WO1988006290A1 - Procede et appareil de controle de la qualite de l'eau - Google Patents

Procede et appareil de controle de la qualite de l'eau Download PDF

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Publication number
WO1988006290A1
WO1988006290A1 PCT/GB1988/000096 GB8800096W WO8806290A1 WO 1988006290 A1 WO1988006290 A1 WO 1988006290A1 GB 8800096 W GB8800096 W GB 8800096W WO 8806290 A1 WO8806290 A1 WO 8806290A1
Authority
WO
WIPO (PCT)
Prior art keywords
water
clarifier
process water
streaming
scd
Prior art date
Application number
PCT/GB1988/000096
Other languages
English (en)
Inventor
Michael John Blanchard
Original Assignee
Analaq Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB878703670A external-priority patent/GB8703670D0/en
Priority claimed from GB878714529A external-priority patent/GB8714529D0/en
Application filed by Analaq Limited filed Critical Analaq Limited
Publication of WO1988006290A1 publication Critical patent/WO1988006290A1/fr
Priority to NO884544A priority Critical patent/NO884544L/no
Priority to DK570788A priority patent/DK570788D0/da

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/60—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrostatic variables, e.g. electrographic flaw testing

Definitions

  • This invention is concerned with monitoring various process waters which are required to be substantially devoid of polyvalent metal ions, for the incursion of such ions.
  • softened water is required to be substantially devoid of calcium and magnesium ions and certain industrial effluents should be freed from cupric and mercuric ions before discharge into rivers or the sea: de-ionised water is reguired to be freed from all ions not derived from water: condensate from steam-powered turbine operations should be devoid of ions if it is to be recycled, but frequently becomes adulterated with metal cations.
  • Another process water to which the invention relates is ground or river water, domestic waste water or sewage subjected to flocculation treatment.
  • Such processes are operated cyclically through a phase of cation exchange and a phase of regeneration of a partly exhausted cation-exchange material.
  • the cation-exchange material usually a synthetic resin, is regenerated after a set time interval or after a set volume of raw water has been passed through the bed and such intervals or volumes are set to ensure the quality of the process water by allowing only partial exhaustion of the cation-exchange material.
  • This state of affairs is dictated by the lack of a reliable in-line monitor of the quality of the process water, able to detect the first signs of breakthrough of the unwanted cations from a fully exhausted bed. If such a monitor were available, the beds of cation-exchange materials could be run to exhaustion in each cycle leading to savings in the frequency of regenerations and the quantities of regenerant used.
  • Another process water is potable water derived from turbid raw water or sewage by flocculation.
  • the process utilises a flocculating agent, usually alum or a ferric salt, which reacts with negatively charged dispersed particles, forming uncharged floes which more easily agglomerate and are then in a form to sediment faster.
  • a flocculating agent usually alum or a ferric salt
  • Any excess flocculating agent would result in the presence of soluble aluminium or ferric ions or soluble cationic hydroxides of those metals.
  • Gerdes explained the generation of the streaming current in the SCD as requiring the immobilisation of charged particles on the surfaces of the piston and the surrounding cylindrical pot of the SCD, whilst the mobile counter ions asssociated with the par ⁇ ticles are swept downstream through the annular gap between the piston and pot; this relative motion of opposite charges generates the electric current picked up by electrodes spaced apart in the gap.
  • Central to Gerdes' theory is the existence of particulate matter in the liquid under test and Gerdes dismisses the influence of dissolved salts as causing "no problems and not requiring any correction of the SCD reading". This theory and the requirement that the total solids of the treated water must be present in the liquid submitted to the SCD is perpetuated in the literature of those companies currently offering SCD's for sale.
  • a method of monitoring a process water for the presence of unwanted metal cations comprises abstracting samples sequentially from a stream of said process water, urging each sample to flow forwards and backwards through a passage defined between confronting, non-conducting solid surfaces, whilst in contact with two electrodes spaced apart in the directions of the flows and incorporated in an electric current measuring circuit, thereby generating a streaming electrical current characteristic of each sample and monitoring said streaming currents, the method being characterised in that the process water is substantially free from particles above 10 microns, and suitably above 2 microns.
  • clarified water means a process water which, flowed as a continuous stream through an operating SCD for a period of 48 hours, does not deposit accumulated particles within the SCD.
  • a process water which inherently contains solid particles in excess of 10 microns, may be rendered into a clarified water by the removal of the oversized particles.
  • Means to impose constant flow on the stream may be used (e.g. a constant head device: a head of from 10 to 15 centimetres is adequate).
  • the rate of flow of the stream is preferably between 0.5 and 3 litres per minute.
  • Some of the process waters referred to herein are inherently clarified waters. This applies for example to softened water, condensate and de-ionised water.
  • a method of monitoring a treated water for the presence of excess flocculating agent comprising abstracting samples sequentially from a stream of said treated water; urging each sample to flow forwards and backwards through a passage defined between confronting, non-conducting solid surfaces, whilst in contact with two electrodes spaced apart in the directions of the flows and incorporated in an electric current measuring circuit, thereby generating a streaming electrical current characteristic of each sample and monitoring said streaming currents, the method being characterised in that at least a substantial proportion of the floes created in the treated water by the said agent are removed prior to the samples being abstracted therefrom.
  • the confronting surfaces defining the passage should be low energy surfaces with the intention of avoiding the immobilisation of particles thereon.
  • the hydrocyclone has three significant advantages over- sedimentation and filtration: firstly the water of reduced solids content is quickly produced; secondly there is a sharp and selectable cut between the smaller particles retained in the water of reduced solids content and the larger ones in the reject stream; thirdly the hydrocyclone is self-cleaning and is therefore capable of prolonged continuous operation.
  • the hydrocyclone may need to be protected from over-sized particles liable to block the hydrocyclone and in these circumstances we would pass the process water through a screen en route to the hydrocyclone.
  • An alternative to a hydrocyclone is a fine meshed screen, for example a "Fourdrinier wire" - a sheet of woven metal or synthetic polymer filaments adapted to retain solids larger than about 10 microns.
  • the screen can be set at an angle to become self-cleaning.
  • Such a sheet should be calendered to a smooth condition on the face adapted to receive the process water.
  • the smooth face allows the retained solid to fall across the face more easily.
  • Two or more such sheets of increasingly finer mesh may be arranged below each other to subject the process water to serial filtrations.
  • Clarifying by means of an hydrocyclone or a screen may be followed by filtration through a membrane filter if the process water requires additional clarification.
  • the streaming current changes electropositively in sympathy with, but not in direct proportion to the concentration of soluble polyvalent cations.
  • the inclusion of a trace of a cation of higher valency than any already present in the process water produces a greater change in the generated streaming current than when that trace amount is additional to an existing population of similarly charged cations in the water. That the response of an SCD and the method of this invention should be at its most sensitive when monitoring the incursion of foreign cations, is of considerable significance. Nevertheless, the sensitivity to increments in the concentration of already existing cations in the water, is not insignificant.
  • the streaming current signal may simply be recorded or the change in the current consequent on the incursion of the cation may be used to trigger an alarm circuit, or the regeneration sequence of a cation exchange material.
  • the invention includes the apparatus of this invention electrically connected to a regeneration sequence controller and adapted to relay a command signal when the output signal changes electropositively to a predetermined extent.
  • a still further aspect of this invention relates to an apparatus for monitoring flocculation of a raw water comprising a source of clarified raw water, a source of clarified treated water, an SCD adapted to receive flows of the clarified waters and switching means to alternate flows of the clarified waters to the SCD, the duration of each flow being sufficient to allow the SCD to acclimatise to the clarified water and produce a signal characteristic of the clarified water.
  • the present invention comprises a clarifier adapted to clarify a process water, means to impose substantially constant flow conditions on a stream of water from the clarifier and an SCD disposed to receive the stream of water.
  • the pH of the clarified water is an important parameter dependent solely on the dissolved ions of the water: if the pH electrodes are placed in a stream of the clarified water they will need to be cleaned less frequently. It will also be possible to estimate continuously and accurately the colour of the raw water and treated water due to dissolved organic materials and, if necessary, change the set point of the SCD or the pH of the flocculation to eliminate such chromophores.
  • Figure 1 is a flow diagram of an arrangement for using the device of Figure 2 in one embodiment of method according to this invention
  • Figure 2 is a schematic representation of a device for measuring streaming current.
  • Figures 3 to 5 illustrate the relationship between streaming current signals and concentrations of metal cations in three water samples discussed in the following Example 1 and presented in table and graphic form
  • Figures 6 and 7 show streaming current signals obtained in the following Examples 2 and 3.
  • a pipe 1 through which is flowing a treated raw water containing floes has a branch 2 controlled by valve 3.
  • the treated water falls from the branch onto a screen 4 set at angle to displace the retained solids downwardly across the screen.
  • the partially clarified water passing through the screen collects in a container 5 equipped with an overflow 6.
  • Water is withdrawn at the rate of 4 litres per minute from the container via pipe 7 by a pump 8 which feeds the water at 5.6 Kg/cm 2 (80 p.s.i.) via pipe 9 to a 10 millimetre hydrocyclone 10.
  • Clarified water flows from the hydrocyclone via the vortex finder and pipe 11 to a constant head tank 12 having an internal weir 13 (shown as a dotted line), an overflow pipe 14 and a supply pipe 15 delivering the clarified water to an SCD 16.
  • the rate of delivery of the overflow from the hydrocyclone is 3 litres per minute and the ratio of the volumes of overflow to underflow (leaving the hydrocyclone at the apex 17 of the hydrocyclone) is 3:1.
  • FIG. 2 shows, in purely schematic form, (and not to scale) the SCD 16. Electrical connections 20 and 21 connect a sensor 34 and annular silver electrodes 22 and 23 respectively. The electrodes 22 and 23 are let into the inner wall 24 of a cylindrical dashpot 25 made of polytetrafluoroethylene and secured in a chamber 19 by a sleeve 29 having ports 30. A piston 26, also of polytetrafluoroethylene, is connected to an eccentric 27 mounted on the shaft of an electric motor 28.
  • the piston 26 has a throw of 0.64 centimetre in the dashpot 25, the diameter of the piston 26 is 1.27 centimetre; the narrow annular passage 31 between the side wall of the piston and inner wall of the dashpot is 0.013 centimetre wide and the clearance 32 of the piston base from the inner wall of the base of the dashpot at closest approach, is 0.8 centimetre.
  • water from the flow to be monitored is fed through the supply pipe 15 so that clarified water devoid of solid matter, including adventitious dust particles, is discharged under constant head pressure to the inlet flooding the chamber 19 and submerging the dashpot 25 with a changing supply of water which overflows from the chamber 19 at the level 33.
  • the electric motor 28 causes the piston 26 to reciprocate within the dashpot 25 at, say, 230 cycles per second.
  • the withdrawal of the piston 26 within the dashpot 25 draws water from the chamber 19 into, and the reverse stroke expels water from the dashpot 25 through the annular passage 31 between the piston wide wall and the inner wall of the dashpot.
  • the displaced water travels through the gap at an average linear speed of about 1.2 metres per second whilst passing sequentially over the electrodes 22 and 23.
  • the current generated by this process is sensed intermittently, once in each cycle, at similar instants of rapid flow of the displaced water.
  • the current signal is sensed, amplified and displayed by the electrometer sensor 34 connected in series with electrodes 22 and 23 by wires 20 and 21.
  • the constant head tank 12 may optionally be equipped with a fail safe low level sensor (not shown) adapted to switch off the electric motor driving the piston within the SCD, when the water level falls, as may happen if for any reason the supply of water to the constant head tank is interrupted. This preserves the piston from dry-running, an occasional cause of damage to SCD' ⁇ .
  • the signal generated by the SCD operating on the clarified water is characterised as the set point when the operator decides that the quality of the flocculated water is satisfactory. Minor movements of the signal in an electropositive or electronegative sense away from the set point may be used respectively, to decrease or to increase the rate of addition of the flocculating agent to the raw water.
  • a soft water containing 40 parts per million of sodium salts was fed through an SCD and a steady output current of -70 arbitrary units was established after 30 minutes of acclimatisation.
  • a branch pipe from a hard water source was connected to the main, soft water delivery pipe; the branch pipe was equipped with a solenoid valve controlled by a timer which closed the valve for 30 minutes so that only soft water was supplied to the apparatus and then opened the valve so that for a further 30 minutes a mixture of hard and soft water was supplied to the SCD. It was established by chemical tests that the mixture of hard and soft water had a hardness of 6 parts per million of calcium. Thereafter the cycle was twice repeated. Meanwhile, the output signal from the SCD was fed to a chart-recorder and a reproduction of the trace appears in Figure 6.
  • a water-softening, ion exchange bed was run continuously with the effluent softened water monitored by an SCD.
  • the characteristic signal (set point) of -70 units for this particular softened water was recorded on a chart recorder.
  • the trace from the recorder for the latter stages of the run is reproduced in Figure 7.
  • the trace shows about one hour of production of fully softened water and then the effect of the incursion of calcium ions as the hardness broke through. '
  • the breakthrough is a gradual rather than a sudden process and the level of breakthrough even after 120 minutes (e.g. after a further hour) would be a tolerable pollution for most uses of softened water.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Separation Of Suspended Particles By Flocculating Agents (AREA)

Abstract

On détecte la présence de cations métalliques non désirés dans des eaux résiduaires en contrôlant le courant électrique en écoulement qui est produit lorsqu'on fait s'écouler un échantillon d'eau vers l'avant et vers l'arrière à travers un passage étroit (31) défini entre des surfaces solides non conductrices opposées (24, 26), pendant qu'il est en contact avec deux électrodes (22, 23) placées à distance l'une de l'autre dans les directions d'écoulement de l'eau. Les eaux résiduaires sont soit naturellement exemptes de particules supérieures à 10 microns ou sont purifiées par retrait (par exemple par hydrocyclonage et/ou par tamisage) des particules supérieures à 10 microns.
PCT/GB1988/000096 1987-02-17 1988-02-16 Procede et appareil de controle de la qualite de l'eau WO1988006290A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
NO884544A NO884544L (no) 1987-02-17 1988-10-12 Vannkvalitetsovervaakningsmetode og apparat.
DK570788A DK570788D0 (da) 1987-02-17 1988-10-13 Fremgangsmaade og anlaeg til kontrol af vandkvalitet

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB878703670A GB8703670D0 (en) 1987-01-23 1987-02-17 Water quality monitor
GB8703670 1987-02-17
GB878714529A GB8714529D0 (en) 1987-06-22 1987-06-22 Water quality monitor
GB8714529 1987-06-22

Publications (1)

Publication Number Publication Date
WO1988006290A1 true WO1988006290A1 (fr) 1988-08-25

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1988/000096 WO1988006290A1 (fr) 1987-02-17 1988-02-16 Procede et appareil de controle de la qualite de l'eau

Country Status (4)

Country Link
EP (1) EP0346361A1 (fr)
JP (1) JPH02502399A (fr)
AU (1) AU597801B2 (fr)
WO (1) WO1988006290A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0311092A2 (fr) * 1987-10-09 1989-04-12 Zeta Management Ltd. Détecteur sans électrode
EP0415726A1 (fr) * 1989-08-29 1991-03-06 Lasertrim Limited Détecteur de charges en mouvement et système de traitement de liquides utilisant ce détecteur
WO1992015873A1 (fr) * 1991-02-27 1992-09-17 Brook, Basil, William Surveillance d'un courant aqueux

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3369984A (en) * 1966-03-04 1968-02-20 Dow Chemical Co Control apparatus
WO1983004100A1 (fr) * 1982-05-06 1983-11-24 Process Development, Inc. Detecteur a ultrasons d'un flux de courant
EP0096754A1 (fr) * 1982-06-11 1983-12-28 Hoechst Aktiengesellschaft Procédé et dispositif pour la préparation en continu d'eaux usées et pour leur étude analytique à des fins de commande d'une installation d'épuration

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3369984A (en) * 1966-03-04 1968-02-20 Dow Chemical Co Control apparatus
WO1983004100A1 (fr) * 1982-05-06 1983-11-24 Process Development, Inc. Detecteur a ultrasons d'un flux de courant
EP0096754A1 (fr) * 1982-06-11 1983-12-28 Hoechst Aktiengesellschaft Procédé et dispositif pour la préparation en continu d'eaux usées et pour leur étude analytique à des fins de commande d'une installation d'épuration

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0311092A2 (fr) * 1987-10-09 1989-04-12 Zeta Management Ltd. Détecteur sans électrode
EP0311092A3 (fr) * 1987-10-09 1990-08-01 Zeta Management Ltd. Détecteur sans électrode
EP0415726A1 (fr) * 1989-08-29 1991-03-06 Lasertrim Limited Détecteur de charges en mouvement et système de traitement de liquides utilisant ce détecteur
GB2235782B (en) * 1989-08-29 1994-03-09 Lasertrim Ltd Streaming current detector and fluid treatment system using same
WO1992015873A1 (fr) * 1991-02-27 1992-09-17 Brook, Basil, William Surveillance d'un courant aqueux
GB2269018A (en) * 1991-02-27 1994-01-26 Brook Basil William Monitoring aqueous streams
GB2269018B (en) * 1991-02-27 1995-04-05 Brook Basil William Monitoring aqueous streams
US5540845A (en) * 1991-02-27 1996-07-30 Basil William Brook Method of and apparatus for monitoring aqueous streams

Also Published As

Publication number Publication date
JPH02502399A (ja) 1990-08-02
EP0346361A1 (fr) 1989-12-20
AU1293188A (en) 1988-09-14
AU597801B2 (en) 1990-06-07

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