IE41638B1 - Process for removing and recovering precipitation agents fom precipitate containing proteinous substances - Google Patents

Abstract

An alkaline earth metal compound is added to the sludge in a sufficient quantity to bind the proteins. Generally, the pH is then already greater than 6.5, otherwise it is adjusted to above 6.5 by addition of an alkali metal hydroxide or an alkaline earth metal hydroxide. The sludge is then heated to a temperature which is above the coagulation point of the proteins present, a water phase being released which is separated off. This water phase contains the precipitant and can be reused for precipitating proteins. The advantage of the process described here is that not only is a concentration or thickening of the precipitated protein-containing sludge achieved, but also the precipitant is recovered for further use.

Description

It is well known that a number of substances can be used as precipitation agents on an industrial scale to remove proteins from effluents such as process water. The principal group of precipitation agents in use is probably the lignin sulphonic acids and their derivatives. A number of installations based on the use of lignin sulphonic acids have been built in many countries and these installations are employed to purify industrial effluents while recovering a substantial quantity of the proteins, see U.S. Patent No. 3,390,999. Other organic substances that have been used as precipitation agents are organic sulphonates, such as aryl or aryl alkyl sulphonic adis, as described in Canadian Patent No. 882,398, and organic sulphates, such as sulphuric acid esters of monovalent and polyvalent alcohols, such as lauryl sulphate, glyceryltrisulphate and sulphated hexavalent alcohols and sulphated hexavalent carbohydrates, reference here being made to Norwegian Patent No. 117,339 and Canadian Patent No. 887,899. Most of these organic sulphonic acids and sulphates have a very good purifying effect, but to use them for purifying water on an industrial scale involves relatively high costs for chemicals. It is further known that proteins precipitated by means of the said agents can be used as fodder. It would, however, be an advantage if it were possible to lessen the content of said precipitation agents. By reducing the amount of precipitation agents in the precipitate, one would be able at the same time to increase the protein content and thus the commercial value of the materials as fodder. - 2 41638 In the known methods for precipitating proteins, especially from industrial effluents, the precipitate is separated from the hydrous phase by some mechanical method, e.g. flotation, which gives a sludge containing between 5 and 15% solids.

This sludge must often be further concentrated before final treatment.

Concentration can be done by filtering or by centrifugation, after pre-treatment by e.g. heat and/or the addition of calcium in a manner known per se, e.g. as described in Norwegian Patent Application No. 903/72, which was open to public inspection on 21 September 1973.

This appears to be a comparatively effective method of concentration, but the greater part of the precipitation chemicals remain in the sludge phase, while a disproportionately large amount of the proteins pass into the hydrous phase.

The present invention provides a process for the recovery of the precipitation agent from a precipitated material containing protein and precipitation agent wherein an alkaline earth metal compound is added to the precipitated material in a quantity sufficient to bind the protein; if, after such addition, the pH of the material is still below 6.5, an alkaline earth metal hydroxide or alkali metal hydroxide is added to the material until its pH is at least 5.5, the material having a pH of at least 6.5 is then heated to a temperature above the coagulation point of the protein present, and the aqueous phase, containing the precipitation agent, is separated from the protein.

In the present invention» an alkaline earth metal compound is added to the protein sludge ands if necessary, an alkali or alkaline earth metal hydroxide is added until a pH of preferably about 7-9 and particularly 7.5-9, is obtained. The proteinaceous mixture is then preferably heated, e.g. with superheated steam during which the protein complex formed between the precipitation agent and protein decomposes and the protein coagulates as an alkaline earth metal proteinate and the precipitation agent dissolves in the separated aqueous phase. By washing the coagulated proteinate, it is possible to recover the precipitation agent almost quantitatively. If an alkaline earth metal hydroxide, e.g. Ca(0H)2, only is used to form proteinate and to adjust pH if required, before the protein sludge is heated, a smaller proportion of the precipitation agent is dissolved in the aqueous phase and consequently less precipitation agent is recovered,. probably because the alkaline earth metal salts of the precipitation agent are less soluble. One advantage of using only calcium is, that the coagulated material has a firmer consistency and separates better, it is, for example, easier to filter.

By using an alkaline earth metal compound, e.g. Ca(0H)2 in a quantity sufficient to form an alkaline earth proteinate and using an alkali metal hydroxide, e.g. NaOH, if required for neutralization, the precipitation agent will dissolve as alkaline salt that is highly soluble and thus make it possible to recover the precipitation agent almost quantitatively.

The aqueous phase may be separated from the coagulated alkaline earth metal proteinate by filtration or by centrifugation e.g. in a cooled centrifuge, and the solid protein may be washed with warm water and the water washings combined with the aqueous phase to maximise recovery of the precipitation agent.

The aqueous phase, containing the recovered precipitation agent, may be used, in accordance with a further aspect of the invention, to precipitate protein in an aqueous medium containing protein by bringing the aqueous phase and aqueous medium into contact with one another.

The following Examples are given to illustrate the invention.

In the accompanying drawings: Figs. 1 & 2 shows graphically experimental data from Examples 1 and II, Figs. 3 & 4 shows graphically experimental data from Example III and Fig. 5 shows graphically experimental data from Example V.

Example I The sludge used for the experiment was ligno-protein sludge 20 separated by precipitation of proteins in slaughterhouse effluents with 14.5% solids.

The sludge Had a pH of 4.1 and calcium hydroxide was added to raise the pH to 8.0. The sludge was then heated to a temperature of 95°C, at which temperature the sludge coagulated. After 1-2 minutes, the sludge was centrifuged and the centrifugate was thereafter used as precipitation agent for a protein solution for which the optimal dosage of pure ligno-sulphonic acid was known. A certain quantity of the centrifugate was added to the protein solution together with varying quantities of ligno-sulphonic acid. The protein material in the solution was precipitated and organic substance was measured in the resulting decantate by determining COD (chemical oxygen demand).

Slaughterhouse effluents of the same quality as used to precipitate the ligno-protein sludge being examined, was used as protein solution for the recovery test.

The result of the experiment are shown in the following table. - 6 416 3 8 TABLE FOR EXAMPLE I Dosage (for 500 ml protein solution) COD in decantate mg/02/l %COD reduction Line No. Ligno- sulphonate mg/1 Sulphuric acid mg/1 Centrifugate ml 0 0 0 4690 0 0 600 0 3836 17.14 0 700 5 1259 73.15 50 It II 1178 74.89 100 II II 1189 74.64 1 150 II II 1239 73.59 200 II It 1276 72.79 250 II II 1300 72.79 0 600 0 3886 17.14 0 700 5 1259 73.15 2 0 II 10 1341 71.41 0 II 15 1706 63.64 250 600 0 1036 77.91 300 » 0 1016 78.34 3 350 II 0 1022 78.20 400' II 0 1075 77.07 The table and lines clearly show that the centrifugate contains a large quantity of recovered precipitation agent. Precipitation of protein solution with centrifugate alone gave the best results when 5 ml centrifugate was added to 500 ml protein solution. In this COD reduction is 73.5% as against 17.14% when only sulphuric acid was added. Line 2 shows that the optimal quantity of centrifugate for precipitation of protein solution should be about 8 ml per 500 ml, whereby one would obtain a COD number in the decantate of about 1.190 mg. 0.,/1, corresponding to a COD reduction of about 74.6%. Comparing this with the extrapolated part of line 3, it should be possible to set the quantity of recovered precipitation agent as being equivalent to a dosage of about 175 mg/1 or about 87 mg/500 ml.

This means that the concentration of precipitation agent in the centrifugate should be approx. — mg/ml or approx. 10 g/1.

IS Line 1 shows that the optimal dosage of ligno-sulphonate in addition to 5ml centrifugate per 500 ml is about 70 mg/1. If more lignosulphonate is added, precipation of protein solution will be less efffective owing to overdosage. This over-dosage effect can clearly be seen from line 3, which shows 300 mg/1 as the optimal ligno20 sulphonate dosage. As COD reduction is not improved by adding more than about 70 mg/1 1 ligno-sulphonate in addition to 5 ml centrifugate -841638 (see line 1), one can assume that recovered precipitation agent in the centrifugate is equivalent to a dosage of about 300-70 = 230 mg/1, or approx. 115 mg per 500 ml. Based on this assumption, the centrifugate added contains 115 - mg/ml or approx. 20 g/l.

EXAMPLE II A certain quantity of calcium chloride was added to the same sludge as used for Example 1, followed by the use of sodium hydroxide to adjust pH to 8.0. The sludge was then heated to 95°C, when ΐθ coagulation occurred, and after 1-2 minutes at this temperature the specimen was subjected to centrifugation. The centrifugate was analyzed and used as a source for ligno-sulphonate for addition to protein solution. Unexpectedly it proved that better precipitation of the proteins was achieved by using this centrifugate as precipitation agent, and the resulting hydrous phase was clear and clean. The hydrous phase of the specimens was analysed for COD to obtain an indication of the recovery of protein precipitation agent.

The results of the test are given in the following table.

TABLE FOR EXAMPLE II Dosage(for 500 ml protein solution) COD in decantate mg 02/l % COD reduction Line No. Ligno- sulphonate mg/l Sulphuric acid mg/l Central fugate ml 0 0 0 4590 0 0 600 0 3886 17.14 0 700 5 1126 75.99 50 II 11 1084 76.88 100 u II 1117 76.18 4 150 It II 1148 75.52 200 tl If 1173 74.98 250 u It o 1210 74.20 0 700 5 1126 75.99 0 11 10 1146 75.56 5 0 tl 15 1312 72.02 The results from Example II can best be compared with the results from Example I by comparing line 4 (Ex. II) with line 1 (Ex. I) and line 5 (Ex.II) with line 2 (Ex. I).

In relation to line 1, line 4 shows that in Example II a better COD reduction is obtained than in Example I and that the optimal dosage is somewhat lower than in Example I. This means that the centrifugate produced by coagulation with CaCl2 and NaOH contains more precipitation agent than in Example I.

This is further illustrated by comparing the results from the protein precipitation test with centrifugate alone. Line 5 (Ex. II) lies clearly below line 2 (Ex. 1), which shows that the specific COD reduction is better with centrifugate from Ex. II. Furthermore, line 5 rises less than line 2 when the quantity of centrifugate exceeds the optimal dosage, which means that the proportion of substances without protein precipitating properties is less in the centrifugate from Example II than in that from Example I.

EXAMPLE III Varying quantities of calcium hydroxide were added to 3 specimens of the same sludge as used for Examples I and II, to obtain pH numbers 7, 8 and 9 respectively before coagulation at 95° C. Centrifugation was carried out as in Example I and the centrifugates were examined as described in Examples I and II.

The results of the test are given in the following table.

II TABLE FOR EXAMPLE III pH when coagulated Dosage (for 500 ml protein solution) COD in decantate mg 02/l % COD reduction Line No. Ligno sulphonate mg/1 Sulphuric acid mg/1 Centrifugate mg/1 7 0 700 5 1.372 70.74 8 0 700 5 1.259 73.16 6 9 0 700 5 1.168 75.09 7 50 700 5 1.265 73.02 8 50 700 5 1.178 74.88 7 9 50 700 5 1.143 75.62 7 100 700 5 1.225 73.88 8 100 700 5 1.189 74.64 8 9 100 700 5 1.202 74.37 Comparing the results here in the same way as in Examples I and II gives an indication of the dependence upon or significance of the pH for coagulation of the precipitated protein material.

Line 6, which shows the protein precipitation test with centrifugate alone, indicates a distinct improvement in precipitation effect for centrifugate from coagulation as the pH increases. Lines 7 and 8 with 50 and 100 mg/1 respectively of additional lignin sulphonate dosage show that an additional dosage of 50 mg/1 to 5 ml centrifugate increases COD reduction as compared with centrifugate alone, but there is very little increase for the centrifugate from coagulation at pH 9. On the other hand, with an additional dosage of 100 mg/1, the COD reduction obtained with the centrifugate from coagulation at pH 9 is worse. Line 9 illustrates this, clearly showing that the optimal additional lignin sulphonate dosage in addition to 5 ml centrifugate is approx. 50 mg/1. If this result is appraised in the same manner as in Example.1, one can assume that the quantity of recovered precipitation agent in the centrifugate from coagulation at pH 9 is equivalent to a dosage of 300-50=250 mg/1, or that the concentration of precipitation agent in the added centrifugate is 125 2o — mg/1 or 25 g/l, which is 25% more than the concentration in the corresponding centrifugate from coagulation at pH 8 (Example I).

EXAMPLE IV specimens each of 100 grams of the same ligno-protein sludge as in Examples I, II and III were coagulated at 95°C after the addition of CaClg and NaOH to two specimens and Ca(0H)2 alone to two specimens, whereby pH was adjusted to 9.

Dehydration of the specimens was done in two different ways, so that one specimen conditioned by CaClg and NaOH and one specimen conditioned by Ca(0H)2 alone were subjected to centrifugation as in the preceding examples, while the two remaining specimens with different conditioning were filtered through a fibre-glass filter Whatman GF/C and washed twice with 50 ml water. (Whatman is a jTrade Mark) The quantities of centrifugate and filtrate were measured and the concentration of precipitation agent was determined by protein precipitation test as in the preceding examples.

RESULTS Conditioning Dehydration method Hydrous phase quantity ml . Precipitation agent yield % yield Concentration mg/ml Recovered mg CaClg+NaOH Centrifuge 58 35 2.030 66.6 CaCl2+NaOH Filter 121 20 2.420 79.5 Ca(0H)2 Centrifuge 72 25 1.800 59.1 Ca(0H)2 Filter 150 15 2.250 73.9 - 14 41638 In addition filtration speed and volume yield were examined by using cold (15°C) and warm (65°C) water for washing out the coagulated material. Furthermore tests were carried out by adding cold water (15°C) after coagulation and by stirring to cool the material before separation. These additional tests showed as expected that filtration speed and yield volume are greatest when warm water is used for washing out the coagulated material, but by adding cold water and stirring before separation one obtained greater filtration speed and yield volume for the hydrous phase. Cooling the material to about 50°C before separation therefore appears advantageous.

The yield volumes for centrifugation and filtration show that separability is best for sludge conditioned by Ca(0H)2 alone, while the precipitation agent yield shows that conditioning with CaClg and NaOH before coagulation gives best recovery of precipitation agent from the protein material.

According to the consumption of lignin sulphonate for producing the sludge and according to residue analysis of lignin sulphonate in the effluents treated, the ligno-protein sludge containing 14.5% solids, contains in the solids 21% lignin sulphonate which is equivalent to 14.5X0.21=3.045 mg lignin sulphonate in 100 g sludge.

As the table shows, for coagulated sludge conditioned by CaCl2+ NaOH or by Ca(0H)2 alone, the recovered yield of precipitation agent can be increased from 66,6 to 79.5% and 59.1 to 73.9% respectively by washing out with water.

EXAMPLE V To examine the possibility of removing other precipitation agents from precipitated protein material, different types of protein sludge were produced by precipitation of effluent containing proteins, using the following precipitation agents: Lauryl sulphate Glyceryl trisulphate n-Dodecyl-benzene-sulphoni c aci d Aluminium sulphate.

The same slaughterhouse effluents were used, with C0D=4.590 mg 0/1, as for the production of ligno-protein sludge in the four preceding examples. Parallel tests were carried out with effluents from destructive plant for slaughterhouse waste (production of meatbone meal and technical fats) and with diluted blood water from pig slaughtering.

The separated sludge was brought to pH 9 by the addition of Ca(0H)2, coagulated at 95°C, and centrifugation was carried out. The centrifugates from the different types of sludge were subjected to the same protein precipitation tests as the preceding examples, 5, and 15 ml being used as precipitation agent for the same slaugherhouse effluents as described in the preceding examples. Sulphuric acid was added to obtain pH=3 for all precipitations except precipitation of the centrifugate from the sludge precipitated by aluminium sulphate, for which pH was adjusted to 6. The decantates from the protein precipitation tests were characterized by determining COD which served for calculating the amount of precipitation agent recovered.

RESULTS Precipitation agent Dosage of centrifugate for 500 ml ml COD in decantate mg 0/1 %COD reduction Line Lauryl sulphate 5 1.426 68.9 10 1.172 74.5 10 15 1.542 66.4 Glycerol tri sulphate 5 2.380 48.1 10 1.438 68.7 11 15 1.567 65.8 n-0odecy1-benzene sulphonic acid 5 2.135 53.5 66.7 12 10 1.529 15 1.813 34.0 Aluminium sulphate 5 3.220 29.8 10 3.072 33.0 13 15 3.030 34.0 Compared with the results from Example I, line 2, one can see that the precipitation ageht is removed from the precipitated protein material in the same way. For organic sulphonates and sulphates the degree of recovery is comparable, while it is substantially lower for aluminium sulphate. Nevertheless it is obvious that the method as claimed is generally applicable for removing precipitation agents from precipitated protein material in such a form that they can be re-used.

Claims (5)

1. Process for the recovery of the precipitation agent from a precipitated material containing protein and precipitation agent wherein an alkaline earth metal compound is added to the precipitated 5 material in a quantity sufficient to bind the protein; if, after such addition, the pH of the material is still below 6.5, an alkaline earth metal hydroxide or alkali metal hydroxide is added to the material until its pH is at least 6.5, the material having a pH of at least 6.5 is then heated to a temperature above the coagulation point of the 10 protein present, and the aqueous phase, containing the precipitation agent, is separated from the protein.

2. Process according to claim 1, wherein an alkaline earth metal salt, is used as the alkaline earth metal compound and an alkali metal hydroxide is used to raise the pH to at least 6.5. 15

3. Process according to claim 2, wherein the alkaline earth metal salt is calcium chloride and the alkali metal hydroxide is sodium hydroxide.

4. Process according to claim 1 or 2, wherein an alkaline earth metal hydroxide, is used to bind the protein and to raise the pH 20 to at least 6.5. 5. Process according to claim 4, wherein the alkaline earth metal hydroxide is calcium hydroxide. 6. Process according to any one of the preceding claims, wherein the pH of the material is adjusted to 7.5-9 prior to separation of the aqueous phase from the protein. 7. Process according to any one of the preceding claims, 5 wherein the protinaceous material having a pH of at least 6.5 is heated with superheated steam for at least two minutes to facilitate coagulation of the protein. 8. Process according to any one of the preceding claims wherein the aqueous phase is separated from the protein by 10 filtration. 9. Process according to any one of claims 1-7, wherein the aqueous phase is separated from the protein by centrifugation. 10. Process according to claim 9, wherein the centrifuge is cooled. 15 Π, Process according to any one of claims 0-10, wherein a solid protein residue is washed with warm water and the water washings combined with the separated aqueous phase. 12, Process according to claim 1, substantially as hereinbefore described with reference to any one of the Examples. 13. An aqueous solution of precipitation agent obtained by a process according to any one of the preceding claims. 14. A process for precipitating protein from an aqueous medium containing protein which comprises bringing the medium into

5. Contact with an aqueous solution of precipitation agent according to claim 13.