drawback of processes of this type is, however, that they do require an initial saturation of the granular m'dium.

The purpose of the present invention is to provide a water-purification method which involves the passage of the water being treated through a fluidized granular medium without any preliminary saturation of this medium in a fixed bed and, for some applications, without the addition of chemical flacalation reagents.

The phenomenon by which particles suspended in a liquid are flucailated is connected with two main parameters; a) the repulsive-attractive forces between particles, which may be modified by the addition of appropriate reagents; b) the velocity gradient, or hydraulic gradient L i i 3 1 G, which is defined by the following equation:

P

h G

PV

where: P is the power used in the system, I is the dynamic viscosity of the liquid phase aid V the volume of the liquid phase.

In order to set up a viscosity gradient, most floculators use stirring energy.

i 10 The inventors have however demonstrated that granular media can be used in floculation processes and the energy degraded corresponding to the pressure i drop.

A fluidized bed of granular material can be used i 15 with advantage for this purpose.

S- firstly, the fall in pressure is constant j throughout the fluidization field; S- secondly, it can be shown that the ratio G/Go of the velocity gradient to the velocity gradient in i 20 the prefluidized state varies little in function of the i number of fluidizations (the ratio of superficial velocity S to incipient fluidization superficial velocity)$ S- finally, the ratio Gt/Goto of the number of I 5 CAMP Gt in the state under study to the number of SCAMP Goto in the prefluidized state also varies little.

S This means that by calculating a floralator in a Sfluidized bed at the incipient fluidizatiop,the actual S. yield of the flcculator can easily be transposed to the fluidization field.

Furthermore, it is of interest to note that at the fluidization minimum, Go is proportional to the apparent density of the material making up the bed and to the mean diameter of the granules.

Similarly, Goto is proportional to the ratio Ho/d of the height,Ho,of the fixed bed to the mean :r I I et Ott t diameter, d of the granules and is independent of the density of the material used.

The present invention is based on the above-described properties of fluidized beds as a means of production of a hydraulic gradient and on the self-flocaiating property of waste water in the systems which are described below.

Consequently, the present invention concerns a process for the separation of suspended matter in water which is characterised by the fact that this water is passed through a granular medium in a fluidized bed, without prior saturation of the granular medium in a Sfixed bed, that the floatulated aggregates are collected downstream from the aforesaid bed, and that ,.15 they are then subjected to a liquid/solid separation process, such as settling in order to obtain an effluent which is partially purified of the initial pollution and aggregates of flooculated particles.

The fleaoclation phenomenon which occurs in the fluidized bed traps some of the dissolved polluting matter, just as in the usual clarifloaxlation process a partially purified effluent is obtained.

In the fluidized bed, the granular medium may undergo expansion of the order of 30 to 200 percent.

25 In order to obtain a fluidized bed, any packing material may be used, such as sand, and this may have low particle-size, of the order of 50 pm to 1 cm.

This granular material may be heavier or lighter than water, since the passage of liquid through the 30 granular medium occurs as an .upwaid flow if the material chosen is heavier than water and as a downward flow if it is lighter than water. The specific gravity of this material should be of the order of 0.8 to 3 g/cm3 The apparent space-time of the water under

I~

it t t t 9- 1 treatment should be of the order of 3 to 10 minutes, with a velocity of between 0.01 to 200 m/h.

The fluidization number (ratio of the superficial velocity of the treated liquid to the minimum fluidization velocity of the granular material) should be of the order ofl.lto In cases in which the suspended particles take the form of an unstable colloid, the process according to the invention can be employed without the addition of flo lating agents 'in which case, self-floctation of the.suspended' material occurs- or.with the addition of a flocculating agent. In cases in which the suspended particles are not auto-flocculant,the addition of a flocculating agent to the treated medium will usually be necessary.

In both cases, and in a totally unexpected fashion, the inventors have demonstrated that in order to promote flccculation of these suspended particles, it is helpful to add to the suspension to be purified either before the floccdation treatment or during this tzeatment,secondary sludges from the treatment of waste water. When the treatment medium itself consists of waste water, it suffices to recycle some of the separated aggregates into the inflow of the circuit containing the granular medium in the i 25 fluidized bed.

SWithout engaging the patentability of the invention by this hypothesis, the work of the inventors has demonstrated that the bacteria of the banal S' microflora of waste water secrete polysaccharides which are able to form a mucilage which serves not only to bind bacterial cells, but also to bind the microscopic particles of the suspension.

The simplified diagrams which are appended illustrate various methods of operating the invention.These diagrams, which are, of course, in no way exhaustive, show the

I

I

I

*1 44,4 I C

I,

I I V £4 C Clef

IC',

44 044 4 a 4* 4 0 40 *44 ICC

C

following features: Figure 1 shows a.-treatment system for waste water, in which the waste water circulates in an upward flow through a reactor with a fluidized bed consisting 5 of particlesof a-material with a specific gravity greater than 1; FiLgure 2 shows an analogous system, in whirr. the waste water circulate6 in a -ownward flow through a reactor in which the particlesof the fluidized bed have a specific gravity of less than. 1; Figures 3 to 5 are diagrams showing other systems utilizing the invention.

The system shown in Figure 1 involves a reactor, 1, which is fed with water for treatment through a is pipeline, 2, at its base, and which contains a fluidized bed, 3, consisting of particles of a material with a specific gravity greater than that of water.

The treated water containing the particle aggregates formed as a result of the passage of the waste water through the fluidized bed,3, is evacuated via the pipeline, 4, at the top of the reactor,1, to a settling tank,5, from the floor of which the sludges, 6, are evacuated via pipeline 7 whereas 25 the purified water is collected from the upper part of this tank via pipeline 8.

As was described earlier, in cases in which the paiticles suspended in the treated water are of organic origin, as is the case when sewage water is- to be treated, the process according to the invention can be operated without the addition of the* usual f 'culating agents, although these may be used to accelerate the flocciiation process. If the suspended particles are inorganic, flocculating agents will be required and in either case a suitable flocculating agent would be constitt~d by waste sludge from -1! r 7 1 secondary waste water treatment. If the sewage water is to be treated some of the waste sludge settled in the sedimentation could be recycled through reactor I via pipeline 9 and pipeline 7.

In Figure 2, the reactor, 11, is fed by sewage water by pipeline 12 which is at the top of the reactor,1; the reactor contains a fluidized bed, 13, consisting of particles of a material witha specific gravity of less than 1.

The treated water containing the aggregates of particles formed by passage through the fluidized bed is collected at the base of the reactor,13, by a duct, 14, and evacuated into a settling tank, at the base of which sludges, 16, are collected i by a pipeline,17, and from the top of which i purified water is collected by a pipeline 18.

Figure 3 illustrates the application of the i process according to the invention in cases in which the velocity of the liquid to be treated and brought 0 to the base of the reactor,20, via a pipeline, 21, Iis less than the decantation velocity of the aggregates, S 22, formed. These aggregates are held in suspension S' at the top of the fluidized bed, 23, whence they can be evacuated horizontally from the reactor via a I 25 pipeline, 24, and the partially purified water is evacuated also from the upper part of the reactor via pipeline A similar solution may be adopted even in cases in which the velocity of the liquid for treatment, which is brought in via pipeline 30 to the base of the reactor,31, which contains the fluidized bed,32, (see Figure 4) is greater than the decantation velocity of the aggregates,36, formed. All that is needed is the provision of a tank, 33, at the top of the reactor, 31, which has a cross-section greater than 1 that of the base of the reactor and sufficiently great for the velocity of the partially purified water which flows through it to be less than the decantation velocity of the aggregates, 36. The aggregates are held in suspension at the base of the tank, 33, from which position they can be evacuated via pipeline 34, whilst the partially purified water is evacuated from the the top of the tank via pipeline Figure 5 shows another method of operating the invention, in which the reactor, 40, containing the fluidized bed, 41, is fed at a velocity exceeding the decantation velocity of the aggregates formed. In 00t °this case, the reactor, 40, is fitted with a multitubular °o decantor 43, at its top.

The aggregates are deposited in the lower regions of the inclinedtubes of this settler ie at the top of the reactor, 40, whence they are evacuated via pipeline 44 and the purified liquid is evacuated via pipeline 45 from the upper part of the settler,43.

These various operating methods for the invention are not, of course, exhaustive; I it The Examples which follow demonstrate the Sadvantages of the invention.

EXAMPLE 1 This Example illustrates the auto-flotculation of particles suspended in waste water, without the addition of reagents, using the process of the invention.

Waste water, with a total BOD 5 of 200 mg/l and containing 200 mg/l of suspended matter, is upflowed through a column with a diameter of cm and packed with sand having a density of 1.7 g/cm and with a mean particle size of 270 um.

The heightof the fixed granular bed is 1.40 m.

The sand bed expands by 50% and the upper space-time -is 7 minutes, the velocity being 10 m/h.

The treated water, contaiaiing aggregates of suspended matter is then transferred to a settling tank, where the sludges obtained after a flow-time of 7 minutes have a concentration of 5 g/L. After settling for minutes, the sludges have a concentration of g/l.

After passage through the settling tank, the

BOD

5 of the treated water is reduced by 90% and the 10 suspended matter reduced by 70 to 85%, varying from one test to another.

EXAMPLE 2 This Example also demonstrates auto-flcrulation of particles in suspension obtained by means of the process according to the invention. A cylindrical column, with a diameter of 10 cm and a length of 2.1 m is used. This column is packed to a height of 1.1 m with builders!, sand, sieved to pass particles 200 to 400 pm in diameter, with a mean diameter of 350 Unm.

The density of this sahd is 2.7 g/cm and the minimum fluidization velocity 4.23 m/h.

The effluent obtained after treatment of water for purification in this column requires clarification; the determinations are therefore carried out using clarified water after standard decantation in a test o rube for 15 minutes.

The system is fed with gridded waste water with Sl the following mean characteristics: S suspended solids: 150 mg/1 0 total organic carbon: 67 mg/l Stemperature: 18 0

C.

This water is treated in the column without the addition of any coagulant and at various circulating velocities.

are shown in Table I (below) The results obtained are shown in Table I (below).

4' 0 4' Ow Superficial velocity of Expansion of granular Suspended solids Total organic carbon water (rn/h) bed removal efficiency ()abatement efficiency(% 17.3 20.3 50.8 ii 11 1 The effluent is very readily clarified and on average the sludge volume index is 35 cm After decanting for 15 minutes in a test-tube, the sludge obtained presents concentrations of solids of over 10 g/1.

EXAMPLE 3 This Example demonstrates the operation of the process according to the invention with the addition of reagents. The system used is the same as that described above with the injection of ferric chloride, FeC l 3 to the influent.

The water fed into the system is the same as that described in the previous Example. Tests are carried out USing various concentrations of FeC1 3 All tests are carried out with a sand-bed expansion of 50% ie a velocity of 20.3 m/h.

The results obtained are shown in Table II below.

TABLE II r 4* FeC1 3 concentration Suspended solids Total organic carbon (mg/l) removal efficiency abatement efficiency 0 52 47 58 53 100 77 66 150 >80 73 250 >80 73 350 80 73 r 12 1 These results show that the addition of a reagent increases the purification efficiency to a given required level.

EXAMPLE 4 This Example concerns the effects of the addition of waste sludges, from waste-water treatment to liquids undergoing treatment by the process according to the invention.

Two series of tests were run: the usual "jar test": the jar-test unit used being that of the Water Research Centre model; -a fluidized bed flcculator in compliance with the invention. The specifications of this flo lator are as follows: a cylindrical column 3 cm in diameter and packed with sand particle size 165 pm and density 3 2.7 g/cm Determinations were carried out using the supernatant after 15 minutes decantation I in a test-tube.

vsystem was fed with a suspension of bentonite 20 w -flocuiating propensity. This suspension ws treated with ferric chloride, the usual coagulant, which w as used as a reference substance. The flcculation obtained ,twacompared with that obtained using thickened sludges obtained from an activated -sludge urban water-treatment station (secondary thickened sludges-

STS).

I. Jar tests concentration of bentonite 150 mg/l velocity gradient 60 s 30 The testswere carried out using varying amounts of reagent. The results are presented in Table III (below).

I I I Reagent Concentration of reagent Turbidity elimination efficiency added (mg/1) No reagent O FeCl 3 60 STS 60 FeGl 3 120 92 STS 120 FeCl 3 200 92 STS 200 These results demonstrate that secondary sludges can 20 be used as the flocltating agent with efficiency similar to if not better than, those obtained with a chemical coagulant.

2. Fluidized bed tests Only secondary sludges (STS) were used. The system operated at a fluidization number of 8.35, which 25 is equivalent to 70% expansion and an upflow superficial velocity of 9.4 m/h. The inflow concentration of bentonite was 150 mg/l.

The tests were carried out using various concentrations of STS. The results obtained are presented in Table IV below.

I~r 4 4 44r 4 44 £o *o 4 4 4 04 1 STS Concentration Suspended solids 6lirnination (mg/i) efficiency (mg/i) 0 77 100 150 200 These examples demonstrate the high efficiency of the process according to the invention.

I I I I II t tIlt 4

II

I I I lit t I It I I I II

III"

I

'I

I I It. I

I

CA* III S S

Claims (8)

1. Process for the separation of suspended matter in water, characterised by the fact that the water is passed through granular material in a fluidized bed without prior saturation of the granular material in a fixed bed, and by the fact that flocculated aggregates are collected downstream of the fluidized bed and which are subsequently subjected to liquid/solid separation techniques, in order to produce separately an effluent, which is partially purified of its pollution, and aggregates of flocculated particles.

2. A process as claimed in claim 1 wherein the rrcr liquid/solid separation technique used is settling. S 3. Process, according to any one of Claims 1 and 2, further characterised by the fact that the granular material used in the fluidized bed undergoes expansion from 30 to 200 percent.

4. Process, according to any one of Claims 1, 2 or 3, characterised by the fact that the fluidization number is between 1.1 and Process according to any one of Claims 1 to 4, characterised by the fact that the upflow superficial velocity of the water under treatment is between 0.01 and 200 m/h.

6. Process according to any one of Claims 1 to characterised by the fact that the height of the above- mentioned granular material of the fluidized bed is between 1 0 cm and 5 m.

7. Process according to any one of Claims 1 to 6, characterised by the fact that the particle-size of the granular material of the fluidized bed is between 50 pm and 1 cm.

8. Process according to any one of Claims 1 to 7, characterised by the fact that the density of the granular material is between 0.8 and 3 g/cm 3

9. Process according to Claim 8, characterised by the fact that the granular material of the fluidized bed has a

16. specific gravity of over 1 and that the water under treatment flows upwards through the fluidized bed. Process according to any one of Claims 1 to 4, 6 to 8, characterised by the fact that the granular material of the fluidized bed has a specific gravity of less than 1 and that the water under treatment flows downwards through the fluidized bed. 11. Process according to any one of Claims 1 to characterised by the fact that the water to be treated passes through the fluidized bed without the addition of any flocculating agent. 12. Process according to any one of Claims 1 to a characterised by the fact that the water crossing the oo0 fluidized bed does contain an added flocculation agent. COCO o° 13. Process according to Claim 12, characterised by the 0 o° fact that the said flocculating agent consists of secondary sludge from waste water treatment. 14. Process according to Claim 13, applied to the purification of sewage waste water and characterised by the fact that some of the sludge separated from this waste water is recycled by feeding back through the granular medium in the fluidized bed to serve as a flocculating agent. DATED this 17th day of January, 1990. MORNEX LIMITED SWATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD, HAWTHORN, VICTORIA, AUSTRALIA. LCG:KS:BB(7.24)