GB2060430A - Regeneration of ion exchange resins - Google Patents

Abstract

An effluent, for example, from a distillery which has high biochemical oxygen demand (B.O.D.) created by the presence of oxygen demanding anions, is treated in an ion-exchange resin bed, e.g. an anion exchange bed, to produce treated effluent of lower B.O.D. The bed is regenerated with an acidic or basic regenerant, e.g. sodium or ammonium hydroxide, to obtain spent regenerant. The spent regenerant, after addition of fresh acid or base, is used in successive regenerations to build up the concentration of salts which can be removed in portion as product. <IMAGE>

Description

SPECIFICATION Effluent treatment This invention relates to the recovery of dissolved ionic material. Particularly, but not exclusively, the invention relates to the treatment, prior to discharge to a watercourse, of condensate of high biochemical oxygen demand (B.O.D.) from the evaporations in distilleries and fermentation industries.

In distilleries the residue recovered from the still after distillation, known in the art as "pot ale" or "spent wash" is concentrated by evaporation to produce a syrup which represents one commercial by-product of the distillery. The condensate obtained by the aforementioned concentration, known as "foul condensate" has high organic acidity which produces a high B.O.D. Before the foul condensate can be discharged to a watercourse as effluent, it must be treated to neutralise the acidity and to reduce the B.O.D. in order to comply with statutory regulations.

Foul condenstate, after neutralisation with lime, has hitherto been treated in what are known as "biotowers" or by an activated sludge process so as to produce the high standard of effluent purity demanded by regulations. The design of such treatment is dependent on the level of B.O.D. in the foul condensate and this is subject to considerable variation depending upon factors not associated with the effluent plant. The result of this variation is that the plant is either larger than necessary to cope with the normal level of B.O.D.

or periodically the plant discharges effluent outside the specified limits of design or authority consent.

An object of this invention is to provide an improved effluent treatment process.

According to the present invention there is provided a process for recovering dissolved ionic material comprising: in a treatment cycle, feeding to a bed of ion-exchange resin in free acid or base form a liquid containing ions to be recovered, thereby to remove the ions and to give treated effluent; in a regeneration cycle, treating the bed with a regenerant thereby to produce spent regenerant containing salts of the ions, wherein the regenerant contains spent regenerant and an acid or base in a quantity not exceeding the ion exchange capacity of the bed; and recovering as product a portion of the spent regenerant containing the dissolved salts.

As a preferred embodiment of this invention there is provided an effluent treatment process comprising: in a treatment cycle, feeding to a bed of anion-exchange resin in free base form an effluent liquid of high acidic biochemical oxygen demand, thereby to remove oxygen-demanding anions and to give treated effluent; in a regeneration cycle, treating the bed with a basic regenerant thereby to produce spent regenerant containing salts of the oxygen-demanding anions, wherein the basic regenerant contains spent regenerant and a base in a quantity not exceeding the anion exchange capacity of the bed; and recovering portions of the spent regenerant containing dissolved salts.

The regenerant is preferably sodium or ammonium hydroxide. The product produced in the regeneration cycle may be used commercially as, for example, an additive to animal feedstock or as a fertilizer.

The treated effluent may be further process in conventional effluent treatment plant to ensure statutory water quality.

One advantage of the process of this invention is that it removes the acidity and a portion of the species responsible for the B.O.D. and thus reduces significantly the variation in effluent composition since it is these components which tend to vary widely under normal plant operation.

The reduction of the variation in effluent composition prevents or reduces shock B.O.D.

loading of the conventional effluent plant and promotes smooth running thereof and thus enables the plant to operate efficiently to produce consistently acceptable final effluent quality for discharge.

Some of the obvious advantages may be summarised as follows: a) The specified limits of authority consent are far more easily met.

b) Existing plants will cope with extended production without conventional effluent plant extension.

c) New plants would be designed with smaller conventional effluent plants.

d) Sludge production will be reduced easing problems of disposal of the product of conventional plants.

e) A by-product will be produced which is easily disposed of commercially.

The process of the invention uses ion-exchange resins for absorption of organic acids from foul condensate using regeneration with bases, the process retains the acids as salts in concentrated spent regenerant and this with treated effluent are the only products to be disposed of. The concentrated spent regenerant in the form of the sodium, ammonium or other salt may be sold as a commercial product, used for animal feeding or for fertilizer. The treated foul condensate may be further processed in a conventional plant but with a much reduced B.O.D. load than otherwise.

No special plant is required in order to operate the invention, one typical set-up is shown schematically in the accompanying figure.

The plant consists of an upright elongate vessel containing resin provided with an inlet at the top and an outlet at the bottom. An inlet for regenerant is provided at a level approximately at the top of the resin bed. The bed of resin is supported on a perforate plate and the space below the plate is preferably filled with inert granules to improve flow characteristics. A conductivity cell, connected to monitoring apparatus, is located in the outlet line. Associated pipe and valve work is provided to permit separate collection of several fractions according to the monitored conductivity.

In use, during the regeneration cycle, spent regenerant is collected in a reservoir. In the treatment cycle, high B.O.D. foul condensate is passed through the bed and onward to further treatment in a biological plant. The spent regenerant, with added base, is used to provide regenerant for subsequent regeneration.

As the regenerant is recycled successively the concentration of dissolved salts builds up and when the concentration is sufficiently high a portion of the spent regenerant is removed from the process as product.

It is preferred that during regeneration conditions of plug flow are established for flow of regenerant through the bed as this gives efficient recovery of salts and sharp changes in conductivity thus simplifying control of the system.

In optimum running conditions a sharp rise in conductivity occurs when regenerant passes through the cell and a sharp lowering occurs when the treatment cycle occurs. Thus, if such conditions can be established the wash down period is minimised. If conditions are less than optimal it is preferable to collect several fractions of effluent in accordance with their conductivity.

It will be appreciated that, while the primary intended use of this invention is to produce from a high B.O.D. liquid a treated effluent of low B.O.D.

and a relatively concentrated solution of salts of some of the substances responsible for the B.O.D., there is a general application to the recovery of dissolved ionic material in relatively high concentration. By recycling the regenerant the concentration of dissolved material therein increases progressively and thus provides a useful technique for recovery of ionic species.

The invention will now be described, by way of illustration, by the following Examples.

EXAMPLE 1 A single bed of anion-exchange resin was set up in an arrangement to minimise back-mixing during regeneration. The resin used was IRA 67 produced by Rohm and Hass (IRA 67 is a Trade Mark). The resin was converted to free base form using 5% ammonia solution.

Foul condensate of high acidic B.O.D. was run through the bed and the outlet conductivity was monitored. Normal outlet conductivity during the treatment cycle was around 1 50 ssmhos and began to rise as the resin became exhausted.

When the outlet conductivity reached 250 ,umhos the outflow was diverted to recycle to the foul condensate holding tank and regeneration was begun using a volume of 5% ammonia rather less than equivalent to the exchange capacity of the bed. When the volume of regenerant had all passed into the bed, the flow of foul condensate was recommended. When outlet conductivity reached 600 ,umhos the flow was diverted to the spent regenerant tank.

The conductivity rose to a very high value during the regeneration cycle and then dropped as the treated condensate began to emerge. When the value reached 600 mhos the outflow was diverted to run on to a biological treatment plant for further processing before discharge to drain.

The collected spent regenerant was used to make-up the next batch of regenerant by adding the calculated amount of ammonia.

After several regenerations in the manner described the concentration of dissolved salts was sufficient for portions of the spent regenerant to be removed as product of the process.

EXAMPLE 2 A single bed ion exchange plant is set up with a regeneration facility designed to minimise mixing of regenerant with the process liquor.

Many ion exchange resins can be used, but one suitable is IRA 67 produced by Rohm and Hass (IRA 67 is a Trade Mark). This is charged into the bed and regenerant, 5% ammonia solution, is passed through to convert to the free base form.

Foul condensate process liquor is then run through until the resin bed is exhausted. The bed is then regenerated using 5% ammonia and the spent regenerant collection is made up in three parts.

1. Weak initial running too strong for effluent but too weak for collection as strong spent regenerant.

2. Strong spent regenerant.

3. Weak final runnings, as 1 initial runnings, and collected with them.

The running of the plant is monitored by continuous measurement of outlet conductivity.

The change from processed effluent to weak initial runnings is made when the conductivity reaches 600 micromhos as is the change from weak final runnings to subsequent effluent collection. The change from weak initial runnings to strong spent regenerant and back to weak final runnings is made by monitoring the specific gravity, the change back being made at 1.01. The process then continues with processed effluent averaging 1100 B.O.D. compared with 2650 ppm, prior to treatment. The collected mixture of weak initial and final runnings is used to prepare the 5% ammonia solution for the next regeneration.

EXAMPLE 3 In this Example the process described in Example 1 was repeated but using sodium hydroxide as regenerant.

EXAMPLE 4 The process was in all essential respect the same as that described in Example 1, except that two columns A and B are used in series. On exhaustion of the first in series A the feed is switched to B only, whilst the A is regenerated.

After regeneration, the A column becomes second in series until the exhaustion of B which is then regenerated whilst A takes the flow alone. This operation allows continuous flow of good quality treated condensate whereas the single column system has interrupted flow whilst regeneration takes place.

Other modifications of the process are possible where mixture of different regenerants are used, different conditions are used to separate processed condensate, weak runnings, and strong runnings, and different methods are used to measure the cuts as alternatives to specific gravity and conductivity: also other resins and column combinations may be used.

Claims (6)

1. A process for recovering dissolved ionic material comprising: in a treatment cycle, feeding to a bed of ion-exchange resin in free acid or base form a liquid containing ions to be recovered, thereby to remove the ions and to give treated effluent; in a regeneration cycle, treating the bed with a regenerant thereby to produce spent regenerant containing salts of the ions, wherein the regenerant contains spent regenerant and an acid or base in a quantity not exceeding the ion exchange capacity of the bed; and recovering as product a portion of the spent regenerant containing the dissolved salts.

2. An effluent treatment process comprising: in a treatment cycle, feeding to a bed of anionexchange resin in free base form an effluent liquid of high acidic biochemical oxygen demand, thereby to remove oxygen-demanding anions and to give treated effluent; in a regeneration cycle, treating the bed with a basic regenerant thereby to produce spent regenerant containing salts of the oxygen-demanding anions, wherein the basic regenerant contains spent regenerant and a base in a quantity not exceeding the anion exchange capacity of the bed; and recovering portions of the spent regenerant containing dissolved salts.

3. A process according to claim 2, in which the basic regenerant contains sodium hydroxide and/or ammonium hydroxide.

4. A process according to claim 2 or claim 3, in which the concentration of dissolved salts is maintained at not less than 1 5 weight percent.

5. A process according to claim 2 or 3 or 4, in which the treated effluent is further treated in a biological treatment plant prior to discharge.

6. A process according to claim 1, substantially as hereinbefore described.