AU2248500A - Alloy water treatment - Google Patents

Description

AUSTRALIA

PATENTS ACT 1990

ORIGINAL

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I 4 STANDARD PATENT ALLOY WATER TREATMENT AQUATIC MECHANICAL SERVICES Pty. Ltd.

March 22, 2000 This invention relates to a method and an apparatus for water treatment. In particular a method and apparatus to dissolve liberate a metal into water for the sole purpose of clarifying the water to be suitable for human and industrial uses.

BACKGROUND ART Surface waters and ground waters used to supply treated water to communities contain many impurities which have to be removed by the water provider before the treated water can be delivered. Impurities are removed by the addition of chemicals, sedimentation, filtration and disinfection.

The most difficult impurity to remove is the fine colloidal clay particles which are small enough in size as to pass through a 0.1 micron filter pad or membrane and Humic, Fulvic acids. The use of any filtration method to filter out these colloidal impurities is not practical or economical and filtration will not remove humic or fulvic acids. Chemicals and polymers are added to raw water streams to act as flocculants and coagulants and in time the colloidal fines will settle out of solution and /or become filterable.

The use of chemicals and polymers to clarify water requires equipment and operating expertise to provide the correct chemical addition and maintenance of pH levels required for the optimum reaction properties of the chemical being added.

The most common chemical compounds used are those containing aluminium and iron salts which react with water to form insoluble hydroxides. Chemical compounds such as aluminium sulphate A2[SO413] 25 181H20 or aluminium oxide A12 03 which as a commercial product is 8%W/W. Ferric compounds are used in the same manner.

When these insoluble hyroxides are formed they come out as a very fluffy floe whose large surface areas carry a positive charge. This active surface not only attaches itself to electronegative particles in the water but will also attract and hold the electronegative acidic humic and fulvic acids. The precipitate will settle out of solution in time and may also form a surface sludge. However, this precipitation will only take place within a certain range of pH values. Aluminium and iron precipitate best at slightly acid pH with aluminium best at pH 6-7 and iron best at pH 5-6. These chemicals must also be thoroughly mixed with the water being treated to be effective then allowed a quiescent stage for settling purposes.

A high degree of expertise and knowledge is required to successfully and economically treat water in this manner and to avoid chemical overdosing and excessive chemical sludge deposits which have to be disposed of into the environment. Dosing rates can vary between Omg/l and These problems are overcome by the present invention which utilises the electrolytic decomposition of chemical compounds to treat such waters as described without the need to add further chemicals nor the need to adjust pH levels.

Electrolysis is the process whereby an electric current is used to promote the decomposition of chemical compounds. The use of electrolysis to commercially produce elements of hydrogen, oxygen, chlorine, hypochlorite, aluminium, iron and copper recovery, electroplating and many others are widely known and many techniques are protected by patents.

Faraday's First Law states "The mass of a given element liberated at an electrode during electrolysis is directly proportional to the quantity of electricity which passes through the solution".

OBJECT OF THE INVENTION It is an object of this invention to provide an apparatus and method which includes contacting surface and ground waters containing impurities with electrodes connected to a power source to liberate elements which will 15 provide electropositively charged ions in the aqueous solution to attract S.negatively charged impurities to aid the removal of these impurities from the .aqueous solution.

Another object of this invention is to provide a method of dissolving S. liberating] an alloy into water for the removal of suspended impurities.

Another object of this invention is to provide an electrolytic apparatus to Sdissolve liberate] the alloy in water.

Another object of this invention is to provide an electrolytic apparatus that has a low energy requirement and has the capability to be operated by normal S •electric power supply, solar power, wind power or battery power.

Another object of this invention is that aluminium [Al] is the dominant metal salt dissolved liberated into the water.

A further object of this invention is to provide an apparatus that will provide water suitable for human and industrial use.

DISCLOSURE OF THE INVENTION An experimental apparatus was constructed consisting of two rectangular tanks, an electrolytic element and power supply. Refer Figure 1 "Experimental apparatus". Tank TI has a volume of 40 litres, inlet and outlet ports and a surface screen upstream of the outlet port. Tank T2 has a volume of 40 litres and an outlet port. The electrolytic element is constructed of a titanium 200mm x 65mm plate acting as the anode and a titanium 200mm x 65mm plate acting as the cathode. The power supply consists of a 240VAC input transformer providing a 9VDC x 4A output.

A 200mm x 65mm aluminium alloy plate was prepared for attaching to the electrolytic element.

Experiments were carried out at Bow Hill, South Australia using water taken directly from the River Murray which contains very high levels of suspended colloidal clays.

The first experiment was conducted with the aluminium alloy plate connected to the cathode of the element and the whole element immersed in Tank T1 filled with river water. After three hours there was a minor surface sludge evident but no evidence of sludge precipitation or drop out.

A measurement of the current at the anode provided a reading of 0.46 amperes.

The element was removed and the aluminium alloy plate connected to the anode and the element immersed in the water in Tank T1. Refer Figure 2 "Electrolytic cell electrode assembly". Within five minutes a significant surface sludge had formed which had a light to medium brown appearance.

The current measured 0.58 amperes at the anode and 0.46 amperes at the cathode.

Tank TI was then emptied and refilled with river water and a sample analysed. The element was immersed and the apparatus operated for three hours when a sample was analysed. The equipment used for the analysis of the water consisted of Palintest and Hanna photometer microprocessors.

20 Analytical results River water 3 hour treatment Turbidity 47 FTU 13 FTU Free chlorine 0 mg/l 5.0 mg/I pH 7.75 7.8 Calcium hardness 30 mg/I as CaCO3 40 mg/I Total alkalinity 75 mg/1 as CaCO3 95 mg/1 S: A raw water flow to tank T1 was commenced at a measured flow rate of litres per hour where the discharge from Tank TI flowed to Tank T2 where Tank T2 was to act as a second settling tank and the apparatus allowed to operate for a continuous twelve hour period. At the end of twelve hours a sample of water taken from the outlet of Tank T2 was analysed.

Analytical results Turbidity 1.11 FTU Free chlorine 1.45 mg/l pH 7.35 Calcium hardness 45 mg/l as CaCO3 Total alkalinity 85 mg/I as CaCO3 Aluminium not detected The experiments demonstrate the unique properties and advantages of using electrolysis apparatus to dissolve liberate] the base metal aluminium into water containing colloidal impurities to provide positively charged particles which in turn attract the negatively charged colloidal particles to form particles in sizes suitable to settle out or become filterable.

Another unique property is the observation that the pH has remained alkaline unlike the acidic pH created with the addition of coagulants such as aluminium sulphate to water.

The invention can provide significant quantities of useable water with low power requirements and therefore the invention may find many applications through variations of the specific apparatus and techniques described in the experiments and will be evident to those skilled in the art of electrolysis and 0o coagulation/flocculation of suspended particles in water treatment.

To determine the long term viability of the invention process a large trial plant was constructed which consisted of a dual compartment tank fabricated from aluminium3.0mm thick sheet, an aluminium frame to support two activated carbon filters, an ultra filtration 50,000 MW cut off filter, a pressure pump system, electrical power unit and an inline electrolytic cell.

Refer Figure 3 "Water conditioner trial plant" and Figure 7 "Electrolytic cell and housing".

The treatment tank has a total water holding volume of 570 litres with 285 litres contained in each compartment. The hydraulic flow of water through 20 the plant is outlined in Figure 4 "Hydraulic flow schematic". The raw water enters compartment 1 of the treatment tank via a ball float valve and with the compartment full of raw water the electric current to the cell is switched on and electrolysis of the water commences and runs continuously for six hours.

In this period approximately 2205 mgs of aluminium oxide [A1203] was .25 liberated from the aluminium anode into the water which represents a dose rate of 7.7mg/l.

Trial plant current 0.58 amperes time 6 hours 21600 seconds equivalent weights, aluminium 8.99, oxygen 8.

Mass of Aluminium 8.99 x0.58 x21600 1.167 grams 96500 Mass of Oxygen 8.0 x 0.58 x 21600 1.038 grams 96500 Total Mass of Aluminium oxide 2.205 grams The aluminium oxide hydrolyses in the water to form the insoluble aluminium hydroxide AI[OH]3 which is electropositively charged and therefore attracts in large quantities electronegatively charged particles in the water.

This was evidenced by the initial formation of a white floc which rapidly changed in colour to deep brown colour representative of the colour of the water being electrolysed. The gases evolving from the electrodes creates a thin surface sludge as the gases rise to the water surface and as this surface sludge thickens larger particles break away and settle to the tank floor.

The activity at the electrodes creates convection of movement of the water and the forming sludges and this movement assists in the particles making contact and enhances the capability of this invention to remove suspended impurities from water.

After the six hours had elapsed the clarified water in compartment I was allowed to flow at a rate of 2 litres per minute via a gate valve in the partition of the treatment tank into compartment 2. This flow of water allowed raw water from an external source to flow into compartment 1 at a flow rate of 2 litres a minute at a continuous rate. It was noted that floc rapidly formed at the raw water inlet which indicated a residual of electropositively charged ions in compartment 1.

When compartment 2 reached near capacity a sample of the electrolysed water was taken and analysed. The results of the analysis were virtually identical to analysis of the water from the experimental plant.

S 20 When compartment 2 reached capacity the pressure pump system was "switched on and the clarified water passed through the activated carbon filters and the ultrafiltration membrane at a continuous regulated flow of 2 litres per minute. A pipe line taken at the discharge of the pump prior to the S"filters is connected to the electrolytic cell housing to provide a low flow of water through the cell into compartment 1.

The filtrate flows to a storage tank fitted with a float ball valve and on this tank filling and the treatment tank full, the pressure pump system switches off and is activated when water is drawn from the filtrate tank for use.

30 The concentrate is returned to the treatment tank and is recycled through the treatment process and in this way there is no loss of water through the whole process except for the very small amount when the UF and carbon filters are flushed every three months.

35 This plant operated at the inventor's residence on the River Murray for a period of six months and all water used inside the home including drinking water was drawn from the filtrate water tank during this period. The daily use varied between 300 500 litres per day which is a recognised daily domestic use excluding external irrigation. During this period no form of disinfection was introduced to the filtrate tank.

Periodic testing of water samples taken from compartment 2 provided results consistent with previous analysis results.

Periodic testing of the filtrate water provided the following average results.

Turbidity 0.1 0.2 FTU Colour clear Free chlorine nil Total chlorine nil pH 7.2-7.4 TDS 400mgl Aluminium not detected Microbial testing was not carried out as the UF membrane removes E-coli and other bacteria and virus cysts such as cryptosporidium.

The UF filter was flushed with clean water at monthly intervals with a flushing time required of about three minutes for the dirty flush water to become clear. This fact is further evidence that a very high percentage of suspended impurities is removed by the invention process prior to the water passing through the UF filter membrane.

Under the condition of passing untreated surface water to an ultrafiltration membrane it would be expected by an experienced operator that the membrane would require daily cleansing and have a short service life.

To further establish the invention as a viable commercial product the plant in the existing form was relocated nearby to the premises of a house boat hire s company to continue the trial work under actual working conditions. The plant is providing clean water to the Managers' Residences including 20 drinking water and providing drinking water to the fleet of houseboats.

The daily output requirement is generally about 2000 litres /day.

i As a result of this trial work the inventor has established the electromotive force and the electrolytic cell configuration to accomplish an average flow rate output of 3000 Its/day.

The buildup of hydroxides and other deposits on the cathode is a normal function of electrolysis of this type of solution and therefore regular cleaning 30 of the cathode is required.

30 *se The electrodes have been re-configured to have identical anode /cathode electrodes which has allowed for periodic reversal of polarity of the :~electrodes which assists in maintaining a relatively clean cathode and therefore an efficient current density.

Periodic testing of the electric current flowing through the cell revealed that overnight when water temperatures reduced and during cold weather the electric current flow reduced by upto 50% dependant upon the water temperature and as a result of the constant voltage with variable current output of the transformer device installed.

The device has been replaced with a transformer which provides a variable voltage of 20-50 volts DC and a constant current across the electrodes of 1.1 amperes under all conditions prevailing in treating surface and ground waters. Refer Figure 6 "Electrical layout Trial Plant". The current density at the anode is 78.5 amps/ M2 The electrolytic cell is now liberating 696 milligrams per hour of positively charged ions in the form of aluminium oxide which is a dose rate of 5.8mg/l at a flow rate of 120ts/hour according to the following calculations.

Claims (12)

1. An electrolytic water treatment apparatus comprising: an electrolytic cell comprising a liquid containing vessel and a pair of electrodes, a power source providing voltage and current to the electrodes, a controller adapted to control the voltage and current to the electrodes, the electrode acting as the anode consist of an aluminium alloy plate attached to a titanium plate, the electrode acting as the cathode consist of a titanium plate.

2. An apparatus of claim I wherein each electrode has an aluminium alloy plate attached to a titanium plate and each electrode is identical.

3. An apparatus of claim I wherein a controller adapted to periodically reverse the voltage to the electrodes is included.

4. An apparatus of claim 1 wherein the controller adapted to control voltage and current to the electrodes is adapted to control a variable voltage and a fixed current to the electrodes.

5. An apparatus of claim 4 wherein the current density of the anode is not less than one ampere/cubic centimetre/second and not greater than one hundred amperes/cubic centimetre/second.

6. An apparatus of claim 1 wherein the electrode acting as the anode is an 20 aluminium alloy solid rod and the cathode is titanium.

7. An apparatus of claim 6 wherein the power source is a twelve volt direct current lead storage cell and the anode is connected directly to "the positive terminal and the cathode connected directly to the negative terminal of the lead storage cell.

8. A method of treating ground and surface waters containing impurities including the steps of passing said impure waters through a water containing vessel and a pair of electrodes and applying a varying 30 voltage and fixed current across said electrodes.

9. A method of claim 8 wherein the polarity of the voltage to the electrodes is reversed periodically. 35

10. A method of claim 8 wherein the electrodes are immersed in a vessel containing said impure water.

11. A method of claim 8 wherein the said impure water has been electrolysed, a step providing a quiescent stage for the settlement of suspended and precipitated impurities is included.

12. A method of claim 8 wherein a step providing filtration of the settled water is included to produce water suitable for human use and industrial purposes.