the electrolytic cell 1 comprises in succession an anolyte compartment a defined by an anode plate 2 and a first cation exchange membrane 3 , an acid compartment b defined by the first cation exchange membrane and an anion exchange membrane 4 , a whey compartment c defined by the anion exchange membrane and a second cation exchange membrane 5 and intended for the whey or the liquid based on whey which is to be treated , and a base compartment d defined by the second cation exchange membrane and a cathode plate 6 . the anode can be formed by conventional plate electrodes used in electrolytic cells , such as a platinated titan electrode . the cathode can correspondingly be formed by conventional plate electrodes used in electrolytic cells , e . g . of stainless steel . the following net reactions occur at the anode and the cathode : ## str1 ## the ion exchange membranes can be conventional ion - selective semi - permeable cation exchange membranes and anion exchange membranes used in electrodialysis . in the cell the ion exchange membranes and the electrode plates are assembled into a stack in which the ion exchange membranes are separated from each other and / or from the electrode plates by means of conventional spacers . individual cells can be connected in series and / or in parallel . a liquid recirculation 7 is connected with the whey compartment c , an acid recirculation 8 is connected with the acid compartment b , a base recirculation 9 is connected with the base compartment d , and an anolyte compartment b . the independent liquid recirculations connected with the different compartments of the cell are provided with separate pumps 11 , containers 12 and outlets . the recirculations , particularly the acid , base and anolyte recirculations , can be connected with the respective recirculations of other cells . the process according to the invention can be carried out in a batchwise manner , whereby the demineralized liquid and the resultant acid and base solutions are recovered . the process can also be carried out continuously , whereby the recirculation of the liquid to be demineralized can be continuously supplied with fresh liquid while demineralized liquid is being removed from the circulation . the acid and base recirculations can be correspondingly made continuous . when several cells are used the recirculations can be connected with the respective recirculations of another cell or other cells . in the anolyte recirculation connected with the anolyte compartment , the starting solution is an aqueous solution of an acid , preferably an aqueous solution of a 0 . 5 to 3 % by weight acid . the most suitable anolyte solution is an aqueous solution of 1 % sulphuric acid . in the acid recirculation connected with the acid compartment , the starting solution is an acid solution having an anion composition corresponding to that of the liquid to be treated which is selected from whey and liquids based on whey , or lactic acid . preferably , said acid solution is used as a starting liquid in the acid recirculation means . when an acid solution has an anion composition corresponding to that of whey , its anion composition resembles that of whey and preferably is similar to that of whey . in the base recirculation connected with the base compartment , the starting solution is a base solution with a cation composition corresponding to that of the liquid to be treated which is selected from whey and liquids based on whey , or sodium hydroxide . preferably , said base solution is used as a starting solution in the base recirculation . when a base solution has a cation composition corresponding to that of whey , its cation composition resembles that of whey and preferably is similar to that of whey . in the liquid recirculation connected with the whey compartment , the starting solution is e . g . cheese whey , acid whey , permeate obtained from the ultrafiltration of whey , or mother liquor from the production of lactose as such or concentrated to a dry matter content of no more than 40 % by weight . a suitable process temperature is 0 ° to 60 ° c ., preferably 20 ° to 50 ° c . the process according to the invention is particularly suitable for use in the demineralization of whey . the composition of typical cheese whey is shown in the following table 1 ; the composition of acid whey is nearly similar to that of cheese whey . table 1______________________________________composition of typical cheese whey______________________________________dry content 6 . 0 % by weightlactose 4 . 5 % &# 34 ; protein 0 . 7 % &# 34 ; fat 0 . 1 % &# 34 ; ash 0 . 5 % &# 34 ; calcium 350 mg / 1magnesium 90 &# 34 ; sodium 450 &# 34 ; potassium 1400 &# 34 ; phosphor 450 &# 34 ; chloride 1000 &# 34 ; lactic acid 900 &# 34 ; citric acid 1400 &# 34 ; ______________________________________ the cation and anion composition of whey appears from table 1 . in the electrolytic cell shown in the drawing , the cations contained in the whey recirculation , such as k + and na + ions , migrate through the cation exchange membrane into the base recirculation , where they form hydroxides with oh - ions formed at the cathode , so that the base recirculations is concentrated and the amount of hydroxides corresponding to these particular ions is increased in the base recirculation . if an aqueous solution of sodium hydroxide is used as a starting solution in the base recirculation , it is converted to a mixture of the aqueous solutions of potassium , sodium , calcium och magnesium hydroxides during the process . at the same time anions contained in the whey recirculation , such as cl - and po 4 3 - ions , migrate through the anion exchange membrane into the acid recirculation , where they form corresponding acids with h + ions migrated into the acid recirculation from the anolyte recirculation through the cation exchange membrane , so that the acid recirculation is concentrated . if an aqueous solution of lactic acid is used as a starting solution in the acid recirculation , it is converted into a mixture of the aqueous solutions of citric acid , lactic acid , hydrochloric acid and phosphoric acid during the process . being physically separated from a foodstuff , the base and acid mixtures forming the base recirculation and the acid recirculation can obviously be regarded as suitable for use in foodstuffs as such . said acid and base mixtures could thus be used e . g . in washings and ph adjustments at the same plant or they could be sold to other food manufacturers after concentration , if necessary . demineralized liquid , such as whey , is recovered as such or is concentrated and dried into a powder for further use . whey is preferably concentrated before electrolysis for improving conductivity and the demineralizing efficiency dependent thereon . the process according to the invention can also be used in the treatment of liquids based on whey and having the same salt composition as whey . such liquids include the ultrafiltration permeate of whey and the mother liquor formed in the production of lactose . whey proteins are recovered in the ultrafiltration of whey while permeate is obtained as a side product containing the ingredients which have passed through the ultrafiltration membrane , i . e ., lactose , whey salts and low - molecular nitrogen compounds . in the lactose manufacture , lactose is removed from whey by crystallization , thus obtaining a mother liquor containing the whey salts , for instance . these possibilities are also described in the examples , where the percentages are percentages by weight . the tests were carried out with a stackpack electrolysis apparatus of ionics inc ., comprising 18 four - part electrolytic cells . the effective membrane area of each cell was 232 cm 2 , the effective membrane area of the whole stack being 0 . 42 m 2 . the tests were carried out in a batchwise manner so that the whey , acid and base compartments formed separate recirculations with their pumps and containers ; in addition , the anolyte compartment comprises separate recirculation in which 1 % sulphuric acid was circulated . 3 % lactic acid was used as a starting solution in the acid recirculation and 3 % sodium hydroxide in the base recirculation . 20 % cheese whey concentrate having a ph of 5 . 3 was used as a raw material . table 2 shows the parameters of the test and table 3 the results obtained from the test . table 2__________________________________________________________________________parameters in the demineralization of cheese whey concentrate ( ph 5 . 3 ) when using electrolysis flowtime temperature current / cell voltage / cell current density whey acid base anolyte ( min ) (° c .) ( a ) ( v ) ( a / m . sup . 2 ) ( l / min ) __________________________________________________________________________0 24 4 . 2 5 . 7 180 1 . 6 2 . 5 5 . 3 5 . 310 28 3 . 7 5 . 8 160 0 . 7 1 . 3 3 . 1 3 . 020 31 3 . 4 6 . 0 150 0 . 8 1 . 3 3 . 3 3 . 130 34 3 . 0 6 . 2 130 0 . 8 1 . 4 3 . 3 3 . 140 36 2 . 5 6 . 3 110 0 . 9 1 . 4 3 . 4 3 . 250 38 1 . 8 6 . 5 80 1 . 0 1 . 4 3 . 5 3 . 3__________________________________________________________________________ table 3______________________________________results from the demineralization of cheesewhey concentrate ( ph 5 . 3 ) when using electrolysis time ( min ) 0 10 20 30 40 50______________________________________whey recirculationdry matter (° brix ) 19 . 0 18 . 5 18 . 2 18 . 1 17 . 9 17 . 6conductivity ( ms / cm ) 9 . 5 4 . 3 3 . 0 2 . 0 1 . 2 0 . 7phosphor , soluble ( mg / kg ) 830 550 390 280 200 140chloride ( g / kg ) 3 . 7 1 . 1 0 . 65 0 . 35 0 . 18 0 . 10ph 5 . 3 5 . 2 5 . 0 4 . 8 4 . 6 4 . 3ash (%) 1 . 5 0 . 24calcium ( mg / kg ) 1100 290magnesium ( mg / kg ) 230 74sodium ( mg / kg ) 1600 320potassium ( mg / kg ) 4400 430protein (%) 2 . 5 2 . 6lactose (%) 13 . 7 13 . 8solution volume ( 1 ) 7 . 3 6 . 7acid recirculationtitratable acidity (% lactic acid ) 2 . 2 2 . 8 3 . 1 3 . 3 3 . 4 3 . 5conductivity ( ms / cm ) 3 . 3 22 28 31 33 34ph 2 . 2 1 . 4 1 . 3 1 . 2 1 . 2 1 . 2phosphor , soluble ( mg / kg ) 10 150 260 380 470 540chloride ( g / kg ) 0 . 12 2 . 2 2 . 9 3 . 2 3 . 3 3 . 3solution volume ( 1 ) 6 . 1 8 . 1base recirculationtitratable acidity (% sodium hydroxide ) 2 . 4 2 . 6 2 . 7 2 . 9 3 . 1 3 . 2conductivity ( ms / cm ) 74 78 83 88 90 93solution volume ( 1 ) 4 . 6 4 . 6______________________________________ the current density was adjusted at the beginning of the run to 4 . 2 a / cell and it was not adjusted during the run . the apparatus did not comprise temperature adjusting means , wherefore the temperature of the solutions rose during the run . as appears from table 3 , the whey salts are removed similarly as in conventional demineralization techniques , simultaneously obtaining acid and base . lactose and protein do not migrate through the membranes to any greater extent . example 1 was repeated except that the ph of the whey concentrate was adjusted for run ( a ) prior to the run to 6 . 3 and for run ( b ) prior to the run to 4 . 3 . these changes did not substantially affect the results . concentrated acid whey obtained from the production of casein was used as raw material . table 4 shows the parameters and table 5 the analysis results . with the exception of the ray material , the conditions were the same as in example 1 . table 4__________________________________________________________________________parameters in the demineralization of an acid whey concentrate ( ph 4 . 1 ) when using electrolysis flowtime temperature current / cell voltage / cell current density whey acid base anolyte ( min ) (° c .) ( a ) ( v ) ( a / m . sup . 2 ) ( l / min ) __________________________________________________________________________0 27 4 . 2 5 . 3 180 1 . 6 2 . 5 5 . 4 5 . 410 32 4 . 0 5 . 5 170 0 . 7 1 . 3 3 . 0 3 . 020 35 3 . 4 5 . 5 150 0 . 8 1 . 4 3 . 0 3 . 030 37 2 . 7 6 . 0 120 0 . 9 1 . 4 3 . 1 3 . 040 39 1 . 8 6 . 3 80 1 . 0 1 . 4 3 . 0 3 . 1__________________________________________________________________________ table 5______________________________________results from the demineralization of acid wheyconcentrate ( ph 4 . 1 ) when electrolysis was used time ( min ) 0 10 20 30 40______________________________________whey recirculationdry matter (° brix ) 15 . 8 14 . 9 14 . 6 14 . 1 13 . 9conductivity ( ms / cm ) 12 . 3 6 . 7 3 . 6 1 . 4 0 . 5phosphor , soluble ( mg / kg ) 1200 1090 870 550 200chloride ( g / kg ) 9 . 1 4 . 1 1 . 9 0 . 55 0 . 12ph 4 . 1 4 . 1 4 . 0 4 . 2 4 . 3solution volume ( 1 ) 3 . 2 2 . 8acid recirculationtitratable acidity (% lactic acid ) 2 . 2 3 . 0 3 . 5 3 . 7 3 . 9conductivity ( ms / cm ) 2 . 2 20 28 34 35ph 2 . 3 1 . 4 1 . 2 1 . 1 1 . 1phosphor , soluble ( mg / kg ) 9 43 100 220 390chloride ( g / kg ) 0 . 1 3 . 1 4 . 5 5 . 4 5 . 8solution volume ( 1 ) 5 . 5 5 . 6base recirculationtitratable alkalinity (% sodium hydroxide ) 2 . 5 2 . 7 2 . 8 2 . 9 3 . 0conductivity ( ms / cm ) 63 66 68 70 71solution volume ( 1 ) 4 . 1 4 . 0______________________________________ example 3 was repeated except that the raw material used was concentrated acid whey . the ph of the concentrate , however , was adjusted to 6 . 1 before electrolysis . this change had no greater effect on the test results . concentrated permeate obtained from the ultrafiltration of whey was used as a raw material . table 6 shows the parameters and table 7 the test results . otherwise the conditions were the same as in example 1 . table 6__________________________________________________________________________parameters in the demineralization of permeate concentrate when usingelectrolysis flowtime temperature current / cell voltage / cell current density whey acid base anolyte ( min ) (° c .) ( a ) ( v ) ( a / m . sup . 2 ) ( l / min ) __________________________________________________________________________0 27 4 . 2 5 . 5 180 1 . 8 2 . 5 5 . 2 5 . 210 31 3 . 6 5 . 7 160 0 . 9 1 . 3 3 . 1 3 . 020 35 2 . 5 6 . 2 110 0 . 9 1 . 4 3 . 3 3 . 230 36 1 . 5 6 . 5 60 1 . 0 1 . 4 3 . 5 3 . 3__________________________________________________________________________ table 7______________________________________results from the demineralization of a permeateconcentrate when using electrolysis time ( min ) 0 10 20 30______________________________________whey recirculationdry matter (° brix ) 17 . 2 16 . 5 16 . 2 16 . 1conductivity ( ms / cm ) 9 . 1 3 . 0 1 . 0 0 . 3phosphor , soluble ( mg / kg ) 750 440 180 60chloride ( g / kg ) 3 . 5 0 . 1ph 5 . 2 5 . 1 4 . 3 3 . 4solution volume ( 1 ) 3 . 8 3 . 6acid recirculationtitratable acidity (% lactic acid ) 2 . 2 2 . 8 3 . 1 3 . 2conductivity ( ms / cm ) 3 . 7 21 24 25ph 2 . 1 1 . 5 1 . 4 1 . 3solution volume ( 1 ) 6 . 0 6 . 6base recirculationtitratable alkalinity (% sodium hydroxide ) 2 . 3 2 . 5 2 . 6 2 . 7conductivity ( ms / cm ) 75 81 84 87solution volume ( 1 ) 4 . 8 4 . 8______________________________________ the demineralization test was carried out as described in example 1 but the raw material used was unconcentrated whey ( dry matter 6 %). table 8 shows the most important parameters and results . table 8______________________________________the most important parameters and results ofthe demineralization of unconcentrated cheese whey tempera - current / voltage / current wheytime ture cell cell density conduct . ( min ) (° c .) ( a ) ( v ) ( a / m . sup . 2 ) ( ms / cm ) ______________________________________0 21 4 . 2 6 . 7 180 3 . 15 24 1 . 9 7 . 7 82 1 . 210 26 1 . 2 8 . 0 52 0 . 6______________________________________ it appears from the table that unconcentrated whey , too , demineralizes well whereas a rapid decrease occurs in the current and current density due to the low conductivity . therefore it is preferable to demineralize concentrated whey . the demineralization test was carried out as described in example 1 except that the raw material used was a mother liquor formed in the production of lactose and having a dry matter of about 20 %. the following table 9 shows the most important parameters and results . table 9______________________________________the most important parameters and results inthe demineralization of a mother liquor formedin the production of lactose conduct . conduct . conduct . tempera - current - of mother of acid of basetime ture density liquor solution solution ( min ) (° c .) ( a / m . sup . 2 ) ( ms / cm ) ( ms / cm ) ( ms / cm ) ______________________________________0 24 180 17 2 . 8 7910 29 180 9 . 5 25 8420 32 170 6 . 7 35 9030 35 150 4 . 3 40 9540 36 110 2 . 8 42 9850 39 86 1 . 8 43 10060 41 68 1 . 2 43 102______________________________________ it appears from the table that the process is also well suited for a mother liquor formed in the production of lactose . the raw material used was the same cheese whey concentrate as in example 1 and the run conditions were the same with the exception that the starting solution used in the acid recirculation was not 3 % lactic acid but a 1 % acid solution having an anion composition corresponding to that of whey . correspondingly , the startng solution used in the base recirculation was not 3 % sodium hydroxide but a 1 % base solution having a cation composition corresponding to that of whey . the compositions of these solutions are given in tables 10 and 11 . the acid and base recirculation solution after the first run was used as a starting solution in the next run . the acid and base recirculation solutions after the second run were used as starting solutions in the third run . after the third run the compositions of the solutions were analyzed and they are shown in tables 10 and 11 . table 10______________________________________composition of the acid solution before thefirst run and after the third run hydrochl . phosphoric lactic citric acid acid acid acid______________________________________acid before run i 0 . 25 % 0 . 25 % 0 . 25 % 0 . 25 % acid after run iii 0 . 83 % 0 . 60 % 0 . 78 % 0 . 67 % ______________________________________ table 11______________________________________composition of the base solution before the first runand after the third run koh naoh ca ( oh ). sub . 2 mg ( oh ). sub . 2______________________________________base before run i 0 . 65 % 0 . 22 % 0 . 11 % 0 . 02 % base after run iii 2 . 1 % 0 . 68 % 0 . 25 % 0 . 04 % ______________________________________ the acid produced in example 8 was concentrated by evaporating to a concentration of 30 %. the solution was completely clear and slightly yellowish in colour . the ph of the whey drink was adjusted from 4 . 5 to 3 . 8 with said acid . normally , the ph adjustment is carried out by means of citric acid . a test panel observed no difference when comparing a drink adjusted with said acid solution with a normal product . the base produced in example 8 was used for adjusting the ph of curd whey from 4 . 5 to 6 . 0 before drying . normally , the ph is adjusted with sodium hydroxide . the drying of a curd whey neutralized with said base solution was as successful as that of a normal product and the powders had an equally good taste .