WO1994020420A1

WO1994020420A1 - Improvements to ionic disinfection systems

Info

Publication number: WO1994020420A1
Application number: PCT/GB1994/000488
Authority: WO
Inventors: John Hayes
Original assignee: Tarn Pure Technology Corp.
Priority date: 1993-03-12
Filing date: 1994-03-11
Publication date: 1994-09-15
Also published as: EP0691936A1; GB9305122D0

Abstract

An ionic disinfection system comprises a chamber through which liquid e.g. water to be disinfected is arranged to pass. Electrodes of copper and a noble metal such as silver are dispersed in the chamber and a DC power supply is connected to the electrodes. The voltage of the power supply is set at a level to ensure production of cupric (Cu2) ions and adjustment to the level of dosing the liquid with ions is achieved by providing a pulsating output from the power supply with an adjustable on/off ratio.

Description

Improvements to Ionic Disinfection Systems

The present invention relates to ionic disinfection systems.

A number of systems have been developed that are designed to release copper and/or silver ions into a liquid eg. water for disinfection, and it has been seen that some systems are less effective than others in controlling the growth of algae and/or bacteria. From experience, it has been shown that the voltage applied to the emitting electrodes determines the form of copper released into solution, namely that, at higher voltages, cupric (Cu2) copper is released and at lower voltages cuprous (Cul) copper is released. Cupric (Cu2) has two electrons missing whereas cuprous (Cul) has one missing.

It has been shown that there is a synergistic effect, increasing the efficacy, when silver and copper ions are released together. Efficacy is further enhanced if the copper is released in its cupric (Cu2) form and brings about a greater attraction to the targeted organisms.

Commercial equipment must have the ability to increase or decrease the number of ions released so that the correct level is obtained, depending on the amount of water or liquid to be treated. Previously the method of achieving control was to vary the applied voltage to the electrodes thus setting the desired current. The disadvantage of this is that it is not possible to apply the full voltage to the electrodes if the output has to be reduced, thus a system running at half output would be running at half voltage. Where water conductivity is high, maximum current is reached at a reduced voltage, thus cuprous (Cul) ions are released.

The present invention contains circuitry that maintains a voltage on the electrodes so that cupric (Cu2) copper is released. To allow adjustment to the level of dosing, instead of varying the applied voltage, control is obtained by providing a pulsating output and adjusting the mark/space ratio or on/off time of the output. For instance, it is proposed that the polarity of the voltage applied to the electrodes will be reversed at periodic intervals eg. 30 sees to avoid plating out problems. To adjust or set the output of ions to the desired level, the number of seconds that current will flow may be set between 1 and 30 seconds in each direction thus allowing full control of output, but maintaining full voltage and ensuring cupric (Cu2) ions are released.

A further development may be included to control, other than manually, the mark/space ratio or on/off time by sensing the flow of current between the electrodes in a manner that should the current be reduced the 'on¹ ratio is increased and conversely if the current increases the 'on' time is reduced, thus maintaining a constant level of ion release.

Features and advantages of the present invention will become apparent from the following description of embodiment thereof given by way of example with reference to the accompanying drawings, in which:-

Fig. 1 is a block diagram of an ionic disinfection system according to the present invention;

Fig. 2 is a block diagram of a modified form of ionic disinfection system according to the present invention; and

Fig. 3 is a graph for aiding understanding of the operation of a part of the system shown in Fig. 2.

As shown in Fig. 1, an ionic disinfection system comprises a power supply 10 for producing a stabilized DC output voltage at a pre-settable level from a mains supply. The output voltage from the power supply 10 is applied to two or more electrodes 12 via a polarity switching module 14 which periodically reverses the polarity of the output from the power sμpply.

The power supply operates on either 110/240v 50/60HZ. Output - low voltage depending on size of system may be between 15-50v. For example, for a specific model, the nominal output may be 30v. Preset adjustment allows, say, lOv higher or lower (tapped transformer) to compensate for water or liquid conductivity. If conductivity is high, current may be excessive therefore voltage may have to be dropped or electrodes spaced further apart. Conversely, with low conductivity, maximum voltage is required to obtain sufficient current or electrodes may need to be placed closer to each other. (Obviously more, or larger, electrodes can be fitted to increase current). Also note the power supply will vary in size depending on the amount of current required.

The electrodes can be of copper and/or silver and if both copper and silver are present the ratio of the two metals can be varied depending on the size of system being constructed and the water being treated. It is also possible to replace all or part of the silver content by another noble metal such as gold or platinum. This has been found to be efficacious where a high level of chlorides are present in the liquid to be treated eg. brine or salt water. Under these conditions it has been found that silver ions form silver chloride which is only partly soluble, thus reducing the efficacy of the silver content.

Connected to the switching module 14 is a mark/space ratio module 16 provided with a ratio control device 17 whereby the output of the switching module 14 can be inhibited for a period of time so as to produce a pulsating output the on time of which is adjustable to vary the time average of current supplied to the electrodes 12 at the then prevailing polarity and preset voltage.

The switching module 14 feeds the power to electrodes 12 and contains silicon controlled rectifiers which reverse the output polarity to the electrodes. This is triggered by the polarity and mark/space ratio timing circuit 16. The mark/space or on/off ratio is controlled by a potentiometer that will set the 'on' time during each polarity reversal. For instance, if the polarity is switched ever 30 seconds, the control will allow power to flow from 1 to 30 seconds depending on the setting of the control. Therefore, at full output, current will flow for a full 30 seconds, then polarity will be reversed and full output for another 30 seconds. If half output is required, the current will flow 15 seconds in every 30 seconds.

If desired, the ratio control device 17 in the form of a potentiometer can manually adjustable and form the only adjustment of the mark/space ratio of the pulses. Additionally, it is possible to use the device 17 simply as an initial setting device and incorporate a feedback loop 20 incorporating a resistance coupled to one of the electrodes for feeding back to the mark/space ratio module 16 a signal representative of the current flowing in the electrodes so that if the conductivity of the liquid in which the electrodes are immersed changes, the on/off ratio will be adjusted automatically.

Fig. 2 shows an arrangement similar to Fig. 1 and in which like parts are indicated by like reference numbers. Here, the current detection in the feedback loop is achieved by an inductive loop 21.

Fig. 3 shows the relationship between current flowing in the electrodes sensed by the feedback device and the on time or pulse width for both the arrangements shown in Figs. 1 and 2. If the conductivity of the water changes the on/off ratio will automatically adjust ie. if current drops, the 'on' time or pulse width will be lengthened to maintain the average current and the desired level. Conversely, if the current increases the unit will produce a shorter pulse of current.

The voltages and times specified above are by way of example of typical values which may be encountered in practice. However, variations in voltage, current and time as well as number and spacing of electrodes are permissible depending on the exact use to which the system is being put.

The level of currents output from the power supply can very depending on a number of factors such as the conductivity of the liquid. Typically, currents of the order of hundreds of milliamps will be used but it is possible for currents of 1 amp or more to occur. The power supply should be chosen to have a sufficient capacity to allow the supply of power at an appropriate current level for the application to which the apparatus is put.

Claims

CLAIMS :

1. An ionic disinfection system comprising a chamber through which liquid to be disinfected is arranged to pass, electrodes disposed within the chamber and containing a proportion of copper and a DC power supply connected to the electrodes for causing copper ions to be discharged, in use into the liquid, characterised in that a voltage source of the power supply is fixed at a level high enough to cause cupric ions to be discharged and means are provided for producing pulses of said voltage to cause periodic discharge of cupric ions.

2. A system according to claim 1, wherein the pulse producing means is a switching circuit for periodically connecting the voltage source to the electrodes.

3. A system according to claim 2, wherein the on/off ratio of the switching circuit is changeable.

4. A system according to claim 3, wherein the switching means is provided with manual means for changing the on/off ratio.

5. A system according to claim 2 or 3, wherein the switching means is provided with a means for sensing output current to the electrodes and for automatically changing the on/off ratio.

6. A system according to any one of the preceding claims wherein means are provided for reversing the polarity of the voltage applied to the electrodes.

7. A system according to any one of the preceding claims wherein the voltage is set at a level between 15 and 50 volts.

8. A system according to claim 7, wherein the voltage is set at a level between 20 and 40 volts.