GB2046620A - Liquid treatment by ion-exchange - Google Patents

Abstract

Effluent which contains caustic hydroxyl ions is passed through a strong base ion exchange resin in the chloride form and the resin is regenerated by means of a chloride salt.

Description

SPECIFICATION Liquid treatment method and apparatus This invention relates to a method and apparatus for the treatment of liquid. In a preferred embodiment of the invention, water-borne effluents produced by a conventional bottle washing machine are treated so that the water can be recycled.

The machine incorporates a washing process which operates in three phases. In the first phase effluent is produced which is highly polluted and its recovery would be both uneconomic and impracticable. In the second phase the bottles are totally immersed in a bath containing a cleansing agent which is an alkaline substance in solution and has a temperature in the region of 46"C. The third phase provides a final rinse and the effluent from this phase is treated by a method in accordance with the present invention.

In order to reduce the ever increasing demands made upon water resources by manufacturing processes, an economical way oftreating mild effluent, in particular, and recycling the treated liquid for re-use is desirable. The fact that the waste produced by the final rinse process of commercial bottle washers may account for up to 50% of the water requirements of a bottling factory emphasisesthe opportunity forthe conservation of water, chemicals and energy that could be made by a viable treatment process.

Most effluents produced from rinsing processes, as well as containing small quantities of solids in suspension, more pertinently contain the residue of cleansing agents which are most usually alkaline in nature. If the water is to be recycled, both kinds of pollutant have to be removed during each cycle of treatment, otherwise an undesirable level of concentration will occur over a period of constant re-use.

Suspended solids may be removed by a simple system of filtration. Alkaline substances can only be treated chemically. Where bicarbonates predominate, it is well-known to remove or convert the alkalinity by using either acids or ion exchange resins. The conversion of caustic hydroxyls has hitherto only been carried out in practice by means of acids, notably hydrochloric acid. Acids are expensive and, since the acid is consumed during this process, it is preferable, if possible, not to use this process.

The present invention provides an apparatus and a method that enables the conversion of hydroxyl alkalinity to be accomplished comparatively easily.

The apparatus can be constructed in such a way that it is economic to install, operate and maintain and provides reliable operation with efficient use of the materials and the treatment ofthe liquid.

An embodiment of the invention will now be described, by way of example, with reference to the schematic diagram shown in the single figure ofthe accompanying drawing.

In the drawing there is shown a bottle washer 1 having a pre-rinse phase 2, a detergent soak phase 3 and a final rinse phase 4. Effluent from phase 1 is discharged into a drain 5 and effluent from phase 3 is discharged into a tank A. An overflow 6 from the tank A discharges into a drain 7. The effluent in the tank A is passed via an output pipe 8 and a pump B to a conventional filtration system C in which suspended solids are separated and removed.

At D there is provided a chloride/hydroxide ion exchange vessel which contains a known strong base anion resin R in chlorine form.

The output from the filtration system C is connected on a line 9 via inlet valves 10 and 11 to the chloride/hydroxide exchanger D. A further input to the exchanger D from the filtration system C is applied on a line 12 via an ejector means Land an input valve 13. Brine can be fed from a tank K via an ejector suction valve 14, the ejector means L, the line 12 and the inlet valve 13.

Outputs from the exchanger D can be fed via a valve 15 to a drain 16, via a valve 17 to a conduit 18 and via a valve 19 to a drain 20.

Connected to the condut 18 are a first pH sensor E, acid dosing equipment F and a second pH sensor M.

The conduit 18 is connected via cooler G to a water storage tank H. The output from the storage tank H is connected via a conduit 21 to the first phase 2 and the third phase 4 of the bottle washer 1. A supply of fresh water to the tank H is provided via a valve 22.

In operation effluent from the third phase 4 ofthe bottle washer is passed to the tank A and thence via the pump B and the conduit 8 to the filtration system C. The filtered effluent is then passed via conduit9 and inlet valve 10 to the exchanger D. In the particular embodiment being described, the effluent contains caustic soda (Na OH). By passing the effluent through the chloride/hydroxide exchanger D, the following reaction with the ion exchange resin R in the chloride form results RCl+NaOH ROH+NaCl.

The pH value of the output from the exchanger D in conduit 18 is monitored by the sensory. The pH value can be used to give an indication of the end of the useful life ofthe ion exchange resin R, whereupon the valves 10 and 17 can be closed, either manually or automatically so that the exchanger D is taken out of the treatment cycle and the resin R can be regenerated. In the particular embodiment being described the resin R is regenerated when the pH value detected by the sensor E is between 8.3 and 8.8.The pH value of the effluent from the third stage 4 of the bottle washer is commonly between 12 and 14 and should the output of the exchanger D not be completely neutralized, as detected by the sensor E, a further small reduction of the pH value can be achieved by dosing the output in the conduit 18 by means of hydrochloric acid from the equipment F, according to the amount by which the pH value deviates from neutral. After a further check of the pH value by means of the sensor M, the output of the exchanger D is passed through the cooler G and fed into the tank H.

During the regeneration of the ion exchange resin material R, the valves 10 and 17 are initially closed, and the valves 11 and 15 are opened. Water from the filter unit C is then passed via conduit 9 and valve 11 into the exchanger D so that it passes up through the resin R and, in addition to loosening the resin, flushes out any suspended solids which have been accumulated during the operation ofthe exchanger D. This "backwash" liquid is discharged through the valve 15 to the drain 16.

In the next stage of regeneration, the valves 11 and 15 are also closed and the valves 13 and 19 are opened. A solution of common salt (Na Cl), referred to as brine, is drawn from the tank K by ejector suction valve means 14 and passed to the exchanger D via valve 13 and the ejector means L so that it is in a diluted state when it enters the exchanger D. The strength of the brine is preferably in the range of 8%-12%. The brine passesthroughthe ion exchange resin R and effects an exchange ofthe chloride and hydroxyl ions as follows:- Na Cl + ROH = RCI + Na OH The brine is subsequently discharged through the outlet valve 19 to the drain 20.

In the next stage of regeneration, the valve 14 is closed and water is passed via the conduit 12, the ejector means Land the valve 13 to the exchanger D to provide a slow rinse through the ion exchange resin R. The slow rinse liquid displaces any surplus brine and is discharged via the valve 19 to the drain 20.

In the final stage, the valve 13 is closed, and the valve 10 is opened, thereby allowing a comparatively fast rinse of the resin R to take place. This rinsing liquid also passes via the valve 19 to the drain 20 to complete the displacement of any surplus brine and flush out any regeneration wastes in the form of Na OH and Na2 CO3.

If a suitable raw water supply is not readily available for the backwash and rinsing steps, it is possible to use the filtered, but otherwise untreated, effluent in the way shown in the drawing.

Although the invention has been described, by way of example, with reference to a particular embodiment, it would be appreciated that variations and modifications can be made within the scope of the invention. For example the valves 10,11,13,14, 15, 17 and 19, instead of being operated manually, could be motorised and operated sequentially, in the way described, automatically according to the pH level detected bythe sensorE and a presettiming sequence. It will also be appreciated that the liquids introduced into the exchanger D in the regeneration process for brining and rinsing can flow in either direction through the exchanger D, i.e. either counter to the direction in which the effluent undergoing treatment flows or co-directional with it.In the particular embodiment, each of the integers A-G and their ancillary apparatus are housed in a single unit, although it will be appreciated that the integers can be arranged with only certain of them in the unit.

Suitable strong base ion exchange resins in the chloride form for use as the resin R in the exchanger O are Duolite (Registered Trade Mark) A102D sup plied by the Diamond Shamrock Corporation and Amberlite (Registered Trade Mark) IRA410 supplied by Messrs. Rohm and Haas.

It will be appreciated that, although, in the preferred embodiments, the method has been described in its application to the treatment of effluent from a bottle washing machine, it can be employed in other applications, for example in the treatment of waster which is to be subjected to furthertreatment by way, for example, of reverse osmosis.

Claims (8)

1. A method oftreating a liquid, for example an effluent, which contains an alkaline in the form of a hydroxyl, including the steps of passing the liquid through a strong base ion exchange resin the chloride form and regenerating the resin by means of a chloride salt.

2. A method as claimed in claim 1 which includes the steps of detecting the pH value of the treated liquid and further adjusting the pH value of the treated liquid by the addition of an acid.

3. A method as claimed in claim 1 which includes the step of detecting the pH value of the treated liquid and initiating the step of regeneration according to the pH level.

4. A method as claimed in any one of the preceding claims in which the step of regeneration includes a first step of washing the ion exchange resin by passing a washing liquid through the resin in the opposite direction to that in which the first mentioned liquid passes during treatment, passing the chloride saltthroughthe resin and rinsing the resin by passing a liquid through the resin in the same direction as that in which the first mentioned liquid passes during treatment.

5. Apparatusforuse in the method claimed in claim 1 including a un it which houses means to receive liquid to be treated, an ion exchanger containing an ion exchange resin in the chloride form, a filter connected between the receiving means and the ion exchanger, means to detect the pH value of the treated liquid obtained from the ion exchanger and a cooler, the output from the exchanger being connected to the cooler, a tank containing a solution of a chloride salt for regenerating the ion exchange resin and means to pass the solution of the salt through the resin to regenerate the resin.

6. Apparatus as claimed in claim 1 including acid dosing equipment connected to the output from the exchanger and arranged to dose the treated liquid according to the detected value of the pH.

7. A method of treating effluent substantially as described herein with reference to the single figure of the accompanying drawing.

8. Apparatus for use in treating effluent substantially as described herein with reference to the single figure ofthe accompanying drawling.